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Streaming BSON

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  • Reading from a BSON Stream
  • Writing a Sequence of BSON Documents

bson_reader_t provides a streaming reader which can be initialized with a filedescriptor or memory region. bson_writer_t provides a streaming writer which can be initialized with a memory region. (Streaming BSON to a file descriptor is not yet supported.)

Reading from a BSON Stream

bson_reader_t provides a convenient API to read sequential BSON documents from a file-descriptor or memory buffer. The bson_reader_read function will read forward in the underlying stream and return a bson_t that can be inspected and iterated upon.

#include <stdio.h>
#include <bson/bson.h>
int
main (int argc, char *argv[])
{
  bson_reader_t *reader;
  const bson_t *doc;
  bson_error_t error;
  bool eof;
  reader = bson_reader_new_from_file ("mycollection.bson", &error);
  if (!reader) {
     fprintf (stderr, "Failed to open file.\n");
     return 1;
  }
  while ((doc = bson_reader_read (reader, &eof))) {
     char *str = bson_as_canonical_extended_json (doc, NULL);
     printf ("%s\n", str);
     bson_free (str);
  }
  if (!eof) {
     fprintf (stderr,
              "corrupted bson document found at %u\n",
              (unsigned) bson_reader_tell (reader));
  }
  bson_reader_destroy (reader);
  return 0;
}

See bson_reader_new_from_fd, bson_reader_new_from_file, and bson_reader_new_from_data for more information.

Writing a Sequence of BSON Documents

bson_writer_t provides a convenient API to write a sequence of BSON documents to a memory buffer that can grow with realloc(). The bson_writer_begin and bson_writer_end functions will manage the underlying buffer while building the sequence of documents.

This could also be useful if you want to write to a network packet while serializing the documents from a higher level language, (but do so just after the packets header).

#include <stdio.h>
#include <bson/bson.h>
#include <assert.h>
int
main (int argc, char *argv[])
{
  bson_writer_t *writer;
  bson_t *doc;
  uint8_t *buf = NULL;
  size_t buflen = 0;
  bool r;
  int i;
  writer = bson_writer_new (&buf, &buflen, 0, bson_realloc_ctx, NULL);
  for (i = 0; i < 10000; i++) {
     r = bson_writer_begin (writer, &doc);
     assert (r);
     r = BSON_APPEND_INT32 (doc, "i", i);
     assert (r);
     bson_writer_end (writer);
  }
  bson_free (buf);
  return 0;
}

See bson_writer_new for more information.

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