mongoc_reference - Man Page

The MongoDB C Driver, also known as "libmongoc", is a library for using MongoDB from C applications, and for writing MongoDB drivers in higher-level languages.

It depends on libbson to generate and parse BSON documents, the native data format of MongoDB.

This section contains tutorials on how to get started with the basics of using the C driver.

There are a few methods of obtaining the mongo-c-driver codebase:

This page details how to download, unpack, configure, and build libbson and libmongoc from their original source-code form.

The following page uses a few named "variables" that you must decide up-front. When you see such a value referrenced in a tutorial step, you should substitute the value into that step.

SEE ALSO:

Before we begin, know what version of mongo-c-driver you will be downloading. A list of available versions can be found on the GitHub repository tags page. (The current version written for this documentation is 1.26.2.)

For the remainder of this page, $VERSION will refer to the version number of mongo-c-driver that you will be building for this tutorial.

There are two primary recommended methods of obtaining the mongo-c-driver source code:

1.

Clone the repository using git (recommended). (See below)

2.

Download a source archive at a specific version. (See below)

IMPORTANT:

It is highly recommended that new users use a stable released version of the driver, rather than building from a development branch. When you git clone or download an archive of the repository, be sure to specify a release tag (e.g. with Git's --branch argument).

Using Git, the C driver repository can be cloned from the GitHub URL https://github.com/mongodb/mongo-c-driver.git. Git tags for released versions are named after the version for which they correspond (e.g. "1.26.2"). To clone the repository using the command line, the following command may be used:

$ git clone https://github.com/mongodb/mongo-c-driver.git --branch="$VERSION" "$SOURCE"

TIP:

Despite the name, git-clone's --branch argument may also be used to clone from repository tags.

An archived snapshot of the repository can be obtained from the GitHub Releases Page. The mongo-c-driver-x.y.z.tar.gz archive attached to any release contains the minimal set of files that you'll need for the build.

The above commands will create a new directory mongo-c-driver-$VERSION within the directory in which you ran the tar/Expand-Archive command (note: PowerShell will create an additional intermediate subdirectory of the same name). This directory is the root of the driver source tree (which we refer to as $SOURCE in these documents). The $SOURCE directory should contain the top-level CMakeLists.txt file.

In order to build the project, a few prerequisites need to be available.

Both libmongoc and libbson projects use CMake for build configuration.

NOTE:

For the remainder of this page, it will be assumed that cmake is available as a command on your PATH environment variable and can be executed as "cmake" from a shell. You can test this by requesting the --version from CMake from the command line:

$ cmake --version
cmake version 3.21.4

CMake suite maintained and supported by Kitware (kitware.com/cmake).

NOTE:

If you intend to build libbson only, then CMake is sufficient for the build. Additional C driver features may require additional external dependencies be installed, but we will not worry about them here.

IMPORTANT:

If you are building with Xcode [1] or Visual Studio [2], you may need to execute CMake from within a special environment in which the respective toolchain is available.

Let the name $BUILD be the path $SOURCE/_build. This will be the directory where our built files will be written by CMake.

With the source directory for mongo-c-driver at $SOURCE and build directory $BUILD, the following command can be executed from a command-line to configure the project with both libbson and libmongoc:

$ cmake -S $SOURCE -B $BUILD \
  -D ENABLE_EXTRA_ALIGNMENT=OFF \
  -D ENABLE_AUTOMATIC_INIT_AND_CLEANUP=OFF \
  -D CMAKE_BUILD_TYPE=RelWithDebInfo \
  -D BUILD_VERSION="$VERSION" \
  -D ENABLE_MONGOC=OFF

If all dependencies are satisfied, the above command should succeed and end with:

$ cmake …
## … (Lines of output) …
-- Generating done
-- Build files have been written to: $BUILD

If configuration failed with an error, refer to the CMake output for error messages and information. Ensure that configuration succeeds before proceeding.

After successfully configuring the project, the build can be executed by using CMake:

$ cmake --build $BUILD --config RelWithDebInfo --parallel

If configured properly and all dependencies are satisfied, then the above command should proceed to compile and link the configured components. If the above command fails, then there is likely an error with your environment, or you are using an unsupported/untested platform. Refer to the build tool output for more information.

Let $PREFIX be the path $SOURCE/_install. We can use CMake to install the built results:

$ cmake --install "$BUILD" --prefix "$PREFIX" --config RelWithDebInfo

This command will install the mongo-c-driver build results into the $PREFIX directory.

SEE ALSO:

If you followed the above steps starting from Configuring for libbson, your final result with only contain libbson and not the full C database driver library. Building of libmongoc is enabled/disabled using the ENABLE_MONGOC CMake variable. Re-run CMake again, but set ENABLE_MONGOC to TRUE:

$ cmake -D ENABLE_MONGOC=ON $BUILD

If the above command succeeds, then the project has been reconfigured to build with libmongoc. Follow the process at Building the Project and Installing the Built Results again to build and install libmongoc.

The libmongoc and libbson libraries are often available in the package management repositories of common Linux distributions and macOS via Homebrew.

NOTE:

For Windows, it is recommended to instead build the libraries from source, for maximum compatibility with the local toolchain. Building from source can be automated by using a from-source library package management tool such as Conan or vcpkg (See: Cross Platform Installs Using Library Package Managers).

CAUTION:

If you install and use prebuilt binaries from a third-party packager, it is possible that it lags behind the version of the libraries described in these documentation pages (1.26.2). Note the version that you install and keep it in mind when reading these pages.

For the most up-to-date versions of the C driver libraries, prefer to instead build from source.

SEE ALSO:

For a listing and common reference on available packages, refer to Package Installation Reference.

Various library package managers offer libbson and libmongoc as installable packages, including Conan and vcpkg. This section will detail how to install using those tools.

NOTE:

This page will not detail how to get started using vcpkg. For that, refer to Get started with vcpkg

With CMake, the standard config-file package will be available, as well as the generated IMPORTED targets:

CMakeLists.txt

find_package(mongoc-1.0 CONFIG REQUIRED)
target_link_libraries(my-application
    PRIVATE $<IF:$<TARGET_EXISTS:mongo::mongoc_shared>,mongo::mongoc_shared,mongo::mongoc_static>)

NOTE:

The large $<IF:$<TARGET_EXISTS...>:...> generator expression (cmake-generator-expressions(7)) can be used to switch the link type of libmongoc based on whichever form is available from the find_package() command. libmongoc supports building with both dynamic and static library types, but vcpkg will only install one of the two library types at a time.

Configuring a CMake project with vcpkg integration is a matter of setting the CMake toolchain file at the initial configure command:

$ cmake -S . -B _build -D CMAKE_TOOLCHAIN_FILE=$VCPKG_ROOT/scripts/buildsystems/vcpkg.cmake

The names and process of installing libbson and libmongoc varies between distributions, but generally follows a similar pattern.

The following Linux distributions provide libbson and libmongoc packages:

• Fedora via dnf
• RedHat Enterprise Linux (RHEL) 7 and Newer and distribusions based on RHEL 7 or newer, including CentOS, Rocky Linux, and AlmaLinux, via yum/dnf and EPEL.
• Debian and Debian-based distributions, including Ubuntu and Ubuntu derivatives, via APT.

SEE ALSO:

For a list of available packages and package options, see: Package Installation Reference.

In RedHat-based Linux distributions, including Fedora, CentOS, Rocky Linux, and AlmaLinux, the C driver libraries can be installed with Yum/DNF.

NOTE:

For Fedora and enterprise Linux of version 8 or greater, it is recommended to use the dnf command in place of any yum command.

IMPORTANT:

Except for Fedora:

The C driver libraries are only available in version 7 and newer of the respective enterprise Linux distributions. However, the C driver libraries are not available in the default repositories, but can be obtained by enabling the EPEL repositories. This can be done by installing the epel-release package:

# yum install epel-release

epel-release must be installed before attempting to install the C driver libraries (i.e. one cannot install them both in a single yum install command).

To install libbson only, install the libbson-devel package:

# yum install libbson-devel

To install the full C database driver (libmongoc), install mongo-c-driver-devel:

## (This package will transitively install libbson-devel)
# yum install mongo-c-driver-devel

To check which version is available, see https://packages.fedoraproject.org/pkgs/mongo-c-driver/mongo-c-driver-devel.

The development packages (ending in -devel) include files required to build applications using libbson and libmongoc. To only install the libraries without development files, install the libbson or mongo-c-driver-libs packages.

In Debian-based Linux distributions, including Ubuntu and Ubuntu derivatives, libbson and libmongoc are available in the distribution repositories via APT, and can be installed as libbson-dev and libmongoc-dev, respectively:

## Update repository information, if necessary:
# apt update

To install only libbson:

# apt install libbson-dev

To install libmongoc (which will also install libbson):

# apt install libmongoc-dev

To check which version is available, run apt-cache policy libmongoc-dev.

The development packages (ending in -dev) include files required to build applications using libbson and libmongoc. To only install the libraries without development files, install the libbson-1.0-0 or libmongoc-1.0-0 packages.

If you are using a macOS system, the C driver libraries (including both libmongoc and libbson) may be installed using the Homebrew package manager [1] with the following command:

$ brew install mongo-c-driver

NOTE:

Homebrew does not provide separate packages for libbson and libmongoc.

[1]

The Homebrew package manager is not installed by default on macOS. For information on installing Homebrew, refer to the Homebrew installation documentation page.

This documentation is rendered using Sphinx. To easily ensure that all tooling matches expected versions, it is recommended to use Poetry to install and run the required tools.

TIP:

To install the required tooling, use the poetry install command, enabling documentation dependencies:

$ poetry install --with=docs

This will create a user-local Python virtualenv that contains the necessary tools for building this documentation. The poetry install command only needs to be run when the pyproject.toml file is changed.

Poetry can be used to execute the sphinx-build command:

$ poetry run sphinx-build -b dirhtml "./src/libmongoc/doc" "./_build/docs/html"

This command will generate the HTML documentation in the _build/docs/html subdirectory.

TIP:

To quickly view the rendered HTML pages, a simple local HTTP server can be spawned on the command line by using Python's built-in http.server module:

$ poetry run python -m http.server --directory=_build/docs/html

By default, this will serve the documentation at http://127.0.0.1:8000, which you can open in any web browser to see the rendered pages.

IMPORTANT:

The "cookbook" is for problem-solving, and deeper dives into approach particular tasks. It may assume some prior knowledge, and these are not tutorials themselves! For learning the basics, see the Tutorials section.

IMPORTANT:

This page assumes that you can successfully configure and build the components that you wish to install, which is detailed and explained on the Building the C Driver Libraries from Source tutorial page. Whereas that tutorial walks through getting the sources built and a minimal install working, this page will offer deeper guidance on the nuance and available options for installing the mongo-c-driver libraries from such a from-source build.

mongo-c-driver uses CMake to generate its installation rules, and installs a variety of artifacts of interest. For integration with downstream programs, the Config-file Packages and pkg-config files would be of particular interest.

If you are intending to import libbson or libmongoc via CMake or pkg-config, it can be helpful to be aware of how the respective tool searches for package metadata.

We will call the directory for the user-local installation $PREFIX. Selecting the path to this directory is somewhat arbitrary, but there are some recommendations to consider. The $PREFIX directory is the path that you will give to CMake or pkg-config when configuring a downstream project.

It is recommended that you install custom-built mongo-c-driver libraries in an unprivileged filesystem location particular to the user account.

If you wish to install the mongo-c-driver libraries in a directory that is visible to all users, there are a few standard options.

After you have successfully configured and built the libraries and have selected a suitable $PREFIX, you can install the built results. Let the name $BUILD refer to the directory where you executed the build (this is the directory that contains CMakeCache.txt, among many other files).

From a command line, the installation into your chosen $PREFIX can be run via CMake using the cmake --install subcommand:

$ cmake --install "$BUILD" --prefix "$PREFIX"

IMPORTANT:

If you configured the libraries while using a multi-config generator (e.g Visual Studio, Xcode), then you will also need to pass the --config command-line option, and must pass the value for the build configuration that you wish to install. For any chosen value of --config used for installation, you must also have previously executed a cmake --build within that directory with that same --config value.

NOTE:

If you chose to use a system-wide installation $PREFIX, it is possible that you will need to execute the installation as a privileged user. If you cannot run or do not want to run the installation as a privileged user, you should instead use a per-user installation prefix.

HINT:

It is not necessary to set a CMAKE_INSTALL_PREFIX if you use the --prefix command-line option with cmake --install. The --prefix option will override whatever was specified by CMAKE_INSTALL_PREFIX when the project was configured.

libbson and libmongoc are available from several package management tools on a variety of systems.

IMPORTANT:

This table details the names and usage notes of such packages.

NOTE:

The development packages (ending in -dev or -devel) include files required to build applications using libbson and libmongoc.

SEE ALSO:

For a step-by-step tutorial on installing packages, refer to Installing Prebuilt MongoDB C Driver Libraries.

The mongo-c-driver Conan recipe includes several build settings that correspond to the configure-time build settings available when building the mongo-c-driver project.

SEE ALSO:

[1]

Conan will use OpenSSL as the default TLS backend, even on platforms that ship with their own TLS implementation (e.g. Windows and macOS). This behavior differs from the upstream default-configured libmongoc or the vcpkg distribution of mongo-c-driver, which both default to use the TLS implementation preferred for the target platform.

The mongo-c-driver package offered by vcpkg supports several optional features.

SEE ALSO:

• The vcpkg libbson port
• The vcpkg mongo-c-driver port

This page documents information about the target platforms and toolchains that are supported by the mongo-c-driver libraries.

The following operating systems are continually tested with mongo-c-driver:

The following compilers are continually tested for mongo-c-driver:

The following CPU architectures are continually tested for mongo-c-driver:

Other platforms and toolchains are not tested, but similar versions of the above platforms should work. If you encounter a platform or toolchain that you expect to work and find that it does not, please open an issue describing the problem, and/or open a GitHub Pull Request to fix it.

Simple pull requests to fix unsupported platforms are welcome, but will be considered on a case-by-case basis. The acceptance of a pull request to fix the libraries on an unsupported platform does not imply full support of that platform.

This guide offers a brief introduction to the MongoDB C Driver.

For more information on the C API, please refer to the API Reference.

For detailed instructions on installing the MongoDB C Driver on a particular platform, please see the installation guide.

To run the examples in this tutorial, MongoDB must be installed and running on localhost on the default port, 27017. To check if it is up and running, connect to it with the MongoDB shell.

$ mongosh --host localhost --port 27017 --quiet
Enterprise rs0 [direct: primary] test> db.version()
7.0.0
>

All libmongoc's functions and types are available in one header file. Simply include mongoc/mongoc.h:

#include <mongoc/mongoc.h>

The libmongoc installation includes a CMake config-file package, so you can use CMake's find_package command to import libmongoc's CMake target and link to libmongoc (as a shared library):

CMakeLists.txt

# Specify the minimum version you require.
find_package (mongoc-1.0 1.7 REQUIRED)

# The "hello_mongoc.c" sample program is shared among four tests.
add_executable (hello_mongoc ../../hello_mongoc.c)
target_link_libraries (hello_mongoc PRIVATE mongo::mongoc_shared)

You can also use libmongoc as a static library instead: Use the mongo::mongoc_static CMake target:

# Specify the minimum version you require.
find_package (mongoc-1.0 1.7 REQUIRED)

# The "hello_mongoc.c" sample program is shared among four tests.
add_executable (hello_mongoc ../../hello_mongoc.c)
target_link_libraries (hello_mongoc PRIVATE mongo::mongoc_static)

If you're not using CMake, use pkg-config on the command line to set header and library paths:

gcc -o hello_mongoc hello_mongoc.c $(pkg-config --libs --cflags libmongoc-1.0)

Or to statically link to libmongoc:

gcc -o hello_mongoc hello_mongoc.c $(pkg-config --libs --cflags libmongoc-static-1.0)

If you aren't using CMake or pkg-config, paths and libraries can be managed manually.

$ gcc -o hello_mongoc hello_mongoc.c \
    -I/usr/local/include/libbson-1.0 -I/usr/local/include/libmongoc-1.0 \
    -lmongoc-1.0 -lbson-1.0
$ ./hello_mongoc
{ "ok" : 1.000000 }

For Windows users, the code can be compiled and run with the following commands. (This assumes that the MongoDB C Driver has been installed to C:\mongo-c-driver; change the include directory as needed.)

C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 hello_mongoc.c
C:\> hello_mongoc
{ "ok" : 1.000000 }

See the libmongoc and Visual Studio guide.

Access MongoDB with a mongoc_client_t. It transparently connects to standalone servers, replica sets and sharded clusters on demand. To perform operations on a database or collection, create a mongoc_database_t or mongoc_collection_t struct from the mongoc_client_t.

At the start of an application, call mongoc_init() before any other libmongoc functions. At the end, call the appropriate destroy function for each collection, database, or client handle, in reverse order from how they were constructed. Call mongoc_cleanup() before exiting.

The example below establishes a connection to a standalone server on localhost, registers the client application as "connect-example," and performs a simple command.

More information about database operations can be found in the CRUD Operations and Executing Commands sections. Examples of connecting to replica sets and sharded clusters can be found in the Advanced Connections page, while examples of data compression can be found in the Data Compression page.

hello_mongoc.c

#include <mongoc/mongoc.h>

int
main (int argc, char *argv[])
{
   const char *uri_string = "mongodb://localhost:27017";
   mongoc_uri_t *uri;
   mongoc_client_t *client;
   mongoc_database_t *database;
   mongoc_collection_t *collection;
   bson_t *command, reply, *insert;
   bson_error_t error;
   char *str;
   bool retval;

   /*
    * Required to initialize libmongoc's internals
    */
   mongoc_init ();

   /*
    * Optionally get MongoDB URI from command line
    */
   if (argc > 1) {
      uri_string = argv[1];
   }

   /*
    * Safely create a MongoDB URI object from the given string
    */
   uri = mongoc_uri_new_with_error (uri_string, &error);
   if (!uri) {
      fprintf (stderr,
               "failed to parse URI: %s\n"
               "error message:       %s\n",
               uri_string,
               error.message);
      return EXIT_FAILURE;
   }

   /*
    * Create a new client instance
    */
   client = mongoc_client_new_from_uri (uri);
   if (!client) {
      return EXIT_FAILURE;
   }

   /*
    * Register the application name so we can track it in the profile logs
    * on the server. This can also be done from the URI (see other examples).
    */
   mongoc_client_set_appname (client, "connect-example");

   /*
    * Get a handle on the database "db_name" and collection "coll_name"
    */
   database = mongoc_client_get_database (client, "db_name");
   collection = mongoc_client_get_collection (client, "db_name", "coll_name");

   /*
    * Do work. This example pings the database, prints the result as JSON and
    * performs an insert
    */
   command = BCON_NEW ("ping", BCON_INT32 (1));

   retval = mongoc_client_command_simple (
      client, "admin", command, NULL, &reply, &error);

   if (!retval) {
      fprintf (stderr, "%s\n", error.message);
      return EXIT_FAILURE;
   }

   str = bson_as_json (&reply, NULL);
   printf ("%s\n", str);

   insert = BCON_NEW ("hello", BCON_UTF8 ("world"));

   if (!mongoc_collection_insert_one (collection, insert, NULL, NULL, &error)) {
      fprintf (stderr, "%s\n", error.message);
   }

   bson_destroy (insert);
   bson_destroy (&reply);
   bson_destroy (command);
   bson_free (str);

   /*
    * Release our handles and clean up libmongoc
    */
   mongoc_collection_destroy (collection);
   mongoc_database_destroy (database);
   mongoc_uri_destroy (uri);
   mongoc_client_destroy (client);
   mongoc_cleanup ();

   return EXIT_SUCCESS;
}

Documents are stored in MongoDB's data format, BSON. The C driver uses libbson to create BSON documents. There are several ways to construct them: appending key-value pairs, using BCON, or parsing JSON.

A BSON document, represented as a bson_t in code, can be constructed one field at a time using libbson's append functions.

For example, to create a document like this:

{
   born : ISODate("1906-12-09"),
   died : ISODate("1992-01-01"),
   name : {
      first : "Grace",
      last : "Hopper"
   },
   languages : [ "MATH-MATIC", "FLOW-MATIC", "COBOL" ],
   degrees: [ { degree: "BA", school: "Vassar" }, { degree: "PhD", school: "Yale" } ]
}

Use the following code:

#include <bson/bson.h>

int
main (int argc, char *argv[])
{
   struct tm born = {0};
   struct tm died = {0};
   const char *lang_names[] = {"MATH-MATIC", "FLOW-MATIC", "COBOL"};
   const char *schools[] = {"Vassar", "Yale"};
   const char *degrees[] = {"BA", "PhD"};
   uint32_t i;
   bson_t *document;
   bson_t child;
   bson_array_builder_t *bab;
   char *str;

   document = bson_new ();

   /*
    * Append { "born" : ISODate("1906-12-09") } to the document.
    * Passing -1 for the length argument tells libbson to calculate the
    * string length.
    */
   born.tm_year = 6; /* years are 1900-based */
   born.tm_mon = 11; /* months are 0-based */
   born.tm_mday = 9;
   bson_append_date_time (document, "born", -1, mktime (&born) * 1000);

   /*
    * Append { "died" : ISODate("1992-01-01") } to the document.
    */
   died.tm_year = 92;
   died.tm_mon = 0;
   died.tm_mday = 1;

   /*
    * For convenience, this macro passes length -1 by default.
    */
   BSON_APPEND_DATE_TIME (document, "died", mktime (&died) * 1000);

   /*
    * Append a subdocument.
    */
   BSON_APPEND_DOCUMENT_BEGIN (document, "name", &child);
   BSON_APPEND_UTF8 (&child, "first", "Grace");
   BSON_APPEND_UTF8 (&child, "last", "Hopper");
   bson_append_document_end (document, &child);

   /*
    * Append array of strings. Generate keys "0", "1", "2".
    */
   BSON_APPEND_ARRAY_BUILDER_BEGIN (document, "languages", &bab);
   for (i = 0; i < sizeof lang_names / sizeof (char *); ++i) {
      bson_array_builder_append_utf8 (bab, lang_names[i], -1);
   }
   bson_append_array_builder_end (document, bab);

   /*
    * Array of subdocuments:
    *    degrees: [ { degree: "BA", school: "Vassar" }, ... ]
    */
   BSON_APPEND_ARRAY_BUILDER_BEGIN (document, "degrees", &bab);
   for (i = 0; i < sizeof degrees / sizeof (char *); ++i) {
      bson_array_builder_append_document_begin (bab, &child);
      BSON_APPEND_UTF8 (&child, "degree", degrees[i]);
      BSON_APPEND_UTF8 (&child, "school", schools[i]);
      bson_array_builder_append_document_end (bab, &child);
   }
   bson_append_array_builder_end (document, bab);

   /*
    * Print the document as a JSON string.
    */
   str = bson_as_canonical_extended_json (document, NULL);
   printf ("%s\n", str);
   bson_free (str);

   /*
    * Clean up allocated bson documents.
    */
   bson_destroy (document);
   return 0;
}

See the libbson documentation for all of the types that can be appended to a bson_t.

BSON C Object Notation, BCON for short, is an alternative way of constructing BSON documents in a manner closer to the intended format. It has less type-safety than BSON's append functions but results in less code.

#include <bson/bson.h>

int
main (int   argc,
      char *argv[])
{
   struct tm born = { 0 };
   struct tm died = { 0 };
   bson_t   *document;
   char     *str;

   born.tm_year = 6;
   born.tm_mon = 11;
   born.tm_mday = 9;

   died.tm_year = 92;
   died.tm_mon = 0;
   died.tm_mday = 1;

   document = BCON_NEW (
      "born", BCON_DATE_TIME (mktime (&born) * 1000),
      "died", BCON_DATE_TIME (mktime (&died) * 1000),
      "name", "{",
      "first", BCON_UTF8 ("Grace"),
      "last", BCON_UTF8 ("Hopper"),
      "}",
      "languages", "[",
      BCON_UTF8 ("MATH-MATIC"),
      BCON_UTF8 ("FLOW-MATIC"),
      BCON_UTF8 ("COBOL"),
      "]",
      "degrees", "[",
      "{", "degree", BCON_UTF8 ("BA"), "school", BCON_UTF8 ("Vassar"), "}",
      "{", "degree", BCON_UTF8 ("PhD"), "school", BCON_UTF8 ("Yale"), "}",
      "]");

   /*
    * Print the document as a JSON string.
    */
   str = bson_as_canonical_extended_json (document, NULL);
   printf ("%s\n", str);
   bson_free (str);

   /*
    * Clean up allocated bson documents.
    */
   bson_destroy (document);
   return 0;
}

Notice that BCON can create arrays, subdocuments and arbitrary fields.

For single documents, BSON can be created from JSON strings via bson_new_from_json.

#include <bson/bson.h>

int
main (int   argc,
      char *argv[])
{
   bson_error_t error;
   bson_t      *bson;
   char        *string;

   const char *json = "{\"name\": {\"first\":\"Grace\", \"last\":\"Hopper\"}}";
   bson = bson_new_from_json ((const uint8_t *)json, -1, &error);

   if (!bson) {
      fprintf (stderr, "%s\n", error.message);
      return EXIT_FAILURE;
   }

   string = bson_as_canonical_extended_json (bson, NULL);
   printf ("%s\n", string);
   bson_free (string);

   return 0;
}

To initialize BSON from a sequence of JSON documents, use bson_json_reader_t.

This section demonstrates the basics of using the C Driver to interact with MongoDB.

To insert documents into a collection, first obtain a handle to a mongoc_collection_t via a mongoc_client_t. Then, use mongoc_collection_insert_one() to add BSON documents to the collection. This example inserts into the database "mydb" and collection "mycoll".

When finished, ensure that allocated structures are freed by using their respective destroy functions.

#include <bson/bson.h>
#include <mongoc/mongoc.h>
#include <stdio.h>

int
main (int   argc,
      char *argv[])
{
    mongoc_client_t *client;
    mongoc_collection_t *collection;
    bson_error_t error;
    bson_oid_t oid;
    bson_t *doc;

    mongoc_init ();

    client = mongoc_client_new ("mongodb://localhost:27017/?appname=insert-example");
    collection = mongoc_client_get_collection (client, "mydb", "mycoll");

    doc = bson_new ();
    bson_oid_init (&oid, NULL);
    BSON_APPEND_OID (doc, "_id", &oid);
    BSON_APPEND_UTF8 (doc, "hello", "world");

    if (!mongoc_collection_insert_one (
           collection, doc, NULL, NULL, &error)) {
        fprintf (stderr, "%s\n", error.message);
    }

    bson_destroy (doc);
    mongoc_collection_destroy (collection);
    mongoc_client_destroy (client);
    mongoc_cleanup ();

    return 0;
}

Compile the code and run it:

$ gcc -o insert insert.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./insert

On Windows:

C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 insert.c
C:\> insert

To verify that the insert succeeded, connect with the MongoDB shell.

$ mongo
MongoDB shell version: 3.0.6
connecting to: test
> use mydb
switched to db mydb
> db.mycoll.find()
{ "_id" : ObjectId("55ef43766cb5f36a3bae6ee4"), "hello" : "world" }
>

To query a MongoDB collection with the C driver, use the function mongoc_collection_find_with_opts(). This returns a cursor to the matching documents. The following examples iterate through the result cursors and print the matches to stdout as JSON strings.

Use a document as a query specifier; for example,

{ "color" : "red" }

will match any document with a field named "color" with value "red". An empty document {} can be used to match all documents.

This first example uses an empty query specifier to find all documents in the database "mydb" and collection "mycoll".

#include <bson/bson.h>
#include <mongoc/mongoc.h>
#include <stdio.h>

int
main (int argc, char *argv[])
{
   mongoc_client_t *client;
   mongoc_collection_t *collection;
   mongoc_cursor_t *cursor;
   const bson_t *doc;
   bson_t *query;
   char *str;

   mongoc_init ();

   client =
      mongoc_client_new ("mongodb://localhost:27017/?appname=find-example");
   collection = mongoc_client_get_collection (client, "mydb", "mycoll");
   query = bson_new ();
   cursor = mongoc_collection_find_with_opts (collection, query, NULL, NULL);

   while (mongoc_cursor_next (cursor, &doc)) {
      str = bson_as_canonical_extended_json (doc, NULL);
      printf ("%s\n", str);
      bson_free (str);
   }

   bson_destroy (query);
   mongoc_cursor_destroy (cursor);
   mongoc_collection_destroy (collection);
   mongoc_client_destroy (client);
   mongoc_cleanup ();

   return 0;
}

Compile the code and run it:

$ gcc -o find find.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./find
{ "_id" : { "$oid" : "55ef43766cb5f36a3bae6ee4" }, "hello" : "world" }

On Windows:

C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 find.c
C:\> find
{ "_id" : { "$oid" : "55ef43766cb5f36a3bae6ee4" }, "hello" : "world" }

To look for a specific document, add a specifier to query. This example adds a call to BSON_APPEND_UTF8() to look for all documents matching {"hello" : "world"}.

#include <bson/bson.h>
#include <mongoc/mongoc.h>
#include <stdio.h>

int
main (int argc, char *argv[])
{
   mongoc_client_t *client;
   mongoc_collection_t *collection;
   mongoc_cursor_t *cursor;
   const bson_t *doc;
   bson_t *query;
   char *str;

   mongoc_init ();

   client = mongoc_client_new (
      "mongodb://localhost:27017/?appname=find-specific-example");
   collection = mongoc_client_get_collection (client, "mydb", "mycoll");
   query = bson_new ();
   BSON_APPEND_UTF8 (query, "hello", "world");

   cursor = mongoc_collection_find_with_opts (collection, query, NULL, NULL);

   while (mongoc_cursor_next (cursor, &doc)) {
      str = bson_as_canonical_extended_json (doc, NULL);
      printf ("%s\n", str);
      bson_free (str);
   }

   bson_destroy (query);
   mongoc_cursor_destroy (cursor);
   mongoc_collection_destroy (collection);
   mongoc_client_destroy (client);
   mongoc_cleanup ();

   return 0;
}

$ gcc -o find-specific find-specific.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./find-specific
{ "_id" : { "$oid" : "55ef43766cb5f36a3bae6ee4" }, "hello" : "world" }

C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 find-specific.c
C:\> find-specific
{ "_id" : { "$oid" : "55ef43766cb5f36a3bae6ee4" }, "hello" : "world" }

This code snippet gives an example of using mongoc_collection_update_one() to update the fields of a document.

Using the "mydb" database, the following example inserts an example document into the "mycoll" collection. Then, using its _id field, the document is updated with different values and a new field.

#include <bson/bson.h>
#include <mongoc/mongoc.h>
#include <stdio.h>

int
main (int argc, char *argv[])
{
   mongoc_collection_t *collection;
   mongoc_client_t *client;
   bson_error_t error;
   bson_oid_t oid;
   bson_t *doc = NULL;
   bson_t *update = NULL;
   bson_t *query = NULL;

   mongoc_init ();

   client =
      mongoc_client_new ("mongodb://localhost:27017/?appname=update-example");
   collection = mongoc_client_get_collection (client, "mydb", "mycoll");

   bson_oid_init (&oid, NULL);
   doc = BCON_NEW ("_id", BCON_OID (&oid), "key", BCON_UTF8 ("old_value"));

   if (!mongoc_collection_insert_one (collection, doc, NULL, &error)) {
      fprintf (stderr, "%s\n", error.message);
      goto fail;
   }

   query = BCON_NEW ("_id", BCON_OID (&oid));
   update = BCON_NEW ("$set",
                      "{",
                      "key",
                      BCON_UTF8 ("new_value"),
                      "updated",
                      BCON_BOOL (true),
                      "}");

   if (!mongoc_collection_update_one (
          collection, query, update, NULL, NULL, &error)) {
      fprintf (stderr, "%s\n", error.message);
      goto fail;
   }

fail:
   if (doc)
      bson_destroy (doc);
   if (query)
      bson_destroy (query);
   if (update)
      bson_destroy (update);

   mongoc_collection_destroy (collection);
   mongoc_client_destroy (client);
   mongoc_cleanup ();

   return 0;
}

Compile the code and run it:

$ gcc -o update update.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./update

On Windows:

C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 update.c
C:\> update
{ "_id" : { "$oid" : "55ef43766cb5f36a3bae6ee4" }, "hello" : "world" }

To verify that the update succeeded, connect with the MongoDB shell.

$ mongo
MongoDB shell version: 3.0.6
connecting to: test
> use mydb
switched to db mydb
> db.mycoll.find({"updated" : true})
{ "_id" : ObjectId("55ef549236fe322f9490e17b"), "updated" : true, "key" : "new_value" }
>

This example illustrates the use of mongoc_collection_delete_one() to delete a document.

The following code inserts a sample document into the database "mydb" and collection "mycoll". Then, it deletes all documents matching {"hello" : "world"}.

#include <bson/bson.h>
#include <mongoc/mongoc.h>
#include <stdio.h>

int
main (int argc, char *argv[])
{
   mongoc_client_t *client;
   mongoc_collection_t *collection;
   bson_error_t error;
   bson_oid_t oid;
   bson_t *doc;

   mongoc_init ();

   client =
      mongoc_client_new ("mongodb://localhost:27017/?appname=delete-example");
   collection = mongoc_client_get_collection (client, "test", "test");

   doc = bson_new ();
   bson_oid_init (&oid, NULL);
   BSON_APPEND_OID (doc, "_id", &oid);
   BSON_APPEND_UTF8 (doc, "hello", "world");

   if (!mongoc_collection_insert_one (collection, doc, NULL, &error)) {
      fprintf (stderr, "Insert failed: %s\n", error.message);
   }

   bson_destroy (doc);

   doc = bson_new ();
   BSON_APPEND_OID (doc, "_id", &oid);

   if (!mongoc_collection_delete_one (
          collection, doc, NULL, NULL, &error)) {
      fprintf (stderr, "Delete failed: %s\n", error.message);
   }

   bson_destroy (doc);
   mongoc_collection_destroy (collection);
   mongoc_client_destroy (client);
   mongoc_cleanup ();

   return 0;
}

Compile the code and run it:

$ gcc -o delete delete.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./delete

On Windows:

C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 delete.c
C:\> delete

Use the MongoDB shell to prove that the documents have been removed successfully.

$ mongo
MongoDB shell version: 3.0.6
connecting to: test
> use mydb
switched to db mydb
> db.mycoll.count({"hello" : "world"})
0
>

Counting the number of documents in a MongoDB collection is similar to performing a find operation. This example counts the number of documents matching {"hello" : "world"} in the database "mydb" and collection "mycoll".

#include <bson/bson.h>
#include <mongoc/mongoc.h>
#include <stdio.h>

int
main (int argc, char *argv[])
{
   mongoc_client_t *client;
   mongoc_collection_t *collection;
   bson_error_t error;
   bson_t *doc;
   int64_t count;

   mongoc_init ();

   client =
      mongoc_client_new ("mongodb://localhost:27017/?appname=count-example");
   collection = mongoc_client_get_collection (client, "mydb", "mycoll");
   doc = bson_new_from_json (
      (const uint8_t *) "{\"hello\" : \"world\"}", -1, &error);

   count = mongoc_collection_count (
      collection, MONGOC_QUERY_NONE, doc, 0, 0, NULL, &error);

   if (count < 0) {
      fprintf (stderr, "%s\n", error.message);
   } else {
      printf ("%" PRId64 "\n", count);
   }

   bson_destroy (doc);
   mongoc_collection_destroy (collection);
   mongoc_client_destroy (client);
   mongoc_cleanup ();

   return 0;
}

Compile the code and run it:

$ gcc -o count count.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./count
1

On Windows:

C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 count.c
C:\> count
1

The driver provides helper functions for executing MongoDB commands on client, database and collection structures. The _simple variants return booleans indicating success or failure.

This example executes the ping command against the database "mydb".

