libcbor - Man Page

Name

libcbor — libcbor Documentation

Documentation for version 0.7.0, updated on Jan 26, 2021.

Overview

libcbor is a C library for parsing and generating CBOR, the general-purpose schema-less binary data format.

Main features
  • Complete RFC conformance [1]
  • Robust C99 implementation
  • Layered architecture offers both control and convenience
  • Flexible memory management
  • No shared global state - threading friendly [2]
  • Proper handling of UTF-8
  • Full support for streams & incremental processing
  • Extensive documentation and test suite
  • No runtime dependencies, small footprint
[1]

See rfc_conformance

[2]

With the exception of custom memory allocators (see api/item_reference_counting)

Contents

Getting started

Pre-built Linux packages are distributed from the libcbor website.

OS X users can use Homebrew:

brew tap pjk/libcbor
brew install libcbor

For other platforms, you will need to compile it from source.

Building & installing libcbor

Prerequisites:
  • C99 compiler
  • CMake 2.8 or newer (might also be called cmakesetup, cmake-gui or ccmake depending on the installed version and system)
  • C build system CMake can target (make, Apple Xcode, MinGW, ...)
NOTE:

As of May 2015, not even the 2015 release candidate of Visual Studio supports C99. While CMake will be happy to generate a VS solution that you can play with, libcbor currently cannot be compiled using the MSVC toolchain. ICC, GCC under Cygwin, and MinGW's GCC will all work. The MinGW build process is described below.

Configuration options

A handful of configuration flags can be passed to cmake. The following table lists libcbor compile-time directives and several important generic flags.

OptionMeaningDefaultPossible values
CMAKE_C_COMPILERC compiler to useccgcc, clang, clang-3.5, ...
CMAKE_INSTALL_PREFIXInstallation prefixSystem-dependent/usr/local/lib, ...
HUGE_FUZZFuzz test with 8GB of dataOFFON, OFF
SANE_MALLOCAssume malloc will refuse unreasonable allocationsOFFON, OFF
COVERAGEGenerate test coverage instrumentationOFFON, OFF
WITH_TESTSBuild unit tests (see development)OFFON, OFF

The following configuration options will also be defined as macros[#]_ in <cbor/common.h> and can therefore be used in client code:

OptionMeaningDefaultPossible values
CBOR_CUSTOM_ALLOCEnable custom allocator supportOFFON, OFF
CBOR_PRETTY_PRINTERInclude a pretty-printing routineONON, OFF
CBOR_BUFFER_GROWTHFactor for buffer growth & shrinking2Decimals > 1
[1]

ON & OFF will be translated to 1 and 0 using cmakedefine.

If you want to pass other custom configuration options, please refer to http://www.cmake.org/Wiki/CMake_Useful_Variables.

Building using make

CMake will generate a Makefile and other configuration files for the build. As a rule of thumb, you should configure the build outside of the source tree in order to keep different configurations isolated. If you are unsure where to execute the build, just use a temporary directory:

cd $(mktemp -d /tmp/cbor_build.XXXX)

Now, assuming you are in the directory where you want to build, execute the following to configure the build and run make

cmake -DCMAKE_BUILD_TYPE=Release path_to_libcbor_dir
make cbor cbor_shared

Both the shared (libcbor.so) and the static (libcbor.a) libraries should now be in the src subdirectory.

In order to install the libcbor headers and libraries, the usual

make install

is what your're looking for. Root permissions are required on most systems when using the default installation prefix.

Portability

libcbor is highly portable and works on both little- and big-endian systems regardless of the operating system. After building on an exotic platform, you might wish to verify the result by running the test suite. If you encounter any problems, please report them to the issue tracker.

libcbor is known to successfully work on ARM Android devices. Cross-compilation is possible with arm-linux-gnueabi-gcc.

Linking with libcbor

If you include and linker paths include the directories to which libcbor has been installed, compiling programs that uses libcbor requires no extra considerations.

You can verify that everything has been set up properly by creating a file with the following contents

#include <cbor.h>
#include <stdio.h>

int main(int argc, char * argv[])
{
    printf("Hello from libcbor %s\n", CBOR_VERSION);
}

and compiling it

cc hello_cbor.c -lcbor -o hello_cbor

libcbor also comes with pkg-config support. If you install libcbor with a custom prefix, you can use pkg-config to resolve the headers and objects:

cc $(pkg-config --cflags libcbor) hello_cbor.c $(pkg-config --libs libcbor) -o hello_cbor

A note on linkage

libcbor is primarily intended to be linked statically. The shared library versioning scheme generally follows SemVer, but is irregular for the 0.X.Y development branch for historical reasons. The following version identifiers are used as a part of the SONAME (Linux) or the dylib "Compatibility version" (OS X):

  • 0.Y for the 0.Y.Z branch. Patches are backwards compatible, minor releases are generally not and require re-compilation of any dependent code.
  • X for the X.Y.Z stable versions starting 1.X.Y. All minor release of the major version are backwards compatible.
WARNING:

Please note that releases up to and including v0.6.0 may export misleading .so/.dylib version number.

MinGW build instructions

Prerequisites:
  • MinGW
  • CMake GUI

First of all, create a folder that will be used for the output. For this demonstration, we will use cbor_out. Start CMake and select the source path and the destination folder. [image]

Then hit the 'Configure' button. You will be prompted to select the build system: [image]

Choose MinGW and confirm.

NOTE:

If you select Visual Studio at this point, a MSVC project will be generated for you. This is useful if you just want to browse through the source code.

You can then adjust the build options. The defaults will work just fine. Hit 'Generate' when you are done. [image]

You can then adjust the build options. The defaults will work just fine. Hit 'Generate' when you are done.

Open the shell, navigate to the output directory, and run mingw32-make cbor cbor_shared. [image]

libcbor will be built and your .dll should be ready at this point [image]

Feel free to also try building and running some of the examples, e.g. mingw32-make sort [image]

Troubleshooting

cbor.h not found: The headers directory is probably not in your include path. First, verify the installation location by checking the installation log. If you used make, it will look something like

...
-- Installing: /usr/local/include/cbor
-- Installing: /usr/local/include/cbor/callbacks.h
-- Installing: /usr/local/include/cbor/encoding.h
...

Make sure that CMAKE_INSTALL_PREFIX (if you provided it) was correct. Including the path path during compilation should suffice, e.g.:

cc -I/usr/local/include hello_cbor.c -lcbor -o hello_cbor

cannot find -lcbor during linking: Most likely the same problem as before. Include the installation directory in the linker shared path using -R, e.g.:

cc -Wl,-rpath,/usr/local/lib -lcbor -o hello_cbor

shared library missing during execution: Verify the linkage using ldd, otool, or similar and adjust the compilation directives accordingly:

⇒  ldd hello_cbor
    linux-vdso.so.1 =>  (0x00007ffe85585000)
    libcbor.so => /usr/local/lib/libcbor.so (0x00007f9af69da000)
    libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f9af65eb000)
    /lib64/ld-linux-x86-64.so.2 (0x00007f9af6be9000)

compilation failed: If your compiler supports C99 yet the compilation has failed, please report the issue to the issue tracker.

Usage & preliminaries

Version information

libcbor exports its version using three self-explanatory macros:

  • CBOR_MAJOR_VERSION
  • CBOR_MINOR_VERSION
  • CBOR_PATCH_VERSION

The CBOR_VERSION is a string concatenating these three identifiers into one (e.g. 0.2.0).

In order to simplify version comparisons, the version is also exported as

#define CBOR_HEX_VERSION ((CBOR_MAJOR_VERSION << 16) | (CBOR_MINOR_VERSION << 8) | CBOR_PATCH_VERSION)

Since macros are difficult to work with through FFIs, the same information is also available through three uint8_t constants, namely

  • cbor_major_version
  • cbor_minor_version
  • cbor_patch_version

Headers to include

The cbor.h header includes all the symbols. If, for any reason, you don't want to include all the exported symbols, feel free to use just some of the cbor/*.h headers:

  • cbor/arrays.h - api/type_4
  • cbor/bytestrings.h - api/type_2
  • cbor/callbacks.h - Callbacks used for streaming/decoding
  • cbor/common.h - Common utilities - always transitively included
  • cbor/data.h - Data types definitions - always transitively included
  • cbor/encoding.h - Streaming encoders for streaming/encoding
  • cbor/floats_ctrls.h - api/type_7
  • cbor/ints.h - api/type_0_1
  • cbor/maps.h - api/type_5
  • cbor/serialization.h - High level serialization such as cbor_serialize()
  • cbor/streaming.h - Home of cbor_stream_decode()
  • cbor/strings.h - api/type_3
  • cbor/tags.h - api/type_6

Using libcbor

If you want to get more familiar with CBOR, we recommend the cbor.io website. Once you get the grasp of what is it CBOR does, the examples (located in the examples directory) should give you a good feel of the API. The API documentation should then provide with all the information you may need.

