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BSON_RESERVE_BUFFER(3)		    libbson		BSON_RESERVE_BUFFER(3)

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.

1.30.2				 Apr 12, 2025		BSON_RESERVE_BUFFER(3)

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