#include <bson/bson.h>
#include <mongoc/mongoc.h>
#include <stdio.h>

int
main (int argc, char *argv[])
{
   mongoc_client_t *client;
   bson_error_t error;
   bson_t *command;
   bson_t reply;
   char *str;

   mongoc_init ();

   client = mongoc_client_new (
      "mongodb://localhost:27017/?appname=executing-example");

   command = BCON_NEW ("ping", BCON_INT32 (1));
   if (mongoc_client_command_simple (
          client, "mydb", command, NULL, &reply, &error)) {
      str = bson_as_canonical_extended_json (&reply, NULL);
      printf ("%s\n", str);
      bson_free (str);
   } else {
      fprintf (stderr, "Failed to run command: %s\n", error.message);
   }

   bson_destroy (command);
   bson_destroy (&reply);
   mongoc_client_destroy (client);
   mongoc_cleanup ();

   return 0;
}

Compile the code and run it:

$ gcc -o executing executing.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./executing
{ "ok" : { "$numberDouble" : "1.0" }, "$clusterTime" : { "clusterTime" : { "$timestamp" : { "t" : 1682609211, "i" : 1 } }, "signature" : { "hash" : { "$binary" : { "base64" : "AAAAAAAAAAAAAAAAAAAAAAAAAAA=", "subType" : "00" } }, "keyId" : { "$numberLong" : "0" } } }, "operationTime" : { "$timestamp" : { "t" : 1682609211, "i" : 1 } } }

On Windows:

C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 executing.c
C:\> executing
{ "ok" : { "$numberDouble" : "1.0" }, "$clusterTime" : { "clusterTime" : { "$timestamp" : { "t" : 1682609211, "i" : 1 } }, "signature" : { "hash" : { "$binary" : { "base64" : "AAAAAAAAAAAAAAAAAAAAAAAAAAA=", "subType" : "00" } }, "keyId" : { "$numberLong" : "0" } } }, "operationTime" : { "$timestamp" : { "t" : 1682609211, "i" : 1 } } }

The MongoDB C Driver is thread-unaware in the vast majority of its operations. This means it is up to the programmer to guarantee thread-safety.

However, mongoc_client_pool_t is thread-safe and is used to fetch a mongoc_client_t in a thread-safe manner. After retrieving a client from the pool, the client structure should be considered owned by the calling thread. When the thread is finished, the client should be placed back into the pool.

example-pool.c

/* gcc example-pool.c -o example-pool $(pkg-config --cflags --libs
 * libmongoc-1.0) */

/* ./example-pool [CONNECTION_STRING] */

#include <mongoc/mongoc.h>
#include <pthread.h>
#include <stdio.h>

static pthread_mutex_t mutex;
static bool in_shutdown = false;

static void *
worker (void *data)
{
   mongoc_client_pool_t *pool = data;
   mongoc_client_t *client;
   bson_t ping = BSON_INITIALIZER;
   bson_error_t error;
   bool r;

   BSON_APPEND_INT32 (&ping, "ping", 1);

   while (true) {
      client = mongoc_client_pool_pop (pool);
      /* Do something with client. If you are writing an HTTP server, you
       * probably only want to hold onto the client for the portion of the
       * request performing database queries.
       */
      r = mongoc_client_command_simple (
         client, "admin", &ping, NULL, NULL, &error);

      if (!r) {
         fprintf (stderr, "%s\n", error.message);
      }

      mongoc_client_pool_push (pool, client);

      pthread_mutex_lock (&mutex);
      if (in_shutdown || !r) {
         pthread_mutex_unlock (&mutex);
         break;
      }

      pthread_mutex_unlock (&mutex);
   }

   bson_destroy (&ping);
   return NULL;
}

int
main (int argc, char *argv[])
{
   const char *uri_string = "mongodb://127.0.0.1/?appname=pool-example";
   mongoc_uri_t *uri;
   bson_error_t error;
   mongoc_client_pool_t *pool;
   pthread_t threads[10];
   unsigned i;
   void *ret;

   pthread_mutex_init (&mutex, NULL);
   mongoc_init ();

   if (argc > 1) {
      uri_string = argv[1];
   }

   uri = mongoc_uri_new_with_error (uri_string, &error);
   if (!uri) {
      fprintf (stderr,
               "failed to parse URI: %s\n"
               "error message:       %s\n",
               uri_string,
               error.message);
      return EXIT_FAILURE;
   }

   pool = mongoc_client_pool_new (uri);
   mongoc_client_pool_set_error_api (pool, 2);

   for (i = 0; i < 10; i++) {
      pthread_create (&threads[i], NULL, worker, pool);
   }

   sleep (10);
   pthread_mutex_lock (&mutex);
   in_shutdown = true;
   pthread_mutex_unlock (&mutex);

   for (i = 0; i < 10; i++) {
      pthread_join (threads[i], &ret);
   }

   mongoc_client_pool_destroy (pool);
   mongoc_uri_destroy (uri);

   mongoc_cleanup ();

   return EXIT_SUCCESS;
}

To find information on advanced topics, browse the rest of the C driver guide or the official MongoDB documentation.

For help with common issues, consult the Troubleshooting page. To report a bug or request a new feature, follow these instructions.

This guide covers the use of authentication options with the MongoDB C Driver. Ensure that the MongoDB server is also properly configured for authentication before making a connection. For more information, see the MongoDB security documentation.

The MongoDB C driver supports several authentication mechanisms through the use of MongoDB connection URIs.

By default, if a username and password are provided as part of the connection string (and an optional authentication database), they are used to connect via the default authentication mechanism of the server.

To select a specific authentication mechanism other than the default, see the list of supported mechanism below.

mongoc_client_t *client = mongoc_client_new ("mongodb://user:password@localhost/?authSource=mydb");

Currently supported values for the authMechanism connection string option are:

• SCRAM-SHA-1
• MONGODB-CR (deprecated)
• GSSAPI
• PLAIN
• X509
• MONGODB-AWS

MongoDB 4.0 introduces support for authenticating using the SCRAM protocol with the more secure SHA-256 hash described in RFC 7677. Using this authentication mechanism means that the password is never actually sent over the wire when authenticating, but rather a computed proof that the client password is the same as the password the server knows. In MongoDB 4.0, the C driver can determine the correct default authentication mechanism for users with stored SCRAM-SHA-1 and SCRAM-SHA-256 credentials:

mongoc_client_t *client =  mongoc_client_new ("mongodb://user:password@localhost/?authSource=mydb");
/* the correct authMechanism is negotiated between the driver and server. */

Alternatively, SCRAM-SHA-256 can be explicitly specified as an authMechanism.

mongoc_client_t *client =  mongoc_client_new ("mongodb://user:password@localhost/?authMechanism=SCRAM-SHA-256&authSource=mydb");

The default authentication mechanism before MongoDB 4.0 is SCRAM-SHA-1 (RFC 5802). Using this authentication mechanism means that the password is never actually sent over the wire when authenticating, but rather a computed proof that the client password is the same as the password the server knows.

mongoc_client_t *client = mongoc_client_new ("mongodb://user:password@localhost/?authMechanism=SCRAM-SHA-1&authSource=mydb");

NOTE:

SCRAM-SHA-1 authenticates against the admin database by default. If the user is created in another database, then specifying the authSource is required.

The MONGODB-CR authMechanism is deprecated and will no longer function in MongoDB 4.0. Instead, specify no authMechanism and the driver will use an authentication mechanism compatible with your server.

NOTE:

On UNIX-like environments, Kerberos support requires compiling the driver against Cyrus SASL.

On Windows, Kerberos support requires compiling the driver against Windows Native SSPI or Cyrus SASL. The default configuration of the driver will use Windows Native SSPI. Using Cyrus SASL on Windows requires configuring the CMake option CYRUS_PLUGIN_PATH_PREFIX to the absolute path prefix of the GSSAPI plugin to enable loading the plugin.

To modify the default configuration, use the cmake option ENABLE_SASL.

GSSAPI (Kerberos) authentication is available in the Enterprise Edition of MongoDB. To authenticate using GSSAPI, the MongoDB C driver must be installed with SASL support.

On UNIX-like environments, run the kinit command before using the following authentication methods:

$ kinit mongodbuser@EXAMPLE.COM
mongodbuser@EXAMPLE.COM's Password:
$ klistCredentials cache: FILE:/tmp/krb5cc_1000
        Principal: mongodbuser@EXAMPLE.COM

  Issued                Expires               Principal
Feb  9 13:48:51 2013  Feb  9 23:48:51 2013  krbtgt/EXAMPLE.COM@EXAMPLE.COM

Now authenticate using the MongoDB URI. GSSAPI authenticates against the $external virtual database, so a database does not need to be specified in the URI. Note that the Kerberos principal must be URL-encoded:

mongoc_client_t *client;

client = mongoc_client_new ("mongodb://mongodbuser%40EXAMPLE.COM@mongo-server.example.com/?authMechanism=GSSAPI");

NOTE:

GSSAPI authenticates against the $external database, so specifying the authSource database is not required.

The driver supports these GSSAPI properties:

• CANONICALIZE_HOST_NAME: This might be required with Cyrus-SASL when the hosts report different hostnames than what is used in the Kerberos database. The default is "false".
• SERVICE_NAME: Use a different service name than the default, "mongodb".

Set properties in the URL:

mongoc_client_t *client;

client = mongoc_client_new ("mongodb://mongodbuser%40EXAMPLE.COM@mongo-server.example.com/?authMechanism=GSSAPI&"
                            "authMechanismProperties=SERVICE_NAME:other,CANONICALIZE_HOST_NAME:true");

If you encounter errors such as Invalid net address, check if the application is behind a NAT (Network Address Translation) firewall. If so, create a ticket that uses forwardable and addressless Kerberos tickets. This can be done by passing -f -A to kinit.

$ kinit -f -A mongodbuser@EXAMPLE.COM

NOTE:

The MongoDB C Driver must be compiled with SASL support in order to use SASL PLAIN authentication.

MongoDB Enterprise Edition supports the SASL PLAIN authentication mechanism, initially intended for delegating authentication to an LDAP server. Using the SASL PLAIN mechanism is very similar to the challenge response mechanism with usernames and passwords. This authentication mechanism uses the $external virtual database for LDAP support:

NOTE:

mongoc_client_t *client;

client = mongoc_client_new ("mongodb://user:password@example.com/?authMechanism=PLAIN");

PLAIN authenticates against the $external database, so specifying the authSource database is not required.

NOTE:

The MongoDB C Driver must be compiled with TLS support for X.509 authentication support. Once this is done, start a server with the following options:

$ mongod --tlsMode requireTLS --tlsCertificateKeyFile server.pem --tlsCAFile ca.pem

The MONGODB-X509 mechanism authenticates a username derived from the distinguished subject name of the X.509 certificate presented by the driver during TLS negotiation. This authentication method requires the use of TLS connections with certificate validation.

mongoc_client_t *client;
mongoc_ssl_opt_t ssl_opts = { 0 };

ssl_opts.pem_file = "mycert.pem";
ssl_opts.pem_pwd = "mycertpassword";
ssl_opts.ca_file = "myca.pem";
ssl_opts.ca_dir = "trust_dir";
ssl_opts.weak_cert_validation = false;

client = mongoc_client_new ("mongodb://x509_derived_username@localhost/?authMechanism=MONGODB-X509");
mongoc_client_set_ssl_opts (client, &ssl_opts);

MONGODB-X509 authenticates against the $external database, so specifying the authSource database is not required. For more information on the x509_derived_username, see the MongoDB server x.509 tutorial.

NOTE:

The MONGODB-AWS mechanism authenticates to MongoDB servers with credentials provided by AWS Identity and Access Management (IAM).

To authenticate, create a user with an associated Amazon Resource Name (ARN) on the $external database, and specify the MONGODB-AWS authMechanism in the URI.

mongoc_uri_t *uri = mongoc_uri_new ("mongodb://localhost/?authMechanism=MONGODB-AWS");

Since MONGODB-AWS always authenticates against the $external database, so specifying the authSource database is not required.

Credentials include the access key id, secret access key, and optional session token. They may be obtained from the following ways.

Credentials may be passed directly in the URI as username/password.

mongoc_uri_t *uri = mongoc_uri_new ("mongodb://<access key id>:<secret access key>localhost/?authMechanism=MONGODB-AWS");

This may include a session token passed with authMechanismProperties.

mongoc_uri_t *uri = mongoc_uri_new ("mongodb://<access key id>:<secret access key>localhost/?authMechanism=MONGODB-AWS&authMechanismProperties=AWS_SESSION_TOKEN:<token>");

If credentials are not passed through the URI, libmongoc will check for the following environment variables.

• AWS_ACCESS_KEY_ID
• AWS_SECRET_ACCESS_KEY
• AWS_SESSION_TOKEN (optional)

If credentials are not passed in the URI or with environment variables, libmongoc will check if the environment variable AWS_CONTAINER_CREDENTIALS_RELATIVE_URI is set, and if so, attempt to retrieve temporary credentials from the ECS task metadata by querying a link local address.

If credentials are not passed in the URI or with environment variables, and the environment variable AWS_CONTAINER_CREDENTIALS_RELATIVE_URI is not set, libmongoc will attempt to retrieve temporary credentials from the EC2 machine metadata by querying link local addresses.

The following is a short list of things to check when you have a problem.

• Did you call mongoc_init() in main()? If not, you will likely see a segfault.
• Have you leaked any clients or cursors as can be found with mongoc-stat <PID>?
• Have packets been delivered to the server? See egress bytes from mongoc-stat <PID>.
• Does ASAN show any leaks? Ensure you call mongoc_cleanup() at the end of your process to cleanup lingering allocations from the MongoDB C driver.
• If compiling your own copy of MongoDB C Driver, consider using the cmake option -DENABLE_TRACING=ON to enable function tracing and hex dumps of network packets to STDERR and STDOUT.

The MongoDB C Driver comes with an optional and unique feature to help developers and sysadmins troubleshoot problems in production. Performance counters are available for each process using the C Driver. If available, the counters can be accessed outside of the application process via a shared memory segment. The counters may be used graph statistics about your application process easily from tools like Munin or Nagios. For example, the command watch --interval=0.5 -d mongoc-stat $PID may be used to monitor an application.

Performance counters are only available on Linux platforms and macOS arm64 platforms that support shared memory segments. On supported platforms, they are enabled by default. Applications can be built without the counters by specifying the cmake option -DENABLE_SHM_COUNTERS=OFF. Additionally, if performance counters are already compiled, they can be disabled at runtime by specifying the environment variable MONGOC_DISABLE_SHM.

Performance counters keep track of the following:

• Active and Disposed Cursors
• Active and Disposed Clients, Client Pools, and Socket Streams.
• Number of operations sent and received, by type.
• Bytes transferred and received.
• Authentication successes and failures.
• Number of wire protocol errors.

NOTE:

An operation is considered "sent" when one or more bytes of the corresponding message is written to the stream, regardless of whether the entire message is successfully written or if the operation ultimately succeeds or fails. This does not include bytes that may be written during the stream connection process, such as TLS handshake messages.

To access counters for a given process, simply provide the process id to the mongoc-stat program installed with the MongoDB C Driver.

$ mongoc-stat 22203
   Operations : Egress Total        : The number of sent operations.                    : 13247
   Operations : Ingress Total       : The number of received operations.                : 13246
   Operations : Egress Queries      : The number of sent Query operations.              : 13247
   Operations : Ingress Queries     : The number of received Query operations.          : 0
   Operations : Egress GetMore      : The number of sent GetMore operations.            : 0
   Operations : Ingress GetMore     : The number of received GetMore operations.        : 0
   Operations : Egress Insert       : The number of sent Insert operations.             : 0
   Operations : Ingress Insert      : The number of received Insert operations.         : 0
   Operations : Egress Delete       : The number of sent Delete operations.             : 0
   Operations : Ingress Delete      : The number of received Delete operations.         : 0
   Operations : Egress Update       : The number of sent Update operations.             : 0
   Operations : Ingress Update      : The number of received Update operations.         : 0
   Operations : Egress KillCursors  : The number of sent KillCursors operations.        : 0
   Operations : Ingress KillCursors : The number of received KillCursors operations.    : 0
   Operations : Egress Msg          : The number of sent Msg operations.                : 0
   Operations : Ingress Msg         : The number of received Msg operations.            : 0
   Operations : Egress Reply        : The number of sent Reply operations.              : 0
   Operations : Ingress Reply       : The number of received Reply operations.          : 13246
      Cursors : Active              : The number of active cursors.                     : 1
      Cursors : Disposed            : The number of disposed cursors.                   : 13246
      Clients : Active              : The number of active clients.                     : 1
      Clients : Disposed            : The number of disposed clients.                   : 0
      Streams : Active              : The number of active streams.                     : 1
      Streams : Disposed            : The number of disposed streams.                   : 0
      Streams : Egress Bytes        : The number of bytes sent.                         : 794931
      Streams : Ingress Bytes       : The number of bytes received.                     : 589694
      Streams : N Socket Timeouts   : The number of socket timeouts.                    : 0
 Client Pools : Active              : The number of active client pools.                : 1
 Client Pools : Disposed            : The number of disposed client pools.              : 0
     Protocol : Ingress Errors      : The number of protocol errors on ingress.         : 0
         Auth : Failures            : The number of failed authentication requests.     : 0
         Auth : Success             : The number of successful authentication requests. : 0

Think you've found a bug? Want to see a new feature in the MongoDB C driver? Please open a case in our issue management tool, JIRA:

• Create an account and login.
• Navigate to the CDRIVER project.
• Click Create Issue - Please provide as much information as possible about the issue type and how to reproduce it.

Bug reports in JIRA for all driver projects (i.e. CDRIVER, CSHARP, JAVA) and the Core Server (i.e. SERVER) project are public.

Enable TLS by including tls=true in the URI.

mongoc_uri_t *uri = mongoc_uri_new ("mongodb://localhost:27017/");
mongoc_uri_set_option_as_bool (uri, MONGOC_URI_TLS, true);

mongoc_client_t *client = mongoc_client_new_from_uri (uri);

The following URI options may be used to further configure TLS:

Alternatively, the mongoc_ssl_opt_t struct may be used to configure TLS with mongoc_client_set_ssl_opts() or mongoc_client_pool_set_ssl_opts(). Most of the configurable options can be set using the Connection String URI.

The only exclusions are crl_file and ca_dir. Those may only be set with mongoc_ssl_opt_t.

When MongoDB is started with TLS enabled, it will by default require the client to provide a client certificate issued by a certificate authority specified by --tlsCAFile, or an authority trusted by the native certificate store in use on the server.

To provide the client certificate, set the tlsCertificateKeyFile in the URI to a PEM armored certificate file.

mongoc_uri_t *uri = mongoc_uri_new ("mongodb://localhost:27017/");
mongoc_uri_set_option_as_bool (uri, MONGOC_URI_TLS, true);
mongoc_uri_set_option_as_utf8 (uri, MONGOC_URI_TLSCERTIFICATEKEYFILE, "/path/to/client-certificate.pem");

mongoc_client_t *client = mongoc_client_new_from_uri (uri);

The MongoDB C Driver will automatically verify the validity of the server certificate, such as issued by configured Certificate Authority, hostname validation, and expiration.

To overwrite this behavior, it is possible to disable hostname validation, OCSP endpoint revocation checking, revocation checking entirely, and allow invalid certificates.

This behavior is controlled using the tlsAllowInvalidHostnames, tlsDisableOCSPEndpointCheck, tlsDisableCertificateRevocationCheck, and tlsAllowInvalidCertificates options respectively. By default, all are set to false.

It is not recommended to change these defaults as it exposes the client to Man In The Middle attacks (when tlsAllowInvalidHostnames is set), invalid certificates (when tlsAllowInvalidCertificates is set), or potentially revoked certificates (when tlsDisableOCSPEndpointCheck or tlsDisableCertificateRevocationCheck are set).

By default, libmongoc will attempt to find a supported TLS library and enable TLS support. This is controlled by the cmake flag ENABLE_SSL, which is set to AUTO by default. Valid values are:

• AUTO the default behavior. Link to the system's native TLS library, or attempt to find OpenSSL.
• DARWIN link to Secure Transport, the native TLS library on macOS.
• WINDOWS link to Secure Channel, the native TLS library on Windows.
• OPENSSL link to OpenSSL (libssl). An optional install path may be specified with OPENSSL_ROOT.
• LIBRESSL link to LibreSSL's libtls. (LibreSSL's compatible libssl may be linked to by setting OPENSSL).
• OFF disable TLS support.

The MongoDB C Driver uses OpenSSL, if available, on Linux and Unix platforms (besides macOS). Industry best practices and some regulations require the use of TLS 1.1 or newer, which requires at least OpenSSL 1.0.1. Check your OpenSSL version like so:

$ openssl version

Ensure your system's OpenSSL is a recent version (at least 1.0.1), or install a recent version in a non-system path and build against it with:

cmake -DOPENSSL_ROOT_DIR=/absolute/path/to/openssl

When compiled against OpenSSL, the driver will attempt to load the system default certificate store, as configured by the distribution. That can be overridden by setting the tlsCAFile URI option or with the fields ca_file and ca_dir in the mongoc_ssl_opt_t.

The Online Certificate Status Protocol (OCSP) (see RFC 6960) is fully supported when using OpenSSL 1.0.1+ with the following notes:

• When a crl_file is set with mongoc_ssl_opt_t, and the crl_file revokes the server's certificate, the certificate is considered revoked (even if the certificate has a valid stapled OCSP response)

The MongoDB C Driver supports LibreSSL through the use of OpenSSL compatibility checks when configured to compile against openssl. It also supports the new libtls library when configured to build against libressl.

When compiled against the Windows native libraries, the crl_file option of a mongoc_ssl_opt_t is not supported, and will issue an error if used.

Setting tlsDisableOCSPEndpointCheck and tlsDisableCertificateRevocationCheck has no effect.

The Online Certificate Status Protocol (OCSP) (see RFC 6960) is partially supported with the following notes:

• The Must-Staple extension (see RFC 7633) is ignored. Connection may continue if a Must-Staple certificate is presented with no stapled response (unless the client receives a revoked response from an OCSP responder).
• Connection will continue if a Must-Staple certificate is presented without a stapled response and the OCSP responder is down.

The MongoDB C Driver supports the Windows native TLS library (Secure Channel, or SChannel), and its native crypto library (Cryptography API: Next Generation, or CNG).

When compiled against the Windows native libraries, the ca_dir option of a mongoc_ssl_opt_t is not supported, and will issue an error if used.

Encrypted PEM files (e.g., setting tlsCertificateKeyPassword) are also not supported, and will result in error when attempting to load them.

When tlsCAFile is set, the driver will only allow server certificates issued by the authority (or authorities) provided. When no tlsCAFile is set, the driver will look up the Certificate Authority using the System Local Machine Root certificate store to confirm the provided certificate.

When crl_file is set with mongoc_ssl_opt_t, the driver will import the revocation list to the System Local Machine Root certificate store.

Setting tlsDisableOCSPEndpointCheck has no effect.

The Online Certificate Status Protocol (OCSP) (see RFC 6960) is partially supported with the following notes:

• The Must-Staple extension (see RFC 7633) is ignored. Connection may continue if a Must-Staple certificate is presented with no stapled response (unless the client receives a revoked response from an OCSP responder).
• When a crl_file is set with mongoc_ssl_opt_t, and the crl_file revokes the server's certificate, the OCSP response takes precedence. E.g. if the server presents a certificate with a valid stapled OCSP response, the certificate is considered valid even if the crl_file marks it as revoked.
• Connection will continue if a Must-Staple certificate is presented without a stapled response and the OCSP responder is down.

The MongoDB C Driver supports the Darwin (OS X, macOS, iOS, etc.) native TLS library (Secure Transport), and its native crypto library (Common Crypto, or CC).

When compiled against Secure Transport, the ca_dir and crl_file options of a mongoc_ssl_opt_t are not supported. An error is issued if either are used.

When tlsCAFile is set, the driver will only allow server certificates issued by the authority (or authorities) provided. When no tlsCAFile is set, the driver will use the Certificate Authorities in the currently unlocked keychains.

Setting tlsDisableOCSPEndpointCheck and tlsDisableCertificateRevocationCheck has no effect.

The Online Certificate Status Protocol (OCSP) (see RFC 6960) is partially supported with the following notes.

• The Must-Staple extension (see RFC 7633) is ignored. Connection may continue if a Must-Staple certificate is presented with no stapled response (unless the client receives a revoked response from an OCSP responder).
• Connection will continue if a Must-Staple certificate is presented without a stapled response and the OCSP responder is down.

Drivers for some other languages provide helper functions to perform certain common tasks. In the C Driver we must explicitly build commands to send to the server.

First we'll write some code to insert sample data:

doc-common-insert.c

/* Don't try to compile this file on its own. It's meant to be #included
   by example code */

/* Insert some sample data */
bool
insert_data (mongoc_collection_t *collection)
{
   mongoc_bulk_operation_t *bulk;
   enum N { ndocs = 4 };
   bson_t *docs[ndocs];
   bson_error_t error;
   int i = 0;
   bool ret;

   bulk = mongoc_collection_create_bulk_operation_with_opts (collection, NULL);

   docs[0] = BCON_NEW ("x", BCON_DOUBLE (1.0), "tags", "[", "dog", "cat", "]");
   docs[1] = BCON_NEW ("x", BCON_DOUBLE (2.0), "tags", "[", "cat", "]");
   docs[2] = BCON_NEW (
      "x", BCON_DOUBLE (2.0), "tags", "[", "mouse", "cat", "dog", "]");
   docs[3] = BCON_NEW ("x", BCON_DOUBLE (3.0), "tags", "[", "]");

   for (i = 0; i < ndocs; i++) {
      mongoc_bulk_operation_insert (bulk, docs[i]);
      bson_destroy (docs[i]);
      docs[i] = NULL;
   }

   ret = mongoc_bulk_operation_execute (bulk, NULL, &error);

   if (!ret) {
      fprintf (stderr, "Error inserting data: %s\n", error.message);
   }

   mongoc_bulk_operation_destroy (bulk);
   return ret;
}

/* A helper which we'll use a lot later on */
void
print_res (const bson_t *reply)
{
   char *str;
   BSON_ASSERT (reply);
   str = bson_as_canonical_extended_json (reply, NULL);
   printf ("%s\n", str);
   bson_free (str);
}

This is how to use the explain command in MongoDB 3.2+:

explain.c

bool
explain (mongoc_collection_t *collection)
{
   bson_t *command;
   bson_t reply;
   bson_error_t error;
   bool res;

   command = BCON_NEW ("explain",
                       "{",
                       "find",
                       BCON_UTF8 (COLLECTION_NAME),
                       "filter",
                       "{",
                       "x",
                       BCON_INT32 (1),
                       "}",
                       "}");
   res = mongoc_collection_command_simple (
      collection, command, NULL, &reply, &error);
   if (!res) {
      fprintf (stderr, "Error with explain: %s\n", error.message);
      goto cleanup;
   }

   /* Do something with the reply */
   print_res (&reply);

cleanup:
   bson_destroy (&reply);
   bson_destroy (command);
   return res;
}

common-operations.c

/*
 * Copyright 2016 MongoDB, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */


#include <mongoc/mongoc.h>
#include <stdio.h>


const char *COLLECTION_NAME = "things";

#include "../doc-common-insert.c"
#include "explain.c"


int
main (int argc, char *argv[])
{
   mongoc_database_t *database = NULL;
   mongoc_client_t *client = NULL;
   mongoc_collection_t *collection = NULL;
   mongoc_uri_t *uri = NULL;
   bson_error_t error;
   char *host_and_port;
   int res = 0;

   if (argc < 2 || argc > 3) {
      fprintf (stderr,
               "usage: %s MONGOD-1-CONNECTION-STRING "
               "[MONGOD-2-HOST-NAME:MONGOD-2-PORT]\n",
               argv[0]);
      fprintf (stderr,
               "MONGOD-1-CONNECTION-STRING can be "
               "of the following forms:\n");
      fprintf (stderr, "localhost\t\t\t\tlocal machine\n");
      fprintf (stderr, "localhost:27018\t\t\t\tlocal machine on port 27018\n");
      fprintf (stderr,
               "mongodb://user:pass@localhost:27017\t"
               "local machine on port 27017, and authenticate with username "
               "user and password pass\n");
      return EXIT_FAILURE;
   }

   mongoc_init ();

   if (strncmp (argv[1], "mongodb://", 10) == 0) {
      host_and_port = bson_strdup (argv[1]);
   } else {
      host_and_port = bson_strdup_printf ("mongodb://%s", argv[1]);
   }

   uri = mongoc_uri_new_with_error (host_and_port, &error);
   if (!uri) {
      fprintf (stderr,
               "failed to parse URI: %s\n"
               "error message:       %s\n",
               host_and_port,
               error.message);
      res = EXIT_FAILURE;
      goto cleanup;
   }

   client = mongoc_client_new_from_uri (uri);
   if (!client) {
      res = EXIT_FAILURE;
      goto cleanup;
   }

   mongoc_client_set_error_api (client, 2);
   database = mongoc_client_get_database (client, "test");
   collection = mongoc_database_get_collection (database, COLLECTION_NAME);

   printf ("Inserting data\n");
   if (!insert_data (collection)) {
      res = EXIT_FAILURE;
      goto cleanup;
   }

   printf ("explain\n");
   if (!explain (collection)) {
      res = EXIT_FAILURE;
      goto cleanup;
   }

cleanup:
   if (collection) {
      mongoc_collection_destroy (collection);
   }

   if (database) {
      mongoc_database_destroy (database);
   }

   if (client) {
      mongoc_client_destroy (client);
   }

   if (uri) {
      mongoc_uri_destroy (uri);
   }

   bson_free (host_and_port);
   mongoc_cleanup ();
   return res;
}

First launch two separate instances of mongod (must be done from separate shells):

$ mongod

$ mkdir /tmp/db2
$ mongod --dbpath /tmp/db2 --port 27018 # second instance

Now compile and run the example program:

$ cd examples/common_operations/$ gcc -Wall -o example common-operations.c $(pkg-config --cflags --libs libmongoc-1.0)$ ./example localhost:27017 localhost:27018
Inserting data
explain
{
   "executionStats" : {
      "allPlansExecution" : [],
      "executionStages" : {
         "advanced" : 19,
         "direction" : "forward" ,
         "docsExamined" : 76,
         "executionTimeMillisEstimate" : 0,
         "filter" : {
            "x" : {
               "$eq" : 1
            }
         },
         "invalidates" : 0,
         "isEOF" : 1,
         "nReturned" : 19,
         "needTime" : 58,
         "needYield" : 0,
         "restoreState" : 0,
         "saveState" : 0,
         "stage" : "COLLSCAN" ,
         "works" : 78
      },
      "executionSuccess" : true,
      "executionTimeMillis" : 0,
      "nReturned" : 19,
      "totalDocsExamined" : 76,
      "totalKeysExamined" : 0
   },
   "ok" : 1,
   "queryPlanner" : {
      "indexFilterSet" : false,
      "namespace" : "test.things",
      "parsedQuery" : {
         "x" : {
            "$eq" : 1
         }
      },
      "plannerVersion" : 1,
      "rejectedPlans" : [],
      "winningPlan" : {
         "direction" : "forward" ,
         "filter" : {
            "x" : {
               "$eq" : 1
            }
         },
         "stage" : "COLLSCAN"
      }
   },
   "serverInfo" : {
      "gitVersion" : "05552b562c7a0b3143a729aaa0838e558dc49b25" ,
      "host" : "MacBook-Pro-57.local",
      "port" : 27017,
      "version" : "3.2.6"
   }
}

The following guide contains information specific to certain types of MongoDB configurations.

For an example of connecting to a simple standalone server, see the Tutorial. To establish a connection with authentication options enabled, see the Authentication page. To see an example of a connection with data compression, see the Data Compression page.

Connecting to a replica set is much like connecting to a standalone MongoDB server. Simply specify the replica set name using the ?replicaSet=myreplset URI option.

#include <bson/bson.h>
#include <mongoc/mongoc.h>

int
main (int argc, char *argv[])
{
   mongoc_client_t *client;

   mongoc_init ();

   /* Create our MongoDB Client */
   client = mongoc_client_new (
      "mongodb://host01:27017,host02:27017,host03:27017/?replicaSet=myreplset");

   /* Do some work */
   /* TODO */

   /* Clean up */
   mongoc_client_destroy (client);
   mongoc_cleanup ();

   return 0;
}

TIP:

Multiple hostnames can be specified in the MongoDB connection string URI, with a comma separating hosts in the seed list.

It is recommended to use a seed list of members of the replica set to allow the driver to connect to any node.

To connect to a sharded cluster, specify the mongos nodes the client should connect to. The C Driver will automatically detect that it has connected to a mongos sharding server.

If more than one hostname is specified, a seed list will be created to attempt failover between the mongos instances.

WARNING:

#include <bson/bson.h>
#include <mongoc/mongoc.h>

int
main (int argc, char *argv[])
{
   mongoc_client_t *client;

   mongoc_init ();

   /* Create our MongoDB Client */
   client = mongoc_client_new ("mongodb://myshard01:27017/");

   /* Do something with client ... */

   /* Free the client */
   mongoc_client_destroy (client);

   mongoc_cleanup ();

   return 0;
}

The MongoDB C Driver will automatically resolve IPv6 addresses from host names. However, to specify an IPv6 address directly, wrap the address in [].

mongoc_uri_t *uri = mongoc_uri_new ("mongodb://[::1]:27017");

If connecting to a hostname that has both IPv4 and IPv6 DNS records, the behavior follows RFC-6555. A connection to the IPv6 address is attempted first. If IPv6 fails, then a connection is attempted to the IPv4 address. If the connection attempt to IPv6 does not complete within 250ms, then IPv4 is tried in parallel. Whichever succeeds connection first cancels the other. The successful DNS result is cached for 10 minutes.

As a consequence, attempts to connect to a mongod only listening on IPv4 may be delayed if there are both A (IPv4) and AAAA (IPv6) DNS records associated with the host.

To avoid a delay, configure hostnames to match the MongoDB configuration. That is, only create an A record if the mongod is only listening on IPv4.

On UNIX-like systems, the C Driver can connect directly to a MongoDB server using a UNIX domain socket. Pass the URL-encoded path to the socket, which must be suffixed with .sock. For example, to connect to a domain socket at /tmp/mongodb-27017.sock:

mongoc_uri_t *uri = mongoc_uri_new ("mongodb://%2Ftmp%2Fmongodb-27017.sock");

Include username and password like so:

mongoc_uri_t *uri = mongoc_uri_new ("mongodb://user:pass@%2Ftmp%2Fmongodb-27017.sock");

These are instructions for configuring TLS/SSL connections.

To run a server locally (on port 27017, for example):

$ mongod --port 27017 --tlsMode requireTLS --tlsCertificateKeyFile server.pem --tlsCAFile ca.pem

Add /?tls=true to the end of a client URI.

mongoc_client_t *client = NULL;
client = mongoc_client_new ("mongodb://localhost:27017/?tls=true");

MongoDB requires client certificates by default, unless the --tlsAllowConnectionsWithoutCertificates is provided. The C Driver can be configured to present a client certificate using the URI option tlsCertificateKeyFile, which may be referenced through the constant MONGOC_URI_TLSCERTIFICATEKEYFILE.

mongoc_client_t *client = NULL;
mongoc_uri_t *uri = mongoc_uri_new ("mongodb://localhost:27017/?tls=true");
mongoc_uri_set_option_as_utf8 (uri, MONGOC_URI_TLSCERTIFICATEKEYFILE, "client.pem");

client = mongoc_client_new_from_uri (uri);

The client certificate provided by tlsCertificateKeyFile must be issued by one of the server trusted Certificate Authorities listed in --tlsCAFile, or issued by a CA in the native certificate store on the server when omitted.

See Configuring TLS for more information on the various TLS related options.

This content has been relocated to the Data Compression page.

The full list of connection options can be found in the mongoc_uri_t docs.

Certain socket/connection related options are not configurable:

The MongoDB C driver has two connection modes: single-threaded and pooled. Single-threaded mode is optimized for embedding the driver within languages like PHP. Multi-threaded programs should use pooled mode: this mode minimizes the total connection count, and in pooled mode background threads monitor the MongoDB server topology, so the program need not block to scan it.

In single mode, your program creates a mongoc_client_t directly:

mongoc_client_t *client = mongoc_client_new (
   "mongodb://hostA,hostB/?replicaSet=my_rs");

The client connects on demand when your program first uses it for a MongoDB operation. Using a non-blocking socket per server, it begins a check on each server concurrently, and uses the asynchronous poll or select function to receive events from the sockets, until all have responded or timed out. Put another way, in single-threaded mode the C Driver fans out to begin all checks concurrently, then fans in once all checks have completed or timed out. Once the scan completes, the client executes your program's operation and returns.