Creating and serializing items

#include "cbor.h"
#include <stdio.h>

int main(int argc, char * argv[])
{
    /* Preallocate the map structure */
    cbor_item_t * root = cbor_new_definite_map(2);
    /* Add the content */
    cbor_map_add(root, (struct cbor_pair) {
        .key = cbor_move(cbor_build_string("Is CBOR awesome?")),
        .value = cbor_move(cbor_build_bool(true))
    });
    cbor_map_add(root, (struct cbor_pair) {
        .key = cbor_move(cbor_build_uint8(42)),
        .value = cbor_move(cbor_build_string("Is the answer"))
    });
    /* Output: `length` bytes of data in the `buffer` */
    unsigned char * buffer;
    size_t buffer_size, length = cbor_serialize_alloc(root, &buffer, &buffer_size);

    fwrite(buffer, 1, length, stdout);
    free(buffer);

    fflush(stdout);
    cbor_decref(&root);
}

Reading serialized data

#include "cbor.h"
#include <stdio.h>

/*
 * Reads data from a file. Example usage:
 * $ ./examples/readfile examples/data/nested_array.cbor
 */

int main(int argc, char * argv[])
{
    FILE * f = fopen(argv[1], "rb");
    fseek(f, 0, SEEK_END);
    size_t length = (size_t)ftell(f);
    fseek(f, 0, SEEK_SET);
    unsigned char * buffer = malloc(length);
    fread(buffer, length, 1, f);

    /* Assuming `buffer` contains `info.st_size` bytes of input data */
    struct cbor_load_result result;
    cbor_item_t * item = cbor_load(buffer, length, &result);
    /* Pretty-print the result */
    cbor_describe(item, stdout);
    fflush(stdout);
    /* Deallocate the result */
    cbor_decref(&item);

    fclose(f);
}

Using the streaming parser

#include "cbor.h"
#include <stdio.h>
#include <string.h>

/*
 * Illustrates how one might skim through a map (which is assumed to have
 * string keys and values only), looking for the value of a specific key
 *
 * Use the examples/data/map.cbor input to test this.
 */

const char * key = "a secret key";
bool key_found = false;

void find_string(void * _ctx, cbor_data buffer, size_t len)
{
    if (key_found) {
        printf("Found the value: %*s\n", (int) len, buffer);
        key_found = false;
    } else if (len == strlen(key)) {
        key_found = (memcmp(key, buffer, len) == 0);
    }
}

int main(int argc, char * argv[])
{
    FILE * f = fopen(argv[1], "rb");
    fseek(f, 0, SEEK_END);
    size_t length = (size_t)ftell(f);
    fseek(f, 0, SEEK_SET);
    unsigned char * buffer = malloc(length);
    fread(buffer, length, 1, f);

    struct cbor_callbacks callbacks = cbor_empty_callbacks;
    struct cbor_decoder_result decode_result;
    size_t bytes_read = 0;
    callbacks.string = find_string;
    while (bytes_read < length) {
        decode_result = cbor_stream_decode(buffer + bytes_read,
                                           length - bytes_read,
                                           &callbacks, NULL);
        bytes_read += decode_result.read;
    }

    fclose(f);
}

API

The data API is centered around cbor_item_t, a generic handle for any CBOR item. There are functions to

  • create items,
  • set items' data,
  • parse serialized data into items,
  • manage, move, and links item together.

The single most important thing to keep in mind is: cbor_item_t is an opaque type and should only be manipulated using the appropriate functions! Think of it as an object.

The libcbor API closely follows the semantics outlined by CBOR standard. This part of the documentation provides a short overview of the CBOR constructs, as well as a general introduction to the libcbor API. Remaining reference can be found in the following files structured by data types.

The API is designed to allow both very tight control & flexibility and general convenience with sane defaults. [1] For example, client with very specific requirements (constrained environment, custom application protocol built on top of CBOR, etc.) may choose to take full control (and responsibility) of memory and data structures management by interacting directly with the decoder. Other clients might want to take control of specific aspects (streamed collections, hash maps storage), but leave other responsibilities to libcbor. More general clients might prefer to be abstracted away from all aforementioned details and only be presented complete data structures.

libcbor provides
  • stateless encoders and decoders
  • encoding and decoding drivers, routines that coordinate encoding and decoding of complex structures
  • data structures to represent and transform CBOR structures
  • routines for building and manipulating these structures
  • utilities for inspection and debugging

Types of items

Every cbor_item_t has a cbor_type associated with it - these constants correspond to the types specified by the CBOR standard:

enum cbor_type

Specifies the Major type of cbor_item_t.

Values:

enumerator CBOR_TYPE_UINT

0 - positive integers

enumerator CBOR_TYPE_NEGINT

1 - negative integers

enumerator CBOR_TYPE_BYTESTRING

2 - byte strings

enumerator CBOR_TYPE_STRING

3 - strings

enumerator CBOR_TYPE_ARRAY

4 - arrays

enumerator CBOR_TYPE_MAP

5 - maps

enumerator CBOR_TYPE_TAG

6 - tags

enumerator CBOR_TYPE_FLOAT_CTRL

7 - decimals and special values (true, false, nil, ...)

To find out the type of an item, one can use

cbor_type cbor_typeof(const cbor_item_t *item)

Get the type of the item.

Return

The type

Parameters
  • item[borrow]:

Please note the distinction between functions like cbor_isa_uint() and cbor_is_int(). The following functions work solely with the major type value.

Binary queries

Alternatively, there are functions to query each particular type.

WARNING:

Passing an invalid cbor_item_t reference to any of these functions results in undefined behavior.

bool cbor_isa_uint(const cbor_item_t *item)

Does the item have the appropriate major type?

Return

Is the item an CBOR_TYPE_UINT?

Parameters
  • item[borrow]: the item
bool cbor_isa_negint(const cbor_item_t *item)

Does the item have the appropriate major type?

Return

Is the item a CBOR_TYPE_NEGINT?

Parameters
  • item[borrow]: the item
bool cbor_isa_bytestring(const cbor_item_t *item)

Does the item have the appropriate major type?

Return

Is the item a CBOR_TYPE_BYTESTRING?

Parameters
  • item[borrow]: the item
bool cbor_isa_string(const cbor_item_t *item)

Does the item have the appropriate major type?

Return

Is the item a CBOR_TYPE_STRING?

Parameters
  • item[borrow]: the item
bool cbor_isa_array(const cbor_item_t *item)

Does the item have the appropriate major type?

Return

Is the item an CBOR_TYPE_ARRAY?

Parameters
  • item[borrow]: the item
bool cbor_isa_map(const cbor_item_t *item)

Does the item have the appropriate major type?

Return

Is the item a CBOR_TYPE_MAP?

Parameters
  • item[borrow]: the item
bool cbor_isa_tag(const cbor_item_t *item)

Does the item have the appropriate major type?

Return

Is the item a CBOR_TYPE_TAG?

Parameters
  • item[borrow]: the item
bool cbor_isa_float_ctrl(const cbor_item_t *item)

Does the item have the appropriate major type?

Return

Is the item a CBOR_TYPE_FLOAT_CTRL?

Parameters
  • item[borrow]: the item

Logical queries

These functions provide information about the item type from a more high-level perspective

bool cbor_is_int(const cbor_item_t *item)

Is the item an integer, either positive or negative?

Return

Is the item an integer, either positive or negative?

Parameters
  • item[borrow]: the item
bool cbor_is_float(const cbor_item_t *item)

Is the item an a floating point number?

Return

Is the item a floating point number?

Parameters
  • item[borrow]: the item
bool cbor_is_bool(const cbor_item_t *item)

Is the item an a boolean?

Return

Is the item a boolean?

Parameters
  • item[borrow]: the item
bool cbor_is_null(const cbor_item_t *item)

Does this item represent null

WARNING:

This is in no way related to the value of the pointer. Passing a

null pointer will most likely result in a crash.

.INDENT 7.0

Return

Is the item (CBOR logical) null?

Parameters
  • item[borrow]: the item
bool cbor_is_undef(const cbor_item_t *item)

Does this item represent undefined

WARNING:

Care must be taken to distinguish nulls and undefined values in

C.

