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.TH "BSON_RESERVE_BUFFER" "3" "Apr 02, 2024" "1.26.2" "libbson"
.SH SYNOPSIS
.INDENT 0.0
.INDENT 3.5
.sp
.EX
uint8_t *
bson_reserve_buffer (bson_t *bson, uint32_t size);
.EE
.UNINDENT
.UNINDENT
.SH PARAMETERS
.INDENT 0.0
.IP \(bu 2
\fBbson\fP: An initialized \fI\%bson_t\fP\&.
.IP \(bu 2
\fBsize\fP: The length in bytes of the new buffer.
.UNINDENT
.SH DESCRIPTION
.sp
Grow the internal buffer of \fBbson\fP to \fBsize\fP and set the document length to \fBsize\fP\&. Useful for eliminating copies when reading BSON bytes from a stream.
.sp
First, initialize \fBbson\fP with \fI\%bson_init()\fP or \fI\%bson_new()\fP, then call this function. After it returns, the length of \fBbson\fP is set to \fBsize\fP but its contents are uninitialized memory: you must fill the contents with a BSON document of the correct length before any other operations.
.sp
The document must be freed with \fI\%bson_destroy()\fP\&.
.SH RETURNS
.sp
A pointer to the internal buffer, which is at least \fBsize\fP bytes, or NULL if the space could not be allocated.
.SH EXAMPLE
.sp
Use \fBbson_reserve_buffer\fP to write a function that takes a \fI\%bson_t\fP pointer and reads a file into it directly:
.INDENT 0.0
.INDENT 3.5
.sp
.EX
#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 (\(dqCouldn\(aqt get file size\(dq);
      return 1;
   }

   size = ftell (fp);
   if (size == EOF) {
      perror (\(dqCouldn\(aqt get file size\(dq);
      return 1;
   }

   if (size > INT32_MAX) {
      fprintf (stderr, \(dqFile too large\en\(dq);
      return 1;
   }

   /* reserve buffer space \- bson is temporarily invalid */
   buffer = bson_reserve_buffer (bson, (uint32_t) size);
   if (!buffer) {
      fprintf (stderr, \(dqCouldn\(aqt reserve %ld bytes\(dq, size);
      return false;
   }

   /* read file directly into the buffer */
   rewind (fp);
   if (fread ((void *) buffer, 1, (size_t) size, fp) < (size_t) size) {
      perror (\(dqCouldn\(aqt read file\(dq);
      return false;
   }

   return true;
}

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

   /* stack\-allocated, initialized bson_t */
   bson_t bson = BSON_INITIALIZER;

   if (!(fp = fopen (\(dqdocument.bson\(dq, \(dqrb\(dq))) {
      perror (\(dqCouldn\(aqt read file\(dq);
      return 1;
   }

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

   json = bson_as_canonical_extended_json (&bson, NULL);
   printf (\(dq%s\en\(dq, json);

   bson_free (json);
   bson_destroy (&bson);

   return 0;
}
.EE
.UNINDENT
.UNINDENT
.SH AUTHOR
MongoDB, Inc
.SH COPYRIGHT
2017-present, MongoDB, Inc
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