In single mode, the client re-scans the server topology roughly once per minute. If more than a minute has elapsed since the previous scan, the next operation on the client will block while the client completes its scan. This interval is configurable with heartbeatFrequencyMS in the connection string. (See mongoc_uri_t.)

A single client opens one connection per server in your topology: these connections are used both for scanning the topology and performing normal operations.

To activate pooled mode, create a mongoc_client_pool_t:

mongoc_uri_t *uri = mongoc_uri_new (
   "mongodb://hostA,hostB/?replicaSet=my_rs");

mongoc_client_pool_t *pool = mongoc_client_pool_new (uri);

When your program first calls mongoc_client_pool_pop(), the pool launches monitoring threads in the background. Monitoring threads independently connect to all servers in the connection string. As monitoring threads receive hello responses from the servers, they update the shared view of the server topology. Additional monitoring threads and connections are created as new servers are discovered. Monitoring threads are terminated when servers are removed from the shared view of the server topology.

Each thread that executes MongoDB operations must check out a client from the pool:

mongoc_client_t *client = mongoc_client_pool_pop (pool);

/* use the client for operations ... */

mongoc_client_pool_push (pool, client);

The mongoc_client_t object is not thread-safe, only the mongoc_client_pool_t is.

When the driver is in pooled mode, your program's operations are unblocked as soon as monitoring discovers a usable server. For example, if a thread in your program is waiting to execute an "insert" on the primary, it is unblocked as soon as the primary is discovered, rather than waiting for all secondaries to be checked as well.

The pool opens one connection per server for monitoring, and each client opens its own connection to each server it uses for application operations. Background monitoring threads re-scan servers independently roughly every 10 seconds. This interval is configurable with heartbeatFrequencyMS in the connection string. (See mongoc_uri_t.)

The connection string can also specify waitQueueTimeoutMS to limit the time that mongoc_client_pool_pop() will wait for a client from the pool.  (See mongoc_uri_t.)  If waitQueueTimeoutMS is specified, then it is necessary to confirm that a client was actually returned:

mongoc_uri_t *uri = mongoc_uri_new (
   "mongodb://hostA,hostB/?replicaSet=my_rs&waitQueueTimeoutMS=1000");

mongoc_client_pool_t *pool = mongoc_client_pool_new (uri);

mongoc_client_t *client = mongoc_client_pool_pop (pool);

if (client) {
   /* use the client for operations ... */

   mongoc_client_pool_push (pool, client);
} else {
   /* take appropriate action for a timeout */
}

See Connection Pool Options to configure pool size and behavior, and see mongoc_client_pool_t for an extended example of a multi-threaded program that uses the driver in pooled mode.

The following guide explains how data compression support works between the MongoDB server and client. It also shows an example of how to connect to a server with data compression.

MongoDB 3.4 added Snappy compression support, while zlib compression was added in 3.6, and zstd compression in 4.2. To enable compression support the client must be configured with which compressors to use:

mongoc_client_t *client = NULL;
client = mongoc_client_new ("mongodb://localhost:27017/?compressors=snappy,zlib,zstd");

The compressors option specifies the priority order of compressors the client wants to use. Messages are compressed if the client and server share any compressors in common.

Note that the compressor used by the server might not be the same compressor as the client used.  For example, if the client uses the connection string compressors=zlib,snappy the client will use zlib compression to send data (if possible), but the server might still reply using snappy, depending on how the server was configured.

The driver must be built with zlib and/or snappy and/or zstd support to enable compression support, any unknown (or not compiled in) compressor value will be ignored.

Cursors exist on a MongoDB server. However, the mongoc_cursor_t structure gives the local process a handle to the cursor. It is possible for errors to occur on the server while iterating a cursor on the client. Even a network partition may occur. This means that applications should be robust in handling cursor failures.

While iterating cursors, you should check to see if an error has occurred. See the following example for how to robustly check for errors.

static void
print_all_documents (mongoc_collection_t *collection)
{
   mongoc_cursor_t *cursor;
   const bson_t *doc;
   bson_error_t error;
   bson_t query = BSON_INITIALIZER;
   char *str;

   cursor = mongoc_collection_find_with_opts (collection, query, NULL, NULL);

   while (mongoc_cursor_next (cursor, &doc)) {
      str = bson_as_canonical_extended_json (doc, NULL);
      printf ("%s\n", str);
      bson_free (str);
   }

   if (mongoc_cursor_error (cursor, &error)) {
      fprintf (stderr, "Failed to iterate all documents: %s\n", error.message);
   }

   mongoc_cursor_destroy (cursor);
}

The MongoDB C driver will automatically destroy a server-side cursor when mongoc_cursor_destroy() is called. Failure to call this function when done with a cursor will leak memory client side as well as consume extra memory server side. If the cursor was configured to never timeout, it will become a memory leak on the server.

Tailable cursors are cursors that remain open even after they've returned a final result. This way, if more documents are added to a collection (i.e., to the cursor's result set), then you can continue to call mongoc_cursor_next() to retrieve those additional results.

Here's a complete test case that demonstrates the use of tailable cursors.

NOTE:

An example to tail the oplog from a replica set.

mongoc-tail.c

#include <bson/bson.h>
#include <mongoc/mongoc.h>
#include <stdio.h>
#include <stdlib.h>

#ifdef _WIN32
#define sleep(_n) Sleep ((_n) *1000)
#endif


static void
print_bson (const bson_t *b)
{
   char *str;

   str = bson_as_canonical_extended_json (b, NULL);
   fprintf (stdout, "%s\n", str);
   bson_free (str);
}


static mongoc_cursor_t *
query_collection (mongoc_collection_t *collection, uint32_t last_time)
{
   mongoc_cursor_t *cursor;
   bson_t query;
   bson_t gt;
   bson_t opts;

   BSON_ASSERT (collection);

   bson_init (&query);
   BSON_APPEND_DOCUMENT_BEGIN (&query, "ts", &gt);
   BSON_APPEND_TIMESTAMP (&gt, "$gt", last_time, 0);
   bson_append_document_end (&query, &gt);

   bson_init (&opts);
   BSON_APPEND_BOOL (&opts, "tailable", true);
   BSON_APPEND_BOOL (&opts, "awaitData", true);

   cursor = mongoc_collection_find_with_opts (collection, &query, &opts, NULL);

   bson_destroy (&query);
   bson_destroy (&opts);

   return cursor;
}


static void
tail_collection (mongoc_collection_t *collection)
{
   mongoc_cursor_t *cursor;
   uint32_t last_time;
   const bson_t *doc;
   bson_error_t error;
   bson_iter_t iter;

   BSON_ASSERT (collection);

   last_time = (uint32_t) time (NULL);

   while (true) {
      cursor = query_collection (collection, last_time);
      while (!mongoc_cursor_error (cursor, &error) &&
             mongoc_cursor_more (cursor)) {
         if (mongoc_cursor_next (cursor, &doc)) {
            if (bson_iter_init_find (&iter, doc, "ts") &&
                BSON_ITER_HOLDS_TIMESTAMP (&iter)) {
               bson_iter_timestamp (&iter, &last_time, NULL);
            }
            print_bson (doc);
         }
      }
      if (mongoc_cursor_error (cursor, &error)) {
         if (error.domain == MONGOC_ERROR_SERVER) {
            fprintf (stderr, "%s\n", error.message);
            exit (1);
         }
      }

      mongoc_cursor_destroy (cursor);
      sleep (1);
   }
}


int
main (int argc, char *argv[])
{
   mongoc_collection_t *collection;
   mongoc_client_t *client;
   mongoc_uri_t *uri;
   bson_error_t error;

   if (argc != 2) {
      fprintf (stderr, "usage: %s MONGO_URI\n", argv[0]);
      return EXIT_FAILURE;
   }

   mongoc_init ();

   uri = mongoc_uri_new_with_error (argv[1], &error);
   if (!uri) {
      fprintf (stderr,
               "failed to parse URI: %s\n"
               "error message:       %s\n",
               argv[1],
               error.message);
      return EXIT_FAILURE;
   }

   client = mongoc_client_new_from_uri (uri);
   if (!client) {
      return EXIT_FAILURE;
   }

   mongoc_client_set_error_api (client, 2);

   collection = mongoc_client_get_collection (client, "local", "oplog.rs");

   tail_collection (collection);

   mongoc_collection_destroy (collection);
   mongoc_uri_destroy (uri);
   mongoc_client_destroy (client);

   return EXIT_SUCCESS;
}

Let's compile and run this example against a replica set to see updates as they are made.

$ gcc -Wall -o mongoc-tail mongoc-tail.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./mongoc-tail mongodb://example.com/?replicaSet=myReplSet
{
    "h" : -8458503739429355503,
    "ns" : "test.test",
    "o" : {
        "_id" : {
            "$oid" : "5372ab0a25164be923d10d50"
        }
    },
    "op" : "i",
    "ts" : {
        "$timestamp" : {
            "i" : 1,
            "t" : 1400023818
        }
    },
    "v" : 2
}

The line of output is a sample from performing db.test.insert({}) from the mongo shell on the replica set.

SEE ALSO:

mongoc_cursor_set_max_await_time_ms().

This tutorial explains how to take advantage of MongoDB C driver bulk write operation features. Executing write operations in batches reduces the number of network round trips, increasing write throughput.

First we need to fetch a bulk operation handle from the mongoc_collection_t.

mongoc_bulk_operation_t *bulk =
   mongoc_collection_create_bulk_operation_with_opts (collection, NULL);

We can now start inserting documents to the bulk operation. These will be buffered until we execute the operation.

The bulk operation will coalesce insertions as a single batch for each consecutive call to mongoc_bulk_operation_insert(). This creates a pipelined effect when possible.

To execute the bulk operation and receive the result we call mongoc_bulk_operation_execute().

bulk1.c

#include <assert.h>
#include <mongoc/mongoc.h>
#include <stdio.h>

static void
bulk1 (mongoc_collection_t *collection)
{
   mongoc_bulk_operation_t *bulk;
   bson_error_t error;
   bson_t *doc;
   bson_t reply;
   char *str;
   bool ret;
   int i;

   bulk = mongoc_collection_create_bulk_operation_with_opts (collection, NULL);

   for (i = 0; i < 10000; i++) {
      doc = BCON_NEW ("i", BCON_INT32 (i));
      mongoc_bulk_operation_insert (bulk, doc);
      bson_destroy (doc);
   }

   ret = mongoc_bulk_operation_execute (bulk, &reply, &error);

   str = bson_as_canonical_extended_json (&reply, NULL);
   printf ("%s\n", str);
   bson_free (str);

   if (!ret) {
      fprintf (stderr, "Error: %s\n", error.message);
   }

   bson_destroy (&reply);
   mongoc_bulk_operation_destroy (bulk);
}

int
main (void)
{
   mongoc_client_t *client;
   mongoc_collection_t *collection;
   const char *uri_string = "mongodb://localhost/?appname=bulk1-example";
   mongoc_uri_t *uri;
   bson_error_t error;

   mongoc_init ();

   uri = mongoc_uri_new_with_error (uri_string, &error);
   if (!uri) {
      fprintf (stderr,
               "failed to parse URI: %s\n"
               "error message:       %s\n",
               uri_string,
               error.message);
      return EXIT_FAILURE;
   }

   client = mongoc_client_new_from_uri (uri);
   if (!client) {
      return EXIT_FAILURE;
   }

   mongoc_client_set_error_api (client, 2);
   collection = mongoc_client_get_collection (client, "test", "test");

   bulk1 (collection);

   mongoc_uri_destroy (uri);
   mongoc_collection_destroy (collection);
   mongoc_client_destroy (client);

   mongoc_cleanup ();

   return EXIT_SUCCESS;
}

Example reply document:

{"nInserted"   : 10000,
 "nMatched"    : 0,
 "nModified"   : 0,
 "nRemoved"    : 0,
 "nUpserted"   : 0,
 "writeErrors" : []
 "writeConcernErrors" : [] }

MongoDB C driver also supports executing mixed bulk write operations. A batch of insert, update, and remove operations can be executed together using the bulk write operations API.

Ordered bulk write operations are batched and sent to the server in the order provided for serial execution. The reply document describes the type and count of operations performed.

bulk2.c

#include <assert.h>
#include <mongoc/mongoc.h>
#include <stdio.h>

static void
bulk2 (mongoc_collection_t *collection)
{
   mongoc_bulk_operation_t *bulk;
   bson_error_t error;
   bson_t *query;
   bson_t *doc;
   bson_t *opts;
   bson_t reply;
   char *str;
   bool ret;
   int i;

   bulk = mongoc_collection_create_bulk_operation_with_opts (collection, NULL);

   /* Remove everything */
   query = bson_new ();
   mongoc_bulk_operation_remove (bulk, query);
   bson_destroy (query);

   /* Add a few documents */
   for (i = 1; i < 4; i++) {
      doc = BCON_NEW ("_id", BCON_INT32 (i));
      mongoc_bulk_operation_insert (bulk, doc);
      bson_destroy (doc);
   }

   /* {_id: 1} => {$set: {foo: "bar"}} */
   query = BCON_NEW ("_id", BCON_INT32 (1));
   doc = BCON_NEW ("$set", "{", "foo", BCON_UTF8 ("bar"), "}");
   mongoc_bulk_operation_update_many_with_opts (bulk, query, doc, NULL, &error);
   bson_destroy (query);
   bson_destroy (doc);

   /* {_id: 4} => {'$inc': {'j': 1}} (upsert) */
   opts = BCON_NEW ("upsert", BCON_BOOL (true));
   query = BCON_NEW ("_id", BCON_INT32 (4));
   doc = BCON_NEW ("$inc", "{", "j", BCON_INT32 (1), "}");
   mongoc_bulk_operation_update_many_with_opts (bulk, query, doc, opts, &error);
   bson_destroy (query);
   bson_destroy (doc);
   bson_destroy (opts);

   /* replace {j:1} with {j:2} */
   query = BCON_NEW ("j", BCON_INT32 (1));
   doc = BCON_NEW ("j", BCON_INT32 (2));
   mongoc_bulk_operation_replace_one_with_opts (bulk, query, doc, NULL, &error);
   bson_destroy (query);
   bson_destroy (doc);

   ret = mongoc_bulk_operation_execute (bulk, &reply, &error);

   str = bson_as_canonical_extended_json (&reply, NULL);
   printf ("%s\n", str);
   bson_free (str);

   if (!ret) {
      printf ("Error: %s\n", error.message);
   }

   bson_destroy (&reply);
   mongoc_bulk_operation_destroy (bulk);
}

int
main (void)
{
   mongoc_client_t *client;
   mongoc_collection_t *collection;
   const char *uri_string = "mongodb://localhost/?appname=bulk2-example";
   mongoc_uri_t *uri;
   bson_error_t error;

   mongoc_init ();

   uri = mongoc_uri_new_with_error (uri_string, &error);
   if (!uri) {
      fprintf (stderr,
               "failed to parse URI: %s\n"
               "error message:       %s\n",
               uri_string,
               error.message);
      return EXIT_FAILURE;
   }

   client = mongoc_client_new_from_uri (uri);
   if (!client) {
      return EXIT_FAILURE;
   }

   mongoc_client_set_error_api (client, 2);
   collection = mongoc_client_get_collection (client, "test", "test");

   bulk2 (collection);

   mongoc_uri_destroy (uri);
   mongoc_collection_destroy (collection);
   mongoc_client_destroy (client);

   mongoc_cleanup ();

   return EXIT_SUCCESS;
}

Example reply document:

{ "nInserted"   : 3,
  "nMatched"    : 2,
  "nModified"   : 2,
  "nRemoved"    : 10000,
  "nUpserted"   : 1,
  "upserted"    : [{"index" : 5, "_id" : 4}],
  "writeErrors" : []
  "writeConcernErrors" : [] }

The index field in the upserted array is the 0-based index of the upsert operation; in this example, the sixth operation of the overall bulk operation was an upsert, so its index is 5.

Unordered bulk write operations are batched and sent to the server in arbitrary order where they may be executed in parallel. Any errors that occur are reported after all operations are attempted.

In the next example the first and third operations fail due to the unique constraint on _id. Since we are doing unordered execution the second and fourth operations succeed.

bulk3.c

#include <assert.h>
#include <mongoc/mongoc.h>
#include <stdio.h>

static void
bulk3 (mongoc_collection_t *collection)
{
   bson_t opts = BSON_INITIALIZER;
   mongoc_bulk_operation_t *bulk;
   bson_error_t error;
   bson_t *query;
   bson_t *doc;
   bson_t reply;
   char *str;
   bool ret;

   /* false indicates unordered */
   BSON_APPEND_BOOL (&opts, "ordered", false);
   bulk = mongoc_collection_create_bulk_operation_with_opts (collection, &opts);
   bson_destroy (&opts);

   /* Add a document */
   doc = BCON_NEW ("_id", BCON_INT32 (1));
   mongoc_bulk_operation_insert (bulk, doc);
   bson_destroy (doc);

   /* remove {_id: 2} */
   query = BCON_NEW ("_id", BCON_INT32 (2));
   mongoc_bulk_operation_remove_one (bulk, query);
   bson_destroy (query);

   /* insert {_id: 3} */
   doc = BCON_NEW ("_id", BCON_INT32 (3));
   mongoc_bulk_operation_insert (bulk, doc);
   bson_destroy (doc);

   /* replace {_id:4} {'i': 1} */
   query = BCON_NEW ("_id", BCON_INT32 (4));
   doc = BCON_NEW ("i", BCON_INT32 (1));
   mongoc_bulk_operation_replace_one (bulk, query, doc, false);
   bson_destroy (query);
   bson_destroy (doc);

   ret = mongoc_bulk_operation_execute (bulk, &reply, &error);

   str = bson_as_canonical_extended_json (&reply, NULL);
   printf ("%s\n", str);
   bson_free (str);

   if (!ret) {
      printf ("Error: %s\n", error.message);
   }

   bson_destroy (&reply);
   mongoc_bulk_operation_destroy (bulk);
   bson_destroy (&opts);
}

int
main (void)
{
   mongoc_client_t *client;
   mongoc_collection_t *collection;
   const char *uri_string = "mongodb://localhost/?appname=bulk3-example";
   mongoc_uri_t *uri;
   bson_error_t error;

   mongoc_init ();

   uri = mongoc_uri_new_with_error (uri_string, &error);
   if (!uri) {
      fprintf (stderr,
               "failed to parse URI: %s\n"
               "error message:       %s\n",
               uri_string,
               error.message);
      return EXIT_FAILURE;
   }

   client = mongoc_client_new_from_uri (uri);
   if (!client) {
      return EXIT_FAILURE;
   }

   mongoc_client_set_error_api (client, 2);
   collection = mongoc_client_get_collection (client, "test", "test");

   bulk3 (collection);

   mongoc_uri_destroy (uri);
   mongoc_collection_destroy (collection);
   mongoc_client_destroy (client);

   mongoc_cleanup ();

   return EXIT_SUCCESS;
}

Example reply document:

{ "nInserted"    : 0,
  "nMatched"     : 1,
  "nModified"    : 1,
  "nRemoved"     : 1,
  "nUpserted"    : 0,
  "writeErrors"  : [
    { "index"  : 0,
      "code"   : 11000,
      "errmsg" : "E11000 duplicate key error index: test.test.$_id_ dup key: { : 1 }" },
    { "index"  : 2,
      "code"   : 11000,
      "errmsg" : "E11000 duplicate key error index: test.test.$_id_ dup key: { : 3 }" } ],
  "writeConcernErrors" : [] }

Error: E11000 duplicate key error index: test.test.$_id_ dup key: { : 1 }

The bson_error_t domain is MONGOC_ERROR_COMMAND and its code is 11000.

This feature is only available when using MongoDB 3.2 and later.

By default bulk operations are validated against the schema, if any is defined. In certain cases however it may be necessary to bypass the document validation.

bulk5.c

#include <assert.h>
#include <mongoc/mongoc.h>
#include <stdio.h>

static void
bulk5_fail (mongoc_collection_t *collection)
{
   mongoc_bulk_operation_t *bulk;
   bson_error_t error;
   bson_t *doc;
   bson_t reply;
   char *str;
   bool ret;

   bulk = mongoc_collection_create_bulk_operation_with_opts (collection, NULL);

   /* Two inserts */
   doc = BCON_NEW ("_id", BCON_INT32 (31));
   mongoc_bulk_operation_insert (bulk, doc);
   bson_destroy (doc);

   doc = BCON_NEW ("_id", BCON_INT32 (32));
   mongoc_bulk_operation_insert (bulk, doc);
   bson_destroy (doc);

   /* The above documents do not comply to the schema validation rules
    * we created previously, so this will result in an error */
   ret = mongoc_bulk_operation_execute (bulk, &reply, &error);

   str = bson_as_canonical_extended_json (&reply, NULL);
   printf ("%s\n", str);
   bson_free (str);

   if (!ret) {
      printf ("Error: %s\n", error.message);
   }

   bson_destroy (&reply);
   mongoc_bulk_operation_destroy (bulk);
}

static void
bulk5_success (mongoc_collection_t *collection)
{
   mongoc_bulk_operation_t *bulk;
   bson_error_t error;
   bson_t *doc;
   bson_t reply;
   char *str;
   bool ret;

   bulk = mongoc_collection_create_bulk_operation_with_opts (collection, NULL);

   /* Allow this document to bypass document validation.
    * NOTE: When authentication is enabled, the authenticated user must have
    * either the "dbadmin" or "restore" roles to bypass document validation */
   mongoc_bulk_operation_set_bypass_document_validation (bulk, true);

   /* Two inserts */
   doc = BCON_NEW ("_id", BCON_INT32 (31));
   mongoc_bulk_operation_insert (bulk, doc);
   bson_destroy (doc);

   doc = BCON_NEW ("_id", BCON_INT32 (32));
   mongoc_bulk_operation_insert (bulk, doc);
   bson_destroy (doc);

   ret = mongoc_bulk_operation_execute (bulk, &reply, &error);

   str = bson_as_canonical_extended_json (&reply, NULL);
   printf ("%s\n", str);
   bson_free (str);

   if (!ret) {
      printf ("Error: %s\n", error.message);
   }

   bson_destroy (&reply);
   mongoc_bulk_operation_destroy (bulk);
}

int
main (void)
{
   bson_t *options;
   bson_error_t error;
   mongoc_client_t *client;
   mongoc_collection_t *collection;
   mongoc_database_t *database;
   const char *uri_string = "mongodb://localhost/?appname=bulk5-example";
   mongoc_uri_t *uri;

   mongoc_init ();

   uri = mongoc_uri_new_with_error (uri_string, &error);
   if (!uri) {
      fprintf (stderr,
               "failed to parse URI: %s\n"
               "error message:       %s\n",
               uri_string,
               error.message);
      return EXIT_FAILURE;
   }

   client = mongoc_client_new_from_uri (uri);
   if (!client) {
      return EXIT_FAILURE;
   }

   mongoc_client_set_error_api (client, 2);
   database = mongoc_client_get_database (client, "testasdf");

   /* Create schema validator */
   options = BCON_NEW (
      "validator", "{", "number", "{", "$gte", BCON_INT32 (5), "}", "}");
   collection =
      mongoc_database_create_collection (database, "collname", options, &error);

   if (collection) {
      bulk5_fail (collection);
      bulk5_success (collection);
      mongoc_collection_destroy (collection);
   } else {
      fprintf (stderr, "Couldn't create collection: '%s'\n", error.message);
   }

   bson_free (options);
   mongoc_uri_destroy (uri);
   mongoc_database_destroy (database);
   mongoc_client_destroy (client);

   mongoc_cleanup ();

   return EXIT_SUCCESS;
}

Running the above example will result in:

{ "nInserted" : 0,
  "nMatched" : 0,
  "nModified" : 0,
  "nRemoved" : 0,
  "nUpserted" : 0,
  "writeErrors" : [
    { "index" : 0,
      "code" : 121,
      "errmsg" : "Document failed validation" } ] }

Error: Document failed validation

{ "nInserted" : 2,
  "nMatched" : 0,
  "nModified" : 0,
  "nRemoved" : 0,
  "nUpserted" : 0,
  "writeErrors" : [] }

The bson_error_t domain is MONGOC_ERROR_COMMAND.

By default bulk operations are executed with the write_concern of the collection they are executed against. A custom write concern can be passed to the mongoc_collection_create_bulk_operation_with_opts() method. Write concern errors (e.g. wtimeout) will be reported after all operations are attempted, regardless of execution order.

bulk4.c

#include <assert.h>
#include <mongoc/mongoc.h>
#include <stdio.h>

static void
bulk4 (mongoc_collection_t *collection)
{
   bson_t opts = BSON_INITIALIZER;
   mongoc_write_concern_t *wc;
   mongoc_bulk_operation_t *bulk;
   bson_error_t error;
   bson_t *doc;
   bson_t reply;
   char *str;
   bool ret;

   wc = mongoc_write_concern_new ();
   mongoc_write_concern_set_w (wc, 4);
   mongoc_write_concern_set_wtimeout_int64 (wc, 100); /* milliseconds */
   mongoc_write_concern_append (wc, &opts);

   bulk = mongoc_collection_create_bulk_operation_with_opts (collection, &opts);

   /* Two inserts */
   doc = BCON_NEW ("_id", BCON_INT32 (10));
   mongoc_bulk_operation_insert (bulk, doc);
   bson_destroy (doc);

   doc = BCON_NEW ("_id", BCON_INT32 (11));
   mongoc_bulk_operation_insert (bulk, doc);
   bson_destroy (doc);

   ret = mongoc_bulk_operation_execute (bulk, &reply, &error);

   str = bson_as_canonical_extended_json (&reply, NULL);
   printf ("%s\n", str);
   bson_free (str);

   if (!ret) {
      printf ("Error: %s\n", error.message);
   }

   bson_destroy (&reply);
   mongoc_bulk_operation_destroy (bulk);
   mongoc_write_concern_destroy (wc);
   bson_destroy (&opts);
}

int
main (void)
{
   mongoc_client_t *client;
   mongoc_collection_t *collection;
   const char *uri_string = "mongodb://localhost/?appname=bulk4-example";
   mongoc_uri_t *uri;
   bson_error_t error;

   mongoc_init ();

   uri = mongoc_uri_new_with_error (uri_string, &error);
   if (!uri) {
      fprintf (stderr,
               "failed to parse URI: %s\n"
               "error message:       %s\n",
               uri_string,
               error.message);
      return EXIT_FAILURE;
   }

   client = mongoc_client_new_from_uri (uri);
   if (!client) {
      return EXIT_FAILURE;
   }

   mongoc_client_set_error_api (client, 2);
   collection = mongoc_client_get_collection (client, "test", "test");

   bulk4 (collection);

   mongoc_uri_destroy (uri);
   mongoc_collection_destroy (collection);
   mongoc_client_destroy (client);

   mongoc_cleanup ();

   return EXIT_SUCCESS;
}

Example reply document and error message:

{ "nInserted"    : 2,
  "nMatched"     : 0,
  "nModified"    : 0,
  "nRemoved"     : 0,
  "nUpserted"    : 0,
  "writeErrors"  : [],
  "writeConcernErrors" : [
    { "code"   : 64,
      "errmsg" : "waiting for replication timed out" }
] }

Error: waiting for replication timed out

The bson_error_t domain is MONGOC_ERROR_WRITE_CONCERN if there are write concern errors and no write errors. Write errors indicate failed operations, so they take precedence over write concern errors, which mean merely that the write concern is not satisfied yet.

This feature is only available when using MongoDB 3.4 and later.

bulk-collation.c

#include <mongoc/mongoc.h>
#include <stdio.h>

static void
bulk_collation (mongoc_collection_t *collection)
{
   mongoc_bulk_operation_t *bulk;
   bson_t *opts;
   bson_t *doc;
   bson_t *selector;
   bson_t *update;
   bson_error_t error;
   bson_t reply;
   char *str;
   uint32_t ret;

   /* insert {_id: "one"} and {_id: "One"} */
   bulk = mongoc_collection_create_bulk_operation_with_opts (collection, NULL);
   doc = BCON_NEW ("_id", BCON_UTF8 ("one"));
   mongoc_bulk_operation_insert (bulk, doc);
   bson_destroy (doc);

   doc = BCON_NEW ("_id", BCON_UTF8 ("One"));
   mongoc_bulk_operation_insert (bulk, doc);
   bson_destroy (doc);

   /* "One" normally sorts before "one"; make "one" come first */
   opts = BCON_NEW ("collation",
                    "{",
                    "locale",
                    BCON_UTF8 ("en_US"),
                    "caseFirst",
                    BCON_UTF8 ("lower"),
                    "}");

   /* set x=1 on the document with _id "One", which now sorts after "one" */
   update = BCON_NEW ("$set", "{", "x", BCON_INT64 (1), "}");
   selector = BCON_NEW ("_id", "{", "$gt", BCON_UTF8 ("one"), "}");
   mongoc_bulk_operation_update_one_with_opts (
      bulk, selector, update, opts, &error);

   ret = mongoc_bulk_operation_execute (bulk, &reply, &error);

   str = bson_as_canonical_extended_json (&reply, NULL);
   printf ("%s\n", str);
   bson_free (str);

   if (!ret) {
      printf ("Error: %s\n", error.message);
   }

   bson_destroy (&reply);
   bson_destroy (update);
   bson_destroy (selector);
   bson_destroy (opts);
   mongoc_bulk_operation_destroy (bulk);
}

int
main (void)
{
   mongoc_client_t *client;
   mongoc_collection_t *collection;
   const char *uri_string = "mongodb://localhost/?appname=bulk-collation";
   mongoc_uri_t *uri;
   bson_error_t error;

   mongoc_init ();

   uri = mongoc_uri_new_with_error (uri_string, &error);
   if (!uri) {
      fprintf (stderr,
               "failed to parse URI: %s\n"
               "error message:       %s\n",
               uri_string,
               error.message);
      return EXIT_FAILURE;
   }

   client = mongoc_client_new_from_uri (uri);
   if (!client) {
      return EXIT_FAILURE;
   }

   mongoc_client_set_error_api (client, 2);
   collection = mongoc_client_get_collection (client, "db", "collection");
   bulk_collation (collection);

   mongoc_uri_destroy (uri);
   mongoc_collection_destroy (collection);
   mongoc_client_destroy (client);

   mongoc_cleanup ();

   return EXIT_SUCCESS;
}

Running the above example will result in:

{ "nInserted" : 2,
   "nMatched" : 1,
   "nModified" : 1,
   "nRemoved" : 0,
   "nUpserted" : 0,
   "writeErrors" : [  ]
}

Set "w" to zero for an unacknowledged write. The driver sends unacknowledged writes using the legacy opcodes OP_INSERT, OP_UPDATE, and OP_DELETE.

bulk6.c

#include <mongoc/mongoc.h>
#include <stdio.h>

static void
bulk6 (mongoc_collection_t *collection)
{
   bson_t opts = BSON_INITIALIZER;
   mongoc_write_concern_t *wc;
   mongoc_bulk_operation_t *bulk;
   bson_error_t error;
   bson_t *doc;
   bson_t *selector;
   bson_t reply;
   char *str;
   bool ret;

   wc = mongoc_write_concern_new ();
   mongoc_write_concern_set_w (wc, 0);
   mongoc_write_concern_append (wc, &opts);

   bulk = mongoc_collection_create_bulk_operation_with_opts (collection, &opts);

   doc = BCON_NEW ("_id", BCON_INT32 (10));
   mongoc_bulk_operation_insert (bulk, doc);
   bson_destroy (doc);

   selector = BCON_NEW ("_id", BCON_INT32 (11));
   mongoc_bulk_operation_remove_one (bulk, selector);
   bson_destroy (selector);

   ret = mongoc_bulk_operation_execute (bulk, &reply, &error);

   str = bson_as_canonical_extended_json (&reply, NULL);
   printf ("%s\n", str);
   bson_free (str);

   if (!ret) {
      printf ("Error: %s\n", error.message);
   }

   bson_destroy (&reply);
   mongoc_bulk_operation_destroy (bulk);
   mongoc_write_concern_destroy (wc);
   bson_destroy (&opts);
}

int
main (void)
{
   mongoc_client_t *client;
   mongoc_collection_t *collection;
   const char *uri_string = "mongodb://localhost/?appname=bulk6-example";
   mongoc_uri_t *uri;
   bson_error_t error;

   mongoc_init ();

   uri = mongoc_uri_new_with_error (uri_string, &error);
   if (!uri) {
      fprintf (stderr,
               "failed to parse URI: %s\n"
               "error message:       %s\n",
               uri_string,
               error.message);
      return EXIT_FAILURE;
   }

   client = mongoc_client_new_from_uri (uri);
   if (!client) {
      return EXIT_FAILURE;
   }

   mongoc_client_set_error_api (client, 2);
   collection = mongoc_client_get_collection (client, "test", "test");

   bulk6 (collection);

   mongoc_uri_destroy (uri);
   mongoc_collection_destroy (collection);
   mongoc_client_destroy (client);

   mongoc_cleanup ();

   return EXIT_SUCCESS;
}

The reply document is empty:

{ }

See the Driver Bulk API Spec, which describes bulk write operations for all MongoDB drivers.

This document provides a number of practical examples that display the capabilities of the aggregation framework.

The Aggregations using the Zip Codes Data Set examples uses a publicly available data set of all zipcodes and populations in the United States. These data are available at: zips.json.

Let's check if everything is installed.

Use the following command to load zips.json data set into mongod instance:

$ mongoimport --drop -d test -c zipcodes zips.json

Let's use the MongoDB shell to verify that everything was imported successfully.

$ mongo test
connecting to: test
> db.zipcodes.count()
29467
> db.zipcodes.findOne()
{
      "_id" : "35004",
      "city" : "ACMAR",
      "loc" : [
              -86.51557,
              33.584132
      ],
      "pop" : 6055,
      "state" : "AL"
}

Each document in this collection has the following form:

{
  "_id" : "35004",
  "city" : "Acmar",
  "state" : "AL",
  "pop" : 6055,
  "loc" : [-86.51557, 33.584132]
}

In these documents:

• The _id field holds the zipcode as a string.
• The city field holds the city name.
• The state field holds the two letter state abbreviation.
• The pop field holds the population.
• The loc field holds the location as a [latitude, longitude] array.

To get all states with a population greater than 10 million, use the following aggregation pipeline:

aggregation1.c

#include <mongoc/mongoc.h>
#include <stdio.h>

static void
print_pipeline (mongoc_collection_t *collection)
{
   mongoc_cursor_t *cursor;
   bson_error_t error;
   const bson_t *doc;
   bson_t *pipeline;
   char *str;

   pipeline = BCON_NEW ("pipeline",
                        "[",
                        "{",
                        "$group",
                        "{",
                        "_id",
                        "$state",
                        "total_pop",
                        "{",
                        "$sum",
                        "$pop",
                        "}",
                        "}",
                        "}",
                        "{",
                        "$match",
                        "{",
                        "total_pop",
                        "{",
                        "$gte",
                        BCON_INT32 (10000000),
                        "}",
                        "}",
                        "}",
                        "]");

   cursor = mongoc_collection_aggregate (
      collection, MONGOC_QUERY_NONE, pipeline, NULL, NULL);

   while (mongoc_cursor_next (cursor, &doc)) {
      str = bson_as_canonical_extended_json (doc, NULL);
      printf ("%s\n", str);
      bson_free (str);
   }

   if (mongoc_cursor_error (cursor, &error)) {
      fprintf (stderr, "Cursor Failure: %s\n", error.message);
   }

   mongoc_cursor_destroy (cursor);
   bson_destroy (pipeline);
}

int
main (void)
{
   mongoc_client_t *client;
   mongoc_collection_t *collection;
   const char *uri_string =
      "mongodb://localhost:27017/?appname=aggregation-example";
   mongoc_uri_t *uri;
   bson_error_t error;

   mongoc_init ();

   uri = mongoc_uri_new_with_error (uri_string, &error);
   if (!uri) {
      fprintf (stderr,
               "failed to parse URI: %s\n"
               "error message:       %s\n",
               uri_string,
               error.message);
      return EXIT_FAILURE;
   }

   client = mongoc_client_new_from_uri (uri);
   if (!client) {
      return EXIT_FAILURE;
   }

   mongoc_client_set_error_api (client, 2);
   collection = mongoc_client_get_collection (client, "test", "zipcodes");

   print_pipeline (collection);

   mongoc_uri_destroy (uri);
   mongoc_collection_destroy (collection);
   mongoc_client_destroy (client);

   mongoc_cleanup ();

   return EXIT_SUCCESS;
}

You should see a result like the following:

{ "_id" : "PA", "total_pop" : 11881643 }
{ "_id" : "OH", "total_pop" : 10847115 }
{ "_id" : "NY", "total_pop" : 17990455 }
{ "_id" : "FL", "total_pop" : 12937284 }
{ "_id" : "TX", "total_pop" : 16986510 }
{ "_id" : "IL", "total_pop" : 11430472 }
{ "_id" : "CA", "total_pop" : 29760021 }

The above aggregation pipeline is build from two pipeline operators: $group and $match.