.INDENT 7.0

Return

Is the item (CBOR logical) undefined?

Parameters
  • item[borrow]: the item

Memory management and reference counting

Due to the nature of its domain, libcbor will need to work with heap memory. The stateless decoder and encoder don't allocate any memory.

If you have specific requirements, you should consider rolling your own driver for the stateless API.

Using custom allocator

libcbor gives you with the ability to provide your own implementations of malloc, realloc, and free. This can be useful if you are using a custom allocator throughout your application, or if you want to implement custom policies (e.g. tighter restrictions on the amount of allocated memory).

In order to use this feature, libcbor has to be compiled with the appropriate flags. You can verify the configuration using the CBOR_CUSTOM_ALLOC macro. A simple usage might be as follows:

#if CBOR_CUSTOM_ALLOC
        cbor_set_allocs(malloc, realloc, free);
#else
   #error "libcbor built with support for custom allocation is required"
#endif
void cbor_set_allocs(_cbor_malloc_t custom_malloc, _cbor_realloc_t custom_realloc, _cbor_free_t custom_free)

Sets the memory management routines to use.

Only available when CBOR_CUSTOM_ALLOC is truthy

WARNING:

This function modifies the global state and should therefore be

used accordingly. Changing the memory handlers while allocated items exist will result in a free/malloc mismatch. This function is not thread safe with respect to both itself and all the other libcbor functions that work with the heap. .. note:: realloc implementation must correctly support NULL reallocation (see e.g. http://en.cppreference.com/w/c/memory/realloc)

Parameters
  • custom_malloc: malloc implementation
  • custom_realloc: realloc implementation
  • custom_free: free implementation

Reference counting

As CBOR items may require complex cleanups at the end of their lifetime, there is a reference counting mechanism in place. This also enables very simple GC when integrating libcbor into managed environment. Every item starts its life (by either explicit creation, or as a result of parsing) with reference count set to 1. When the refcount reaches zero, it will be destroyed.

Items containing nested items will be destroyed recursively - refcount of every nested item will be decreased by one.

The destruction is synchronous and renders any pointers to items with refcount zero invalid immediately after calling the cbor_decref().

cbor_item_t *cbor_incref(cbor_item_t *item)

Increases the reference count by one.

No dependent items are affected.

Return

the input reference

Parameters
  • item[incref]: item the item
void cbor_decref(cbor_item_t **item)

Decreases the reference count by one, deallocating the item if needed.

In case the item is deallocated, the reference count of any dependent items is adjusted accordingly in a recursive manner.

Parameters
  • item[take]: the item. Set to NULL if deallocated
void cbor_intermediate_decref(cbor_item_t *item)

Decreases the reference count by one, deallocating the item if needed.

Convenience wrapper for cbor_decref when its set-to-null behavior is not needed

Parameters
  • item[take]: the item
size_t cbor_refcount(const cbor_item_t *item)

Get the reference count.

WARNING:

This does not account for transitive references.

Return

the reference count

Parameters
  • item[borrow]: the item
cbor_item_t *cbor_move(cbor_item_t *item)

Provides CPP-like move construct.

Decreases the reference count by one, but does not deallocate the item even if its refcount reaches zero. This is useful for passing intermediate values to functions that increase reference count. Should only be used with functions that incref their arguments.

WARNING:

If the item is moved without correctly increasing the reference

count afterwards, the memory will be leaked.

Return

the item with reference count decreased by one

Parameters
  • item[take]: the item
cbor_item_t *cbor_copy(cbor_item_t *item)

Deep copy of an item.

All the reference counts in the new structure are set to one.

Return

new CBOR deep copy

Parameters
  • item[borrow]: item to copy

Decoding

The following diagram illustrates the relationship among different parts of libcbor from the decoding standpoint.

┌──────────────────────────────────────────────────────────────────────────────────────────────┐
│                                                                                              │
│                                      Client application                                      │
│                                                                                              │
│                                                 ┌────────────────────────────────────────────┘
│                                                 │                     ↕
│                                                 │ ┌──────────────────────────────────────────┐
│                                                 │ │                                          │
│                                                 │ │          Manipulation routines           │
│                                                 │ │                                          │
│           ┌─────────────────────────────────────┘ └──────────────────────────────────────────┘
│           │     ↑    ↑                  ↑                              ↑
│           │     │    │    ┌─────────────╫──────────┬───────────────────┴─┐
│           │     │   CDS   │             ║          │                     │
│           │     │    │   PDS            ║         PDS                   PDS
│           │     ↓    ↓    ↓             ↓          ↓                     ↓
│           │ ┌─────────────────┐   ┌────────────────────┐   ┌────────────────────────────┐
│           │ │                 │   │                    │   │                            │
│           │ │  Custom driver  │ ↔ │  Streaming driver  │ ↔ │       Default driver       │ ↔ CD
│           │ │                 │   │                    │   │                            │
└───────────┘ └─────────────────┘   └────────────────────┘   └────────────────────────────┘
      ↕                ↕                        ↕                           ↕
┌──────────────────────────────────────────────────────────────────────────────────────────────┐
│                                                                                              │
│                            Stateless event─driven decoder                                    │
│                                                                                              │
└──────────────────────────────────────────────────────────────────────────────────────────────┘

              (PSD = Provided Data Structures, CDS = Custom Data Structures)

This section will deal with the API that is labeled as the "Default driver" in the diagram. That is, routines that decode complete libcbor data items

cbor_item_t *cbor_load(cbor_data source, size_t source_size, struct cbor_load_result *result)

Loads data item from a buffer.

Return

new CBOR item or NULL on failure. In that case, result contains location and description of the error.

Parameters
  • source: The buffer
  • source_size:
  • result[out]: Result indicator. CBOR_ERR_NONE on success

Associated data structures

enum cbor_error_code

Possible decoding errors.

Values:

enumerator CBOR_ERR_NONE

enumerator CBOR_ERR_NOTENOUGHDATA

enumerator CBOR_ERR_NODATA

enumerator CBOR_ERR_MALFORMATED

enumerator CBOR_ERR_MEMERROR

Memory error - item allocation failed.

Is it too big for your allocator?

enumerator CBOR_ERR_SYNTAXERROR

Stack parsing algorithm failed.

struct cbor_load_result

High-level decoding result.

Public Members

struct cbor_error error

Error indicator.

size_t read

Number of bytes read.

struct cbor_error

High-level decoding error.

Public Members

size_t position

Aproximate position.

cbor_error_code code

Description.

Encoding

The easiest way to encode data items is using the cbor_serialize() or cbor_serialize_alloc() functions:

size_t cbor_serialize(const cbor_item_t *item, cbor_mutable_data buffer, size_t buffer_size)

Serialize the given item.

Return

Length of the result. 0 on failure.

Parameters
  • item[borrow]: A data item
  • buffer: Buffer to serialize to
  • buffer_size: Size of the buffer
size_t cbor_serialize_alloc(const cbor_item_t *item, cbor_mutable_data *buffer, size_t *buffer_size)

Serialize the given item, allocating buffers as needed.

WARNING:

It is your responsibility to free the buffer using an

appropriate free implementation.

Return

Length of the result. 0 on failure, in which case buffer is NULL.

Parameters
  • item[borrow]: A data item
  • buffer[out]: Buffer containing the result
  • buffer_size[out]: Size of the buffer

Type-specific serializers

In case you know the type of the item you want to serialize beforehand, you can use one of the type-specific serializers.

NOTE:

Unless compiled in debug mode, these do not verify the type. Passing an incorrect item will result in an undefined behavior.

size_t cbor_serialize_uint(const cbor_item_t *item, cbor_mutable_data buffer, size_t buffer_size)

Serialize an uint.

Return

Length of the result. 0 on failure.

Parameters
  • item[borrow]: A uint
  • buffer: Buffer to serialize to
  • buffer_size: Size of the buffer
size_t cbor_serialize_negint(const cbor_item_t *item, cbor_mutable_data buffer, size_t buffer_size)

Serialize a negint.

Return

Length of the result. 0 on failure.

Parameters
  • item[borrow]: A neging
  • buffer: Buffer to serialize to
  • buffer_size: Size of the buffer
size_t cbor_serialize_bytestring(const cbor_item_t *item, cbor_mutable_data buffer, size_t buffer_size)

Serialize a bytestring.

Return

Length of the result. 0 on failure.

