SYNOPSIS

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

PARAMETERS

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

DESCRIPTION

Grow the internal buffer of bson to total_size and set the document length to total_size. Useful for eliminating copies when reading BSON bytes from a stream.

First, initialize bson with bson_init() or bson_new(), then call this function. After it returns, the length of bson is set to total_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().

Note that, in this usage, the BSON header and footer bytes will not be verified or used by Libbson. The bson_t document length and buffer size limit are both set to total_size regardless of the value encoded in the document header.

RETURNS

A pointer to the internal buffer, which is at least total_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/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_canonical_extended_json (&bson, NULL);


   printf ("%s\n", json);


   bson_free (json);


   bson_destroy (&bson);


   return 0;
}

AUTHOR

MongoDB, Inc

COPYRIGHT

2009-present, MongoDB, Inc.