BSON_RESERVE_BUFFER(3)

BSON_RESERVE_BUFFER(3) 💅✨

okay bestie, this is the libbson page for bson_reserve_buffer() — and it’s honestly kind of a niche little icon, so let’s get into it 🫶

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✨ SYNOPSIS ✨

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

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🎀 PARAMETERS 🎀

• bson — an initialized bson_t. 💖
• total_size — the length in bytes of the new buffer. Must be at least 5 (the size of an empty BSON document). ✨

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🌸 DESCRIPTION 🌸

Grow the internal buffer of bson to total_size and set the document length to total_size. It’s 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.

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💖 RETURNS 💖

A pointer to the internal buffer, which is at least total_size bytes, or NULL if total_size is less than 5 or the space could not be allocated. 💀

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🦋 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;
}

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👑 AUTHOR 👑

MongoDB, Inc

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📜 COPYRIGHT 📜

2009-present, MongoDB, Inc.

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okay that’s the whole page, bestie 💖 this one came from libbson 2.5.6, dated Oct 09, 2026 — mwah 🎀🫶