Parameters
  • item[borrow]: A bytestring
  • buffer: Buffer to serialize to
  • buffer_size: Size of the buffer
size_t cbor_serialize_string(const cbor_item_t *item, cbor_mutable_data buffer, size_t buffer_size)

Serialize a string.

Return

Length of the result. 0 on failure.

Parameters
  • item[borrow]: A string
  • buffer: Buffer to serialize to
  • buffer_size: Size of the buffer
size_t cbor_serialize_array(const cbor_item_t *item, cbor_mutable_data buffer, size_t buffer_size)

Serialize an array.

Return

Length of the result. 0 on failure.

Parameters
  • item[borrow]: An array
  • buffer: Buffer to serialize to
  • buffer_size: Size of the buffer
size_t cbor_serialize_map(const cbor_item_t *item, cbor_mutable_data buffer, size_t buffer_size)

Serialize a map.

Return

Length of the result. 0 on failure.

Parameters
  • item[borrow]: A map
  • buffer: Buffer to serialize to
  • buffer_size: Size of the buffer
size_t cbor_serialize_tag(const cbor_item_t *item, cbor_mutable_data buffer, size_t buffer_size)

Serialize a tag.

Return

Length of the result. 0 on failure.

Parameters
  • item[borrow]: A tag
  • buffer: Buffer to serialize to
  • buffer_size: Size of the buffer
size_t cbor_serialize_float_ctrl(const cbor_item_t *item, cbor_mutable_data buffer, size_t buffer_size)

Serialize a.

Return

Length of the result. 0 on failure.

Parameters
  • item[borrow]: A float or ctrl
  • buffer: Buffer to serialize to
  • buffer_size: Size of the buffer

Types 0 & 1 – Positive and negative integers

CBOR has two types of integers – positive (which may be effectively regarded as unsigned), and negative. There are four possible widths for an integer – 1, 2, 4, or 8 bytes. These are represented by

enum cbor_int_width

Possible widths of CBOR_TYPE_UINT items.

Values:

enumerator CBOR_INT_8

enumerator CBOR_INT_16

enumerator CBOR_INT_32

enumerator CBOR_INT_64

Type 0 - positive integers

Corresponding cbor_typeCBOR_TYPE_UINT
Number of allocationsOne per lifetime
Storage requirementssizeof(cbor_item_t) + sizeof(uint*_t)

Note: once a positive integer has been created, its width cannot be changed.

Type 1 - negative integers

Corresponding cbor_typeCBOR_TYPE_NEGINT
Number of allocationsOne per lifetime
Storage requirementssizeof(cbor_item_t) + sizeof(uint*_t)

Note: once a positive integer has been created, its width cannot be changed.

Type 0 & 1

Due to their largely similar semantics, the following functions can be used for both Type 0 and Type 1 items. One can convert between them freely using the conversion functions.

Actual Type of the integer can be checked using item types API.

An integer item is created with one of the four widths. Because integers' storage is bundled together with the handle, the width cannot be changed over its lifetime.

WARNING:

Due to the fact that CBOR negative integers represent integers in the range [-1, -2^N], cbor_set_uint API is somewhat counter-intuitive as the resulting logical value is 1 less. This behavior is necessary in order to permit uniform manipulation with the full range of permitted values. For example, the following snippet

cbor_item_t * item = cbor_new_int8();
cbor_mark_negint(item);
cbor_set_uint8(0);

will produce an item with the logical value of -1. There is, however, an upside to this as well: There is only one representation of zero.

Building new items

cbor_item_t *cbor_build_uint8(uint8_t value)

Constructs a new positive integer.

Return

new positive integer or NULL on memory allocation failure

Parameters
  • value: the value to use
cbor_item_t *cbor_build_uint16(uint16_t value)

Constructs a new positive integer.

Return

new positive integer or NULL on memory allocation failure

Parameters
  • value: the value to use
cbor_item_t *cbor_build_uint32(uint32_t value)

Constructs a new positive integer.

Return

new positive integer or NULL on memory allocation failure

Parameters
  • value: the value to use
cbor_item_t *cbor_build_uint64(uint64_t value)

Constructs a new positive integer.

Return

new positive integer or NULL on memory allocation failure

Parameters
  • value: the value to use

Retrieving values

uint8_t cbor_get_uint8(const cbor_item_t *item)

Extracts the integer value.

Return

the value

Parameters
  • item[borrow]: positive or negative integer
uint16_t cbor_get_uint16(const cbor_item_t *item)

Extracts the integer value.

Return

the value

Parameters
  • item[borrow]: positive or negative integer
uint32_t cbor_get_uint32(const cbor_item_t *item)

Extracts the integer value.

Return

the value

Parameters
  • item[borrow]: positive or negative integer
uint64_t cbor_get_uint64(const cbor_item_t *item)

Extracts the integer value.

Return

the value

Parameters
  • item[borrow]: positive or negative integer

Setting values

void cbor_set_uint8(cbor_item_t *item, uint8_t value)

Assigns the integer value.

Parameters
  • item[borrow]: positive or negative integer item
  • value: the value to assign. For negative integer, the logical value is -value - 1
void cbor_set_uint16(cbor_item_t *item, uint16_t value)

Assigns the integer value.

Parameters
  • item[borrow]: positive or negative integer item
  • value: the value to assign. For negative integer, the logical value is -value - 1
void cbor_set_uint32(cbor_item_t *item, uint32_t value)

Assigns the integer value.

Parameters
  • item[borrow]: positive or negative integer item
  • value: the value to assign. For negative integer, the logical value is -value - 1
void cbor_set_uint64(cbor_item_t *item, uint64_t value)

Assigns the integer value.

Parameters
  • item[borrow]: positive or negative integer item
  • value: the value to assign. For negative integer, the logical value is -value - 1

Dealing with width

cbor_int_width cbor_int_get_width(const cbor_item_t *item)

Queries the integer width.

Return

the width

Parameters
  • item[borrow]: positive or negative integer item

Dealing with signedness

void cbor_mark_uint(cbor_item_t *item)

Marks the integer item as a positive integer.

The data value is not changed

Parameters
  • item[borrow]: positive or negative integer item
void cbor_mark_negint(cbor_item_t *item)

Marks the integer item as a negative integer.

The data value is not changed

Parameters
  • item[borrow]: positive or negative integer item

Creating new items

cbor_item_t *cbor_new_int8()

Allocates new integer with 1B width.

The width cannot be changed once allocated

Return

new positive integer or NULL on memory allocation failure. The value is not initialized

cbor_item_t *cbor_new_int16()

Allocates new integer with 2B width.

The width cannot be changed once allocated

Return

new positive integer or NULL on memory allocation failure. The value is not initialized

cbor_item_t *cbor_new_int32()

Allocates new integer with 4B width.

The width cannot be changed once allocated

Return

new positive integer or NULL on memory allocation failure. The value is not initialized

cbor_item_t *cbor_new_int64()

Allocates new integer with 8B width.

The width cannot be changed once allocated

Return

new positive integer or NULL on memory allocation failure. The value is not initialized

Type 2 – Byte strings

CBOR byte strings are just (ordered) series of bytes without further interpretation (unless there is a tag). Byte string's length may or may not be known during encoding. These two kinds of byte strings can be distinguished using cbor_bytestring_is_definite() and cbor_bytestring_is_indefinite() respectively.

In case a byte string is indefinite, it is encoded as a series of definite byte strings. These are called "chunks". For example, the encoded item

0xf5            Start indefinite byte string
    0x41        Byte string (1B long)
        0x00
    0x41        Byte string (1B long)
        0xff
    0xff        "Break" control token

represents two bytes, 0x00 and 0xff. This on one hand enables streaming messages even before they are fully generated, but on the other hand it adds more complexity to the client code.

Corresponding cbor_typeCBOR_TYPE_BYTESTRING
Number of allocations (definite)One plus any manipulations with the data
Number of allocations (indefinite)One plus logarithmically many reallocations relative  to chunk count
Storage requirements (definite)sizeof(cbor_item_t) + length(handle)
Storage requirements (indefinite)sizeof(cbor_item_t) * (1 + chunk_count) + chunks

Streaming indefinite byte strings

Please refer to /streaming.

Getting metadata

size_t cbor_bytestring_length(const cbor_item_t *item)

Returns the length of the binary data.

For definite byte strings only

Return

length of the binary data. Zero if no chunk has been attached yet

Parameters
  • item[borrow]: a definite bytestring
bool cbor_bytestring_is_definite(const cbor_item_t *item)

Is the byte string definite?

Return

Is the byte string definite?