The $group pipeline operator requires _id field where we specify grouping; remaining fields specify how to generate composite value and must use one of the group aggregation functions: $addToSet, $first, $last, $max, $min, $avg, $push, $sum. The $match pipeline operator syntax is the same as the read operation query syntax.

The $group process reads all documents and for each state it creates a separate document, for example:

{ "_id" : "WA", "total_pop" : 4866692 }

The total_pop field uses the $sum aggregation function to sum the values of all pop fields in the source documents.

Documents created by $group are piped to the $match pipeline operator. It returns the documents with the value of total_pop field greater than or equal to 10 million.

To get the first three states with the greatest average population per city, use the following aggregation:

pipeline = BCON_NEW ("pipeline", "[",
   "{", "$group", "{", "_id", "{", "state", "$state", "city", "$city", "}", "pop", "{", "$sum", "$pop", "}", "}", "}",
   "{", "$group", "{", "_id", "$_id.state", "avg_city_pop", "{", "$avg", "$pop", "}", "}", "}",
   "{", "$sort", "{", "avg_city_pop", BCON_INT32 (-1), "}", "}",
   "{", "$limit", BCON_INT32 (3) "}",
"]");

This aggregate pipeline produces:

{ "_id" : "DC", "avg_city_pop" : 303450.0 }
{ "_id" : "FL", "avg_city_pop" : 27942.29805615551 }
{ "_id" : "CA", "avg_city_pop" : 27735.341099720412 }

The above aggregation pipeline is build from three pipeline operators: $group, $sort and $limit.

The first $group operator creates the following documents:

{ "_id" : { "state" : "WY", "city" : "Smoot" }, "pop" : 414 }

Note, that the $group operator can't use nested documents except the _id field.

The second $group uses these documents to create the following documents:

{ "_id" : "FL", "avg_city_pop" : 27942.29805615551 }

These documents are sorted by the avg_city_pop field in descending order. Finally, the $limit pipeline operator returns the first 3 documents from the sorted set.

This document provides some practical, simple, examples to demonstrate the distinct and mapReduce commands.

First we'll write some code to insert sample data:

doc-common-insert.c

/* Don't try to compile this file on its own. It's meant to be #included
   by example code */

/* Insert some sample data */
bool
insert_data (mongoc_collection_t *collection)
{
   mongoc_bulk_operation_t *bulk;
   enum N { ndocs = 4 };
   bson_t *docs[ndocs];
   bson_error_t error;
   int i = 0;
   bool ret;

   bulk = mongoc_collection_create_bulk_operation_with_opts (collection, NULL);

   docs[0] = BCON_NEW ("x", BCON_DOUBLE (1.0), "tags", "[", "dog", "cat", "]");
   docs[1] = BCON_NEW ("x", BCON_DOUBLE (2.0), "tags", "[", "cat", "]");
   docs[2] = BCON_NEW (
      "x", BCON_DOUBLE (2.0), "tags", "[", "mouse", "cat", "dog", "]");
   docs[3] = BCON_NEW ("x", BCON_DOUBLE (3.0), "tags", "[", "]");

   for (i = 0; i < ndocs; i++) {
      mongoc_bulk_operation_insert (bulk, docs[i]);
      bson_destroy (docs[i]);
      docs[i] = NULL;
   }

   ret = mongoc_bulk_operation_execute (bulk, NULL, &error);

   if (!ret) {
      fprintf (stderr, "Error inserting data: %s\n", error.message);
   }

   mongoc_bulk_operation_destroy (bulk);
   return ret;
}

/* A helper which we'll use a lot later on */
void
print_res (const bson_t *reply)
{
   char *str;
   BSON_ASSERT (reply);
   str = bson_as_canonical_extended_json (reply, NULL);
   printf ("%s\n", str);
   bson_free (str);
}

This is how to use the distinct command to get the distinct values of x which are greater than 1:

distinct.c

bool
distinct (mongoc_database_t *database)
{
   bson_t *command;
   bson_t reply;
   bson_error_t error;
   bool res;
   bson_iter_t iter;
   bson_iter_t array_iter;
   double val;

   command = BCON_NEW ("distinct",
                       BCON_UTF8 (COLLECTION_NAME),
                       "key",
                       BCON_UTF8 ("x"),
                       "query",
                       "{",
                       "x",
                       "{",
                       "$gt",
                       BCON_DOUBLE (1.0),
                       "}",
                       "}");
   res =
      mongoc_database_command_simple (database, command, NULL, &reply, &error);
   if (!res) {
      fprintf (stderr, "Error with distinct: %s\n", error.message);
      goto cleanup;
   }

   /* Do something with reply (in this case iterate through the values) */
   if (!(bson_iter_init_find (&iter, &reply, "values") &&
         BSON_ITER_HOLDS_ARRAY (&iter) &&
         bson_iter_recurse (&iter, &array_iter))) {
      fprintf (stderr, "Couldn't extract \"values\" field from response\n");
      goto cleanup;
   }

   while (bson_iter_next (&array_iter)) {
      if (BSON_ITER_HOLDS_DOUBLE (&array_iter)) {
         val = bson_iter_double (&array_iter);
         printf ("Next double: %f\n", val);
      }
   }

cleanup:
   /* cleanup */
   bson_destroy (command);
   bson_destroy (&reply);
   return res;
}

A simple example using the map reduce framework. It simply adds up the number of occurrences of each "tag".

First define the map and reduce functions:

constants.c

const char *const COLLECTION_NAME = "things";

/* Our map function just emits a single (key, 1) pair for each tag
   in the array: */
const char *const MAPPER = "function () {"
                           "this.tags.forEach(function(z) {"
                           "emit(z, 1);"
                           "});"
                           "}";

/* The reduce function sums over all of the emitted values for a
   given key: */
const char *const REDUCER = "function (key, values) {"
                            "var total = 0;"
                            "for (var i = 0; i < values.length; i++) {"
                            "total += values[i];"
                            "}"
                            "return total;"
                            "}";
/* Note We can't just return values.length as the reduce function
   might be called iteratively on the results of other reduce
   steps. */

Run the mapReduce command. Use the generic command helpers (e.g. mongoc_database_command_simple()). Do not the read command helpers (e.g. mongoc_database_read_command_with_opts()) because they are considered retryable read operations. If retryable reads are enabled, those operations will retry once on a retryable error, giving undesirable behavior for mapReduce.

map-reduce-basic.c

bool
map_reduce_basic (mongoc_database_t *database)
{
   bson_t reply;
   bson_t *command;
   bool res;
   bson_error_t error;
   mongoc_cursor_t *cursor;
   const bson_t *doc;

   bool query_done = false;

   const char *out_collection_name = "outCollection";
   mongoc_collection_t *out_collection;

   /* Empty find query */
   bson_t find_query = BSON_INITIALIZER;

   /* Construct the mapReduce command */

   /* Other arguments can also be specified here, like "query" or
      "limit" and so on */
   command = BCON_NEW ("mapReduce",
                       BCON_UTF8 (COLLECTION_NAME),
                       "map",
                       BCON_CODE (MAPPER),
                       "reduce",
                       BCON_CODE (REDUCER),
                       "out",
                       BCON_UTF8 (out_collection_name));
   res =
      mongoc_database_command_simple (database, command, NULL, &reply, &error);

   if (!res) {
      fprintf (stderr, "MapReduce failed: %s\n", error.message);
      goto cleanup;
   }

   /* Do something with the reply (it doesn't contain the mapReduce results) */
   print_res (&reply);

   /* Now we'll query outCollection to see what the results are */
   out_collection =
      mongoc_database_get_collection (database, out_collection_name);
   cursor = mongoc_collection_find_with_opts (
      out_collection, &find_query, NULL, NULL);
   query_done = true;

   /* Do something with the results */
   while (mongoc_cursor_next (cursor, &doc)) {
      print_res (doc);
   }

   if (mongoc_cursor_error (cursor, &error)) {
      fprintf (stderr, "ERROR: %s\n", error.message);
      res = false;
      goto cleanup;
   }

cleanup:
   /* cleanup */
   if (query_done) {
      mongoc_cursor_destroy (cursor);
      mongoc_collection_destroy (out_collection);
   }

   bson_destroy (&reply);
   bson_destroy (command);

   return res;
}

You must have replica set running for this.

In this example we contact a secondary in the replica set and do an "inline" map reduce, so the results are returned immediately:

map-reduce-advanced.c

bool
map_reduce_advanced (mongoc_database_t *database)
{
   bson_t *command;
   bson_error_t error;
   bool res = true;
   mongoc_cursor_t *cursor;
   mongoc_read_prefs_t *read_pref;
   const bson_t *doc;

   /* Construct the mapReduce command */
   /* Other arguments can also be specified here, like "query" or "limit"
      and so on */

   /* Read the results inline from a secondary replica */
   command = BCON_NEW ("mapReduce",
                       BCON_UTF8 (COLLECTION_NAME),
                       "map",
                       BCON_CODE (MAPPER),
                       "reduce",
                       BCON_CODE (REDUCER),
                       "out",
                       "{",
                       "inline",
                       "1",
                       "}");

   read_pref = mongoc_read_prefs_new (MONGOC_READ_SECONDARY);
   cursor = mongoc_database_command (
      database, MONGOC_QUERY_NONE, 0, 0, 0, command, NULL, read_pref);

   /* Do something with the results */
   while (mongoc_cursor_next (cursor, &doc)) {
      print_res (doc);
   }

   if (mongoc_cursor_error (cursor, &error)) {
      fprintf (stderr, "ERROR: %s\n", error.message);
      res = false;
   }

   mongoc_cursor_destroy (cursor);
   mongoc_read_prefs_destroy (read_pref);
   bson_destroy (command);

   return res;
}

Here's how to run the example code

basic-aggregation.c

/*
 * Copyright 2016 MongoDB, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */


#include <mongoc/mongoc.h>
#include <stdio.h>


#include "constants.c"

#include "../doc-common-insert.c"
#include "distinct.c"
#include "map-reduce-basic.c"
#include "map-reduce-advanced.c"


int
main (int argc, char *argv[])
{
   mongoc_database_t *database = NULL;
   mongoc_client_t *client = NULL;
   mongoc_collection_t *collection = NULL;
   mongoc_uri_t *uri = NULL;
   bson_error_t error;
   char *host_and_port = NULL;
   int exit_code = EXIT_FAILURE;

   if (argc != 2) {
      fprintf (stderr, "usage: %s CONNECTION-STRING\n", argv[0]);
      fprintf (stderr,
               "the connection string can be of the following forms:\n");
      fprintf (stderr, "localhost\t\t\t\tlocal machine\n");
      fprintf (stderr, "localhost:27018\t\t\t\tlocal machine on port 27018\n");
      fprintf (stderr,
               "mongodb://user:pass@localhost:27017\t"
               "local machine on port 27017, and authenticate with username "
               "user and password pass\n");
      return exit_code;
   }

   mongoc_init ();

   if (strncmp (argv[1], "mongodb://", 10) == 0) {
      host_and_port = bson_strdup (argv[1]);
   } else {
      host_and_port = bson_strdup_printf ("mongodb://%s", argv[1]);
   }

   uri = mongoc_uri_new_with_error (host_and_port, &error);
   if (!uri) {
      fprintf (stderr,
               "failed to parse URI: %s\n"
               "error message:       %s\n",
               host_and_port,
               error.message);
      goto cleanup;
   }

   client = mongoc_client_new_from_uri (uri);
   if (!client) {
      goto cleanup;
   }

   mongoc_client_set_error_api (client, 2);
   database = mongoc_client_get_database (client, "test");
   collection = mongoc_database_get_collection (database, COLLECTION_NAME);

   printf ("Inserting data\n");
   if (!insert_data (collection)) {
      goto cleanup;
   }

   printf ("distinct\n");
   if (!distinct (database)) {
      goto cleanup;
   }

   printf ("map reduce\n");
   if (!map_reduce_basic (database)) {
      goto cleanup;
   }

   printf ("more complicated map reduce\n");
   if (!map_reduce_advanced (database)) {
      goto cleanup;
   }
   
   exit_code = EXIT_SUCCESS;

cleanup:
   if (collection) {
      mongoc_collection_destroy (collection);
   }

   if (database) {
      mongoc_database_destroy (database);
   }

   if (client) {
      mongoc_client_destroy (client);
   }

   if (uri) {
      mongoc_uri_destroy (uri);
   }

   if (host_and_port) {
      bson_free (host_and_port);
   }

   mongoc_cleanup ();
   return exit_code;
}

If you want to try the advanced map reduce example with a secondary, start a replica set (instructions for how to do this can be found here).

Otherwise, just start an instance of MongoDB:

$ mongod

Now compile and run the example program:

$ cd examples/basic_aggregation/
$ gcc -Wall -o agg-example basic-aggregation.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./agg-example localhost

Inserting data
distinct
Next double: 2.000000
Next double: 3.000000
map reduce
{ "result" : "outCollection", "timeMillis" : 155, "counts" : { "input" : 84, "emit" : 126, "reduce" : 3, "output" : 3 }, "ok" : 1 }
{ "_id" : "cat", "value" : 63 }
{ "_id" : "dog", "value" : 42 }
{ "_id" : "mouse", "value" : 21 }
more complicated map reduce
{ "results" : [ { "_id" : "cat", "value" : 63 }, { "_id" : "dog", "value" : 42 }, { "_id" : "mouse", "value" : 21 } ], "timeMillis" : 14, "counts" : { "input" : 84, "emit" : 126, "reduce" : 3, "output" : 3 }, "ok" : 1 }

Download and install libmongoc on your system, then open Visual Studio, select "File→New→Project...", and create a new Win32 Console Application. [image]

Remember to switch the platform from 32-bit to 64-bit: [image]

Right-click on your console application in the Solution Explorer and select "Properties". Choose to edit properties for "All Configurations", expand the "C/C++" options and choose "General". Add to the "Additional Include Directories" these paths:

C:\mongo-c-driver\include\libbson-1.0
C:\mongo-c-driver\include\libmongoc-1.0

[image]

(If you chose a different $PREFIX when you installed mongo-c-driver, your include paths will be different.)

Also in the Properties dialog, expand the "Linker" options and choose "Input", and add to the "Additional Dependencies" these libraries:

C:\mongo-c-driver\lib\bson-1.0.lib
C:\mongo-c-driver\lib\mongoc-1.0.lib

[image]

Adding these libraries as dependencies provides linker symbols to build your application, but to actually run it, libbson's and libmongoc's DLLs must be in your executable path. Select "Debugging" in the Properties dialog, and set the "Environment" option to:

PATH=c:/mongo-c-driver/bin

[image]

Finally, include "mongoc/mongoc.h" in your project's "stdafx.h":

#include <mongoc/mongoc.h>

Following the instructions above, you have dynamically linked your application to the libbson and libmongoc DLLs. This is usually the right choice. If you want to link statically instead, update your "Additional Dependencies" list by removing bson-1.0.lib and mongoc-1.0.lib and replacing them with these libraries:

C:\mongo-c-driver\lib\bson-static-1.0.lib
C:\mongo-c-driver\lib\mongoc-static-1.0.lib
ws2_32.lib
Secur32.lib
Crypt32.lib
BCrypt.lib

[image]

(To explain the purpose of each library: bson-static-1.0.lib and mongoc-static-1.0.lib are static archives of the driver code. The socket library ws2_32 is required by libbson, which uses the socket routine gethostname to help guarantee ObjectId uniqueness. The BCrypt library is used by libmongoc for TLS connections to MongoDB, and Secur32 and Crypt32 are required for enterprise authentication methods like Kerberos.)

Finally, define two preprocessor symbols before including mongoc/mongoc.h in your stdafx.h:

#define BSON_STATIC
#define MONGOC_STATIC
#include <mongoc/mongoc.h>

Making these changes to your project is only required for static linking; for most people, the dynamic-linking instructions above are preferred.

Now you can build and debug applications in Visual Studio that use libbson and libmongoc. Proceed to Making a Connection in the tutorial to learn how connect to MongoDB and perform operations.

To create indexes on a MongoDB collection, use mongoc_collection_create_indexes_with_opts():

// `keys` represents an ascending index on field `x`.
bson_t *keys = BCON_NEW ("x", BCON_INT32 (1));
mongoc_index_model_t *im = mongoc_index_model_new (keys, NULL /* opts */);
if (mongoc_collection_create_indexes_with_opts (
       coll, &im, 1, NULL /* opts */, NULL /* reply */, &error)) {
   printf ("Successfully created index\n");
} else {
   bson_destroy (keys);
   HANDLE_ERROR ("Failed to create index: %s", error.message);
}
bson_destroy (keys);

To list indexes, use mongoc_collection_find_indexes_with_opts():

mongoc_cursor_t *cursor =
   mongoc_collection_find_indexes_with_opts (coll, NULL /* opts */);
printf ("Listing indexes:\n");
const bson_t *got;
while (mongoc_cursor_next (cursor, &got)) {
   char *got_str = bson_as_canonical_extended_json (got, NULL);
   printf ("  %s\n", got_str);
   bson_free (got_str);
}
if (mongoc_cursor_error (cursor, &error)) {
   mongoc_cursor_destroy (cursor);
   HANDLE_ERROR ("Failed to list indexes: %s", error.message);
}
mongoc_cursor_destroy (cursor);

To drop an index, use mongoc_collection_drop_index_with_opts(). The index name may be obtained from the keys document with mongoc_collection_keys_to_index_string():

bson_t *keys = BCON_NEW ("x", BCON_INT32 (1));
char *index_name = mongoc_collection_keys_to_index_string (keys);
if (mongoc_collection_drop_index_with_opts (
       coll, index_name, NULL /* opts */, &error)) {
   printf ("Successfully dropped index\n");
} else {
   bson_free (index_name);
   bson_destroy (keys);
   HANDLE_ERROR ("Failed to drop index: %s", error.message);
}
bson_free (index_name);
bson_destroy (keys);

For a full example, see example-manage-collection-indexes.c.

To create an Atlas Search Index, use the createSearchIndexes command:

bson_t cmd;
// Create command.
{
   char *cmd_str = bson_strdup_printf (
      BSON_STR ({
         "createSearchIndexes" : "%s",
         "indexes" : [ {
            "definition" : {"mappings" : {"dynamic" : false}},
            "name" : "test-index"
         } ]
      }),
      collname);
   ASSERT (bson_init_from_json (&cmd, cmd_str, -1, &error));
   bson_free (cmd_str);
}
if (!mongoc_collection_command_simple (
       coll, &cmd, NULL /* read_prefs */, NULL /* reply */, &error)) {
   bson_destroy (&cmd);
   HANDLE_ERROR ("Failed to run createSearchIndexes: %s", error.message);
}
printf ("Created index: \"test-index\"\n");
bson_destroy (&cmd);

To list Atlas Search Indexes, use the $listSearchIndexes aggregation stage:

const char *pipeline_str =
   BSON_STR ({"pipeline" : [ {"$listSearchIndexes" : {}} ]});
bson_t pipeline;
ASSERT (bson_init_from_json (&pipeline, pipeline_str, -1, &error));
mongoc_cursor_t *cursor =
   mongoc_collection_aggregate (coll,
                                MONGOC_QUERY_NONE,
                                &pipeline,
                                NULL /* opts */,
                                NULL /* read_prefs */);
printf ("Listing indexes:\n");
const bson_t *got;
while (mongoc_cursor_next (cursor, &got)) {
   char *got_str = bson_as_canonical_extended_json (got, NULL);
   printf ("  %s\n", got_str);
   bson_free (got_str);
}
if (mongoc_cursor_error (cursor, &error)) {
   bson_destroy (&pipeline);
   mongoc_cursor_destroy (cursor);
   HANDLE_ERROR ("Failed to run $listSearchIndexes: %s", error.message);
}
bson_destroy (&pipeline);
mongoc_cursor_destroy (cursor);

To update an Atlas Search Index, use the updateSearchIndex command:

bson_t cmd;
// Create command.
{
   char *cmd_str = bson_strdup_printf (
      BSON_STR ({
         "updateSearchIndex" : "%s",
         "definition" : {"mappings" : {"dynamic" : true}},
         "name" : "test-index"
      }),
      collname);
   ASSERT (bson_init_from_json (&cmd, cmd_str, -1, &error));
   bson_free (cmd_str);
}
if (!mongoc_collection_command_simple (
       coll, &cmd, NULL /* read_prefs */, NULL /* reply */, &error)) {
   bson_destroy (&cmd);
   HANDLE_ERROR ("Failed to run updateSearchIndex: %s", error.message);
}
printf ("Updated index: \"test-index\"\n");
bson_destroy (&cmd);

To drop an Atlas Search Index, use the dropSearchIndex command:

bson_t cmd;
// Create command.
{
   char *cmd_str = bson_strdup_printf (
      BSON_STR ({"dropSearchIndex" : "%s", "name" : "test-index"}),
      collname);
   ASSERT (bson_init_from_json (&cmd, cmd_str, -1, &error));
   bson_free (cmd_str);
}
if (!mongoc_collection_command_simple (
       coll, &cmd, NULL /* read_prefs */, NULL /* reply */, &error)) {
   bson_destroy (&cmd);
   HANDLE_ERROR ("Failed to run dropSearchIndex: %s", error.message);
}
printf ("Dropped index: \"test-index\"\n");
bson_destroy (&cmd);

For a full example, see example-manage-search-indexes.c.

This repository contains a .gdbinit file that contains helper functions to aid debugging of data structures. GDB will load this file automatically if you have added the directory which contains the .gdbinit file to GDB's auto-load safe-path, and you start GDB from the directory which holds the .gdbinit file.

You can see the safe-path with show auto-load safe-path on a GDB prompt. You can configure it by setting it in ~/.gdbinit with:

add-auto-load-safe-path /path/to/mongo-c-driver

If you haven't added the path to your auto-load safe-path, or start GDB in another directory, load the file with:

source path/to/mongo-c-driver/.gdbinit

The .gdbinit file defines the printbson function, which shows the contents of a bson_t * variable. If you have a local bson_t, then you must prefix the variable with a &.

An example GDB session looks like:

(gdb) printbson bson
ALLOC [0x555556cd7310 + 0] (len=475)
{
    'bool' : true,
    'int32' : NumberInt("42"),
    'int64' : NumberLong("3000000042"),
    'string' : "Stŕìñg",
    'objectId' : ObjectID("5A1442F3122D331C3C6757E1"),
    'utcDateTime' : UTCDateTime(1511277299031),
    'arrayOfInts' : [
        '0' : NumberInt("1"),
        '1' : NumberInt("2")
    ],
    'embeddedDocument' : {
        'arrayOfStrings' : [
            '0' : "one",
            '1' : "two"
        ],
        'double' : 2.718280,
        'notherDoc' : {
            'true' : NumberInt("1"),
            'false' : false
        }
    },
    'binary' : Binary("02", "3031343532333637"),
    'regex' : Regex("@[a-z]+@", "im"),
    'null' : null,
    'js' : JavaScript("print foo"),
    'jsws' : JavaScript("print foo") with scope: {
        'f' : NumberInt("42"),
        'a' : [
            '0' : 3.141593,
            '1' : 2.718282
        ]
    },
    'timestamp' : Timestamp(4294967295, 4294967295),
    'double' : 3.141593
}

The mongo-c-driver repository contains a script lldb_bson.py that can be imported into an LLDB sessions and allows rich inspection of BSON values.

NOTE:

To activate the script, import it from the LLDB command line:

(lldb) command script import /path/to/mongo-c-driver/lldb_bson.py

Upon success, the message lldb_bson is ready will be printed to the LLDB console.

The import of this script can be made automatic by adding the command to an .lldbinit file. For example: Create a file ~/.lldbinit containing:

command script import /path/to/mongo-c-driver/lldb_bson.py

The docstring at the top of the lldb_bson.py file contains more information on the capabilities of the module.

To enable runtime debug assertions, configure with -DENABLE_DEBUG_ASSERTIONS=ON.

In-Use Encryption consists of two features:

New in MongoDB 4.2, Client-Side Field Level Encryption (also referred to as CSFLE) allows administrators and developers to encrypt specific data fields in addition to other MongoDB encryption features.

With CSFLE, developers can encrypt fields client side without any server-side configuration or directives. CSFLE supports workloads where applications must guarantee that unauthorized parties, including server administrators, cannot read the encrypted data.

Automatic encryption, where sensitive fields in commands are encrypted automatically, requires an Enterprise-only dependency for Query Analysis. See In-Use Encryption for more information.

SEE ALSO:

The MongoDB Manual for Client-Side Field Level Encryption

Automatic encryption is enabled by calling mongoc_client_enable_auto_encryption() on a mongoc_client_t. The following examples show how to set up automatic encryption using mongoc_client_encryption_t to create a new encryption data key.

NOTE:

The following example shows how to specify automatic encryption rules using a schema map set with mongoc_auto_encryption_opts_set_schema_map(). The automatic encryption rules are expressed using a strict subset of the JSON Schema syntax.

Supplying a schema map provides more security than relying on JSON Schemas obtained from the server. It protects against a malicious server advertising a false JSON Schema, which could trick the client into sending unencrypted data that should be encrypted.

JSON Schemas supplied in the schema map only apply to configuring automatic encryption. Other validation rules in the JSON schema will not be enforced by the driver and will result in an error:

client-side-encryption-schema-map.c

#include <mongoc/mongoc.h>
#include <stdio.h>
#include <stdlib.h>

#include "client-side-encryption-helpers.h"

/* Helper method to create a new data key in the key vault, a schema to use that
 * key, and writes the schema to a file for later use. */
static bool
create_schema_file (bson_t *kms_providers,
                    const char *keyvault_db,
                    const char *keyvault_coll,
                    mongoc_client_t *keyvault_client,
                    bson_error_t *error)
{
   mongoc_client_encryption_t *client_encryption = NULL;
   mongoc_client_encryption_opts_t *client_encryption_opts = NULL;
   mongoc_client_encryption_datakey_opts_t *datakey_opts = NULL;
   bson_value_t datakey_id = {0};
   char *keyaltnames[] = {"mongoc_encryption_example_1"};
   bson_t *schema = NULL;
   char *schema_string = NULL;
   size_t schema_string_len;
   FILE *outfile = NULL;
   bool ret = false;

   client_encryption_opts = mongoc_client_encryption_opts_new ();
   mongoc_client_encryption_opts_set_kms_providers (client_encryption_opts,
                                                    kms_providers);
   mongoc_client_encryption_opts_set_keyvault_namespace (
      client_encryption_opts, keyvault_db, keyvault_coll);
   mongoc_client_encryption_opts_set_keyvault_client (client_encryption_opts,
                                                      keyvault_client);

   client_encryption =
      mongoc_client_encryption_new (client_encryption_opts, error);
   if (!client_encryption) {
      goto fail;
   }

   /* Create a new data key and json schema for the encryptedField.
    * https://dochub.mongodb.org/core/client-side-field-level-encryption-automatic-encryption-rules
    */
   datakey_opts = mongoc_client_encryption_datakey_opts_new ();
   mongoc_client_encryption_datakey_opts_set_keyaltnames (
      datakey_opts, keyaltnames, 1);
   if (!mongoc_client_encryption_create_datakey (
          client_encryption, "local", datakey_opts, &datakey_id, error)) {
      goto fail;
   }

   /* Create a schema describing that "encryptedField" is a string encrypted
    * with the newly created data key using deterministic encryption. */
   schema = BCON_NEW ("properties",
                      "{",
                      "encryptedField",
                      "{",
                      "encrypt",
                      "{",
                      "keyId",
                      "[",
                      BCON_BIN (datakey_id.value.v_binary.subtype,
                                datakey_id.value.v_binary.data,
                                datakey_id.value.v_binary.data_len),
                      "]",
                      "bsonType",
                      "string",
                      "algorithm",
                      MONGOC_AEAD_AES_256_CBC_HMAC_SHA_512_DETERMINISTIC,
                      "}",
                      "}",
                      "}",
                      "bsonType",
                      "object");

   /* Use canonical JSON so that other drivers and tools will be
    * able to parse the MongoDB extended JSON file. */
   schema_string = bson_as_canonical_extended_json (schema, &schema_string_len);
   outfile = fopen ("jsonSchema.json", "w");
   if (0 == fwrite (schema_string, sizeof (char), schema_string_len, outfile)) {
      fprintf (stderr, "failed to write to file\n");
      goto fail;
   }

   ret = true;
fail:
   mongoc_client_encryption_destroy (client_encryption);
   mongoc_client_encryption_datakey_opts_destroy (datakey_opts);
   mongoc_client_encryption_opts_destroy (client_encryption_opts);
   bson_free (schema_string);
   bson_destroy (schema);
   bson_value_destroy (&datakey_id);
   if (outfile) {
      fclose (outfile);
   }
   return ret;
}

/* This example demonstrates how to use automatic encryption with a client-side
 * schema map using the enterprise version of MongoDB */
int
main (void)
{
/* The collection used to store the encryption data keys. */
#define KEYVAULT_DB "encryption"
#define KEYVAULT_COLL "__libmongocTestKeyVault"
/* The collection used to store the encrypted documents in this example. */
#define ENCRYPTED_DB "test"
#define ENCRYPTED_COLL "coll"

   int exit_status = EXIT_FAILURE;
   bool ret;
   uint8_t *local_masterkey = NULL;
   uint32_t local_masterkey_len;
   bson_t *kms_providers = NULL;
   bson_error_t error = {0};
   bson_t *index_keys = NULL;
   bson_t *index_opts = NULL;
   mongoc_index_model_t *index_model = NULL;
   bson_json_reader_t *reader = NULL;
   bson_t schema = BSON_INITIALIZER;
   bson_t *schema_map = NULL;

   /* The MongoClient used to access the key vault (keyvault_namespace). */
   mongoc_client_t *keyvault_client = NULL;
   mongoc_collection_t *keyvault_coll = NULL;
   mongoc_auto_encryption_opts_t *auto_encryption_opts = NULL;
   mongoc_client_t *client = NULL;
   mongoc_collection_t *coll = NULL;
   bson_t *to_insert = NULL;
   mongoc_client_t *unencrypted_client = NULL;
   mongoc_collection_t *unencrypted_coll = NULL;

   mongoc_init ();

   /* Configure the master key. This must be the same master key that was used
    * to create the encryption key. */
   local_masterkey =
      hex_to_bin (getenv ("LOCAL_MASTERKEY"), &local_masterkey_len);
   if (!local_masterkey || local_masterkey_len != 96) {
      fprintf (stderr,
               "Specify LOCAL_MASTERKEY environment variable as a "
               "secure random 96 byte hex value.\n");
      goto fail;
   }

   kms_providers = BCON_NEW ("local",
                             "{",
                             "key",
                             BCON_BIN (0, local_masterkey, local_masterkey_len),
                             "}");

   /* Set up the key vault for this example. */
   keyvault_client = mongoc_client_new (
      "mongodb://localhost/?appname=client-side-encryption-keyvault");
   BSON_ASSERT (keyvault_client);

   keyvault_coll = mongoc_client_get_collection (
      keyvault_client, KEYVAULT_DB, KEYVAULT_COLL);
   mongoc_collection_drop (keyvault_coll, NULL);

   /* Create a unique index to ensure that two data keys cannot share the same
    * keyAltName. This is recommended practice for the key vault. */
   index_keys = BCON_NEW ("keyAltNames", BCON_INT32 (1));
   index_opts = BCON_NEW ("unique",
                          BCON_BOOL (true),
                          "partialFilterExpression",
                          "{",
                          "keyAltNames",
                          "{",
                          "$exists",
                          BCON_BOOL (true),
                          "}",
                          "}");
   index_model = mongoc_index_model_new (index_keys, index_opts);
   ret = mongoc_collection_create_indexes_with_opts (keyvault_coll,
                                                     &index_model,
                                                     1,
                                                     NULL /* opts */,
                                                     NULL /* reply */,
                                                     &error);

   if (!ret) {
      goto fail;
   }

   /* Create a new data key and a schema using it for encryption. Save the
    * schema to the file jsonSchema.json */
   ret = create_schema_file (
      kms_providers, KEYVAULT_DB, KEYVAULT_COLL, keyvault_client, &error);

   if (!ret) {
      goto fail;
   }

   /* Load the JSON Schema and construct the local schema_map option. */
   reader = bson_json_reader_new_from_file ("jsonSchema.json", &error);
   if (!reader) {
      goto fail;
   }

   bson_json_reader_read (reader, &schema, &error);

   /* Construct the schema map, mapping the namespace of the collection to the
    * schema describing encryption. */
   schema_map =
      BCON_NEW (ENCRYPTED_DB "." ENCRYPTED_COLL, BCON_DOCUMENT (&schema));

   auto_encryption_opts = mongoc_auto_encryption_opts_new ();
   mongoc_auto_encryption_opts_set_keyvault_client (auto_encryption_opts,
                                                    keyvault_client);
   mongoc_auto_encryption_opts_set_keyvault_namespace (
      auto_encryption_opts, KEYVAULT_DB, KEYVAULT_COLL);
   mongoc_auto_encryption_opts_set_kms_providers (auto_encryption_opts,
                                                  kms_providers);
   mongoc_auto_encryption_opts_set_schema_map (auto_encryption_opts,
                                               schema_map);

   client =
      mongoc_client_new ("mongodb://localhost/?appname=client-side-encryption");
   BSON_ASSERT (client);

   /* Enable automatic encryption. It will determine that encryption is
    * necessary from the schema map instead of relying on the server to provide
    * a schema. */
   ret = mongoc_client_enable_auto_encryption (
      client, auto_encryption_opts, &error);
   if (!ret) {
      goto fail;
   }

   coll = mongoc_client_get_collection (client, ENCRYPTED_DB, ENCRYPTED_COLL);

   /* Clear old data */
   mongoc_collection_drop (coll, NULL);

   to_insert = BCON_NEW ("encryptedField", "123456789");
   ret = mongoc_collection_insert_one (
      coll, to_insert, NULL /* opts */, NULL /* reply */, &error);
   if (!ret) {
      goto fail;
   }
   printf ("decrypted document: ");
   if (!print_one_document (coll, &error)) {
      goto fail;
   }
   printf ("\n");

   unencrypted_client = mongoc_client_new (
      "mongodb://localhost/?appname=client-side-encryption-unencrypted");
   BSON_ASSERT (unencrypted_client);

   unencrypted_coll = mongoc_client_get_collection (
      unencrypted_client, ENCRYPTED_DB, ENCRYPTED_COLL);
   printf ("encrypted document: ");
   if (!print_one_document (unencrypted_coll, &error)) {
      goto fail;
   }
   printf ("\n");

   exit_status = EXIT_SUCCESS;
fail:
   if (error.code) {
      fprintf (stderr, "error: %s\n", error.message);
   }

   bson_free (local_masterkey);
   bson_destroy (kms_providers);
   mongoc_collection_destroy (keyvault_coll);
   mongoc_index_model_destroy (index_model);
   bson_destroy (index_opts);
   bson_destroy (index_keys);
   bson_json_reader_destroy (reader);
   mongoc_auto_encryption_opts_destroy (auto_encryption_opts);
   mongoc_collection_destroy (coll);
   mongoc_client_destroy (client);
   bson_destroy (to_insert);
   mongoc_collection_destroy (unencrypted_coll);
   mongoc_client_destroy (unencrypted_client);
   mongoc_client_destroy (keyvault_client);
   bson_destroy (&schema);
   bson_destroy (schema_map);
   mongoc_cleanup ();
   return exit_status;
}

The MongoDB 4.2 server supports using schema validation to enforce encryption of specific fields in a collection. This schema validation will prevent an application from inserting unencrypted values for any fields marked with the "encrypt" JSON schema keyword.

