bson_reserve_buffer man page

bson_reserve_buffer() — Grow the internal buffer of bson to size and set the document length to size. Useful for eliminating copies when reading BSON bytes from a stream.

Synopsis

uint8_t *
bson_reserve_buffer (bson_t   *bson,
                     uint32_t  size);

Parameters

bson
An initialized bson_t
size
The length in bytes of the new buffer.

Description

Grow the internal buffer of bson to size and set the document length to size

First, initialize bson with bson_init or bson_new , then call this function. After it returns, the length of bson is set to size but its contents are uninitialized memory: you must fill the contents with a BSON document of the correct length before any other operations.

The document must be freed with bson_destroy

Returns

A pointer to the internal buffer, which is at least size bytes, or NULL if the space could not be allocated.

Example

Use bson_reserve_buffer to write a function that takes a bson_t pointer and reads a file into it directly:

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

bool
read_into (bson_t   *bson,
           FILE     *fp)
{
   uint8_t *buffer;
   long size;

   if (fseek(fp, 0L, SEEK_END) < 0) {
      perror ("Couldn't get file size");
      return 1;
   }

   size = ftell (fp);
   if (size == EOF) {
      perror ("Couldn't get file size");
      return 1;
   }

   if (size > INT32_MAX) {
      fprintf (stderr, "File too large\n");
      return 1;
   }

   /* reserve buffer space ‐ bson is temporarily invalid */
   buffer = bson_reserve_buffer (bson, (uint32_t) size);
   if (!buffer) {
      fprintf (stderr, "Couldn't reserve %ld bytes", size);
      return false;
   }

   /* read file directly into the buffer */
   rewind(fp);
   if (fread ((void *) buffer, 1, (size_t) size, fp) < (size_t) size) {
      perror ("Couldn't read file");
      return false;
   }

   return true;
}

int
main ()
{
   FILE *fp;
   char *json;

   /* stack‐allocated, initialized bson_t */
   bson_t bson = BSON_INITIALIZER;

   if (!(fp = fopen ("document.bson", "rb"))) {
      perror ("Couldn't read file");
      return 1;
   }

   read_into (&bson, fp);
   fclose (fp);

   json = bson_as_json (&bson, NULL);
   printf ("%s\n", json);

   bson_free (json);
   bson_destroy (&bson);

   return 0;
}

See also bson_steal and bson_destroy_with_steal

Colophon

This page is part of libbson. Please report any bugs at https://jira.mongodb.org/browse/CDRIVER.

Info

2016‐11‐12 libbson