Parameters
  • item[borrow]: a byte string
bool cbor_bytestring_is_indefinite(const cbor_item_t *item)

Is the byte string indefinite?

Return

Is the byte string indefinite?

Parameters
  • item[borrow]: a byte string
size_t cbor_bytestring_chunk_count(const cbor_item_t *item)

Get the number of chunks this string consist of.

Return

The chunk count. 0 for freshly created items.

Parameters
  • item[borrow]: A indefinite bytestring

Reading data

cbor_mutable_data cbor_bytestring_handle(const cbor_item_t *item)

Get the handle to the binary data.

Definite items only. Modifying the data is allowed. In that case, the caller takes responsibility for the effect on items this item might be a part of

Return

The address of the binary data. NULL if no data have been assigned yet.

Parameters
  • item[borrow]: A definite byte string
cbor_item_t **cbor_bytestring_chunks_handle(const cbor_item_t *item)

Get the handle to the array of chunks.

Manipulations with the memory block (e.g. sorting it) are allowed, but the validity and the number of chunks must be retained.

Return

array of cbor_bytestring_chunk_count definite bytestrings

Parameters
  • item[borrow]: A indefinite byte string

Creating new items

cbor_item_t *cbor_new_definite_bytestring()

Creates a new definite byte string.

The handle is initialized to NULL and length to 0

Return

new definite bytestring. NULL on malloc failure.

cbor_item_t *cbor_new_indefinite_bytestring()

Creates a new indefinite byte string.

The chunks array is initialized to NULL and chunkcount to 0

Return

new indefinite bytestring. NULL on malloc failure.

Building items

cbor_item_t *cbor_build_bytestring(cbor_data handle, size_t length)

Creates a new byte string and initializes it.

The handle will be copied to a newly allocated block

Return

A new byte string with content handle. NULL on malloc failure.

Parameters
  • handle: Block of binary data
  • length: Length of data

Manipulating existing items

void cbor_bytestring_set_handle(cbor_item_t *item, cbor_mutable_data data, size_t length)

Set the handle to the binary data.

Parameters
  • item[borrow]: A definite byte string
  • data: The memory block. The caller gives up the ownership of the block. libcbor will deallocate it when appropriate using its free function
  • length: Length of the data block
bool cbor_bytestring_add_chunk(cbor_item_t *item, cbor_item_t *chunk)

Appends a chunk to the bytestring.

Indefinite byte strings only.

May realloc the chunk storage.

Return

true on success, false on realloc failure. In that case, the refcount of chunk is not increased and the item is left intact.

Parameters
  • item[borrow]: An indefinite byte string
  • item[incref]: A definite byte string

Type 3 – UTF-8 strings

CBOR strings work in much the same ways as type_2.

Corresponding cbor_typeCBOR_TYPE_STRING
Number of allocations (definite)One plus any manipulations with the data
Number of allocations (indefinite)One plus logarithmically many reallocations relative  to chunk count
Storage requirements (definite)sizeof(cbor_item_t) + length(handle)
Storage requirements (indefinite)sizeof(cbor_item_t) * (1 + chunk_count) + chunks

Streaming indefinite strings

Please refer to /streaming.

UTF-8 encoding validation

libcbor considers UTF-8 encoding validity to be a part of the well-formedness notion of CBOR and therefore invalid UTF-8 strings will be rejected by the parser. Strings created by the user are not checked.

Getting metadata

size_t cbor_string_length(const cbor_item_t *item)

Returns the length of the underlying string.

For definite strings only

Return

length of the string. Zero if no chunk has been attached yet

Parameters
  • item[borrow]: a definite string
bool cbor_string_is_definite(const cbor_item_t *item)

Is the string definite?

Return

Is the string definite?

Parameters
  • item[borrow]: a string
bool cbor_string_is_indefinite(const cbor_item_t *item)

Is the string indefinite?

Return

Is the string indefinite?

Parameters
  • item[borrow]: a string
size_t cbor_string_chunk_count(const cbor_item_t *item)

Get the number of chunks this string consist of.

Return

The chunk count. 0 for freshly created items.

Parameters
  • item[borrow]: A indefinite string

Reading data

cbor_mutable_data cbor_string_handle(const cbor_item_t *item)

Get the handle to the underlying string.

Definite items only. Modifying the data is allowed. In that case, the caller takes responsibility for the effect on items this item might be a part of

Return

The address of the underlying string. NULL if no data have been assigned yet.

Parameters
  • item[borrow]: A definite string
cbor_item_t **cbor_string_chunks_handle(const cbor_item_t *item)

Get the handle to the array of chunks.

Manipulations with the memory block (e.g. sorting it) are allowed, but the validity and the number of chunks must be retained.

Return

array of cbor_string_chunk_count definite strings

Parameters
  • item[borrow]: A indefinite string

Creating new items

cbor_item_t *cbor_new_definite_string()

Creates a new definite string.

The handle is initialized to NULL and length to 0

Return

new definite string. NULL on malloc failure.

cbor_item_t *cbor_new_indefinite_string()

Creates a new indefinite string.

The chunks array is initialized to NULL and chunkcount to 0

Return

new indefinite string. NULL on malloc failure.

Building items

cbor_item_t *cbor_build_string(const char *val)

Creates a new string and initializes it.

The val will be copied to a newly allocated block

Return

A new string with content handle. NULL on malloc failure.

Parameters
  • val: A null-terminated UTF-8 string

Manipulating existing items

void cbor_string_set_handle(cbor_item_t *item, cbor_mutable_data data, size_t length)

Set the handle to the underlying string.

WARNING:

Using a pointer to a stack allocated constant is a common

mistake. Lifetime of the string will expire when it goes out of scope and the CBOR item will be left inconsistent.

Parameters
  • item[borrow]: A definite string
  • data: The memory block. The caller gives up the ownership of the block. libcbor will deallocate it when appropriate using its free function
  • length: Length of the data block
bool cbor_string_add_chunk(cbor_item_t *item, cbor_item_t *chunk)

Appends a chunk to the string.

Indefinite strings only.

May realloc the chunk storage.

Return

true on success. false on realloc failure. In that case, the refcount of chunk is not increased and the item is left intact.

Parameters
  • item[borrow]: An indefinite string
  • item[incref]: A definite string

Type 4 – Arrays

CBOR arrays, just like byte strings and strings, can be encoded either as definite, or as indefinite.

Corresponding cbor_typeCBOR_TYPE_ARRAY
Number of allocations (definite)Two plus any manipulations with the data
Number of allocations (indefinite)Two plus logarithmically many reallocations relative to additions
Storage requirements (definite)(sizeof(cbor_item_t) + 1) * size
Storage requirements (indefinite)<= sizeof(cbor_item_t) + sizeof(cbor_item_t) * size * BUFFER_GROWTH

Examples

0x9f        Start indefinite array
    0x01        Unsigned integer 1
    0xff        "Break" control token
0x9f        Start array, 1B length follows
0x20        Unsigned integer 32
    ...        32 items follow

Streaming indefinite arrays

Please refer to /streaming.

Getting metadata

size_t cbor_array_size(const cbor_item_t *item)

Get the number of members.

Return

The number of members

Parameters
  • item[borrow]: An array
size_t cbor_array_allocated(const cbor_item_t *item)

Get the size of the allocated storage.

Return

The size of the allocated storage (number of items)

Parameters
  • item[borrow]: An array
bool cbor_array_is_definite(const cbor_item_t *item)

Is the array definite?

Return

Is the array definite?

Parameters
  • item[borrow]: An array
bool cbor_array_is_indefinite(const cbor_item_t *item)

Is the array indefinite?

Return

Is the array indefinite?

Parameters
  • item[borrow]: An array

Reading data

cbor_item_t **cbor_array_handle(const cbor_item_t *item)

Get the array contents.

The items may be reordered and modified as long as references remain consistent.

Return

cbor_array_size items

Parameters
  • item[borrow]: An array
cbor_item_t *cbor_array_get(const cbor_item_t *item, size_t index)

Get item by index.

Return

incref The item, or NULL in case of boundary violation

Parameters
  • item[borrow]: An array
  • index: The index

Creating new items

cbor_item_t *cbor_new_definite_array(size_t size)

Create new definite array.

Return

new array or NULL upon malloc failure

Parameters
  • size: Number of slots to preallocate
cbor_item_t *cbor_new_indefinite_array()

Create new indefinite array.

Return

new array or NULL upon malloc failure

Modifying items

bool cbor_array_push(cbor_item_t *array, cbor_item_t *pushee)

Append to the end.