The following example shows how to set up automatic encryption using mongoc_client_encryption_t to create a new encryption data key and create a collection with the necessary JSON Schema:

client-side-encryption-server-schema.c

#include <mongoc/mongoc.h>
#include <stdio.h>
#include <stdlib.h>

#include "client-side-encryption-helpers.h"

/* Helper method to create and return a JSON schema to use for encryption.
The caller will use the returned schema for server-side encryption validation.
*/
static bson_t *
create_schema (bson_t *kms_providers,
               const char *keyvault_db,
               const char *keyvault_coll,
               mongoc_client_t *keyvault_client,
               bson_error_t *error)
{
   mongoc_client_encryption_t *client_encryption = NULL;
   mongoc_client_encryption_opts_t *client_encryption_opts = NULL;
   mongoc_client_encryption_datakey_opts_t *datakey_opts = NULL;
   bson_value_t datakey_id = {0};
   char *keyaltnames[] = {"mongoc_encryption_example_2"};
   bson_t *schema = NULL;

   client_encryption_opts = mongoc_client_encryption_opts_new ();
   mongoc_client_encryption_opts_set_kms_providers (client_encryption_opts,
                                                    kms_providers);
   mongoc_client_encryption_opts_set_keyvault_namespace (
      client_encryption_opts, keyvault_db, keyvault_coll);
   mongoc_client_encryption_opts_set_keyvault_client (client_encryption_opts,
                                                      keyvault_client);

   client_encryption =
      mongoc_client_encryption_new (client_encryption_opts, error);
   if (!client_encryption) {
      goto fail;
   }

   /* Create a new data key and json schema for the encryptedField.
    * https://dochub.mongodb.org/core/client-side-field-level-encryption-automatic-encryption-rules
    */
   datakey_opts = mongoc_client_encryption_datakey_opts_new ();
   mongoc_client_encryption_datakey_opts_set_keyaltnames (
      datakey_opts, keyaltnames, 1);
   if (!mongoc_client_encryption_create_datakey (
          client_encryption, "local", datakey_opts, &datakey_id, error)) {
      goto fail;
   }

   /* Create a schema describing that "encryptedField" is a string encrypted
    * with the newly created data key using deterministic encryption. */
   schema = BCON_NEW ("properties",
                      "{",
                      "encryptedField",
                      "{",
                      "encrypt",
                      "{",
                      "keyId",
                      "[",
                      BCON_BIN (datakey_id.value.v_binary.subtype,
                                datakey_id.value.v_binary.data,
                                datakey_id.value.v_binary.data_len),
                      "]",
                      "bsonType",
                      "string",
                      "algorithm",
                      MONGOC_AEAD_AES_256_CBC_HMAC_SHA_512_DETERMINISTIC,
                      "}",
                      "}",
                      "}",
                      "bsonType",
                      "object");

fail:
   mongoc_client_encryption_destroy (client_encryption);
   mongoc_client_encryption_datakey_opts_destroy (datakey_opts);
   mongoc_client_encryption_opts_destroy (client_encryption_opts);
   bson_value_destroy (&datakey_id);
   return schema;
}

/* This example demonstrates how to use automatic encryption with a server-side
 * schema using the enterprise version of MongoDB */
int
main (void)
{
/* The collection used to store the encryption data keys. */
#define KEYVAULT_DB "encryption"
#define KEYVAULT_COLL "__libmongocTestKeyVault"
/* The collection used to store the encrypted documents in this example. */
#define ENCRYPTED_DB "test"
#define ENCRYPTED_COLL "coll"

   int exit_status = EXIT_FAILURE;
   bool ret;
   uint8_t *local_masterkey = NULL;
   uint32_t local_masterkey_len;
   bson_t *kms_providers = NULL;
   bson_error_t error = {0};
   bson_t *index_keys = NULL;
   bson_t *index_opts = NULL;
   mongoc_index_model_t *index_model = NULL;
   bson_json_reader_t *reader = NULL;
   bson_t *schema = NULL;

   /* The MongoClient used to access the key vault (keyvault_namespace). */
   mongoc_client_t *keyvault_client = NULL;
   mongoc_collection_t *keyvault_coll = NULL;
   mongoc_auto_encryption_opts_t *auto_encryption_opts = NULL;
   mongoc_client_t *client = NULL;
   mongoc_collection_t *coll = NULL;
   bson_t *to_insert = NULL;
   mongoc_client_t *unencrypted_client = NULL;
   mongoc_collection_t *unencrypted_coll = NULL;
   bson_t *create_cmd = NULL;
   bson_t *create_cmd_opts = NULL;
   mongoc_write_concern_t *wc = NULL;

   mongoc_init ();

   /* Configure the master key. This must be the same master key that was used
    * to create
    * the encryption key. */
   local_masterkey =
      hex_to_bin (getenv ("LOCAL_MASTERKEY"), &local_masterkey_len);
   if (!local_masterkey || local_masterkey_len != 96) {
      fprintf (stderr,
               "Specify LOCAL_MASTERKEY environment variable as a "
               "secure random 96 byte hex value.\n");
      goto fail;
   }

   kms_providers = BCON_NEW ("local",
                             "{",
                             "key",
                             BCON_BIN (0, local_masterkey, local_masterkey_len),
                             "}");

   /* Set up the key vault for this example. */
   keyvault_client = mongoc_client_new (
      "mongodb://localhost/?appname=client-side-encryption-keyvault");
   BSON_ASSERT (keyvault_client);

   keyvault_coll = mongoc_client_get_collection (
      keyvault_client, KEYVAULT_DB, KEYVAULT_COLL);
   mongoc_collection_drop (keyvault_coll, NULL);

   /* Create a unique index to ensure that two data keys cannot share the same
    * keyAltName. This is recommended practice for the key vault. */
   index_keys = BCON_NEW ("keyAltNames", BCON_INT32 (1));
   index_opts = BCON_NEW ("unique",
                          BCON_BOOL (true),
                          "partialFilterExpression",
                          "{",
                          "keyAltNames",
                          "{",
                          "$exists",
                          BCON_BOOL (true),
                          "}",
                          "}");
   index_model = mongoc_index_model_new (index_keys, index_opts);
   ret = mongoc_collection_create_indexes_with_opts (keyvault_coll,
                                                     &index_model,
                                                     1,
                                                     NULL /* opts */,
                                                     NULL /* reply */,
                                                     &error);

   if (!ret) {
      goto fail;
   }

   auto_encryption_opts = mongoc_auto_encryption_opts_new ();
   mongoc_auto_encryption_opts_set_keyvault_client (auto_encryption_opts,
                                                    keyvault_client);
   mongoc_auto_encryption_opts_set_keyvault_namespace (
      auto_encryption_opts, KEYVAULT_DB, KEYVAULT_COLL);
   mongoc_auto_encryption_opts_set_kms_providers (auto_encryption_opts,
                                                  kms_providers);
   schema = create_schema (
      kms_providers, KEYVAULT_DB, KEYVAULT_COLL, keyvault_client, &error);

   if (!schema) {
      goto fail;
   }

   client =
      mongoc_client_new ("mongodb://localhost/?appname=client-side-encryption");
   BSON_ASSERT (client);

   ret = mongoc_client_enable_auto_encryption (
      client, auto_encryption_opts, &error);
   if (!ret) {
      goto fail;
   }

   coll = mongoc_client_get_collection (client, ENCRYPTED_DB, ENCRYPTED_COLL);

   /* Clear old data */
   mongoc_collection_drop (coll, NULL);

   /* Create the collection with the encryption JSON Schema. */
   create_cmd = BCON_NEW ("create",
                          ENCRYPTED_COLL,
                          "validator",
                          "{",
                          "$jsonSchema",
                          BCON_DOCUMENT (schema),
                          "}");
   wc = mongoc_write_concern_new ();
   mongoc_write_concern_set_wmajority (wc, 0);
   create_cmd_opts = bson_new ();
   mongoc_write_concern_append (wc, create_cmd_opts);
   ret = mongoc_client_command_with_opts (client,
                                          ENCRYPTED_DB,
                                          create_cmd,
                                          NULL /* read prefs */,
                                          create_cmd_opts,
                                          NULL /* reply */,
                                          &error);
   if (!ret) {
      goto fail;
   }

   to_insert = BCON_NEW ("encryptedField", "123456789");
   ret = mongoc_collection_insert_one (
      coll, to_insert, NULL /* opts */, NULL /* reply */, &error);
   if (!ret) {
      goto fail;
   }
   printf ("decrypted document: ");
   if (!print_one_document (coll, &error)) {
      goto fail;
   }
   printf ("\n");

   unencrypted_client = mongoc_client_new (
      "mongodb://localhost/?appname=client-side-encryption-unencrypted");
   BSON_ASSERT (unencrypted_client);

   unencrypted_coll = mongoc_client_get_collection (
      unencrypted_client, ENCRYPTED_DB, ENCRYPTED_COLL);
   printf ("encrypted document: ");
   if (!print_one_document (unencrypted_coll, &error)) {
      goto fail;
   }
   printf ("\n");

   /* Expect a server-side error if inserting with the unencrypted collection.
    */
   ret = mongoc_collection_insert_one (
      unencrypted_coll, to_insert, NULL /* opts */, NULL /* reply */, &error);
   if (!ret) {
      printf ("insert with unencrypted collection failed: %s\n", error.message);
      memset (&error, 0, sizeof (error));
   }

   exit_status = EXIT_SUCCESS;
fail:
   if (error.code) {
      fprintf (stderr, "error: %s\n", error.message);
   }

   bson_free (local_masterkey);
   bson_destroy (kms_providers);
   mongoc_collection_destroy (keyvault_coll);
   mongoc_index_model_destroy (index_model);
   bson_destroy (index_opts);
   bson_destroy (index_keys);
   bson_json_reader_destroy (reader);
   mongoc_auto_encryption_opts_destroy (auto_encryption_opts);
   mongoc_collection_destroy (coll);
   mongoc_client_destroy (client);
   bson_destroy (to_insert);
   mongoc_collection_destroy (unencrypted_coll);
   mongoc_client_destroy (unencrypted_client);
   mongoc_client_destroy (keyvault_client);
   bson_destroy (schema);
   bson_destroy (create_cmd);
   bson_destroy (create_cmd_opts);
   mongoc_write_concern_destroy (wc);

   mongoc_cleanup ();
   return exit_status;
}

Explicit encryption is a MongoDB community feature and does not use Query Analysis (mongocryptd or crypt_shared). Explicit encryption is provided by the mongoc_client_encryption_t class, for example:

client-side-encryption-explicit.c

#include <mongoc/mongoc.h>
#include <stdio.h>
#include <stdlib.h>

#include "client-side-encryption-helpers.h"

/* This example demonstrates how to use explicit encryption and decryption using
 * the community version of MongoDB */
int
main (void)
{
/* The collection used to store the encryption data keys. */
#define KEYVAULT_DB "encryption"
#define KEYVAULT_COLL "__libmongocTestKeyVault"
/* The collection used to store the encrypted documents in this example. */
#define ENCRYPTED_DB "test"
#define ENCRYPTED_COLL "coll"

   int exit_status = EXIT_FAILURE;
   bool ret;
   uint8_t *local_masterkey = NULL;
   uint32_t local_masterkey_len;
   bson_t *kms_providers = NULL;
   bson_error_t error = {0};
   bson_t *index_keys = NULL;
   bson_t *index_opts = NULL;
   mongoc_index_model_t *index_model = NULL;
   bson_t *schema = NULL;
   mongoc_client_t *client = NULL;
   mongoc_collection_t *coll = NULL;
   mongoc_collection_t *keyvault_coll = NULL;
   bson_t *to_insert = NULL;
   bson_t *create_cmd = NULL;
   bson_t *create_cmd_opts = NULL;
   mongoc_write_concern_t *wc = NULL;
   mongoc_client_encryption_t *client_encryption = NULL;
   mongoc_client_encryption_opts_t *client_encryption_opts = NULL;
   mongoc_client_encryption_datakey_opts_t *datakey_opts = NULL;
   char *keyaltnames[] = {"mongoc_encryption_example_3"};
   bson_value_t datakey_id = {0};
   bson_value_t encrypted_field = {0};
   bson_value_t to_encrypt = {0};
   mongoc_client_encryption_encrypt_opts_t *encrypt_opts = NULL;
   bson_value_t decrypted = {0};

   mongoc_init ();

   /* Configure the master key. This must be the same master key that was used
    * to create the encryption key. */
   local_masterkey =
      hex_to_bin (getenv ("LOCAL_MASTERKEY"), &local_masterkey_len);
   if (!local_masterkey || local_masterkey_len != 96) {
      fprintf (stderr,
               "Specify LOCAL_MASTERKEY environment variable as a "
               "secure random 96 byte hex value.\n");
      goto fail;
   }

   kms_providers = BCON_NEW ("local",
                             "{",
                             "key",
                             BCON_BIN (0, local_masterkey, local_masterkey_len),
                             "}");

   /* The mongoc_client_t used to read/write application data. */
   client =
      mongoc_client_new ("mongodb://localhost/?appname=client-side-encryption");
   coll = mongoc_client_get_collection (client, ENCRYPTED_DB, ENCRYPTED_COLL);

   /* Clear old data */
   mongoc_collection_drop (coll, NULL);

   /* Set up the key vault for this example. */
   keyvault_coll =
      mongoc_client_get_collection (client, KEYVAULT_DB, KEYVAULT_COLL);
   mongoc_collection_drop (keyvault_coll, NULL);

   /* Create a unique index to ensure that two data keys cannot share the same
    * keyAltName. This is recommended practice for the key vault. */
   index_keys = BCON_NEW ("keyAltNames", BCON_INT32 (1));
   index_opts = BCON_NEW ("unique",
                          BCON_BOOL (true),
                          "partialFilterExpression",
                          "{",
                          "keyAltNames",
                          "{",
                          "$exists",
                          BCON_BOOL (true),
                          "}",
                          "}");
   index_model = mongoc_index_model_new (index_keys, index_opts);
   ret = mongoc_collection_create_indexes_with_opts (keyvault_coll,
                                                     &index_model,
                                                     1,
                                                     NULL /* opts */,
                                                     NULL /* reply */,
                                                     &error);

   if (!ret) {
      goto fail;
   }

   client_encryption_opts = mongoc_client_encryption_opts_new ();
   mongoc_client_encryption_opts_set_kms_providers (client_encryption_opts,
                                                    kms_providers);
   mongoc_client_encryption_opts_set_keyvault_namespace (
      client_encryption_opts, KEYVAULT_DB, KEYVAULT_COLL);

   /* Set a mongoc_client_t to use for reading/writing to the key vault. This
    * can be the same mongoc_client_t used by the main application. */
   mongoc_client_encryption_opts_set_keyvault_client (client_encryption_opts,
                                                      client);
   client_encryption =
      mongoc_client_encryption_new (client_encryption_opts, &error);
   if (!client_encryption) {
      goto fail;
   }

   /* Create a new data key for the encryptedField.
    * https://dochub.mongodb.org/core/client-side-field-level-encryption-automatic-encryption-rules
    */
   datakey_opts = mongoc_client_encryption_datakey_opts_new ();
   mongoc_client_encryption_datakey_opts_set_keyaltnames (
      datakey_opts, keyaltnames, 1);
   if (!mongoc_client_encryption_create_datakey (
          client_encryption, "local", datakey_opts, &datakey_id, &error)) {
      goto fail;
   }

   /* Explicitly encrypt a field */
   encrypt_opts = mongoc_client_encryption_encrypt_opts_new ();
   mongoc_client_encryption_encrypt_opts_set_algorithm (
      encrypt_opts, MONGOC_AEAD_AES_256_CBC_HMAC_SHA_512_DETERMINISTIC);
   mongoc_client_encryption_encrypt_opts_set_keyid (encrypt_opts, &datakey_id);
   to_encrypt.value_type = BSON_TYPE_UTF8;
   to_encrypt.value.v_utf8.str = "123456789";
   const size_t len = strlen (to_encrypt.value.v_utf8.str);
   BSON_ASSERT (bson_in_range_unsigned (uint32_t, len));
   to_encrypt.value.v_utf8.len = (uint32_t) len;

   ret = mongoc_client_encryption_encrypt (
      client_encryption, &to_encrypt, encrypt_opts, &encrypted_field, &error);
   if (!ret) {
      goto fail;
   }

   to_insert = bson_new ();
   BSON_APPEND_VALUE (to_insert, "encryptedField", &encrypted_field);
   ret = mongoc_collection_insert_one (
      coll, to_insert, NULL /* opts */, NULL /* reply */, &error);
   if (!ret) {
      goto fail;
   }

   printf ("encrypted document: ");
   if (!print_one_document (coll, &error)) {
      goto fail;
   }
   printf ("\n");

   /* Explicitly decrypt a field */
   ret = mongoc_client_encryption_decrypt (
      client_encryption, &encrypted_field, &decrypted, &error);
   if (!ret) {
      goto fail;
   }
   printf ("decrypted value: %s\n", decrypted.value.v_utf8.str);

   exit_status = EXIT_SUCCESS;
fail:
   if (error.code) {
      fprintf (stderr, "error: %s\n", error.message);
   }

   bson_free (local_masterkey);
   bson_destroy (kms_providers);
   mongoc_collection_destroy (keyvault_coll);
   mongoc_index_model_destroy (index_model);
   bson_destroy (index_opts);
   bson_destroy (index_keys);
   mongoc_collection_destroy (coll);
   mongoc_client_destroy (client);
   bson_destroy (to_insert);
   bson_destroy (schema);
   bson_destroy (create_cmd);
   bson_destroy (create_cmd_opts);
   mongoc_write_concern_destroy (wc);
   mongoc_client_encryption_destroy (client_encryption);
   mongoc_client_encryption_datakey_opts_destroy (datakey_opts);
   mongoc_client_encryption_opts_destroy (client_encryption_opts);
   bson_value_destroy (&encrypted_field);
   mongoc_client_encryption_encrypt_opts_destroy (encrypt_opts);
   bson_value_destroy (&decrypted);
   bson_value_destroy (&datakey_id);

   mongoc_cleanup ();
   return exit_status;
}

Although automatic encryption requires MongoDB 4.2 enterprise or a MongoDB 4.2 Atlas cluster, automatic decryption is supported for all users. To configure automatic decryption without automatic encryption set bypass_auto_encryption=True in mongoc_auto_encryption_opts_t:

client-side-encryption-auto-decryption.c

#include <mongoc/mongoc.h>
#include <stdio.h>
#include <stdlib.h>

#include "client-side-encryption-helpers.h"

/* This example demonstrates how to set up automatic decryption without
 * automatic encryption using the community version of MongoDB */
int
main (void)
{
/* The collection used to store the encryption data keys. */
#define KEYVAULT_DB "encryption"
#define KEYVAULT_COLL "__libmongocTestKeyVault"
/* The collection used to store the encrypted documents in this example. */
#define ENCRYPTED_DB "test"
#define ENCRYPTED_COLL "coll"

   int exit_status = EXIT_FAILURE;
   bool ret;
   uint8_t *local_masterkey = NULL;
   uint32_t local_masterkey_len;
   bson_t *kms_providers = NULL;
   bson_error_t error = {0};
   bson_t *index_keys = NULL;
   bson_t *index_opts = NULL;
   mongoc_index_model_t *index_model = NULL;
   bson_t *schema = NULL;
   mongoc_client_t *client = NULL;
   mongoc_collection_t *coll = NULL;
   mongoc_collection_t *keyvault_coll = NULL;
   bson_t *to_insert = NULL;
   bson_t *create_cmd = NULL;
   bson_t *create_cmd_opts = NULL;
   mongoc_write_concern_t *wc = NULL;
   mongoc_client_encryption_t *client_encryption = NULL;
   mongoc_client_encryption_opts_t *client_encryption_opts = NULL;
   mongoc_client_encryption_datakey_opts_t *datakey_opts = NULL;
   char *keyaltnames[] = {"mongoc_encryption_example_4"};
   bson_value_t datakey_id = {0};
   bson_value_t encrypted_field = {0};
   bson_value_t to_encrypt = {0};
   mongoc_client_encryption_encrypt_opts_t *encrypt_opts = NULL;
   bson_value_t decrypted = {0};
   mongoc_auto_encryption_opts_t *auto_encryption_opts = NULL;
   mongoc_client_t *unencrypted_client = NULL;
   mongoc_collection_t *unencrypted_coll = NULL;

   mongoc_init ();

   /* Configure the master key. This must be the same master key that was used
    * to create the encryption key. */
   local_masterkey =
      hex_to_bin (getenv ("LOCAL_MASTERKEY"), &local_masterkey_len);
   if (!local_masterkey || local_masterkey_len != 96) {
      fprintf (stderr,
               "Specify LOCAL_MASTERKEY environment variable as a "
               "secure random 96 byte hex value.\n");
      goto fail;
   }

   kms_providers = BCON_NEW ("local",
                             "{",
                             "key",
                             BCON_BIN (0, local_masterkey, local_masterkey_len),
                             "}");

   client =
      mongoc_client_new ("mongodb://localhost/?appname=client-side-encryption");
   auto_encryption_opts = mongoc_auto_encryption_opts_new ();
   mongoc_auto_encryption_opts_set_keyvault_namespace (
      auto_encryption_opts, KEYVAULT_DB, KEYVAULT_COLL);
   mongoc_auto_encryption_opts_set_kms_providers (auto_encryption_opts,
                                                  kms_providers);

   /* Setting bypass_auto_encryption to true disables automatic encryption but
    * keeps the automatic decryption behavior. bypass_auto_encryption will also
    * disable spawning mongocryptd */
   mongoc_auto_encryption_opts_set_bypass_auto_encryption (auto_encryption_opts,
                                                           true);

   /* Once bypass_auto_encryption is set, community users can enable auto
    * encryption on the client. This will, in fact, only perform automatic
    * decryption. */
   ret = mongoc_client_enable_auto_encryption (
      client, auto_encryption_opts, &error);
   if (!ret) {
      goto fail;
   }

   /* Now that automatic decryption is on, we can test it by inserting a
    * document with an explicitly encrypted value into the collection. When we
    * look up the document later, it should be automatically decrypted for us.
    */
   coll = mongoc_client_get_collection (client, ENCRYPTED_DB, ENCRYPTED_COLL);

   /* Clear old data */
   mongoc_collection_drop (coll, NULL);

   /* Set up the key vault for this example. */
   keyvault_coll =
      mongoc_client_get_collection (client, KEYVAULT_DB, KEYVAULT_COLL);
   mongoc_collection_drop (keyvault_coll, NULL);

   /* Create a unique index to ensure that two data keys cannot share the same
    * keyAltName. This is recommended practice for the key vault. */
   index_keys = BCON_NEW ("keyAltNames", BCON_INT32 (1));
   index_opts = BCON_NEW ("unique",
                          BCON_BOOL (true),
                          "partialFilterExpression",
                          "{",
                          "keyAltNames",
                          "{",
                          "$exists",
                          BCON_BOOL (true),
                          "}",
                          "}");
   index_model = mongoc_index_model_new (index_keys, index_opts);
   ret = mongoc_collection_create_indexes_with_opts (keyvault_coll,
                                                     &index_model,
                                                     1,
                                                     NULL /* opts */,
                                                     NULL /* reply */,
                                                     &error);

   if (!ret) {
      goto fail;
   }

   client_encryption_opts = mongoc_client_encryption_opts_new ();
   mongoc_client_encryption_opts_set_kms_providers (client_encryption_opts,
                                                    kms_providers);
   mongoc_client_encryption_opts_set_keyvault_namespace (
      client_encryption_opts, KEYVAULT_DB, KEYVAULT_COLL);

   /* The key vault client is used for reading to/from the key vault. This can
    * be the same mongoc_client_t used by the application. */
   mongoc_client_encryption_opts_set_keyvault_client (client_encryption_opts,
                                                      client);
   client_encryption =
      mongoc_client_encryption_new (client_encryption_opts, &error);
   if (!client_encryption) {
      goto fail;
   }

   /* Create a new data key for the encryptedField.
    * https://dochub.mongodb.org/core/client-side-field-level-encryption-automatic-encryption-rules
    */
   datakey_opts = mongoc_client_encryption_datakey_opts_new ();
   mongoc_client_encryption_datakey_opts_set_keyaltnames (
      datakey_opts, keyaltnames, 1);
   ret = mongoc_client_encryption_create_datakey (
      client_encryption, "local", datakey_opts, &datakey_id, &error);
   if (!ret) {
      goto fail;
   }

   /* Explicitly encrypt a field. */
   encrypt_opts = mongoc_client_encryption_encrypt_opts_new ();
   mongoc_client_encryption_encrypt_opts_set_algorithm (
      encrypt_opts, MONGOC_AEAD_AES_256_CBC_HMAC_SHA_512_DETERMINISTIC);
   mongoc_client_encryption_encrypt_opts_set_keyaltname (
      encrypt_opts, "mongoc_encryption_example_4");
   to_encrypt.value_type = BSON_TYPE_UTF8;
   to_encrypt.value.v_utf8.str = "123456789";
   const size_t len = strlen (to_encrypt.value.v_utf8.str);
   BSON_ASSERT (bson_in_range_unsigned (uint32_t, len));
   to_encrypt.value.v_utf8.len = (uint32_t) len;

   ret = mongoc_client_encryption_encrypt (
      client_encryption, &to_encrypt, encrypt_opts, &encrypted_field, &error);
   if (!ret) {
      goto fail;
   }

   to_insert = bson_new ();
   BSON_APPEND_VALUE (to_insert, "encryptedField", &encrypted_field);
   ret = mongoc_collection_insert_one (
      coll, to_insert, NULL /* opts */, NULL /* reply */, &error);
   if (!ret) {
      goto fail;
   }

   /* When we retrieve the document, any encrypted fields will get automatically
    * decrypted by the driver. */
   printf ("decrypted document: ");
   if (!print_one_document (coll, &error)) {
      goto fail;
   }
   printf ("\n");

   unencrypted_client =
      mongoc_client_new ("mongodb://localhost/?appname=client-side-encryption");
   unencrypted_coll = mongoc_client_get_collection (
      unencrypted_client, ENCRYPTED_DB, ENCRYPTED_COLL);

   printf ("encrypted document: ");
   if (!print_one_document (unencrypted_coll, &error)) {
      goto fail;
   }
   printf ("\n");

   exit_status = EXIT_SUCCESS;
fail:
   if (error.code) {
      fprintf (stderr, "error: %s\n", error.message);
   }

   bson_free (local_masterkey);
   bson_destroy (kms_providers);
   mongoc_collection_destroy (keyvault_coll);
   mongoc_index_model_destroy (index_model);
   bson_destroy (index_opts);
   bson_destroy (index_keys);
   mongoc_collection_destroy (coll);
   mongoc_client_destroy (client);
   bson_destroy (to_insert);
   bson_destroy (schema);
   bson_destroy (create_cmd);
   bson_destroy (create_cmd_opts);
   mongoc_write_concern_destroy (wc);
   mongoc_client_encryption_destroy (client_encryption);
   mongoc_client_encryption_datakey_opts_destroy (datakey_opts);
   mongoc_client_encryption_opts_destroy (client_encryption_opts);
   bson_value_destroy (&encrypted_field);
   mongoc_client_encryption_encrypt_opts_destroy (encrypt_opts);
   bson_value_destroy (&decrypted);
   bson_value_destroy (&datakey_id);
   mongoc_collection_destroy (unencrypted_coll);
   mongoc_client_destroy (unencrypted_client);
   mongoc_auto_encryption_opts_destroy (auto_encryption_opts);

   mongoc_cleanup ();
   return exit_status;
}

Using Queryable Encryption requires MongoDB Server 7.0 or higher.

See the MongoDB Manual for Queryable Encryption for more information about the feature.

API related to the "rangePreview" algorithm is still experimental and subject to breaking changes!

MongoDB Server 6.0 introduced Queryable Encryption as a Public Technical Preview. MongoDB Server 7.0 includes backwards breaking changes to the Queryable Encryption protocol.

The backwards breaking changes are applied in the client protocol in libmongocrypt 1.8.0. libmongoc 1.24.0 requires libmongocrypt 1.8.0 or newer. libmongoc 1.24.0 no longer supports Queryable Encryption in MongoDB Server <7.0. Using Queryable Encryption libmongoc 1.24.0 and higher requires MongoDB Server >=7.0.

Using Queryable Encryption with libmongocrypt<1.8.0 on a MongoDB Server>=7.0, or using libmongocrypt>=1.8.0 on a MongoDB Server<6.0 will result in a server error when using the incompatible protocol.

SEE ALSO:

The MongoDB Manual for Queryable Encryption

Using In-Use Encryption in the C driver requires the dependency libmongocrypt. See the MongoDB Manual for libmongocrypt installation instructions.

Once libmongocrypt is installed, configure the C driver with -DENABLE_CLIENT_SIDE_ENCRYPTION=ON to require In-Use Encryption be enabled.

$ cd mongo-c-driver
$ mkdir cmake-build && cd cmake-build
$ cmake -DENABLE_AUTOMATIC_INIT_AND_CLEANUP=OFF -DENABLE_CLIENT_SIDE_ENCRYPTION=ON ..
$ cmake --build . --target install

mongoc_client_encryption_t is used for explicit encryption and key management. mongoc_client_enable_auto_encryption() and mongoc_client_pool_enable_auto_encryption() is used to enable automatic encryption.

The Queryable Encryption and CSFLE features share much of the same API with some exceptions.

• The supported algorithms documented in mongoc_client_encryption_encrypt_opts_set_algorithm() do not apply to both features.
• mongoc_auto_encryption_opts_set_encrypted_fields_map() only applies to Queryable Encryption.
• mongoc_auto_encryption_opts_set_schema_map() only applies to CSFLE.

To support the automatic encryption feature, one of the following dependencies are required:

• The mongocryptd executable. See the MongoDB Manual documentation: Install and Configure mongocryptd
• The crypt_shared library. See the MongoDB Manual documentation: Automatic Encryption Shared Library

A mongoc_client_t or mongoc_client_pool_t configured with auto encryption will automatically try to load the crypt_shared library. If loading the crypt_shared library fails, the mongoc_client_t or mongoc_client_pool_t will try to spawn the mongocryptd process from the application's PATH. To configure use of crypt_shared and mongocryptd see mongoc_auto_encryption_opts_set_extra().

Initialize the MongoDB C Driver by calling mongoc_init() exactly once at the beginning of your program. It is responsible for initializing global state such as process counters, SSL, and threading primitives.

Exception to this is mongoc_log_set_handler(), which should be called before mongoc_init() or some log traces would not use your log handling function. See Custom Log Handlers for a detailed example.

Call mongoc_cleanup() exactly once at the end of your program to release all memory and other resources allocated by the driver. You must not call any other MongoDB C Driver functions after mongoc_cleanup(). Note that mongoc_init() does not reinitialize the driver after mongoc_cleanup().

On some platforms the driver can automatically call mongoc_init() before main, and call mongoc_cleanup() as the process exits. This is problematic in situations where related libraries also execute cleanup code on shutdown, and it creates inconsistent rules across platforms. Therefore the automatic initialization and cleanup feature is deprecated, and will be dropped in version 2.0. Meanwhile, for backward compatibility, the feature is enabled by default on platforms where it is available.

For portable, future-proof code, always call mongoc_init() and mongoc_cleanup() yourself, and configure the driver like:

cmake -DENABLE_AUTOMATIC_INIT_AND_CLEANUP=OFF

MongoDB C driver Logging Abstraction

typedef enum {
   MONGOC_LOG_LEVEL_ERROR,
   MONGOC_LOG_LEVEL_CRITICAL,
   MONGOC_LOG_LEVEL_WARNING,
   MONGOC_LOG_LEVEL_MESSAGE,
   MONGOC_LOG_LEVEL_INFO,
   MONGOC_LOG_LEVEL_DEBUG,
   MONGOC_LOG_LEVEL_TRACE,
} mongoc_log_level_t;

#define MONGOC_ERROR(...)
#define MONGOC_CRITICAL(...)
#define MONGOC_WARNING(...)
#define MONGOC_MESSAGE(...)
#define MONGOC_INFO(...)
#define MONGOC_DEBUG(...)

typedef void (*mongoc_log_func_t) (mongoc_log_level_t log_level,
                                   const char *log_domain,
                                   const char *message,
                                   void *user_data);

void
mongoc_log_set_handler (mongoc_log_func_t log_func, void *user_data);
void
mongoc_log (mongoc_log_level_t log_level,
            const char *log_domain,
            const char *format,
            ...) BSON_GNUC_PRINTF (3, 4);
const char *
mongoc_log_level_str (mongoc_log_level_t log_level);
void
mongoc_log_default_handler (mongoc_log_level_t log_level,
                            const char *log_domain,
                            const char *message,
                            void *user_data);
void
mongoc_log_trace_enable (void);
void
mongoc_log_trace_disable (void);

The MongoDB C driver comes with an abstraction for logging that you can use in your application, or integrate with an existing logging system.

To make logging a little less painful, various helper macros are provided. See the following example.

#undef MONGOC_LOG_DOMAIN
#define MONGOC_LOG_DOMAIN "my-custom-domain"

MONGOC_WARNING ("An error occurred: %s", strerror (errno));

The default log handler prints a timestamp and the log message to stdout, or to stderr for warnings, critical messages, and errors.

You can override the handler with mongoc_log_set_handler(). Your handler function is called in a mutex for thread safety.

For example, you could register a custom handler to suppress messages at INFO level and below:

void
my_logger (mongoc_log_level_t log_level,
           const char *log_domain,
           const char *message,
           void *user_data)
{
   /* smaller values are more important */
   if (log_level < MONGOC_LOG_LEVEL_INFO) {
      mongoc_log_default_handler (log_level, log_domain, message, user_data);
   }
}

int
main (int argc, char *argv[])
{
   mongoc_log_set_handler (my_logger, NULL);
   mongoc_init ();

   /* ... your code ...  */

   mongoc_cleanup ();
   return 0;
}

Note that in the example above mongoc_log_set_handler() is called before mongoc_init(). Otherwise, some log traces could not be processed by the log handler.

To restore the default handler:

mongoc_log_set_handler (mongoc_log_default_handler, NULL);

To disable all logging, including warnings, critical messages and errors, provide an empty log handler:

mongoc_log_set_handler (NULL, NULL);

If compiling your own copy of the MongoDB C driver, consider configuring with -DENABLE_TRACING=ON to enable function tracing and hex dumps of network packets to STDERR and STDOUT during development and debugging.

This is especially useful when debugging what may be going on internally in the driver.

Trace messages can be enabled and disabled by calling mongoc_log_trace_enable() and mongoc_log_trace_disable()

NOTE:

« libmongoc

Many C Driver functions report errors by returning false or -1 and filling out a bson_error_t structure with an error domain, error code, and message. Use domain to determine which subsystem generated the error, and code for the specific error. message is a human-readable error description.

SEE ALSO:

Handling Errors in libbson.

In some cases your application must make decisions based on what category of error the driver has returned, but these categories do not correspond perfectly to an error domain or code. In such cases, error labels provide a reliable way to determine how your application should respond to an error.

Any C Driver function that has a bson_t out-parameter named reply may include error labels to the reply, in the form of a BSON field named "errorLabels" containing an array of strings:

{ "errorLabels": [ "TransientTransactionError" ] }

Use mongoc_error_has_label() to test if a reply contains a specific label. See mongoc_client_session_start_transaction() for example code that demonstrates the use of error labels in application logic.

The following error labels are currently defined. Future versions of MongoDB may introduce new labels.

Within a multi-document transaction, certain errors can leave the transaction in an unknown or aborted state. These include write conflicts, primary stepdowns, and network errors. In response, the application should abort the transaction and try the same sequence of operations again in a new transaction.

When mongoc_client_session_commit_transaction() encounters a network error or certain server errors, it is not known whether the transaction was committed. Applications should attempt to commit the transaction again until: the commit succeeds, the commit fails with an error not labeled "UnknownTransactionCommitResult", or the application chooses to give up.

The driver's error reporting began with a design flaw: when the error domain is MONGOC_ERROR_COLLECTION, MONGOC_ERROR_QUERY, or MONGOC_ERROR_COMMAND, the error code might originate from the server or the driver. An application cannot always know where an error originated, and therefore cannot tell what the code means.

For example, if mongoc_collection_update_one() sets the error's domain to MONGOC_ERROR_COLLECTION and its code to 24, the application cannot know whether 24 is the generic driver error code MONGOC_ERROR_COLLECTION_UPDATE_FAILED or the specific server error code "LockTimeout".

