oracular (3) bson_reserve_buffer.3.gz

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. 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 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/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

       2017-present, MongoDB, Inc