For indefinite items, storage may be realloacted. For definite items, only the preallocated capacity is available.

Return

true on success, false on failure

Parameters
  • array[borrow]: An array
  • pushee[incref]: The item to push
bool cbor_array_replace(cbor_item_t *item, size_t index, cbor_item_t *value)

Replace item at an index.

The item being replace will be cbor_decref 'ed.

Return

true on success, false on allocation failure.

Parameters
  • item[borrow]: An array
  • value[incref]: The item to assign
  • index: The index, first item is 0.
bool cbor_array_set(cbor_item_t *item, size_t index, cbor_item_t *value)

Set item by index.

Creating arrays with holes is not possible

Return

true on success, false on allocation failure.

Parameters
  • item[borrow]: An array
  • value[incref]: The item to assign
  • index: The index, first item is 0.

Type 5 – Maps

CBOR maps are the plain old associate hash maps known from JSON and many other formats and languages, with one exception: any CBOR data item can be a key, not just strings. This is somewhat unusual and you, as an application developer, should keep that in mind.

Maps can be either definite or indefinite, in much the same way as type_4.

Corresponding cbor_typeCBOR_TYPE_MAP
Number of allocations (definite)Two plus any manipulations with the data
Number of allocations (indefinite)Two plus logarithmically many reallocations relative to additions
Storage requirements (definite)sizeof(cbor_pair) * size + sizeof(cbor_item_t)
Storage requirements (indefinite)<= sizeof(cbor_item_t) + sizeof(cbor_pair) * size * BUFFER_GROWTH

Streaming maps

Please refer to /streaming.

Getting metadata

size_t cbor_map_size(const cbor_item_t *item)

Get the number of pairs.

Return

The number of pairs

Parameters
  • item[borrow]: A map
size_t cbor_map_allocated(const cbor_item_t *item)

Get the size of the allocated storage.

Return

Allocated storage size (as the number of cbor_pair items)

Parameters
  • item[borrow]: A map
bool cbor_map_is_definite(const cbor_item_t *item)

Is this map definite?

Return

Is this map definite?

Parameters
  • item[borrow]: A map
bool cbor_map_is_indefinite(const cbor_item_t *item)

Is this map indefinite?

Return

Is this map indefinite?

Parameters
  • item[borrow]: A map

Reading data

struct cbor_pair *cbor_map_handle(const cbor_item_t *item)

Get the pairs storage.

Return

Array of cbor_map_size pairs. Manipulation is possible as long as references remain valid.

Parameters
  • item[borrow]: A map

Creating new items

cbor_item_t *cbor_new_definite_map(size_t size)

Create a new definite map.

Return

new definite map. NULL on malloc failure.

Parameters
  • size: The number of slots to preallocate
cbor_item_t *cbor_new_indefinite_map()

Create a new indefinite map.

Return

new definite map. NULL on malloc failure.

Parameters
  • size: The number of slots to preallocate

Modifying items

bool cbor_map_add(cbor_item_t *item, struct cbor_pair pair)

Add a pair to the map.

For definite maps, items can only be added to the preallocated space. For indefinite maps, the storage will be expanded as needed

Return

true on success, false if either reallocation failed or the preallcoated storage is full

Parameters
  • item[borrow]: A map
  • pair[incref]: The key-value pair to add (incref is member-wise)

Type 6 – Semantic tags

Tag are additional metadata that can be used to extend or specialize the meaning or interpretation of the other data items.

For example, one might tag an array of numbers to communicate that it should be interpreted as a vector.

Please consult the official IANA repository of CBOR tags before inventing new ones.

Corresponding cbor_typeCBOR_TYPE_TAG
Number of allocationsOne plus any manipulations with the data reallocations relative  to chunk count
Storage requirementssizeof(cbor_item_t) + the tagged item
cbor_item_t *cbor_new_tag(uint64_t value)

Create a new tag.

Return

new tag. Item reference is NULL. Returns NULL upon memory allocation failure

Parameters
  • value: The tag value. Please consult the tag repository
cbor_item_t *cbor_tag_item(const cbor_item_t *item)

Get the tagged item.

Return

incref the tagged item

Parameters
  • item[borrow]: A tag
uint64_t cbor_tag_value(const cbor_item_t *item)

Get tag value.

Return

The tag value. Please consult the tag repository

Parameters
  • item[borrow]: A tag
void cbor_tag_set_item(cbor_item_t *item, cbor_item_t *tagged_item)

Set the tagged item.

Parameters
  • item[borrow]: A tag
  • tagged_item[incref]: The item to tag

Type 7 – Floats & control tokens

This type combines two completely unrelated types of items -- floating point numbers and special values such as true, false, null, etc. We refer to these special values as 'control values' or 'ctrls' for short throughout the code.

Just like integers, they have different possible width (resulting in different value ranges and precisions).

enum cbor_float_width

Possible widths of CBOR_TYPE_FLOAT_CTRL items.

Values:

enumerator CBOR_FLOAT_0

Internal use - ctrl and special values.

enumerator CBOR_FLOAT_16

Half float.

enumerator CBOR_FLOAT_32

Single float.

enumerator CBOR_FLOAT_64

Double.

Corresponding cbor_typeCBOR_TYPE_FLOAT_CTRL
Number of allocationsOne per lifetime
Storage requirementssizeof(cbor_item_t) + 1/4/8

Getting metadata

bool cbor_float_ctrl_is_ctrl(const cbor_item_t *item)

Is this a ctrl value?

Return

Is this a ctrl value?

Parameters
  • item[borrow]: A float or ctrl item
cbor_float_width cbor_float_get_width(const cbor_item_t *item)

Get the float width.

Return

The width.

Parameters
  • item[borrow]: A float or ctrl item

Reading data

float cbor_float_get_float2(const cbor_item_t *item)

Get a half precision float.

The item must have the corresponding width

Return

half precision value

Parameters
  • [borrow]: A half precision float
float cbor_float_get_float4(const cbor_item_t *item)

Get a single precision float.

The item must have the corresponding width

Return

single precision value

Parameters
  • [borrow]: A signle precision float
double cbor_float_get_float8(const cbor_item_t *item)

Get a double precision float.

The item must have the corresponding width

Return

double precision value

Parameters
  • [borrow]: A double precision float
double cbor_float_get_float(const cbor_item_t *item)

Get the float value represented as double.

Can be used regardless of the width.

Return

double precision value

Parameters
  • [borrow]: Any float
uint8_t cbor_ctrl_value(const cbor_item_t *item)

Reads the control value.

Return

the simple value

Parameters
  • item[borrow]: A ctrl item
bool cbor_get_bool(const cbor_item_t *item)

Get value from a boolean ctrl item.

Return

boolean value

Parameters
  • item[borrow]: A ctrl item

Creating new items

cbor_item_t *cbor_new_ctrl()

Constructs a new ctrl item.

The width cannot be changed once the item is created

Return

new 1B ctrl or NULL upon memory allocation failure

cbor_item_t *cbor_new_float2()

Constructs a new float item.

The width cannot be changed once the item is created

Return

new 2B float or NULL upon memory allocation failure

cbor_item_t *cbor_new_float4()

Constructs a new float item.

The width cannot be changed once the item is created

Return

new 4B float or NULL upon memory allocation failure

cbor_item_t *cbor_new_float8()

Constructs a new float item.

The width cannot be changed once the item is created

Return

new 8B float or NULL upon memory allocation failure

cbor_item_t *cbor_new_null()

Constructs new null ctrl item.

Return

new null ctrl item or NULL upon memory allocation failure

cbor_item_t *cbor_new_undef()

Constructs new undef ctrl item.

Return

new undef ctrl item or NULL upon memory allocation failure

Building items

cbor_item_t *cbor_build_bool(bool value)

Constructs new boolean ctrl item.

Return

new boolen ctrl item or NULL upon memory allocation failure

Parameters
  • value: The value to use
cbor_item_t *cbor_build_ctrl(uint8_t value)

Constructs a ctrl item.

Return

new ctrl item or NULL upon memory allocation failure

Parameters
  • value: the value to use
cbor_item_t *cbor_build_float2(float value)

Constructs a new float.

Return

new float

Parameters
  • value: the value to use
cbor_item_t *cbor_build_float4(float value)

Constructs a new float.

Return

new float or NULL upon memory allocation failure

Parameters
  • value: the value to use
cbor_item_t *cbor_build_float8(double value)

Constructs a new float.

Return

new float or NULL upon memory allocation failure

Parameters
  • value: the value to use

Manipulating existing items

void cbor_set_ctrl(cbor_item_t *item, uint8_t value)

Assign a control value.