To fix this flaw while preserving backward compatibility, the C Driver 1.4 introduces "Error API Versions". Version 1, the default Error API Version, maintains the flawed behavior. Version 2 adds a new error domain, MONGOC_ERROR_SERVER. In Version 2, error codes originating on the server always have error domain MONGOC_ERROR_SERVER or MONGOC_ERROR_WRITE_CONCERN. When the driver uses Version 2 the application can always determine the origin and meaning of error codes. New applications should use Version 2, and existing applications should be updated to use Version 2 as well.

The Error API Versions are defined with MONGOC_ERROR_API_VERSION_LEGACY and MONGOC_ERROR_API_VERSION_2. Set the version with mongoc_client_set_error_api() or mongoc_client_pool_set_error_api().

SEE ALSO:

MongoDB Server Error Codes

This page documents the order of creation and destruction for libmongoc's main struct types.

Call mongoc_init() once, before calling any other libmongoc functions, and call mongoc_cleanup() once before your program exits.

A program that uses libmongoc from multiple threads should create a mongoc_client_pool_t with mongoc_client_pool_new(). Each thread acquires a mongoc_client_t from the pool with mongoc_client_pool_pop() and returns it with mongoc_client_pool_push() when the thread is finished using it. To destroy the pool, first return all clients, then call mongoc_client_pool_destroy().

If your program uses libmongoc from only one thread, create a mongoc_client_t directly with mongoc_client_new() or mongoc_client_new_from_uri(). Destroy it with mongoc_client_destroy().

You can create a mongoc_database_t or mongoc_collection_t from a mongoc_client_t, and create a mongoc_cursor_t or mongoc_bulk_operation_t from a mongoc_collection_t.

Each of these objects must be destroyed before the client they were created from, but their lifetimes are otherwise independent.

You can create a mongoc_gridfs_t from a mongoc_client_t, create a mongoc_gridfs_file_t or mongoc_gridfs_file_list_t from a mongoc_gridfs_t, create a mongoc_gridfs_file_t from a mongoc_gridfs_file_list_t, and create a mongoc_stream_t from a mongoc_gridfs_file_t.

Each of these objects depends on the object it was created from. Always destroy GridFS objects in the reverse of the order they were created. The sole exception is that a mongoc_gridfs_file_t need not be destroyed before the mongoc_gridfs_file_list_t it was created from.

Create mongoc_gridfs_bucket_t with a mongoc_database_t derived from a mongoc_client_t. The mongoc_database_t is independent from the mongoc_gridfs_bucket_t. But the mongoc_client_t must outlive the mongoc_gridfs_bucket_t.

A mongoc_stream_t may be created from the mongoc_gridfs_bucket_t. The mongoc_gridfs_bucket_t must outlive the mongoc_stream_t.

Start a session with mongoc_client_start_session(), use the session for a sequence of operations and multi-document transactions, then free it with mongoc_client_session_destroy(). Any mongoc_cursor_t or mongoc_change_stream_t using a session must be destroyed before the session, and a session must be destroyed before the mongoc_client_t it came from.

By default, sessions are causally consistent. To disable causal consistency, before starting a session create a mongoc_session_opt_t with mongoc_session_opts_new() and call mongoc_session_opts_set_causal_consistency(), then free the struct with mongoc_session_opts_destroy().

Unacknowledged writes are prohibited with sessions.

A mongoc_client_session_t must be used by only one thread at a time. Due to session pooling, mongoc_client_start_session() may return a session that has been idle for some time and is about to be closed after its idle timeout. Use the session within one minute of acquiring it to refresh the session and avoid a timeout.

When configuring a mongoc_client_t for automatic encryption via mongoc_client_enable_auto_encryption(), if a separate key vault client is set in the options (via mongoc_auto_encryption_opts_set_keyvault_client()) the key vault client must outlive the encrypted client.

When configuring a mongoc_client_pool_t for automatic encryption via mongoc_client_pool_enable_auto_encryption(), if a separate key vault client pool is set in the options (via mongoc_auto_encryption_opts_set_keyvault_client_pool()) the key vault client pool must outlive the encrypted client pool.

When creating a mongoc_client_encryption_t, the configured key vault client (set via mongoc_client_encryption_opts_set_keyvault_client()) must outlive the mongoc_client_encryption_t.

The C driver includes two APIs for GridFS.

The older API consists of mongoc_gridfs_t and its derivatives. It contains deprecated API, does not support read preferences, and is not recommended in new applications. It does not conform to the MongoDB GridFS specification.

The newer API consists of mongoc_gridfs_bucket_t and allows uploading/downloading through derived mongoc_stream_t objects. It conforms to the MongoDB GridFS specification.

There is not always a straightforward upgrade path from an application built with mongoc_gridfs_t to mongoc_gridfs_bucket_t (e.g. a mongoc_gridfs_file_t provides functions to seek but mongoc_stream_t does not). But users are encouraged to upgrade when possible.

Options for enabling automatic encryption and decryption for In-Use Encryption.

typedef struct _mongoc_auto_encryption_opts_t mongoc_auto_encryption_opts_t;

SEE ALSO:

In-Use Encryption

Bulk Write Operations

typedef struct _mongoc_bulk_operation_t mongoc_bulk_operation_t;

The opaque type mongoc_bulk_operation_t provides an abstraction for submitting multiple write operations as a single batch.

After adding all of the write operations to the mongoc_bulk_operation_t, call mongoc_bulk_operation_execute() to execute the operation.

WARNING:

SEE ALSO:

Bulk Write Operations

#include <mongoc/mongoc.h>

typedef struct _mongoc_change_stream_t mongoc_change_stream_t;

mongoc_change_stream_t is a handle to a change stream. A collection change stream can be obtained using mongoc_collection_watch().

It is recommended to use a mongoc_change_stream_t and its functions instead of a raw aggregation with a $changeStream stage. For more information see the MongoDB Manual Entry on Change Streams.

example-collection-watch.c

#include <mongoc/mongoc.h>

int
main (void)
{
   bson_t empty = BSON_INITIALIZER;
   const bson_t *doc;
   bson_t *to_insert = BCON_NEW ("x", BCON_INT32 (1));
   const bson_t *err_doc;
   bson_error_t error;
   const char *uri_string;
   mongoc_uri_t *uri;
   mongoc_client_t *client;
   mongoc_collection_t *coll;
   mongoc_change_stream_t *stream;
   mongoc_write_concern_t *wc = mongoc_write_concern_new ();
   bson_t opts = BSON_INITIALIZER;
   bool r;

   mongoc_init ();

   uri_string = "mongodb://"
                "localhost:27017,localhost:27018,localhost:"
                "27019/db?replicaSet=rs0";

   uri = mongoc_uri_new_with_error (uri_string, &error);
   if (!uri) {
      fprintf (stderr,
               "failed to parse URI: %s\n"
               "error message:       %s\n",
               uri_string,
               error.message);
      return EXIT_FAILURE;
   }

   client = mongoc_client_new_from_uri (uri);
   if (!client) {
      return EXIT_FAILURE;
   }

   coll = mongoc_client_get_collection (client, "db", "coll");
   stream = mongoc_collection_watch (coll, &empty, NULL);

   mongoc_write_concern_set_wmajority (wc, 10000);
   mongoc_write_concern_append (wc, &opts);
   r = mongoc_collection_insert_one (coll, to_insert, &opts, NULL, &error);
   if (!r) {
      fprintf (stderr, "Error: %s\n", error.message);
      return EXIT_FAILURE;
   }

   while (mongoc_change_stream_next (stream, &doc)) {
      char *as_json = bson_as_relaxed_extended_json (doc, NULL);
      fprintf (stderr, "Got document: %s\n", as_json);
      bson_free (as_json);
   }

   if (mongoc_change_stream_error_document (stream, &error, &err_doc)) {
      if (!bson_empty (err_doc)) {
         fprintf (stderr,
                  "Server Error: %s\n",
                  bson_as_relaxed_extended_json (err_doc, NULL));
      } else {
         fprintf (stderr, "Client Error: %s\n", error.message);
      }
      return EXIT_FAILURE;
   }

   bson_destroy (to_insert);
   mongoc_write_concern_destroy (wc);
   bson_destroy (&opts);
   mongoc_change_stream_destroy (stream);
   mongoc_collection_destroy (coll);
   mongoc_uri_destroy (uri);
   mongoc_client_destroy (client);
   mongoc_cleanup ();

   return EXIT_SUCCESS;
}

All watch functions accept several options to indicate where a change stream should start returning changes from: resumeAfter, startAfter, and startAtOperationTime.

All changes returned by mongoc_change_stream_next() include a resume token in the _id field. MongoDB 4.2 also includes an additional resume token in each "aggregate" and "getMore" command response, which points to the end of that response's batch. The current token is automatically cached by libmongoc. In the event of an error, libmongoc attempts to recreate the change stream starting where it left off by passing the cached resume token. libmongoc only attempts to resume once, but client applications can access the cached resume token with mongoc_change_stream_get_resume_token() and use it for their own resume logic by passing it as either the resumeAfter or startAfter option.

Additionally, change streams can start returning changes at an operation time by using the startAtOperationTime field. This can be the timestamp returned in the operationTime field of a command reply.

resumeAfter, startAfter, and startAtOperationTime are mutually exclusive options. Setting more than one will result in a server error.

The following example implements custom resuming logic, persisting the resume token in a file.

example-resume.c

#include <mongoc/mongoc.h>

/* An example implementation of custom resume logic in a change stream.
* example-resume starts a client-wide change stream and persists the resume
* token in a file "resume-token.json". On restart, if "resume-token.json"
* exists, the change stream starts watching after the persisted resume token.
*
* This behavior allows a user to exit example-resume, and restart it later
* without missing any change events.
*/
#include <unistd.h>

static const char *RESUME_TOKEN_PATH = "resume-token.json";

static bool
_save_resume_token (const bson_t *doc)
{
   FILE *file_stream;
   bson_iter_t iter;
   bson_t resume_token_doc;
   char *as_json = NULL;
   size_t as_json_len;
   ssize_t r, n_written;
   const bson_value_t *resume_token;

   if (!bson_iter_init_find (&iter, doc, "_id")) {
      fprintf (stderr, "reply does not contain operationTime.");
      return false;
   }
   resume_token = bson_iter_value (&iter);
   /* store the resume token in a document, { resumeAfter: <resume token> }
    * which we can later append easily. */
   file_stream = fopen (RESUME_TOKEN_PATH, "w+");
   if (!file_stream) {
      fprintf (stderr, "failed to open %s for writing\n", RESUME_TOKEN_PATH);
      return false;
   }
   bson_init (&resume_token_doc);
   BSON_APPEND_VALUE (&resume_token_doc, "resumeAfter", resume_token);
   as_json = bson_as_canonical_extended_json (&resume_token_doc, &as_json_len);
   bson_destroy (&resume_token_doc);
   n_written = 0;
   while (n_written < as_json_len) {
      r = fwrite ((void *) (as_json + n_written),
                  sizeof (char),
                  as_json_len - n_written,
                  file_stream);
      if (r == -1) {
         fprintf (stderr, "failed to write to %s\n", RESUME_TOKEN_PATH);
         bson_free (as_json);
         fclose (file_stream);
         return false;
      }
      n_written += r;
   }

   bson_free (as_json);
   fclose (file_stream);
   return true;
}

bool
_load_resume_token (bson_t *opts)
{
   bson_error_t error;
   bson_json_reader_t *reader;
   bson_t doc;

   /* if the file does not exist, skip. */
   if (-1 == access (RESUME_TOKEN_PATH, R_OK)) {
      return true;
   }
   reader = bson_json_reader_new_from_file (RESUME_TOKEN_PATH, &error);
   if (!reader) {
      fprintf (stderr,
               "failed to open %s for reading: %s\n",
               RESUME_TOKEN_PATH,
               error.message);
      return false;
   }

   bson_init (&doc);
   if (-1 == bson_json_reader_read (reader, &doc, &error)) {
      fprintf (stderr, "failed to read doc from %s\n", RESUME_TOKEN_PATH);
      bson_destroy (&doc);
      bson_json_reader_destroy (reader);
      return false;
   }

   printf ("found cached resume token in %s, resuming change stream.\n",
           RESUME_TOKEN_PATH);

   bson_concat (opts, &doc);
   bson_destroy (&doc);
   bson_json_reader_destroy (reader);
   return true;
}

int
main (void)
{
   int exit_code = EXIT_FAILURE;
   const char *uri_string;
   mongoc_uri_t *uri = NULL;
   bson_error_t error;
   mongoc_client_t *client = NULL;
   bson_t pipeline = BSON_INITIALIZER;
   bson_t opts = BSON_INITIALIZER;
   mongoc_change_stream_t *stream = NULL;
   const bson_t *doc;

   const int max_time = 30; /* max amount of time, in seconds, that
                               mongoc_change_stream_next can block. */

   mongoc_init ();
   uri_string = "mongodb://localhost:27017/db?replicaSet=rs0";
   uri = mongoc_uri_new_with_error (uri_string, &error);
   if (!uri) {
      fprintf (stderr,
               "failed to parse URI: %s\n"
               "error message:       %s\n",
               uri_string,
               error.message);
      goto cleanup;
   }

   client = mongoc_client_new_from_uri (uri);
   if (!client) {
      goto cleanup;
   }

   if (!_load_resume_token (&opts)) {
      goto cleanup;
   }
   BSON_APPEND_INT64 (&opts, "maxAwaitTimeMS", max_time * 1000);

   printf ("listening for changes on the client (max %d seconds).\n", max_time);
   stream = mongoc_client_watch (client, &pipeline, &opts);

   while (mongoc_change_stream_next (stream, &doc)) {
      char *as_json;

      as_json = bson_as_canonical_extended_json (doc, NULL);
      printf ("change received: %s\n", as_json);
      bson_free (as_json);
      if (!_save_resume_token (doc)) {
         goto cleanup;
      }
   }

   exit_code = EXIT_SUCCESS;

cleanup:
   mongoc_uri_destroy (uri);
   bson_destroy (&pipeline);
   bson_destroy (&opts);
   mongoc_change_stream_destroy (stream);
   mongoc_client_destroy (client);
   mongoc_cleanup ();
   return exit_code;
}

The following example shows using startAtOperationTime to synchronize a change stream with another operation.

example-start-at-optime.c

/* An example of starting a change stream with startAtOperationTime. */
#include <mongoc/mongoc.h>

int
main (void)
{
   int exit_code = EXIT_FAILURE;
   const char *uri_string;
   mongoc_uri_t *uri = NULL;
   bson_error_t error;
   mongoc_client_t *client = NULL;
   mongoc_collection_t *coll = NULL;
   bson_t pipeline = BSON_INITIALIZER;
   bson_t opts = BSON_INITIALIZER;
   mongoc_change_stream_t *stream = NULL;
   bson_iter_t iter;
   const bson_t *doc;
   bson_value_t cached_operation_time = {0};
   int i;
   bool r;

   mongoc_init ();
   uri_string = "mongodb://localhost:27017/db?replicaSet=rs0";
   uri = mongoc_uri_new_with_error (uri_string, &error);
   if (!uri) {
      fprintf (stderr,
               "failed to parse URI: %s\n"
               "error message:       %s\n",
               uri_string,
               error.message);
      goto cleanup;
   }

   client = mongoc_client_new_from_uri (uri);
   if (!client) {
      goto cleanup;
   }

   /* insert five documents. */
   coll = mongoc_client_get_collection (client, "db", "coll");
   for (i = 0; i < 5; i++) {
      bson_t reply;
      bson_t *insert_cmd = BCON_NEW ("insert",
                                     "coll",
                                     "documents",
                                     "[",
                                     "{",
                                     "x",
                                     BCON_INT64 (i),
                                     "}",
                                     "]");

      r = mongoc_collection_write_command_with_opts (
         coll, insert_cmd, NULL, &reply, &error);
      bson_destroy (insert_cmd);
      if (!r) {
         bson_destroy (&reply);
         fprintf (stderr, "failed to insert: %s\n", error.message);
         goto cleanup;
      }
      if (i == 0) {
         /* cache the operation time in the first reply. */
         if (bson_iter_init_find (&iter, &reply, "operationTime")) {
            bson_value_copy (bson_iter_value (&iter), &cached_operation_time);
         } else {
            fprintf (stderr, "reply does not contain operationTime.");
            bson_destroy (&reply);
            goto cleanup;
         }
      }
      bson_destroy (&reply);
   }

   /* start a change stream at the first returned operationTime. */
   BSON_APPEND_VALUE (&opts, "startAtOperationTime", &cached_operation_time);
   stream = mongoc_collection_watch (coll, &pipeline, &opts);

   /* since the change stream started at the operation time of the first
    * insert, the five inserts are returned. */
   printf ("listening for changes on db.coll:\n");
   while (mongoc_change_stream_next (stream, &doc)) {
      char *as_json;

      as_json = bson_as_canonical_extended_json (doc, NULL);
      printf ("change received: %s\n", as_json);
      bson_free (as_json);
   }

   exit_code = EXIT_SUCCESS;

cleanup:
   mongoc_uri_destroy (uri);
   bson_destroy (&pipeline);
   bson_destroy (&opts);
   if (cached_operation_time.value_type) {
      bson_value_destroy (&cached_operation_time);
   }
   mongoc_change_stream_destroy (stream);
   mongoc_collection_destroy (coll);
   mongoc_client_destroy (client);
   mongoc_cleanup ();
   return exit_code;
}

typedef struct _mongoc_client_encryption_t mongoc_client_encryption_t;

mongoc_client_encryption_t provides utility functions for In-Use Encryption.

mongoc_client_encryption_t is NOT thread-safe and should only be used in the same thread as the mongoc_client_t that is configured via mongoc_client_encryption_opts_set_keyvault_client().

The key vault client, configured via mongoc_client_encryption_opts_set_keyvault_client(), must outlive the mongoc_client_encryption_t.

SEE ALSO:

mongoc_client_enable_auto_encryption()

mongoc_client_pool_enable_auto_encryption()

In-Use Encryption for libmongoc

The MongoDB Manual for Client-Side Field Level Encryption

The MongoDB Manual for Queryable Encryption

typedef struct _mongoc_client_encryption_datakey_opts_t mongoc_client_encryption_datakey_opts_t;

Used to set options for mongoc_client_encryption_create_datakey().

SEE ALSO:

mongoc_client_encryption_create_datakey()

typedef struct _mongoc_client_encryption_rewrap_many_datakey_result_t
   mongoc_client_encryption_rewrap_many_datakey_result_t;

Used to access the result of mongoc_client_encryption_rewrap_many_datakey().

SEE ALSO:

mongoc_client_encryption_rewrap_many_datakey()

typedef struct _mongoc_client_encryption_encrypt_opts_t mongoc_client_encryption_encrypt_opts_t;

Used to set options for mongoc_client_encryption_encrypt().

SEE ALSO:

mongoc_client_encryption_encrypt()

typedef struct _mongoc_client_encryption_encrypt_range_opts_t mongoc_client_encryption_encrypt_range_opts_t;

IMPORTANT:

The Range algorithm is experimental only and not intended for public use. It is subject to breaking changes. This API is part of the experimental Queryable Encryption API and may be subject to breaking changes in future releases.

New in version 1.24.0.

RangeOpts specifies index options for a Queryable Encryption field supporting "rangePreview" queries. Used to set options for mongoc_client_encryption_encrypt().

The options min, max, sparsity, and range must match the values set in the encryptedFields of the destination collection.

For double and decimal128 fields, min/max/precision must all be set, or all be unset.

SEE ALSO:

mongoc_client_encryption_encrypt()
mongoc_client_encryption_encrypt_opts_t

typedef struct _mongoc_client_encryption_opts_t mongoc_client_encryption_opts_t;

Used to set options for mongoc_client_encryption_new().

SEE ALSO:

mongoc_client_encryption_new()

A connection pool for multi-threaded programs. See Connection Pooling.

typedef struct _mongoc_client_pool_t mongoc_client_pool_t

mongoc_client_pool_t is the basis for multi-threading in the MongoDB C driver. Since mongoc_client_t structures are not thread-safe, this structure is used to retrieve a new mongoc_client_t for a given thread. This structure is thread-safe, except for its destructor method, mongoc_client_pool_destroy(), which is not thread-safe and must only be called from one thread.

example-pool.c

/* gcc example-pool.c -o example-pool $(pkg-config --cflags --libs
 * libmongoc-1.0) */

/* ./example-pool [CONNECTION_STRING] */

#include <mongoc/mongoc.h>
#include <pthread.h>
#include <stdio.h>

static pthread_mutex_t mutex;
static bool in_shutdown = false;

static void *
worker (void *data)
{
   mongoc_client_pool_t *pool = data;
   mongoc_client_t *client;
   bson_t ping = BSON_INITIALIZER;
   bson_error_t error;
   bool r;

   BSON_APPEND_INT32 (&ping, "ping", 1);

   while (true) {
      client = mongoc_client_pool_pop (pool);
      /* Do something with client. If you are writing an HTTP server, you
       * probably only want to hold onto the client for the portion of the
       * request performing database queries.
       */
      r = mongoc_client_command_simple (
         client, "admin", &ping, NULL, NULL, &error);

      if (!r) {
         fprintf (stderr, "%s\n", error.message);
      }

      mongoc_client_pool_push (pool, client);

      pthread_mutex_lock (&mutex);
      if (in_shutdown || !r) {
         pthread_mutex_unlock (&mutex);
         break;
      }

      pthread_mutex_unlock (&mutex);
   }

   bson_destroy (&ping);
   return NULL;
}

int
main (int argc, char *argv[])
{
   const char *uri_string = "mongodb://127.0.0.1/?appname=pool-example";
   mongoc_uri_t *uri;
   bson_error_t error;
   mongoc_client_pool_t *pool;
   pthread_t threads[10];
   unsigned i;
   void *ret;

   pthread_mutex_init (&mutex, NULL);
   mongoc_init ();

   if (argc > 1) {
      uri_string = argv[1];
   }

   uri = mongoc_uri_new_with_error (uri_string, &error);
   if (!uri) {
      fprintf (stderr,
               "failed to parse URI: %s\n"
               "error message:       %s\n",
               uri_string,
               error.message);
      return EXIT_FAILURE;
   }

   pool = mongoc_client_pool_new (uri);
   mongoc_client_pool_set_error_api (pool, 2);

   for (i = 0; i < 10; i++) {
      pthread_create (&threads[i], NULL, worker, pool);
   }

   sleep (10);
   pthread_mutex_lock (&mutex);
   in_shutdown = true;
   pthread_mutex_unlock (&mutex);

   for (i = 0; i < 10; i++) {
      pthread_join (threads[i], &ret);
   }

   mongoc_client_pool_destroy (pool);
   mongoc_uri_destroy (uri);

   mongoc_cleanup ();

   return EXIT_SUCCESS;
}

Use a session for a sequence of operations, optionally with causal consistency. See the MongoDB Manual Entry for Causal Consistency.

Start a session with mongoc_client_start_session(), use the session for a sequence of operations and multi-document transactions, then free it with mongoc_client_session_destroy(). Any mongoc_cursor_t or mongoc_change_stream_t using a session must be destroyed before the session, and a session must be destroyed before the mongoc_client_t it came from.

By default, sessions are causally consistent. To disable causal consistency, before starting a session create a mongoc_session_opt_t with mongoc_session_opts_new() and call mongoc_session_opts_set_causal_consistency(), then free the struct with mongoc_session_opts_destroy().

Unacknowledged writes are prohibited with sessions.

A mongoc_client_session_t must be used by only one thread at a time. Due to session pooling, mongoc_client_start_session() may return a session that has been idle for some time and is about to be closed after its idle timeout. Use the session within one minute of acquiring it to refresh the session and avoid a timeout.

A mongoc_client_session_t is only usable in the parent process after a fork. The child process must call mongoc_client_reset() on the client field.

example-session.c

/* gcc example-session.c -o example-session \
 *     $(pkg-config --cflags --libs libmongoc-1.0) */

/* ./example-session [CONNECTION_STRING] */

#include <stdio.h>
#include <mongoc/mongoc.h>


int
main (int argc, char *argv[])
{
   int exit_code = EXIT_FAILURE;

   mongoc_client_t *client = NULL;
   const char *uri_string = "mongodb://127.0.0.1/?appname=session-example";
   mongoc_uri_t *uri = NULL;
   mongoc_client_session_t *client_session = NULL;
   mongoc_collection_t *collection = NULL;
   bson_error_t error;
   bson_t *selector = NULL;
   bson_t *update = NULL;
   bson_t *update_opts = NULL;
   bson_t *find_opts = NULL;
   mongoc_read_prefs_t *secondary = NULL;
   mongoc_cursor_t *cursor = NULL;
   const bson_t *doc;
   char *str;
   bool r;

   mongoc_init ();

   if (argc > 1) {
      uri_string = argv[1];
   }

   uri = mongoc_uri_new_with_error (uri_string, &error);
   if (!uri) {
      fprintf (stderr,
               "failed to parse URI: %s\n"
               "error message:       %s\n",
               uri_string,
               error.message);
      goto done;
   }

   client = mongoc_client_new_from_uri (uri);
   if (!client) {
      goto done;
   }

   mongoc_client_set_error_api (client, 2);

   /* pass NULL for options - by default the session is causally consistent */
   client_session = mongoc_client_start_session (client, NULL, &error);
   if (!client_session) {
      fprintf (stderr, "Failed to start session: %s\n", error.message);
      goto done;
   }

   collection = mongoc_client_get_collection (client, "test", "collection");
   selector = BCON_NEW ("_id", BCON_INT32 (1));
   update = BCON_NEW ("$inc", "{", "x", BCON_INT32 (1), "}");
   update_opts = bson_new ();
   if (!mongoc_client_session_append (client_session, update_opts, &error)) {
      fprintf (stderr, "Could not add session to opts: %s\n", error.message);
      goto done;
   }

   r = mongoc_collection_update_one (
      collection, selector, update, update_opts, NULL /* reply */, &error);

   if (!r) {
      fprintf (stderr, "Update failed: %s\n", error.message);
      goto done;
   }

   bson_destroy (selector);
   selector = BCON_NEW ("_id", BCON_INT32 (1));
   secondary = mongoc_read_prefs_new (MONGOC_READ_SECONDARY);

   find_opts = BCON_NEW ("maxTimeMS", BCON_INT32 (2000));
   if (!mongoc_client_session_append (client_session, find_opts, &error)) {
      fprintf (stderr, "Could not add session to opts: %s\n", error.message);
      goto done;
   };

   /* read from secondary. since we're in a causally consistent session, the
    * data is guaranteed to reflect the update we did on the primary. the query
    * blocks waiting for the secondary to catch up, if necessary, or times out
    * and fails after 2000 ms.
    */
   cursor = mongoc_collection_find_with_opts (
      collection, selector, find_opts, secondary);

   while (mongoc_cursor_next (cursor, &doc)) {
      str = bson_as_json (doc, NULL);
      fprintf (stdout, "%s\n", str);
      bson_free (str);
   }

   if (mongoc_cursor_error (cursor, &error)) {
      fprintf (stderr, "Cursor Failure: %s\n", error.message);
      goto done;
   }

   exit_code = EXIT_SUCCESS;

done:
   if (find_opts) {
      bson_destroy (find_opts);
   }
   if (update) {
      bson_destroy (update);
   }
   if (selector) {
      bson_destroy (selector);
   }
   if (update_opts) {
      bson_destroy (update_opts);
   }
   if (secondary) {
      mongoc_read_prefs_destroy (secondary);
   }
   /* destroy cursor, collection, session before the client they came from */
   if (cursor) {
      mongoc_cursor_destroy (cursor);
   }
   if (collection) {
      mongoc_collection_destroy (collection);
   }
   if (client_session) {
      mongoc_client_session_destroy (client_session);
   }
   if (uri) {
      mongoc_uri_destroy (uri);
   }
   if (client) {
      mongoc_client_destroy (client);
   }

   mongoc_cleanup ();

   return exit_code;
}

typedef bool (*mongoc_client_session_with_transaction_cb_t) (
   mongoc_client_session_t *session,
   void *ctx,
   bson_t **reply,
   bson_error_t *error);

Provide this callback to mongoc_client_session_with_transaction(). The callback should run a sequence of operations meant to be contained within a transaction.  The callback should not attempt to start or commit transactions.

• session: A mongoc_client_session_t.
• ctx: A void* set to the the user-provided ctx passed to mongoc_client_session_with_transaction().
• reply: An optional location for a bson_t or NULL. The callback should set this if it runs any operations against the server and receives replies.
• error: A bson_error_t. The callback should set this if it receives any errors while running operations against the server.

Returns true for success and false on failure. If cb returns false then it should also set error.

SEE ALSO:

mongoc_client_session_with_transaction()

A single-threaded MongoDB connection. See Connection Pooling.

typedef struct _mongoc_client_t mongoc_client_t;

typedef mongoc_stream_t *(*mongoc_stream_initiator_t) (
   const mongoc_uri_t *uri,
   const mongoc_host_list_t *host,
   void *user_data,
   bson_error_t *error);

mongoc_client_t is an opaque type that provides access to a MongoDB server, replica set, or sharded cluster. It maintains management of underlying sockets and routing to individual nodes based on mongoc_read_prefs_t or mongoc_write_concern_t.

The underlying transport for a given client can be customized, wrapped or replaced by any implementation that fulfills mongoc_stream_t. A custom transport can be set with mongoc_client_set_stream_initiator().

mongoc_client_t is NOT thread-safe and should only be used from one thread at a time. When used in multi-threaded scenarios, it is recommended that you use the thread-safe mongoc_client_pool_t to retrieve a mongoc_client_t for your thread.

A mongoc_client_t is only usable in the parent process after a fork. The child process must call mongoc_client_reset().

example-client.c

/* gcc example-client.c -o example-client $(pkg-config --cflags --libs
 * libmongoc-1.0) */

/* ./example-client [CONNECTION_STRING [COLLECTION_NAME]] */

#include <mongoc/mongoc.h>
#include <stdio.h>
#include <stdlib.h>

int
main (int argc, char *argv[])
{
   mongoc_client_t *client;
   mongoc_collection_t *collection;
   mongoc_cursor_t *cursor;
   bson_error_t error;
   const bson_t *doc;
   const char *collection_name = "test";
   bson_t query;
   char *str;
   const char *uri_string = "mongodb://127.0.0.1/?appname=client-example";
   mongoc_uri_t *uri;

   mongoc_init ();
   if (argc > 1) {
      uri_string = argv[1];
   }

   if (argc > 2) {
      collection_name = argv[2];
   }

   uri = mongoc_uri_new_with_error (uri_string, &error);
   if (!uri) {
      fprintf (stderr,
               "failed to parse URI: %s\n"
               "error message:       %s\n",
               uri_string,
               error.message);
      return EXIT_FAILURE;
   }

   client = mongoc_client_new_from_uri (uri);
   if (!client) {
      return EXIT_FAILURE;
   }

   mongoc_client_set_error_api (client, 2);

   bson_init (&query);
   collection = mongoc_client_get_collection (client, "test", collection_name);
   cursor = mongoc_collection_find_with_opts (
      collection,
      &query,
      NULL,  /* additional options */
      NULL); /* read prefs, NULL for default */

   while (mongoc_cursor_next (cursor, &doc)) {
      str = bson_as_canonical_extended_json (doc, NULL);
      fprintf (stdout, "%s\n", str);
      bson_free (str);
   }

   if (mongoc_cursor_error (cursor, &error)) {
      fprintf (stderr, "Cursor Failure: %s\n", error.message);
      return EXIT_FAILURE;
   }

   bson_destroy (&query);
   mongoc_cursor_destroy (cursor);
   mongoc_collection_destroy (collection);
   mongoc_uri_destroy (uri);
   mongoc_client_destroy (client);
   mongoc_cleanup ();

   return EXIT_SUCCESS;
}

typedef struct _mongoc_collection_t mongoc_collection_t;

mongoc_collection_t provides access to a MongoDB collection.  This handle is useful for actions for most CRUD operations, I.e. insert, update, delete, find, etc.

Read preferences and write concerns are inherited from the parent client. They can be overridden by set_* commands if so desired.

Client-side cursor abstraction

typedef struct _mongoc_cursor_t mongoc_cursor_t;

mongoc_cursor_t provides access to a MongoDB query cursor. It wraps up the wire protocol negotiation required to initiate a query and retrieve an unknown number of documents.

Common cursor operations include:

• Determine which host we've connected to with mongoc_cursor_get_host().
• Retrieve more records with repeated calls to mongoc_cursor_next().
• Clone a query to repeat execution at a later point with mongoc_cursor_clone().
• Test for errors with mongoc_cursor_error().

Cursors are lazy, meaning that no connection is established and no network traffic occurs until the first call to mongoc_cursor_next().

mongoc_cursor_t is NOT thread safe. It may only be used from within the thread in which it was created.

Query MongoDB and iterate results

/* gcc example-client.c -o example-client $(pkg-config --cflags --libs
 * libmongoc-1.0) */

/* ./example-client [CONNECTION_STRING [COLLECTION_NAME]] */

#include <mongoc/mongoc.h>
#include <stdio.h>
#include <stdlib.h>

int
main (int argc, char *argv[])
{
   mongoc_client_t *client;
   mongoc_collection_t *collection;
   mongoc_cursor_t *cursor;
   bson_error_t error;
   const bson_t *doc;
   const char *collection_name = "test";
   bson_t query;
   char *str;
   const char *uri_string = "mongodb://127.0.0.1/?appname=client-example";
   mongoc_uri_t *uri;

   mongoc_init ();
   if (argc > 1) {
      uri_string = argv[1];
   }

   if (argc > 2) {
      collection_name = argv[2];
   }

   uri = mongoc_uri_new_with_error (uri_string, &error);
   if (!uri) {
      fprintf (stderr,
               "failed to parse URI: %s\n"
               "error message:       %s\n",
               uri_string,
               error.message);
      return EXIT_FAILURE;
   }

   client = mongoc_client_new_from_uri (uri);
   if (!client) {
      return EXIT_FAILURE;
   }

   mongoc_client_set_error_api (client, 2);

   bson_init (&query);
   collection = mongoc_client_get_collection (client, "test", collection_name);
   cursor = mongoc_collection_find_with_opts (
      collection,
      &query,
      NULL,  /* additional options */
      NULL); /* read prefs, NULL for default */

   while (mongoc_cursor_next (cursor, &doc)) {
      str = bson_as_canonical_extended_json (doc, NULL);
      fprintf (stdout, "%s\n", str);
      bson_free (str);
   }

   if (mongoc_cursor_error (cursor, &error)) {
      fprintf (stderr, "Cursor Failure: %s\n", error.message);
      return EXIT_FAILURE;
   }

   bson_destroy (&query);
   mongoc_cursor_destroy (cursor);
   mongoc_collection_destroy (collection);
   mongoc_uri_destroy (uri);
   mongoc_client_destroy (client);
   mongoc_cleanup ();

   return EXIT_SUCCESS;
}

MongoDB Database Abstraction

typedef struct _mongoc_database_t mongoc_database_t;

mongoc_database_t provides access to a MongoDB database. This handle is useful for actions a particular database object. It is not a container for mongoc_collection_t structures.

Read preferences and write concerns are inherited from the parent client. They can be overridden with mongoc_database_set_read_prefs() and mongoc_database_set_write_concern().

#include <mongoc/mongoc.h>

int
main (int argc, char *argv[])
{
   mongoc_database_t *database;
   mongoc_client_t *client;

   mongoc_init ();

   client = mongoc_client_new ("mongodb://localhost/");
   database = mongoc_client_get_database (client, "test");

   mongoc_database_destroy (database);
   mongoc_client_destroy (client);

   mongoc_cleanup ();

   return 0;
}

WARNING:

Deprecated since version 1.9.0: These flags are deprecated and should not be used in new code.

Please use mongoc_collection_delete_one() or mongoc_collection_delete_many() in new code.

typedef enum {
   MONGOC_DELETE_NONE = 0,
   MONGOC_DELETE_SINGLE_REMOVE = 1 << 0,
} mongoc_delete_flags_t;

Flags for deletion operations

find_and_modify abstraction

mongoc_find_and_modify_opts_t is a builder interface to construct the findAndModify command.

It was created to be able to accommodate new arguments to the findAndModify command.