WARNING:

It is possible to produce an invalid CBOR value by assigning a

invalid value using this mechanism. Please consult the standard before use.

Parameters
  • item[borrow]: A ctrl item
  • value: The simple value to assign. Please consult the standard for allowed values
void cbor_set_bool(cbor_item_t *item, bool value)

Assign a boolean value to a boolean ctrl item.

Parameters
  • item[borrow]: A ctrl item
  • value: The simple value to assign.
void cbor_set_float2(cbor_item_t *item, float value)

Assigns a float value.

Parameters
  • item[borrow]: A half precision float
  • value: The value to assign
void cbor_set_float4(cbor_item_t *item, float value)

Assigns a float value.

Parameters
  • item[borrow]: A single precision float
  • value: The value to assign
void cbor_set_float8(cbor_item_t *item, double value)

Assigns a float value.

Parameters
  • item[borrow]: A double precision float
  • value: The value to assign

Half floats

CBOR supports two bytes wide ("half-precision") floats which are not supported by the C language. libcbor represents them using float <https://en.cppreference.com/w/c/language/type> values throughout the API, which has important implications when manipulating these values.

In particular, if a user uses some of the manipulation APIs (e.g. cbor_set_float2(), cbor_new_float2()) to introduce a value that doesn't have an exect half-float representation, the encoding semantics are given by cbor_encode_half() as follows:

size_t cbor_encode_half(float value, unsigned char *buffer, size_t buffer_size)

Encodes a half-precision float.

Since there is no native representation or semantics for half floats in the language, we use single-precision floats, as every value that can be expressed as a half-float can also be expressed as a float.

This however means that not all floats passed to this function can be unambiguously encoded. The behavior is as follows:.INDENT 7.0

·

Infinity, NaN are preserved

·

Zero is preserved

·

Denormalized numbers keep their sign bit and 10 most significant bit of the significand

·

All other numbers.INDENT 2.0

·

If the logical value of the exponent is < -24, the output is zero

·

If the logical value of the exponent is between -23 and -14, the output is cut off to represent the 'magnitude' of the input, by which we mean (-1)^{signbit} x 1.0e{exponent}. The value in the significand is lost.

·

In all other cases, the sign bit, the exponent, and 10 most significant bits of the significand are kept

Return

number of bytes written

Parameters
  • value:
  • buffer: Target buffer
  • buffer_size: Available space in the buffer
[1]

http://softwareengineering.vazexqi.com/files/pattern.html

Streaming & indefinite items

CBOR strings, byte strings, arrays, and maps can be encoded as indefinite, meaning their length or size is not specified. Instead, they are divided into chunks (strings, byte strings), or explicitly terminated (arrays, maps).

This is one of the most important (and due to poor implementations, underutilized) features of CBOR. It enables low-overhead streaming just about anywhere without dealing with channels or pub/sub mechanism. It is, however, important to recognize that CBOR streaming is not a substitute for  Websockets [1] and similar technologies.

[1]

RFC 6455

Decoding

Another way to decode data using libcbor is to specify a callbacks that will be invoked when upon finding certain items in the input. This service is provided by

struct cbor_decoder_result cbor_stream_decode(cbor_data buffer, size_t buffer_size, const struct cbor_callbacks *callbacks, void *context)

Stateless decoder.

Will try parsing the buffer and will invoke the appropriate callback on success. Decodes one item at a time. No memory allocations occur.

Parameters
  • buffer: Input buffer
  • buffer_size: Length of the buffer
  • callbacks: The callback bundle
  • context: An arbitrary pointer to allow for maintaining context.

To get started, you might want to have a look at the simple streaming example:

#include "cbor.h"
#include <stdio.h>
#include <string.h>

/*
 * Illustrates how one might skim through a map (which is assumed to have
 * string keys and values only), looking for the value of a specific key
 *
 * Use the examples/data/map.cbor input to test this.
 */

const char * key = "a secret key";
bool key_found = false;

void find_string(void * _ctx, cbor_data buffer, size_t len)
{
    if (key_found) {
        printf("Found the value: %*s\n", (int) len, buffer);
        key_found = false;
    } else if (len == strlen(key)) {
        key_found = (memcmp(key, buffer, len) == 0);
    }
}

int main(int argc, char * argv[])
{
    FILE * f = fopen(argv[1], "rb");
    fseek(f, 0, SEEK_END);
    size_t length = (size_t)ftell(f);
    fseek(f, 0, SEEK_SET);
    unsigned char * buffer = malloc(length);
    fread(buffer, length, 1, f);

    struct cbor_callbacks callbacks = cbor_empty_callbacks;
    struct cbor_decoder_result decode_result;
    size_t bytes_read = 0;
    callbacks.string = find_string;
    while (bytes_read < length) {
        decode_result = cbor_stream_decode(buffer + bytes_read,
                                           length - bytes_read,
                                           &callbacks, NULL);
        bytes_read += decode_result.read;
    }

    free(buffer);
    fclose(f);
}

The callbacks are defined by

struct cbor_callbacks

Callback bundle  passed to the decoder.

Public Members

cbor_int8_callback uint8

Unsigned int.

cbor_int16_callback uint16

Unsigned int.

cbor_int32_callback uint32

Unsigned int.

cbor_int64_callback uint64

Unsigned int.

cbor_int64_callback negint64

Negative int.

cbor_int32_callback negint32

Negative int.

cbor_int16_callback negint16

Negative int.

cbor_int8_callback negint8

Negative int.

cbor_simple_callback byte_string_start

Definite byte string.

cbor_string_callback byte_string

Indefinite byte string start.

cbor_string_callback string

Definite string.

cbor_simple_callback string_start

Indefinite string start.

cbor_simple_callback indef_array_start

Definite array.

cbor_collection_callback array_start

Indefinite array.

cbor_simple_callback indef_map_start

Definite map.

cbor_collection_callback map_start

Indefinite map.

cbor_int64_callback tag

Tags.

cbor_float_callback float2

Half float.

cbor_float_callback float4

Single float.

cbor_double_callback float8

Double float.

cbor_simple_callback undefined

Undef.

cbor_simple_callback null

Null.

cbor_bool_callback boolean

Bool.

cbor_simple_callback indef_break

Indefinite item break.

When building custom sets of callbacks, feel free to start from

const struct cbor_callbacks cbor_empty_callbacks

Dummy callback bundle - does nothing.

Callback types definition

typedef void (*cbor_int8_callback)(void*, uint8_t)

Callback prototype.

typedef void (*cbor_int16_callback)(void*, uint16_t)

Callback prototype.

typedef void (*cbor_int32_callback)(void*, uint32_t)

Callback prototype.

typedef void (*cbor_int64_callback)(void*, uint64_t)

Callback prototype.

typedef void (*cbor_simple_callback)(void*)

Callback prototype.

typedef void (*cbor_string_callback)(void*, cbor_data, size_t)

Callback prototype.

typedef void (*cbor_collection_callback)(void*, size_t)

Callback prototype.

typedef void (*cbor_float_callback)(void*, float)

Callback prototype.

typedef void (*cbor_double_callback)(void*, double)

Callback prototype.

typedef void (*cbor_bool_callback)(void*, bool)

Callback prototype.

Encoding

TODO

Tests

Unit tests

There is a comprehensive test suite employing CMocka. You can run all of them using ctest in the build directory. Individual tests are themselves runnable. Please refer to CTest documentation for detailed information on how to specify particular subset of tests.

Testing for memory leaks

Every release is tested for memory correctness. You can run these tests by passing the -T memcheck flag to ctest. [1]

[1]

Project should be configured with -DCMAKE_BUILD_TYPE=Debug to obtain meaningful description of location of the leak. You might also need --dsymutil=yes on OS X.

Code coverage

Every release is inspected using GCOV/LCOV. Platform-independent code should be fully covered by the test suite. Simply run

make coverage

or alternatively run lcov by hand using

lcov --capture --directory . --output-file coverage.info
genhtml coverage.info --output-directory out

Fuzz testing

Every release is tested using a fuzz test. In this test, a huge buffer filled with random data is passed to the decoder. We require that it either succeeds or fail with a sensible error, without leaking any memory. This is intended to simulate real-world situations where data received from the network are CBOR-decoded before any further processing.

RFC conformance

libcbor is, generally speaking, very faithful implementation of RFC 7049. There are, however, some limitations imposed by technical constraints.

Bytestring length

There is no explicit limitation of indefinite length byte strings. [1] libcbor will not handle byte strings with more chunks than the maximum value of size_t. On any sane platform, such string would not fit in the memory anyway. It is, however, possible to process arbitrarily long strings and byte strings using the streaming decoder.

[1]

http://tools.ietf.org/html/rfc7049#section-2.2.2

Half-precision IEEE 754 floats

As of C99 and even C11, there is no standard implementation for 2 bytes floats. libcbor packs them as a float <https://en.cppreference.com/w/c/language/type>. When encoding, libcbor selects the appropriate wire representation based on metadata and the actual value. This applies both to canonical and normal mode.

For more information on half-float serialization, please refer to the section on api_type_7_hard_floats.

Internal mechanics

Internal workings of libcbor are mostly derived from the specification. The purpose of this document is to describe technical choices made during design & implementation and to explicate the reasoning behind those choices.

Terminology

MTBMajor Type Bytehttp://tools.ietf.org/html/rfc7049#section-2.1
DSTDynamically Sized TypeType whose storage requirements cannot be determined

during compilation (originated in the Rust community)

Conventions

API symbols start with cbor_ or CBOR_ prefix, internal symbols have _cbor_ or _CBOR_ prefix.

General notes on the API design

The API design has two main driving priciples:

  1. Let the client manage the memory as much as possible
  2. Behave exactly as specified by the standard

Combining these two principles in practice turns out to be quite difficult. Indefinite-length strings, arrays, and maps require client to handle every fixed-size chunk explicitly in order to

  • ensure the client never runs out of memory due to libcbor
  • use realloc() sparsely and predictably [1]

    • provide strong guarantees about its usage (to prevent latency spikes)
    • provide APIs to avoid realloc() altogether
  • allow proper handling of (streamed) data bigger than available memory
[1]

Reasonable handling of DSTs requires reallocation if the API is to remain sane.

Coding style

This code loosely follows the Linux kernel coding style. Tabs are tabs, and they are 4 characters wide.

Memory layout

CBOR is very dynamic in the sense that it contains many data elements of variable length, sometimes even indefinite length. This section describes internal representation of all CBOR data types.

Generally speaking, data items consist of three parts:

  • a generic handle,
  • the associated metadata,
  • and the actual data
type cbor_item_t

Represents the item. Used as an opaque type

cbor_type type

Type discriminator

size_t refcount

Reference counter. Used by cbor_decref(), cbor_incref()

union cbor_item_metadata metadata

Union discriminated by type. Contains type-specific metadata

unsigned char *data

Contains pointer to the actual data. Small, fixed size items (api/type_0_1, api/type_6, api/type_7) are allocated as a single memory block.

Consider the following snippet

cbor_item_t * item = cbor_new_int8();

then the memory is laid out as follows

+-----------+---------------+---------------+-----------------------------------++-----------+
|           |               |               |                                   ||           |
|   type    |   refcount    |   metadata    |              data                 ||  uint8_t  |
|           |               |               |   (= item + sizeof(cbor_item_t))  ||           |
+-----------+---------------+---------------+-----------------------------------++-----------+
^                                                                                ^
|                                                                                |
+--- item                                                                        +--- item->data

Dynamically sized types (api/type_2, api/type_3, api/type_4, api/type_5) may store handle and data in separate locations. This enables creating large items (e.g byte strings) without realloc() or copying large blocks of memory. One simply attaches the correct pointer to the handle.

type cbor_item_metadata

Union type of the following members, based on the item type:

struct _cbor_int_metadata int_metadata

Used both by both api/type_0_1

struct _cbor_bytestring_metadata bytestring_metadata

struct _cbor_string_metadata string_metadata

struct _cbor_array_metadata array_metadata

struct _cbor_map_metadata map_metadata

struct _cbor_tag_metadata tag_metadata

struct _cbor_float_ctrl_metadata float_ctrl_metadata

Decoding

As outlined in api, there decoding is based on the streaming decoder Essentially, the decoder is a custom set of callbacks for the streaming decoder.

Changelog

Next

0.7.0 (2020-04-25)

0.6.1 (2020-03-26)

  • [Fix bad shared library version number](https://github.com/PJK/libcbor/pull/131)
    • Warning: Shared library built from the 0.6.0 release is erroneously marked as version "0.6.0", which makes it incompatible with future releases including the v0.6.X line even though they may be compatible API/ABI-wise. Refer to the documentation for the new SO versioning scheme.

0.6.0 (2020-03-15)

0.5.0 (2017-02-06)

0.4.0 (2015-12-25)

Breaks build & header compatibility due to:

  • Improved build configuration and feature check macros
  • Endianess configuration fixes (by Erwin Kroon and David Grigsby)
  • pkg-config compatibility (by Vincent Bernat)
  • enable use of versioned SONAME (by Vincent Bernat)
  • better fuzzer (wasn't random until now, ooops)

0.3.1 (2015-05-21)

  • documentation and comments improvements, mostly for the API reference

0.3.0 (2015-05-21)

  • Fixes, polishing, niceties across the code base
  • Updated examples
  • cbor_copy
  • cbor_build_negint8, 16, 32, 64, matching asserts
  • cbor_build_stringn
  • cbor_build_tag
  • cbor_build_float2, ...

0.2.1 (2015-05-17)

  • C99 support

0.2.0 (2015-05-17)

  • cbor_ctrl_bool -> cbor_ctrl_is_bool
  • Added cbor_array_allocated & map equivalent
  • Overhauled endianess conversion - ARM now works as expected
  • 'sort.c' example added
  • Significantly improved and doxyfied documentation

0.1.0 (2015-05-06)

The initial release, yay!

Development

Vision and principles

Consistency and coherence are one of the key characteristics of good software. While the reality is never black and white, it is important libcbor contributors are working towards the same high-level goal. This document attempts to set out the basic principles of libcbor and the rationale behind them. If you are contributing to libcbor or looking to evaluate whether libcbor is the right choice for your project, it might be worthwhile to skim through the section below.

Mission statement

libcbor is the compact, full-featured, and safe CBOR library that works everywhere.

Goals

RFC-conformance and full feature support

Anything the standard allows, libcbor can do.

Why? Because conformance and interoperability is the point of defining standards. Clients expect the support to be feature-complete and there is no significant complexity reduction that can be achieved by slightly cutting corners, which means that the incremental cost of full RFC support is comparatively small over "almost-conformance" seen in many alternatives.

Safety

Untrusted bytes from the network are the typical input.

Why? Because it is the client expectation. Vast majority of security vulnerabilities are violations of contracts -- in other words, bugs -- anyway.

Self-containment

libcbor has no runtime dependencies.

Why? Because any constraint imposed on libcbor has to be enforced transitively, which is difficult and leads to incompatibilities and distribution issues, especially in IoT applications.

Portability

If you can compile C for it, libcbor will work there.

Why? Lowest-common-denominator solution for system-level and IoT software was the original niche of libcbor. Users who rely on libcbor expect future updates to work on their target platform.

Stable and predictable API

libcbor will not break without a warning.

Why? Industry-standard versioning is a basic requirement for production-quality software. This is especially relevant in IoT environments where updates may be costly.

Performance

libcbor is fast and resource-efficient by design

Why? Because the main maintainer is an avid hater of slow bloated software. Who wouldn't want more bang per their electricity buck?

Non-goals

  • Convenience -- libcbor only provides the minimum surface to make it usable
  • FFI/SWIG/interop support -- libcbor is primarily a C library for C clients
  • One-off usecases support -- although there are primitives to reuse, the basic assumption is that most clients want most of CBOR features

Development dependencies

  • CMocka (testing)
  • Python and pip (Sphinx platform)
  • Doxygen
  • Sphinx (documentation)
  • There are some Ruby scripts in misc
  • Valgrind (memory correctness & profiling)
  • GCOV/LCOV (test coverage)
  • clang-format

Installing sphinx

pip install sphinx
pip install sphinx_rtd_theme
pip install breathe
pip install https://github.com/lepture/python-livereload/archive/master.zip
pip install sphinx-autobuild

Further instructions on configuring advanced features can be found at http://read-the-docs.readthedocs.org/en/latest/install.html.

Live preview of docs

cd doc
make livehtml

Set up git hooks

A catch-all git hook that runs clang-format and automatically refreshes the GH pages  contents located in docs can be symlinked:

ln -sf $(pwd)/misc/hooks/pre-commit .git/hooks

Testing and code coverage

Please refer to tests

Author

Pavel Kalvoda

Info

Jan 26, 2021 0.7