As of MongoDB 3.2, the mongoc_write_concern_t specified on the mongoc_collection_t will be used, if any.

flags.c

void
fam_flags (mongoc_collection_t *collection)
{
   mongoc_find_and_modify_opts_t *opts;
   bson_t reply;
   bson_error_t error;
   bson_t query = BSON_INITIALIZER;
   bson_t *update;
   bool success;


   /* Find Zlatan Ibrahimovic, the striker */
   BSON_APPEND_UTF8 (&query, "firstname", "Zlatan");
   BSON_APPEND_UTF8 (&query, "lastname", "Ibrahimovic");
   BSON_APPEND_UTF8 (&query, "profession", "Football player");
   BSON_APPEND_INT32 (&query, "age", 34);
   BSON_APPEND_INT32 (
      &query, "goals", (16 + 35 + 23 + 57 + 16 + 14 + 28 + 84) + (1 + 6 + 62));

   /* Add his football position */
   update = BCON_NEW ("$set", "{", "position", BCON_UTF8 ("striker"), "}");

   opts = mongoc_find_and_modify_opts_new ();

   mongoc_find_and_modify_opts_set_update (opts, update);

   /* Create the document if it didn't exist, and return the updated document */
   mongoc_find_and_modify_opts_set_flags (
      opts, MONGOC_FIND_AND_MODIFY_UPSERT | MONGOC_FIND_AND_MODIFY_RETURN_NEW);

   success = mongoc_collection_find_and_modify_with_opts (
      collection, &query, opts, &reply, &error);

   if (success) {
      char *str;

      str = bson_as_canonical_extended_json (&reply, NULL);
      printf ("%s\n", str);
      bson_free (str);
   } else {
      fprintf (
         stderr, "Got error: \"%s\" on line %d\n", error.message, __LINE__);
   }

   bson_destroy (&reply);
   bson_destroy (update);
   bson_destroy (&query);
   mongoc_find_and_modify_opts_destroy (opts);
}

bypass.c

void
fam_bypass (mongoc_collection_t *collection)
{
   mongoc_find_and_modify_opts_t *opts;
   bson_t reply;
   bson_t *update;
   bson_error_t error;
   bson_t query = BSON_INITIALIZER;
   bool success;


   /* Find Zlatan Ibrahimovic, the striker */
   BSON_APPEND_UTF8 (&query, "firstname", "Zlatan");
   BSON_APPEND_UTF8 (&query, "lastname", "Ibrahimovic");
   BSON_APPEND_UTF8 (&query, "profession", "Football player");

   /* Bump his age */
   update = BCON_NEW ("$inc", "{", "age", BCON_INT32 (1), "}");

   opts = mongoc_find_and_modify_opts_new ();
   mongoc_find_and_modify_opts_set_update (opts, update);
   /* He can still play, even though he is pretty old. */
   mongoc_find_and_modify_opts_set_bypass_document_validation (opts, true);

   success = mongoc_collection_find_and_modify_with_opts (
      collection, &query, opts, &reply, &error);

   if (success) {
      char *str;

      str = bson_as_canonical_extended_json (&reply, NULL);
      printf ("%s\n", str);
      bson_free (str);
   } else {
      fprintf (
         stderr, "Got error: \"%s\" on line %d\n", error.message, __LINE__);
   }

   bson_destroy (&reply);
   bson_destroy (update);
   bson_destroy (&query);
   mongoc_find_and_modify_opts_destroy (opts);
}

update.c

void
fam_update (mongoc_collection_t *collection)
{
   mongoc_find_and_modify_opts_t *opts;
   bson_t *update;
   bson_t reply;
   bson_error_t error;
   bson_t query = BSON_INITIALIZER;
   bool success;


   /* Find Zlatan Ibrahimovic */
   BSON_APPEND_UTF8 (&query, "firstname", "Zlatan");
   BSON_APPEND_UTF8 (&query, "lastname", "Ibrahimovic");

   /* Make him a book author */
   update = BCON_NEW ("$set", "{", "author", BCON_BOOL (true), "}");

   opts = mongoc_find_and_modify_opts_new ();
   /* Note that the document returned is the _previous_ version of the document
    * To fetch the modified new version, use
    * mongoc_find_and_modify_opts_set_flags (opts,
    * MONGOC_FIND_AND_MODIFY_RETURN_NEW);
    */
   mongoc_find_and_modify_opts_set_update (opts, update);

   success = mongoc_collection_find_and_modify_with_opts (
      collection, &query, opts, &reply, &error);

   if (success) {
      char *str;

      str = bson_as_canonical_extended_json (&reply, NULL);
      printf ("%s\n", str);
      bson_free (str);
   } else {
      fprintf (
         stderr, "Got error: \"%s\" on line %d\n", error.message, __LINE__);
   }

   bson_destroy (&reply);
   bson_destroy (update);
   bson_destroy (&query);
   mongoc_find_and_modify_opts_destroy (opts);
}

fields.c

void
fam_fields (mongoc_collection_t *collection)
{
   mongoc_find_and_modify_opts_t *opts;
   bson_t fields = BSON_INITIALIZER;
   bson_t *update;
   bson_t reply;
   bson_error_t error;
   bson_t query = BSON_INITIALIZER;
   bool success;


   /* Find Zlatan Ibrahimovic */
   BSON_APPEND_UTF8 (&query, "lastname", "Ibrahimovic");
   BSON_APPEND_UTF8 (&query, "firstname", "Zlatan");

   /* Return his goal tally */
   BSON_APPEND_INT32 (&fields, "goals", 1);

   /* Bump his goal tally */
   update = BCON_NEW ("$inc", "{", "goals", BCON_INT32 (1), "}");

   opts = mongoc_find_and_modify_opts_new ();
   mongoc_find_and_modify_opts_set_update (opts, update);
   mongoc_find_and_modify_opts_set_fields (opts, &fields);
   /* Return the new tally */
   mongoc_find_and_modify_opts_set_flags (opts,
                                          MONGOC_FIND_AND_MODIFY_RETURN_NEW);

   success = mongoc_collection_find_and_modify_with_opts (
      collection, &query, opts, &reply, &error);

   if (success) {
      char *str;

      str = bson_as_canonical_extended_json (&reply, NULL);
      printf ("%s\n", str);
      bson_free (str);
   } else {
      fprintf (
         stderr, "Got error: \"%s\" on line %d\n", error.message, __LINE__);
   }

   bson_destroy (&reply);
   bson_destroy (update);
   bson_destroy (&fields);
   bson_destroy (&query);
   mongoc_find_and_modify_opts_destroy (opts);
}

sort.c

void
fam_sort (mongoc_collection_t *collection)
{
   mongoc_find_and_modify_opts_t *opts;
   bson_t *update;
   bson_t sort = BSON_INITIALIZER;
   bson_t reply;
   bson_error_t error;
   bson_t query = BSON_INITIALIZER;
   bool success;


   /* Find all users with the lastname Ibrahimovic */
   BSON_APPEND_UTF8 (&query, "lastname", "Ibrahimovic");

   /* Sort by age (descending) */
   BSON_APPEND_INT32 (&sort, "age", -1);

   /* Bump his goal tally */
   update = BCON_NEW ("$set", "{", "oldest", BCON_BOOL (true), "}");

   opts = mongoc_find_and_modify_opts_new ();
   mongoc_find_and_modify_opts_set_update (opts, update);
   mongoc_find_and_modify_opts_set_sort (opts, &sort);

   success = mongoc_collection_find_and_modify_with_opts (
      collection, &query, opts, &reply, &error);

   if (success) {
      char *str;

      str = bson_as_canonical_extended_json (&reply, NULL);
      printf ("%s\n", str);
      bson_free (str);
   } else {
      fprintf (
         stderr, "Got error: \"%s\" on line %d\n", error.message, __LINE__);
   }

   bson_destroy (&reply);
   bson_destroy (update);
   bson_destroy (&sort);
   bson_destroy (&query);
   mongoc_find_and_modify_opts_destroy (opts);
}

opts.c

void
fam_opts (mongoc_collection_t *collection)
{
   mongoc_find_and_modify_opts_t *opts;
   bson_t reply;
   bson_t *update;
   bson_error_t error;
   bson_t query = BSON_INITIALIZER;
   mongoc_write_concern_t *wc;
   bson_t extra = BSON_INITIALIZER;
   bool success;


   /* Find Zlatan Ibrahimovic, the striker */
   BSON_APPEND_UTF8 (&query, "firstname", "Zlatan");
   BSON_APPEND_UTF8 (&query, "lastname", "Ibrahimovic");
   BSON_APPEND_UTF8 (&query, "profession", "Football player");

   /* Bump his age */
   update = BCON_NEW ("$inc", "{", "age", BCON_INT32 (1), "}");

   opts = mongoc_find_and_modify_opts_new ();
   mongoc_find_and_modify_opts_set_update (opts, update);

   /* Abort if the operation takes too long. */
   mongoc_find_and_modify_opts_set_max_time_ms (opts, 100);

   /* Set write concern w: 2 */
   wc = mongoc_write_concern_new ();
   mongoc_write_concern_set_w (wc, 2);
   mongoc_write_concern_append (wc, &extra);

   /* Some future findAndModify option the driver doesn't support conveniently
    */
   BSON_APPEND_INT32 (&extra, "futureOption", 42);
   mongoc_find_and_modify_opts_append (opts, &extra);

   success = mongoc_collection_find_and_modify_with_opts (
      collection, &query, opts, &reply, &error);

   if (success) {
      char *str;

      str = bson_as_canonical_extended_json (&reply, NULL);
      printf ("%s\n", str);
      bson_free (str);
   } else {
      fprintf (
         stderr, "Got error: \"%s\" on line %d\n", error.message, __LINE__);
   }

   bson_destroy (&reply);
   bson_destroy (&extra);
   bson_destroy (update);
   bson_destroy (&query);
   mongoc_write_concern_destroy (wc);
   mongoc_find_and_modify_opts_destroy (opts);
}

fam.c

int
main (void)
{
   mongoc_collection_t *collection;
   mongoc_database_t *database;
   mongoc_client_t *client;
   const char *uri_string =
      "mongodb://localhost:27017/admin?appname=find-and-modify-opts-example";
   mongoc_uri_t *uri;
   bson_error_t error;
   bson_t *options;

   mongoc_init ();

   uri = mongoc_uri_new_with_error (uri_string, &error);
   if (!uri) {
      fprintf (stderr,
               "failed to parse URI: %s\n"
               "error message:       %s\n",
               uri_string,
               error.message);
      return EXIT_FAILURE;
   }

   client = mongoc_client_new_from_uri (uri);
   if (!client) {
      return EXIT_FAILURE;
   }

   mongoc_client_set_error_api (client, 2);
   database = mongoc_client_get_database (client, "databaseName");

   options = BCON_NEW ("validator",
                       "{",
                       "age",
                       "{",
                       "$lte",
                       BCON_INT32 (34),
                       "}",
                       "}",
                       "validationAction",
                       BCON_UTF8 ("error"),
                       "validationLevel",
                       BCON_UTF8 ("moderate"));

   collection = mongoc_database_create_collection (
      database, "collectionName", options, &error);
   if (!collection) {
      fprintf (
         stderr, "Got error: \"%s\" on line %d\n", error.message, __LINE__);
      return EXIT_FAILURE;
   }

   fam_flags (collection);
   fam_bypass (collection);
   fam_update (collection);
   fam_fields (collection);
   fam_opts (collection);
   fam_sort (collection);

   mongoc_collection_drop (collection, NULL);
   bson_destroy (options);
   mongoc_uri_destroy (uri);
   mongoc_database_destroy (database);
   mongoc_collection_destroy (collection);
   mongoc_client_destroy (client);

   mongoc_cleanup ();
   return EXIT_SUCCESS;
}

Outputs:

{
    "lastErrorObject": {
        "updatedExisting": false,
        "n": 1,
        "upserted": {
            "$oid": "56562a99d13e6d86239c7b00"
        }
    },
    "value": {
        "_id": {
            "$oid": "56562a99d13e6d86239c7b00"
        },
        "age": 34,
        "firstname": "Zlatan",
        "goals": 342,
        "lastname": "Ibrahimovic",
        "profession": "Football player",
        "position": "striker"
    },
    "ok": 1
}
{
    "lastErrorObject": {
        "updatedExisting": true,
        "n": 1
    },
    "value": {
        "_id": {
            "$oid": "56562a99d13e6d86239c7b00"
        },
        "age": 34,
        "firstname": "Zlatan",
        "goals": 342,
        "lastname": "Ibrahimovic",
        "profession": "Football player",
        "position": "striker"
    },
    "ok": 1
}
{
    "lastErrorObject": {
        "updatedExisting": true,
        "n": 1
    },
    "value": {
        "_id": {
            "$oid": "56562a99d13e6d86239c7b00"
        },
        "age": 35,
        "firstname": "Zlatan",
        "goals": 342,
        "lastname": "Ibrahimovic",
        "profession": "Football player",
        "position": "striker"
    },
    "ok": 1
}
{
    "lastErrorObject": {
        "updatedExisting": true,
        "n": 1
    },
    "value": {
        "_id": {
            "$oid": "56562a99d13e6d86239c7b00"
        },
        "goals": 343
    },
    "ok": 1
}
{
    "lastErrorObject": {
        "updatedExisting": true,
        "n": 1
    },
    "value": {
        "_id": {
            "$oid": "56562a99d13e6d86239c7b00"
        },
        "age": 35,
        "firstname": "Zlatan",
        "goals": 343,
        "lastname": "Ibrahimovic",
        "profession": "Football player",
        "position": "striker",
        "author": true
    },
    "ok": 1
}

#include <mongoc/mongoc.h>

typedef struct _mongoc_gridfs_file_list_t mongoc_gridfs_file_list_t;

mongoc_gridfs_file_list_t provides a gridfs file list abstraction.  It provides iteration and basic marshalling on top of a regular mongoc_collection_find_with_opts() style query. In interface, it's styled after mongoc_cursor_t.

mongoc_gridfs_file_list_t *list;
mongoc_gridfs_file_t *file;

list = mongoc_gridfs_find (gridfs, query);

while ((file = mongoc_gridfs_file_list_next (list))) {
   do_something (file);

   mongoc_gridfs_file_destroy (file);
}

mongoc_gridfs_file_list_destroy (list);

typedef struct {
   const char *md5;
   const char *filename;
   const char *content_type;
   const bson_t *aliases;
   const bson_t *metadata;
   uint32_t chunk_size;
} mongoc_gridfs_file_opt_t;

This structure contains options that can be set on a mongoc_gridfs_file_t. It can be used by various functions when creating a new gridfs file.

typedef struct _mongoc_gridfs_file_t mongoc_gridfs_file_t;

This structure provides a MongoDB GridFS file abstraction. It provides several APIs.

• readv, writev, seek, and tell.
• General file metadata such as filename and length.
• GridFS metadata such as md5, filename, content_type, aliases, metadata, chunk_size, and upload_date.

This structure is NOT thread-safe and should only be used from one thread at a time.

• mongoc_client_t
• mongoc_gridfs_t
• mongoc_gridfs_file_list_t
• mongoc_gridfs_file_opt_t

#include <mongoc/mongoc.h>

typedef struct _mongoc_gridfs_bucket_t mongoc_gridfs_bucket_t;

mongoc_gridfs_bucket_t provides a spec-compliant MongoDB GridFS implementation, superseding mongoc_gridfs_t. See the GridFS MongoDB documentation.

mongoc_gridfs_bucket_t is NOT thread-safe and should only be used in the same thread as the owning mongoc_client_t.

It is an error to free a mongoc_gridfs_bucket_t before freeing all derived instances of mongoc_stream_t. The owning mongoc_client_t must outlive the mongoc_gridfs_bucket_t.

example-gridfs-bucket.c

#include <stdio.h>
#include <stdlib.h>

#include <mongoc/mongoc.h>

int
main (int argc, char *argv[])
{
   const char *uri_string =
      "mongodb://localhost:27017/?appname=new-gridfs-example";
   mongoc_client_t *client;
   mongoc_database_t *db;
   mongoc_stream_t *file_stream;
   mongoc_gridfs_bucket_t *bucket;
   mongoc_cursor_t *cursor;
   bson_t filter;
   bool res;
   bson_value_t file_id;
   bson_error_t error;
   const bson_t *doc;
   char *str;
   mongoc_init ();

   if (argc != 3) {
      fprintf (stderr, "usage: %s SOURCE_FILE_PATH FILE_COPY_PATH\n", argv[0]);
      return EXIT_FAILURE;
   }

   /* 1. Make a bucket. */
   client = mongoc_client_new (uri_string);
   db = mongoc_client_get_database (client, "test");
   bucket = mongoc_gridfs_bucket_new (db, NULL, NULL, &error);
   if (!bucket) {
      printf ("Error creating gridfs bucket: %s\n", error.message);
      return EXIT_FAILURE;
   }

   /* 2. Insert a file.  */
   file_stream = mongoc_stream_file_new_for_path (argv[1], O_RDONLY, 0);
   res = mongoc_gridfs_bucket_upload_from_stream (
      bucket, "my-file", file_stream, NULL, &file_id, &error);
   if (!res) {
      printf ("Error uploading file: %s\n", error.message);
      return EXIT_FAILURE;
   }

   mongoc_stream_close (file_stream);
   mongoc_stream_destroy (file_stream);

   /* 3. Download the file in GridFS to a local file. */
   file_stream = mongoc_stream_file_new_for_path (argv[2], O_CREAT | O_RDWR, 0);
   if (!file_stream) {
      perror ("Error opening file stream");
      return EXIT_FAILURE;
   }

   res = mongoc_gridfs_bucket_download_to_stream (
      bucket, &file_id, file_stream, &error);
   if (!res) {
      printf ("Error downloading file to stream: %s\n", error.message);
      return EXIT_FAILURE;
   }
   mongoc_stream_close (file_stream);
   mongoc_stream_destroy (file_stream);

   /* 4. List what files are available in GridFS. */
   bson_init (&filter);
   cursor = mongoc_gridfs_bucket_find (bucket, &filter, NULL);

   while (mongoc_cursor_next (cursor, &doc)) {
      str = bson_as_canonical_extended_json (doc, NULL);
      printf ("%s\n", str);
      bson_free (str);
   }

   /* 5. Delete the file that we added. */
   res = mongoc_gridfs_bucket_delete_by_id (bucket, &file_id, &error);
   if (!res) {
      printf ("Error deleting the file: %s\n", error.message);
      return EXIT_FAILURE;
   }

   /* 6. Cleanup. */
   mongoc_stream_close (file_stream);
   mongoc_stream_destroy (file_stream);
   mongoc_cursor_destroy (cursor);
   bson_destroy (&filter);
   mongoc_gridfs_bucket_destroy (bucket);
   mongoc_database_destroy (db);
   mongoc_client_destroy (client);
   mongoc_cleanup ();

   return EXIT_SUCCESS;
}

SEE ALSO:

The MongoDB GridFS specification.

The non spec-compliant mongoc_gridfs_t.

WARNING:

This GridFS implementation does not conform to the MongoDB GridFS specification. For a spec compliant implementation, use mongoc_gridfs_bucket_t.

#include <mongoc/mongoc.h>

typedef struct _mongoc_gridfs_t mongoc_gridfs_t;

mongoc_gridfs_t provides a MongoDB gridfs implementation. The system as a whole is made up of gridfs objects, which contain gridfs_files and gridfs_file_lists.  Essentially, a basic file system API.

There are extensive caveats about the kind of use cases gridfs is practical for. In particular, any writing after initial file creation is likely to both break any concurrent readers and be quite expensive. That said, this implementation does allow for arbitrary writes to existing gridfs object, just use them with caution.

mongoc_gridfs also integrates tightly with the mongoc_stream_t abstraction, which provides some convenient wrapping for file creation and reading/writing.  It can be used without, but its worth looking to see if your problem can fit that model.

WARNING:

mongoc_gridfs_t is NOT thread-safe and should only be used in the same thread as the owning mongoc_client_t.

It is an error to free a mongoc_gridfs_t before freeing all related instances of mongoc_gridfs_file_t and mongoc_gridfs_file_list_t.

example-gridfs.c

#include <assert.h>
#include <mongoc/mongoc.h>
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>

int
main (int argc, char *argv[])
{
   mongoc_gridfs_t *gridfs;
   mongoc_gridfs_file_t *file;
   mongoc_gridfs_file_list_t *list;
   mongoc_gridfs_file_opt_t opt = {0};
   mongoc_client_t *client;
   const char *uri_string = "mongodb://127.0.0.1:27017/?appname=gridfs-example";
   mongoc_uri_t *uri;
   mongoc_stream_t *stream;
   bson_t filter;
   bson_t opts;
   bson_t child;
   bson_error_t error;
   ssize_t r;
   char buf[4096];
   mongoc_iovec_t iov;
   const char *filename;
   const char *command;
   bson_value_t id;

   if (argc < 2) {
      fprintf (stderr, "usage - %s command ...\n", argv[0]);
      return EXIT_FAILURE;
   }

   mongoc_init ();

   iov.iov_base = (void *) buf;
   iov.iov_len = sizeof buf;

   /* connect to localhost client */
   uri = mongoc_uri_new_with_error (uri_string, &error);
   if (!uri) {
      fprintf (stderr,
               "failed to parse URI: %s\n"
               "error message:       %s\n",
               uri_string,
               error.message);
      return EXIT_FAILURE;
   }

   client = mongoc_client_new_from_uri (uri);
   assert (client);
   mongoc_client_set_error_api (client, 2);

   /* grab a gridfs handle in test prefixed by fs */
   gridfs = mongoc_client_get_gridfs (client, "test", "fs", &error);
   assert (gridfs);

   command = argv[1];
   filename = argv[2];

   if (strcmp (command, "read") == 0) {
      if (argc != 3) {
         fprintf (stderr, "usage - %s read filename\n", argv[0]);
         return EXIT_FAILURE;
      }
      file = mongoc_gridfs_find_one_by_filename (gridfs, filename, &error);
      assert (file);

      stream = mongoc_stream_gridfs_new (file);
      assert (stream);

      for (;;) {
         r = mongoc_stream_readv (stream, &iov, 1, -1, 0);

         assert (r >= 0);

         if (r == 0) {
            break;
         }

         if (fwrite (iov.iov_base, 1, r, stdout) != r) {
            MONGOC_ERROR ("Failed to write to stdout. Exiting.\n");
            exit (1);
         }
      }

      mongoc_stream_destroy (stream);
      mongoc_gridfs_file_destroy (file);
   } else if (strcmp (command, "list") == 0) {
      bson_init (&filter);

      bson_init (&opts);
      bson_append_document_begin (&opts, "sort", -1, &child);
      BSON_APPEND_INT32 (&child, "filename", 1);
      bson_append_document_end (&opts, &child);

      list = mongoc_gridfs_find_with_opts (gridfs, &filter, &opts);

      bson_destroy (&filter);
      bson_destroy (&opts);

      while ((file = mongoc_gridfs_file_list_next (list))) {
         const char *name = mongoc_gridfs_file_get_filename (file);
         printf ("%s\n", name ? name : "?");

         mongoc_gridfs_file_destroy (file);
      }

      mongoc_gridfs_file_list_destroy (list);
   } else if (strcmp (command, "write") == 0) {
      if (argc != 4) {
         fprintf (stderr, "usage - %s write filename input_file\n", argv[0]);
         return EXIT_FAILURE;
      }

      stream = mongoc_stream_file_new_for_path (argv[3], O_RDONLY, 0);
      assert (stream);

      opt.filename = filename;

      /* the driver generates a file_id for you */
      file = mongoc_gridfs_create_file_from_stream (gridfs, stream, &opt);
      assert (file);

      id.value_type = BSON_TYPE_INT32;
      id.value.v_int32 = 1;

      /* optional: the following method specifies a file_id of any
         BSON type */
      if (!mongoc_gridfs_file_set_id (file, &id, &error)) {
         fprintf (stderr, "%s\n", error.message);
         return EXIT_FAILURE;
      }

      if (!mongoc_gridfs_file_save (file)) {
         mongoc_gridfs_file_error (file, &error);
         fprintf (stderr, "Could not save: %s\n", error.message);
         return EXIT_FAILURE;
      }

      mongoc_gridfs_file_destroy (file);
   } else {
      fprintf (stderr, "Unknown command");
      return EXIT_FAILURE;
   }

   mongoc_gridfs_destroy (gridfs);
   mongoc_uri_destroy (uri);
   mongoc_client_destroy (client);

   mongoc_cleanup ();

   return EXIT_SUCCESS;
}

SEE ALSO:

The MongoDB GridFS specification.

The spec-compliant mongoc_gridfs_bucket_t.

typedef struct {
   mongoc_host_list_t *next;
   char host[BSON_HOST_NAME_MAX + 1];
   char host_and_port[BSON_HOST_NAME_MAX + 7];
   uint16_t port;
   int family;
   void *padding[4];
} mongoc_host_list_t;

The host and port of a MongoDB server. Can be part of a linked list: for example the return value of mongoc_uri_get_hosts() when multiple hosts are provided in the MongoDB URI.

SEE ALSO:

mongoc_uri_get_hosts() and mongoc_cursor_get_host().

#include <mongoc/mongoc.h>

typedef struct {
   uint8_t twod_sphere_version;
   uint8_t twod_bits_precision;
   double twod_location_min;
   double twod_location_max;
   double haystack_bucket_size;
   uint8_t *padding[32];
} mongoc_index_opt_geo_t;

This structure contains the options that may be used for tuning a GEO index.

SEE ALSO:

mongoc_index_opt_t

mongoc_index_opt_wt_t

WARNING:

Deprecated since version 1.8.0: This structure is deprecated and should not be used in new code. See Manage Collection Indexes.

#include <mongoc/mongoc.h>

typedef struct {
   bool is_initialized;
   bool background;
   bool unique;
   const char *name;
   bool drop_dups;
   bool sparse;
   int32_t expire_after_seconds;
   int32_t v;
   const bson_t *weights;
   const char *default_language;
   const char *language_override;
   mongoc_index_opt_geo_t *geo_options;
   mongoc_index_opt_storage_t *storage_options;
   const bson_t *partial_filter_expression;
   const bson_t *collation;
   void *padding[4];
} mongoc_index_opt_t;

This structure contains the options that may be used for tuning a specific index.

See the createIndexes documentations in the MongoDB manual for descriptions of individual options.

NOTE:

{
   bson_t keys;
   bson_error_t error;
   mongoc_index_opt_t opt;
   mongoc_index_opt_geo_t geo_opt;

   mongoc_index_opt_init (&opt);
   mongoc_index_opt_geo_init (&geo_opt);

   bson_init (&keys);
   BSON_APPEND_UTF8 (&keys, "location", "2d");

   geo_opt.twod_location_min = -123;
   geo_opt.twod_location_max = +123;
   geo_opt.twod_bits_precision = 30;
   opt.geo_options = &geo_opt;

   collection = mongoc_client_get_collection (client, "test", "geo_test");
   if (mongoc_collection_create_index (collection, &keys, &opt, &error)) {
      /* Successfully created the geo index */
   }
   bson_destroy (&keys);
   mongoc_collection_destroy (&collection);
}

SEE ALSO:

mongoc_index_opt_geo_t

mongoc_index_opt_wt_t

#include <mongoc/mongoc.h>

typedef struct {
   mongoc_index_opt_storage_t base;
   const char *config_str;
   void *padding[8];
} mongoc_index_opt_wt_t;

This structure contains the options that may be used for tuning a WiredTiger specific index.

SEE ALSO:

mongoc_index_opt_t

mongoc_index_opt_geo_t

Flags for insert operations

typedef enum {
   MONGOC_INSERT_NONE = 0,
   MONGOC_INSERT_CONTINUE_ON_ERROR = 1 << 0,
} mongoc_insert_flags_t;

#define MONGOC_INSERT_NO_VALIDATE (1U << 31)

These flags correspond to the MongoDB wire protocol. They may be bitwise or'd together. They may modify how an insert happens on the MongoDB server.

#include <mongoc/mongoc.h>

#ifdef _WIN32
typedef struct {
   u_long iov_len;
   char *iov_base;
} mongoc_iovec_t;
#else
typedef struct iovec mongoc_iovec_t;
#endif

The mongoc_iovec_t structure is a portability abstraction for consumers of the mongoc_stream_t interfaces. It allows for scatter/gather I/O through the socket subsystem.

WARNING:

A struct to store optional boolean values.

Used to specify optional boolean flags, which may remain unset.

This is used within mongoc_server_api_t to track whether a flag was explicitly set.

Flags for query operations

typedef enum {
   MONGOC_QUERY_NONE = 0,
   MONGOC_QUERY_TAILABLE_CURSOR = 1 << 1,
   MONGOC_QUERY_SECONDARY_OK = 1 << 2,
   MONGOC_QUERY_OPLOG_REPLAY = 1 << 3,
   MONGOC_QUERY_NO_CURSOR_TIMEOUT = 1 << 4,
   MONGOC_QUERY_AWAIT_DATA = 1 << 5,
   MONGOC_QUERY_EXHAUST = 1 << 6,
   MONGOC_QUERY_PARTIAL = 1 << 7,
} mongoc_query_flags_t;

These flags correspond to the MongoDB wire protocol. They may be bitwise or'd together. They may modify how a query is performed in the MongoDB server.

MongoDB Random Number Generator

void
mongoc_rand_add (const void *buf, int num, double entropy);

void
mongoc_rand_seed (const void *buf, int num);

int
mongoc_rand_status (void);

The mongoc_rand family of functions provide access to the low level randomness primitives used by the MongoDB C Driver.  In particular, they control the creation of cryptographically strong pseudo-random bytes required by some security mechanisms.

While we can usually pull enough entropy from the environment, you may be required to seed the PRNG manually depending on your OS, hardware and other entropy consumers running on the same system.

mongoc_rand_add and mongoc_rand_seed allow the user to directly provide entropy.  They differ insofar as mongoc_rand_seed requires that each bit provided is fully random.  mongoc_rand_add allows the user to specify the degree of randomness in the provided bytes as well.

The mongoc_rand_status function allows the user to check the status of the mongoc PRNG.  This can be used to guarantee sufficient entropy at program startup, rather than waiting for runtime errors to occur.

Read Concern abstraction

New in MongoDB 3.2.

The mongoc_read_concern_t allows clients to choose a level of isolation for their reads. The default, MONGOC_READ_CONCERN_LEVEL_LOCAL, is right for the great majority of applications.

You can specify a read concern on connection objects, database objects, or collection objects.

See readConcern on the MongoDB website for more information.

Read Concern is only sent to MongoDB when it has explicitly been set by mongoc_read_concern_set_level() to anything other than NULL.

For the sake of compatibility with future versions of MongoDB, mongoc_read_concern_set_level() allows any string, not just this list of known read concern levels.

See Read Concern Levels in the MongoDB manual for more information about the individual read concern levels.

Read Preference Modes

typedef enum {
   MONGOC_READ_PRIMARY = (1 << 0),
   MONGOC_READ_SECONDARY = (1 << 1),
   MONGOC_READ_PRIMARY_PREFERRED = (1 << 2) | MONGOC_READ_PRIMARY,
   MONGOC_READ_SECONDARY_PREFERRED = (1 << 2) | MONGOC_READ_SECONDARY,
   MONGOC_READ_NEAREST = (1 << 3) | MONGOC_READ_SECONDARY,
} mongoc_read_mode_t;

This enum describes how reads should be dispatched. The default is MONGOC_READ_PRIMARY.

Please see the MongoDB website for a description of Read Preferences.

A read preference abstraction

mongoc_read_prefs_t provides an abstraction on top of the MongoDB connection read preferences. It allows for hinting to the driver which nodes in a replica set should be accessed first and how.

You can specify a read preference mode on connection objects, database objects, collection objects, or per-operation.  Generally, it makes the most sense to stick with the global default mode, MONGOC_READ_PRIMARY.  All of the other modes come with caveats that won't be covered in great detail here.

Tag sets allow you to specify custom read preferences and write concerns so that your application can target operations to specific members.

Custom read preferences and write concerns evaluate tags sets in different ways: read preferences consider the value of a tag when selecting a member to read from, while write concerns ignore the value of a tag when selecting a member, except to consider whether or not the value is unique.

You can specify tag sets with the following read preference modes:

• primaryPreferred
• secondary
• secondaryPreferred
• nearest

Tags are not compatible with MONGOC_READ_PRIMARY and, in general, only apply when selecting a secondary member of a set for a read operation. However, the nearest read mode, when combined with a tag set, will select the nearest member that matches the specified tag set, which may be a primary or secondary.

Tag sets are represented as a comma-separated list of colon-separated key-value pairs when provided as a connection string, e.g. dc:ny,rack:1.

To specify a list of tag sets, using multiple readPreferenceTags, e.g.

readPreferenceTags=dc:ny,rack:1;readPreferenceTags=dc:ny;readPreferenceTags=

Note the empty value for the last one, which means "match any secondary as a last resort".

Order matters when using multiple readPreferenceTags.

Tag Sets can also be configured using mongoc_read_prefs_set_tags().

All interfaces use the same member selection logic to choose the member to which to direct read operations, basing the choice on read preference mode and tag sets.

When connected to replica set running MongoDB 3.4 or later, the driver estimates the staleness of each secondary based on lastWriteDate values provided in server hello responses.

Max Staleness is the maximum replication lag in seconds (wall clock time) that a secondary can suffer and still be eligible for reads. The default is MONGOC_NO_MAX_STALENESS, which disables staleness checks. Otherwise, it must be a positive integer at least MONGOC_SMALLEST_MAX_STALENESS_SECONDS (90 seconds).

Max Staleness is also supported by sharded clusters of replica sets if all servers run MongoDB 3.4 or later.

When connecting to a sharded cluster running MongoDB 4.4 or later, reads can be sent in parallel to the two "best" hosts.  Once one result returns, any other outstanding operations that were part of the hedged read are cancelled.

When the read preference mode is MONGOC_READ_NEAREST and the sharded cluster is running MongoDB 4.4 or later, hedged reads are enabled by default.  Additionally, hedged reads may be explicitly enabled or disabled by calling mongoc_read_prefs_set_hedge() with a BSON document, e.g.

{
   enabled: true
}

Appropriate values for the enabled key are true or false.

Flags for deletion operations

typedef enum {
   MONGOC_REMOVE_NONE = 0,
   MONGOC_REMOVE_SINGLE_REMOVE = 1 << 0,
} mongoc_remove_flags_t;

These flags correspond to the MongoDB wire protocol. They may be bitwise or'd together. They may change the number of documents that are removed during a remove command.

Flags from server replies

typedef enum {
   MONGOC_REPLY_NONE = 0,
   MONGOC_REPLY_CURSOR_NOT_FOUND = 1 << 0,
   MONGOC_REPLY_QUERY_FAILURE = 1 << 1,
   MONGOC_REPLY_SHARD_CONFIG_STALE = 1 << 2,
   MONGOC_REPLY_AWAIT_CAPABLE = 1 << 3,
} mongoc_reply_flags_t;

These flags correspond to the wire protocol. They may be bitwise or'd together.

A versioned API to use for connections.

Used to specify which version of the MongoDB server's API to use for driver connections.

The server API type takes a mongoc_server_api_version_t. It can optionally be strict about the list of allowed commands in that API version, and can also optionally provide errors for deprecated commands in that API version.

A mongoc_server_api_t can be set on a client, and will then be sent to MongoDB for most commands run using that client.

A representation of server API version numbers.

Used to specify which version of the MongoDB server's API to use for driver connections.

The driver currently supports the following MongoDB API versions:

Server description

#include <mongoc/mongoc.h>
typedef struct _mongoc_server_description_t mongoc_server_description_t

mongoc_server_description_t holds information about a mongod or mongos the driver is connected to.

Clean up a mongoc_server_description_t with mongoc_server_description_destroy() when necessary.

Applications receive a temporary reference to a mongoc_server_description_t as a parameter to an SDAM Monitoring callback that must not be destroyed. See Introduction to Application Performance Monitoring.

SEE ALSO:

mongoc_client_get_server_descriptions().

#include <mongoc/mongoc.h>

typedef struct _mongoc_session_opt_t mongoc_session_opt_t;

Start a session with mongoc_client_start_session(), use the session for a sequence of operations and multi-document transactions, then free it with mongoc_client_session_destroy(). Any mongoc_cursor_t or mongoc_change_stream_t using a session must be destroyed before the session, and a session must be destroyed before the mongoc_client_t it came from.

By default, sessions are causally consistent. To disable causal consistency, before starting a session create a mongoc_session_opt_t with mongoc_session_opts_new() and call mongoc_session_opts_set_causal_consistency(), then free the struct with mongoc_session_opts_destroy().

Unacknowledged writes are prohibited with sessions.

A mongoc_client_session_t must be used by only one thread at a time. Due to session pooling, mongoc_client_start_session() may return a session that has been idle for some time and is about to be closed after its idle timeout. Use the session within one minute of acquiring it to refresh the session and avoid a timeout.

See the example code for mongoc_session_opts_set_causal_consistency().

Portable socket abstraction

#include <mongoc/mongoc.h>

typedef struct _mongoc_socket_t mongoc_socket_t

This structure provides a socket abstraction that is friendlier for portability than BSD sockets directly. Inconsistencies between Linux, various BSDs, Solaris, and Windows are handled here.

typedef struct {
   const char *pem_file;
   const char *pem_pwd;
   const char *ca_file;
   const char *ca_dir;
   const char *crl_file;
   bool weak_cert_validation;
   bool allow_invalid_hostname;
   void *internal;
   void *padding[6];
} mongoc_ssl_opt_t;

This structure is used to set the TLS options for a mongoc_client_t or mongoc_client_pool_t.

Beginning in version 1.2.0, once a pool or client has any TLS options set, all connections use TLS, even if ssl=true is omitted from the MongoDB URI. Before, TLS options were ignored unless tls=true was included in the URI.

As of 1.4.0, the mongoc_client_pool_set_ssl_opts() and mongoc_client_set_ssl_opts() will not only shallow copy the struct, but will also copy the const char*. It is therefore no longer needed to make sure the values remain valid after setting them.

SEE ALSO:

Configuring TLS

mongoc_client_set_ssl_opts()

mongoc_client_pool_set_ssl_opts()

typedef struct _mongoc_stream_buffered_t mongoc_stream_buffered_t;

mongoc_stream_buffered_t should be considered a subclass of mongoc_stream_t. It performs buffering on an underlying stream.

SEE ALSO:

mongoc_stream_buffered_new()

mongoc_stream_destroy()

typedef struct _mongoc_stream_file_t mongoc_stream_file_t

mongoc_stream_file_t is a mongoc_stream_t subclass for working with standard UNIX style file-descriptors.

typedef struct _mongoc_stream_socket_t mongoc_stream_socket_t

mongoc_stream_socket_t should be considered a subclass of mongoc_stream_t that works upon socket streams.

typedef struct _mongoc_stream_t mongoc_stream_t

mongoc_stream_t provides a generic streaming IO abstraction based on a struct of pointers interface. The idea is to allow wrappers, perhaps other language drivers, to easily shim their IO system on top of mongoc_stream_t.

The API for the stream abstraction is currently private and non-extensible.

There are a number of built in stream types that come with mongoc. The default configuration is a buffered unix stream. If TLS is in use, that in turn is wrapped in a tls stream.

SEE ALSO:

mongoc_stream_buffered_t

mongoc_stream_file_t

mongoc_stream_socket_t

mongoc_stream_tls_t

typedef struct _mongoc_stream_tls_t mongoc_stream_tls_t

mongoc_stream_tls_t is a mongoc_stream_t subclass for working with TLS streams.

Status of MongoDB Servers

typedef struct _mongoc_topology_description_t mongoc_topology_description_t;

mongoc_topology_description_t is an opaque type representing the driver's knowledge of the MongoDB server or servers it is connected to. Its API conforms to the SDAM Monitoring Specification.

Applications receive a temporary reference to a mongoc_topology_description_t as a parameter to an SDAM Monitoring callback that must not be destroyed. See Introduction to Application Performance Monitoring.

#include <mongoc/mongoc.h>

typedef struct _mongoc_transaction_opt_t mongoc_transaction_opt_t;

Options for starting a multi-document transaction.

When a session is first created with mongoc_client_start_session(), it inherits from the client the read concern, write concern, and read preference with which to start transactions. Each of these fields can be overridden independently. Create a mongoc_transaction_opt_t with mongoc_transaction_opts_new(), and pass a non-NULL option to any of the mongoc_transaction_opt_t setter functions:

• mongoc_transaction_opts_set_read_concern()
• mongoc_transaction_opts_set_write_concern()
• mongoc_transaction_opts_set_read_prefs()

Pass the resulting transaction options to mongoc_client_session_start_transaction(). Each field set in the transaction options overrides the inherited client configuration.

example-transaction.c

/* gcc example-transaction.c -o example-transaction \
 *     $(pkg-config --cflags --libs libmongoc-1.0) */

/* ./example-transaction [CONNECTION_STRING] */

#include <stdio.h>
#include <mongoc/mongoc.h>


int
main (int argc, char *argv[])
{
   int exit_code = EXIT_FAILURE;

   mongoc_client_t *client = NULL;
   mongoc_database_t *database = NULL;
   mongoc_collection_t *collection = NULL;
   mongoc_client_session_t *session = NULL;
   mongoc_session_opt_t *session_opts = NULL;
   mongoc_transaction_opt_t *default_txn_opts = NULL;
   mongoc_transaction_opt_t *txn_opts = NULL;
   mongoc_read_concern_t *read_concern = NULL;
   mongoc_write_concern_t *write_concern = NULL;
   const char *uri_string = "mongodb://127.0.0.1/?appname=transaction-example";
   mongoc_uri_t *uri;
   bson_error_t error;
   bson_t *doc = NULL;
   bson_t *insert_opts = NULL;
   int32_t i;
   int64_t start;
   bson_t reply = BSON_INITIALIZER;
   char *reply_json;
   bool r;

   mongoc_init ();

   if (argc > 1) {
      uri_string = argv[1];
   }

   uri = mongoc_uri_new_with_error (uri_string, &error);
   if (!uri) {
      MONGOC_ERROR ("failed to parse URI: %s\n"
                    "error message:       %s\n",
                    uri_string,
                    error.message);
      goto done;
   }

   client = mongoc_client_new_from_uri (uri);
   if (!client) {
      goto done;
   }

   mongoc_client_set_error_api (client, 2);
   database = mongoc_client_get_database (client, "example-transaction");

   /* inserting into a nonexistent collection normally creates it, but a
    * collection can't be created in a transaction; create it now */
   collection =
      mongoc_database_create_collection (database, "collection", NULL, &error);

   if (!collection) {
      /* code 48 is NamespaceExists, see error_codes.err in mongodb source */
      if (error.code == 48) {
         collection = mongoc_database_get_collection (database, "collection");
      } else {
         MONGOC_ERROR ("Failed to create collection: %s", error.message);
         goto done;
      }
   }

   /* a transaction's read preferences, read concern, and write concern can be
    * set on the client, on the default transaction options, or when starting
    * the transaction. for the sake of this example, set read concern on the
    * default transaction options. */
   default_txn_opts = mongoc_transaction_opts_new ();
   read_concern = mongoc_read_concern_new ();
   mongoc_read_concern_set_level (read_concern, "snapshot");
   mongoc_transaction_opts_set_read_concern (default_txn_opts, read_concern);
   session_opts = mongoc_session_opts_new ();
   mongoc_session_opts_set_default_transaction_opts (session_opts,
                                                     default_txn_opts);

   session = mongoc_client_start_session (client, session_opts, &error);
   if (!session) {
      MONGOC_ERROR ("Failed to start session: %s", error.message);
      goto done;
   }

   /* in this example, set write concern when starting the transaction */
   txn_opts = mongoc_transaction_opts_new ();
   write_concern = mongoc_write_concern_new ();
   mongoc_write_concern_set_wmajority (write_concern, 1000 /* wtimeout */);
   mongoc_transaction_opts_set_write_concern (txn_opts, write_concern);

   insert_opts = bson_new ();
   if (!mongoc_client_session_append (session, insert_opts, &error)) {
      MONGOC_ERROR ("Could not add session to opts: %s", error.message);
      goto done;
   }

retry_transaction:
   r = mongoc_client_session_start_transaction (session, txn_opts, &error);
   if (!r) {
      MONGOC_ERROR ("Failed to start transaction: %s", error.message);
      goto done;
   }

   /* insert two documents - on error, retry the whole transaction */
   for (i = 0; i < 2; i++) {
      doc = BCON_NEW ("_id", BCON_INT32 (i));
      bson_destroy (&reply);
      r = mongoc_collection_insert_one (
         collection, doc, insert_opts, &reply, &error);

      bson_destroy (doc);

      if (!r) {
         MONGOC_ERROR ("Insert failed: %s", error.message);
         mongoc_client_session_abort_transaction (session, NULL);

         /* a network error, primary failover, or other temporary error in a
          * transaction includes {"errorLabels": ["TransientTransactionError"]},
          * meaning that trying the entire transaction again may succeed
          */
         if (mongoc_error_has_label (&reply, "TransientTransactionError")) {
            goto retry_transaction;
         }

         goto done;
      }

      reply_json = bson_as_json (&reply, NULL);
      printf ("%s\n", reply_json);
      bson_free (reply_json);
   }

   /* in case of transient errors, retry for 5 seconds to commit transaction */
   start = bson_get_monotonic_time ();
   while (bson_get_monotonic_time () - start < 5 * 1000 * 1000) {
      bson_destroy (&reply);
      r = mongoc_client_session_commit_transaction (session, &reply, &error);
      if (r) {
         /* success */
         break;
      } else {
         MONGOC_ERROR ("Warning: commit failed: %s", error.message);
         if (mongoc_error_has_label (&reply, "TransientTransactionError")) {
            goto retry_transaction;
         } else if (mongoc_error_has_label (&reply,
                                            "UnknownTransactionCommitResult")) {
            /* try again to commit */
            continue;
         }

         /* unrecoverable error trying to commit */
         break;
      }
   }

   exit_code = EXIT_SUCCESS;

done:
   bson_destroy (&reply);
   bson_destroy (insert_opts);
   mongoc_write_concern_destroy (write_concern);
   mongoc_read_concern_destroy (read_concern);
   mongoc_transaction_opts_destroy (txn_opts);
   mongoc_transaction_opts_destroy (default_txn_opts);
   mongoc_client_session_destroy (session);
   mongoc_collection_destroy (collection);
   mongoc_database_destroy (database);
   mongoc_uri_destroy (uri);
   mongoc_client_destroy (client);

   mongoc_cleanup ();

   return exit_code;
}

Constants for transaction states

typedef enum {
  MONGOC_TRANSACTION_NONE = 0,
  MONGOC_TRANSACTION_STARTING = 1,
  MONGOC_TRANSACTION_IN_PROGRESS = 2,
  MONGOC_TRANSACTION_COMMITTED = 3,
  MONGOC_TRANSACTION_ABORTED = 4,
} mongoc_transaction_state_t;

These constants describe the current transaction state of a session.

Flags for update operations

typedef enum {
   MONGOC_UPDATE_NONE = 0,
   MONGOC_UPDATE_UPSERT = 1 << 0,
   MONGOC_UPDATE_MULTI_UPDATE = 1 << 1,
} mongoc_update_flags_t;

#define MONGOC_UPDATE_NO_VALIDATE (1U << 31)

These flags correspond to the MongoDB wire protocol. They may be bitwise or'd together. The allow for modifying the way an update is performed in the MongoDB server.

typedef struct _mongoc_uri_t mongoc_uri_t;

mongoc_uri_t provides an abstraction on top of the MongoDB connection URI format. It provides standardized parsing as well as convenience methods for extracting useful information such as replica hosts or authorization information.

See Connection String URI Reference on the MongoDB website for more information.

mongodb[+srv]://                             <1>
   [username:password@]                      <2>
   host1                                     <3>
   [:port1]                                  <4>
   [,host2[:port2],...[,hostN[:portN]]]      <5>
   [/[database]                              <6>
   [?options]]                               <7>

1.

"mongodb" is the specifier of the MongoDB protocol. Use "mongodb+srv" with a single service name in place of "host1" to specify the initial list of servers with an SRV record.

2.

An optional username and password.

3.

The only required part of the uri.  This specifies either a hostname, IPv4 address, IPv6 address enclosed in "[" and "]", or UNIX domain socket.

4.

An optional port number.  Defaults to :27017.

5.

Extra optional hosts and ports.  You would specify multiple hosts, for example, for connections to replica sets.

6.

The name of the database to authenticate if the connection string includes authentication credentials.  If /database is not specified and the connection string includes credentials, defaults to the 'admin' database.

7.

Connection specific options.

NOTE:

Option names are case-insensitive. Do not repeat the same option (e.g. "mongodb://localhost/db?opt=value1&OPT=value2") since this may have unexpected results.

The MongoDB C Driver exposes constants for each supported connection option. These constants make it easier to discover connection options, but their string values can be used as well.

For example, the following calls are equal.

uri = mongoc_uri_new ("mongodb://localhost/?" MONGOC_URI_APPNAME "=applicationName");
uri = mongoc_uri_new ("mongodb://localhost/?appname=applicationName");
uri = mongoc_uri_new ("mongodb://localhost/?appName=applicationName");

To describe a connection to a replica set named 'test' with the following mongod hosts:

• db1.example.com on port 27017
• db2.example.com on port 2500

You would use a connection string that resembles the following.

mongodb://db1.example.com,db2.example.com:2500/?replicaSet=test

If you have configured an SRV record with a name like "_mongodb._tcp.server.example.com" whose records are a list of one or more MongoDB server hostnames, use a connection string like this:

uri = mongoc_uri_new ("mongodb+srv://server.example.com/?replicaSet=rs&appName=applicationName");

The driver prefixes the service name with "_mongodb._tcp.", then performs a DNS SRV query to resolve the service name to one or more hostnames. If this query succeeds, the driver performs a DNS TXT query on the service name (without the "_mongodb._tcp" prefix) for additional URI options configured as TXT records.

On Unix, the MongoDB C Driver relies on libresolv to look up SRV and TXT records. If libresolv is unavailable, then using a "mongodb+srv" URI will cause an error. If your libresolv lacks res_nsearch then the driver will fall back to res_search, which is not thread-safe.

If connecting to a hostname that has both IPv4 and IPv6 DNS records, the behavior follows RFC-6555. A connection to the IPv6 address is attempted first. If IPv6 fails, then a connection is attempted to the IPv4 address. If the connection attempt to IPv6 does not complete within 250ms, then IPv4 is tried in parallel. Whichever succeeds connection first cancels the other. The successful DNS result is cached for 10 minutes.

As a consequence, attempts to connect to a mongod only listening on IPv4 may be delayed if there are both A (IPv4) and AAAA (IPv6) DNS records associated with the host.

To avoid a delay, configure hostnames to match the MongoDB configuration. That is, only create an A record if the mongod is only listening on IPv4.

WARNING:

Setting any of the *timeoutMS options above to either 0 or a negative value is discouraged due to unspecified and inconsistent behavior. The "default value" historically specified as a fallback for 0 or a negative value is NOT related to the default values for the *timeoutMS options documented above. The meaning of a timeout of 0 or a negative value may vary depending on the operation being executed, even when specified by the same URI option. To specify the documented default value for a *timeoutMS option, use the MONGOC_DEFAULT_* constants defined in mongoc-client.h instead.

See Configuring TLS for details about these options and about building libmongoc with TLS support.

The following options have been deprecated and may be removed from future releases of libmongoc.

Clients in a mongoc_client_pool_t share a topology scanner that runs on a background thread. The thread wakes every heartbeatFrequencyMS (default 10 seconds) to scan all MongoDB servers in parallel. Whenever an application operation requires a server that is not known--for example, if there is no known primary and your application attempts an insert--the thread rescans all servers every half-second. In this situation the pooled client waits up to serverSelectionTimeoutMS (default 30 seconds) for the thread to find a server suitable for the operation, then returns an error with domain MONGOC_ERROR_SERVER_SELECTION.

Technically, the total time an operation may wait while a pooled client scans the topology is controlled both by serverSelectionTimeoutMS and connectTimeoutMS. The longest wait occurs if the last scan begins just at the end of the selection timeout, and a slow or down server requires the full connection timeout before the client gives up.

A non-pooled client is single-threaded. Every heartbeatFrequencyMS, it blocks the next application operation while it does a parallel scan. This scan takes as long as needed to check the slowest server: roughly connectTimeoutMS. Therefore the default heartbeatFrequencyMS for single-threaded clients is greater than for pooled clients: 60 seconds.

By default, single-threaded (non-pooled) clients scan only once when an operation requires a server that is not known. If you attempt an insert and there is no known primary, the client checks all servers once trying to find it, then succeeds or returns an error with domain MONGOC_ERROR_SERVER_SELECTION. But if you set serverSelectionTryOnce to "false", the single-threaded client loops, checking all servers every half-second, until serverSelectionTimeoutMS.

The total time an operation may wait for a single-threaded client to scan the topology is determined by connectTimeoutMS in the try-once case, or serverSelectionTimeoutMS and connectTimeoutMS if serverSelectionTryOnce is set "false".

Setting any of the *TimeoutMS options above to 0 will be interpreted as "use the default value".

These options govern the behavior of a mongoc_client_pool_t. They are ignored by a non-pooled mongoc_client_t.

When connected to a replica set, the driver chooses which member to query using the read preference:

1. Choose members whose type matches "readPreference".
2. From these, if there are any tags sets configured, choose members matching the first tag set. If there are none, fall back to the next tag set and so on, until some members are chosen or the tag sets are exhausted.
3. From the chosen servers, distribute queries randomly among the server with the fastest round-trip times. These include the server with the fastest time and any whose round-trip time is no more than "localThresholdMS" slower.

NOTE:

When connecting to more than one mongos, libmongoc's localThresholdMS applies only to the selection of mongos servers. The threshold for selecting among replica set members in shards is controlled by the mongos's localThreshold command line option.

For historical reasons, the following options are available. They should however not be used.

Conditional compilation based on mongoc version

The following preprocessor macros can be used to perform various checks based on the version of the library you are compiling against. This may be useful if you only want to enable a feature on a certain version of the library.

#include <mongoc/mongoc.h>

#define MONGOC_MAJOR_VERSION (x)
#define MONGOC_MINOR_VERSION (y)
#define MONGOC_MICRO_VERSION (z)
#define MONGOC_VERSION_S     "x.y.z"
#define MONGOC_VERSION_HEX   ((1 << 24) | (0 << 16) | (0 << 8) | 0)
#define MONGOC_CHECK_VERSION(major, minor, micro)

Only compile a block on MongoDB C Driver 1.1.0 and newer.

#if MONGOC_CHECK_VERSION(1, 1, 0)
static void
do_something (void)
{
}
#endif

Write Concern abstraction

mongoc_write_concern_t tells the driver what level of acknowledgement to await from the server. The default, MONGOC_WRITE_CONCERN_W_DEFAULT, is right for the great majority of applications.

You can specify a write concern on connection objects, database objects, collection objects, or per-operation. Data-modifying operations typically use the write concern of the object they operate on, and check the server response for a write concern error or write concern timeout. For example, mongoc_collection_drop_index() uses the collection's write concern, and a write concern error or timeout in the response is considered a failure.

Exceptions to this principle are the generic command functions:

• mongoc_client_command()
• mongoc_client_command_simple()
• mongoc_database_command()
• mongoc_database_command_simple()
• mongoc_collection_command()
• mongoc_collection_command_simple()

These generic command functions do not automatically apply a write concern, and they do not check the server response for a write concern error or write concern timeout.

See Write Concern on the MongoDB website for more information.

Set the write concern level with mongoc_write_concern_set_w().

The write concern MONGOC_WRITE_CONCERN_W_ERRORS_IGNORED (value -1) is a deprecated synonym for MONGOC_WRITE_CONCERN_W_UNACKNOWLEDGED (value 0), and will be removed in the next major release.

mongoc_write_concern_set_fsync() is deprecated.

The MongoDB C Driver allows you to monitor all the MongoDB operations the driver executes. This event-notification system conforms to two MongoDB driver specs:

• Command Logging and Monitoring: events related to all application operations.
• SDAM Monitoring: events related to the driver's Server Discovery And Monitoring logic.

To receive notifications, create a mongoc_apm_callbacks_t with mongoc_apm_callbacks_new(), set callbacks on it, then pass it to mongoc_client_set_apm_callbacks() or mongoc_client_pool_set_apm_callbacks().

example-command-monitoring.c

/* gcc example-command-monitoring.c -o example-command-monitoring \
 *     $(pkg-config --cflags --libs libmongoc-1.0) */

/* ./example-command-monitoring [CONNECTION_STRING] */

#include <mongoc/mongoc.h>
#include <stdio.h>


typedef struct {
   int started;
   int succeeded;
   int failed;
} stats_t;


void
command_started (const mongoc_apm_command_started_t *event)
{
   char *s;

   s = bson_as_relaxed_extended_json (
      mongoc_apm_command_started_get_command (event), NULL);
   printf ("Command %s started on %s:\n%s\n\n",
           mongoc_apm_command_started_get_command_name (event),
           mongoc_apm_command_started_get_host (event)->host,
           s);

   ((stats_t *) mongoc_apm_command_started_get_context (event))->started++;

   bson_free (s);
}


void
command_succeeded (const mongoc_apm_command_succeeded_t *event)
{
   char *s;

   s = bson_as_relaxed_extended_json (
      mongoc_apm_command_succeeded_get_reply (event), NULL);
   printf ("Command %s succeeded:\n%s\n\n",
           mongoc_apm_command_succeeded_get_command_name (event),
           s);

   ((stats_t *) mongoc_apm_command_succeeded_get_context (event))->succeeded++;

   bson_free (s);
}


void
command_failed (const mongoc_apm_command_failed_t *event)
{
   bson_error_t error;

   mongoc_apm_command_failed_get_error (event, &error);
   printf ("Command %s failed:\n\"%s\"\n\n",
           mongoc_apm_command_failed_get_command_name (event),
           error.message);

   ((stats_t *) mongoc_apm_command_failed_get_context (event))->failed++;
}


int
main (int argc, char *argv[])
{
   mongoc_client_t *client;
   mongoc_apm_callbacks_t *callbacks;
   stats_t stats = {0};
   mongoc_collection_t *collection;
   bson_error_t error;
   const char *uri_string =
      "mongodb://127.0.0.1/?appname=cmd-monitoring-example";
   mongoc_uri_t *uri;
   const char *collection_name = "test";
   bson_t *docs[2];

   mongoc_init ();

   if (argc > 1) {
      uri_string = argv[1];
   }

   uri = mongoc_uri_new_with_error (uri_string, &error);
   if (!uri) {
      fprintf (stderr,
               "failed to parse URI: %s\n"
               "error message:       %s\n",
               uri_string,
               error.message);
      return EXIT_FAILURE;
   }

   client = mongoc_client_new_from_uri (uri);
   if (!client) {
      return EXIT_FAILURE;
   }

   mongoc_client_set_error_api (client, 2);
   callbacks = mongoc_apm_callbacks_new ();
   mongoc_apm_set_command_started_cb (callbacks, command_started);
   mongoc_apm_set_command_succeeded_cb (callbacks, command_succeeded);
   mongoc_apm_set_command_failed_cb (callbacks, command_failed);
   mongoc_client_set_apm_callbacks (
      client, callbacks, (void *) &stats /* context pointer */);

   collection = mongoc_client_get_collection (client, "test", collection_name);
   mongoc_collection_drop (collection, NULL);

   docs[0] = BCON_NEW ("_id", BCON_INT32 (0));
   docs[1] = BCON_NEW ("_id", BCON_INT32 (1));
   mongoc_collection_insert_many (
      collection, (const bson_t **) docs, 2, NULL, NULL, NULL);

   /* duplicate key error on the second insert */
   mongoc_collection_insert_one (collection, docs[0], NULL, NULL, NULL);

   mongoc_collection_destroy (collection);
   mongoc_apm_callbacks_destroy (callbacks);
   mongoc_uri_destroy (uri);
   mongoc_client_destroy (client);

   printf ("started: %d\nsucceeded: %d\nfailed: %d\n",
           stats.started,
           stats.succeeded,
           stats.failed);

   bson_destroy (docs[0]);
   bson_destroy (docs[1]);

   mongoc_cleanup ();

   return EXIT_SUCCESS;
}

This example program prints:

Command drop started on 127.0.0.1:
{ "drop" : "test" }

Command drop succeeded:
{ "ns" : "test.test", "nIndexesWas" : 1, "ok" : 1.0 }

Command insert started on 127.0.0.1:
{
  "insert" : "test",
  "ordered" : true,
  "documents" : [
    { "_id" : 0 }, { "_id" : 1 }
  ]
}

Command insert succeeded:
{ "n" : 2, "ok" : 1.0 }

Command insert started on 127.0.0.1:
{
  "insert" : "test",
  "ordered" : true,
  "documents" : [
    { "_id" : 0 }
  ]
}

Command insert succeeded:
{
  "n" : 0,
  "writeErrors" : [
    { "index" : 0, "code" : 11000, "errmsg" : "duplicate key" }
  ],
  "ok" : 1.0
}

started: 3
succeeded: 3
failed: 0

The output has been edited and formatted for clarity. Depending on your server configuration, messages may include metadata like database name, logical session ids, or cluster times that are not shown here.

The final "insert" command is considered successful, despite the writeError, because the server replied to the overall command with "ok": 1.

example-sdam-monitoring.c

/* gcc example-sdam-monitoring.c -o example-sdam-monitoring \
 *     $(pkg-config --cflags --libs libmongoc-1.0) */

/* ./example-sdam-monitoring [CONNECTION_STRING] */

#include <mongoc/mongoc.h>
#include <stdio.h>


typedef struct {
   int server_changed_events;
   int server_opening_events;
   int server_closed_events;
   int topology_changed_events;
   int topology_opening_events;
   int topology_closed_events;
   int heartbeat_started_events;
   int heartbeat_succeeded_events;
   int heartbeat_failed_events;
} stats_t;


static void
server_changed (const mongoc_apm_server_changed_t *event)
{
   stats_t *context;
   const mongoc_server_description_t *prev_sd, *new_sd;

   context = (stats_t *) mongoc_apm_server_changed_get_context (event);
   context->server_changed_events++;

   prev_sd = mongoc_apm_server_changed_get_previous_description (event);
   new_sd = mongoc_apm_server_changed_get_new_description (event);

   printf ("server changed: %s %s -> %s\n",
           mongoc_apm_server_changed_get_host (event)->host_and_port,
           mongoc_server_description_type (prev_sd),
           mongoc_server_description_type (new_sd));
}


static void
server_opening (const mongoc_apm_server_opening_t *event)
{
   stats_t *context;

   context = (stats_t *) mongoc_apm_server_opening_get_context (event);
   context->server_opening_events++;

   printf ("server opening: %s\n",
           mongoc_apm_server_opening_get_host (event)->host_and_port);
}


static void
server_closed (const mongoc_apm_server_closed_t *event)
{
   stats_t *context;

   context = (stats_t *) mongoc_apm_server_closed_get_context (event);
   context->server_closed_events++;

   printf ("server closed: %s\n",
           mongoc_apm_server_closed_get_host (event)->host_and_port);
}


static void
topology_changed (const mongoc_apm_topology_changed_t *event)
{
   stats_t *context;
   const mongoc_topology_description_t *prev_td;
   const mongoc_topology_description_t *new_td;
   mongoc_server_description_t **prev_sds;
   size_t n_prev_sds;
   mongoc_server_description_t **new_sds;
   size_t n_new_sds;
   size_t i;
   mongoc_read_prefs_t *prefs;

   context = (stats_t *) mongoc_apm_topology_changed_get_context (event);
   context->topology_changed_events++;

   prev_td = mongoc_apm_topology_changed_get_previous_description (event);
   prev_sds = mongoc_topology_description_get_servers (prev_td, &n_prev_sds);
   new_td = mongoc_apm_topology_changed_get_new_description (event);
   new_sds = mongoc_topology_description_get_servers (new_td, &n_new_sds);

   printf ("topology changed: %s -> %s\n",
           mongoc_topology_description_type (prev_td),
           mongoc_topology_description_type (new_td));

   if (n_prev_sds) {
      printf ("  previous servers:\n");
      for (i = 0; i < n_prev_sds; i++) {
         printf ("      %s %s\n",
                 mongoc_server_description_type (prev_sds[i]),
                 mongoc_server_description_host (prev_sds[i])->host_and_port);
      }
   }

   if (n_new_sds) {
      printf ("  new servers:\n");
      for (i = 0; i < n_new_sds; i++) {
         printf ("      %s %s\n",
                 mongoc_server_description_type (new_sds[i]),
                 mongoc_server_description_host (new_sds[i])->host_and_port);
      }
   }

   prefs = mongoc_read_prefs_new (MONGOC_READ_SECONDARY);

   /* it is safe, and unfortunately necessary, to cast away const here */
   if (mongoc_topology_description_has_readable_server (
          (mongoc_topology_description_t *) new_td, prefs)) {
      printf ("  secondary AVAILABLE\n");
   } else {
      printf ("  secondary UNAVAILABLE\n");
   }

   if (mongoc_topology_description_has_writable_server (
          (mongoc_topology_description_t *) new_td)) {
      printf ("  primary AVAILABLE\n");
   } else {
      printf ("  primary UNAVAILABLE\n");
   }

   mongoc_read_prefs_destroy (prefs);
   mongoc_server_descriptions_destroy_all (prev_sds, n_prev_sds);
   mongoc_server_descriptions_destroy_all (new_sds, n_new_sds);
}


static void
topology_opening (const mongoc_apm_topology_opening_t *event)
{
   stats_t *context;

   context = (stats_t *) mongoc_apm_topology_opening_get_context (event);
   context->topology_opening_events++;

   printf ("topology opening\n");
}


static void
topology_closed (const mongoc_apm_topology_closed_t *event)
{
   stats_t *context;

   context = (stats_t *) mongoc_apm_topology_closed_get_context (event);
   context->topology_closed_events++;

   printf ("topology closed\n");
}


static void
server_heartbeat_started (const mongoc_apm_server_heartbeat_started_t *event)
{
   stats_t *context;

   context =
      (stats_t *) mongoc_apm_server_heartbeat_started_get_context (event);
   context->heartbeat_started_events++;

   printf ("%s heartbeat started\n",
           mongoc_apm_server_heartbeat_started_get_host (event)->host_and_port);
}


static void
server_heartbeat_succeeded (
   const mongoc_apm_server_heartbeat_succeeded_t *event)
{
   stats_t *context;
   char *reply;

   context =
      (stats_t *) mongoc_apm_server_heartbeat_succeeded_get_context (event);
   context->heartbeat_succeeded_events++;

   reply = bson_as_canonical_extended_json (
      mongoc_apm_server_heartbeat_succeeded_get_reply (event), NULL);

   printf (
      "%s heartbeat succeeded: %s\n",
      mongoc_apm_server_heartbeat_succeeded_get_host (event)->host_and_port,
      reply);

   bson_free (reply);
}


static void
server_heartbeat_failed (const mongoc_apm_server_heartbeat_failed_t *event)
{
   stats_t *context;
   bson_error_t error;

   context = (stats_t *) mongoc_apm_server_heartbeat_failed_get_context (event);
   context->heartbeat_failed_events++;
   mongoc_apm_server_heartbeat_failed_get_error (event, &error);

   printf ("%s heartbeat failed: %s\n",
           mongoc_apm_server_heartbeat_failed_get_host (event)->host_and_port,
           error.message);
}


int
main (int argc, char *argv[])
{
   mongoc_client_t *client;
   mongoc_apm_callbacks_t *cbs;
   stats_t stats = {0};
   const char *uri_string =
      "mongodb://127.0.0.1/?appname=sdam-monitoring-example";
   mongoc_uri_t *uri;
   bson_t cmd = BSON_INITIALIZER;
   bson_t reply;
   bson_error_t error;

   mongoc_init ();

   if (argc > 1) {
      uri_string = argv[1];
   }

   uri = mongoc_uri_new_with_error (uri_string, &error);
   if (!uri) {
      fprintf (stderr,
               "failed to parse URI: %s\n"
               "error message:       %s\n",
               uri_string,
               error.message);
      return EXIT_FAILURE;
   }

   client = mongoc_client_new_from_uri (uri);
   if (!client) {
      return EXIT_FAILURE;
   }

   mongoc_client_set_error_api (client, 2);
   cbs = mongoc_apm_callbacks_new ();
   mongoc_apm_set_server_changed_cb (cbs, server_changed);
   mongoc_apm_set_server_opening_cb (cbs, server_opening);
   mongoc_apm_set_server_closed_cb (cbs, server_closed);
   mongoc_apm_set_topology_changed_cb (cbs, topology_changed);
   mongoc_apm_set_topology_opening_cb (cbs, topology_opening);
   mongoc_apm_set_topology_closed_cb (cbs, topology_closed);
   mongoc_apm_set_server_heartbeat_started_cb (cbs, server_heartbeat_started);
   mongoc_apm_set_server_heartbeat_succeeded_cb (cbs,
                                                 server_heartbeat_succeeded);
   mongoc_apm_set_server_heartbeat_failed_cb (cbs, server_heartbeat_failed);
   mongoc_client_set_apm_callbacks (
      client, cbs, (void *) &stats /* context pointer */);

   /* the driver connects on demand to perform first operation */
   BSON_APPEND_INT32 (&cmd, "buildinfo", 1);
   mongoc_client_command_simple (client, "admin", &cmd, NULL, &reply, &error);
   mongoc_uri_destroy (uri);
   mongoc_client_destroy (client);

   printf ("Events:\n"
           "   server changed: %d\n"
           "   server opening: %d\n"
           "   server closed: %d\n"
           "   topology changed: %d\n"
           "   topology opening: %d\n"
           "   topology closed: %d\n"
           "   heartbeat started: %d\n"
           "   heartbeat succeeded: %d\n"
           "   heartbeat failed: %d\n",
           stats.server_changed_events,
           stats.server_opening_events,
           stats.server_closed_events,
           stats.topology_changed_events,
           stats.topology_opening_events,
           stats.topology_closed_events,
           stats.heartbeat_started_events,
           stats.heartbeat_succeeded_events,
           stats.heartbeat_failed_events);

   bson_destroy (&cmd);
   bson_destroy (&reply);
   mongoc_apm_callbacks_destroy (cbs);

   mongoc_cleanup ();

   return EXIT_SUCCESS;
}

Start a 3-node replica set on localhost with set name "rs" and start the program:

./example-sdam-monitoring "mongodb://localhost:27017,localhost:27018/?replicaSet=rs"

This example program prints something like:

topology opening
topology changed: Unknown -> ReplicaSetNoPrimary
  secondary UNAVAILABLE
  primary UNAVAILABLE
server opening: localhost:27017
server opening: localhost:27018
localhost:27017 heartbeat started
localhost:27018 heartbeat started
localhost:27017 heartbeat succeeded: { ... reply ... }
server changed: localhost:27017 Unknown -> RSPrimary
server opening: localhost:27019
topology changed: ReplicaSetNoPrimary -> ReplicaSetWithPrimary
  new servers:
      RSPrimary localhost:27017
  secondary UNAVAILABLE
  primary AVAILABLE
localhost:27019 heartbeat started
localhost:27018 heartbeat succeeded: { ... reply ... }
server changed: localhost:27018 Unknown -> RSSecondary
topology changed: ReplicaSetWithPrimary -> ReplicaSetWithPrimary
  previous servers:
      RSPrimary localhost:27017
  new servers:
      RSPrimary localhost:27017
      RSSecondary localhost:27018
  secondary AVAILABLE
  primary AVAILABLE
localhost:27019 heartbeat succeeded: { ... reply ... }
server changed: localhost:27019 Unknown -> RSSecondary
topology changed: ReplicaSetWithPrimary -> ReplicaSetWithPrimary
  previous servers:
      RSPrimary localhost:27017
      RSSecondary localhost:27018
  new servers:
      RSPrimary localhost:27017
      RSSecondary localhost:27018
      RSSecondary localhost:27019
  secondary AVAILABLE
  primary AVAILABLE
topology closed

Events:
   server changed: 3
   server opening: 3
   server closed: 0
   topology changed: 4
   topology opening: 1
   topology closed: 1
   heartbeat started: 3
   heartbeat succeeded: 3
   heartbeat failed: 0

The driver connects to the mongods on ports 27017 and 27018, which were specified in the URI, and determines which is primary. It also discovers the third member, "localhost:27019", and adds it to the topology.

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