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# JSON

Libbson provides routines for converting to and from the JSON format. In particular, it supports the MongoDB extended JSON format.

## Converting BSON to JSON

There are often times where you might want to convert a BSON document to JSON. It is convenient for debugging as well as an interchange format. To help with this, Libbson contains the functions bson_as_canonical_extended_json() and bson_as_relaxed_extended_json(). The canonical format preserves BSON type information for values that may have ambiguous representations in JSON (e.g. numeric types).

    bson_t *b;
    size_t len;
    char *str;

    b = BCON_NEW ("a", BCON_INT32 (1));

    str = bson_as_canonical_extended_json (b, &len);
    printf ("%s\n", str);
    bson_free (str);

    bson_destroy (b);

    { "a" : { "$numberInt": "1" } }

The relaxed format prefers JSON primitives for numeric values and may be used if type fidelity is not required.

    bson_t *b;
    size_t len;
    char *str;

    b = BCON_NEW ("a", BCON_INT32 (1));

    str = bson_as_relaxed_extended_json (b, &len);
    printf ("%s\n", str);
    bson_free (str);

    bson_destroy (b);

    { "a" : 1 }

## Converting JSON to BSON

Converting back from JSON is also useful and common enough that we added bson_init_from_json() and bson_new_from_json().

The following example creates a new bson_t from the JSON string `{"a":1}`.

    bson_t *b;
    bson_error_t error;

    b = bson_new_from_json ("{\"a\":1}", -1, &error);

    if (!b) {
       printf ("Error: %s\n", error.message);
    } else {
       bson_destroy (b);
    }

## Streaming JSON Parsing

Libbson provides bson_json_reader_t to allow for parsing a sequence of JSON documents into BSON. The interface is similar to bson_reader_t but expects the input to be in the MongoDB extended JSON format.

    /*
     * Copyright 2013 MongoDB, Inc.
     *
     * Licensed under the Apache License, Version 2.0 (the "License");
     * you may not use this file except in compliance with the License.
     * You may obtain a copy of the License at
     *
     *   http://www.apache.org/licenses/LICENSE-2.0
     *
     * Unless required by applicable law or agreed to in writing, software
     * distributed under the License is distributed on an "AS IS" BASIS,
     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     * See the License for the specific language governing permissions and
     * limitations under the License.
     */

    /*
     * This program will print each JSON document contained in the provided files
     * as a BSON string to STDOUT.
     */

    #include <bson/bson.h>
    #include <stdlib.h>
    #include <stdio.h>

    int
    main (int argc, char *argv[])
    {
       bson_json_reader_t *reader;
       bson_error_t error;
       const char *filename;
       bson_t doc = BSON_INITIALIZER;
       int i;
       int b;

       /*
        * Print program usage if no arguments are provided.
        */
       if (argc == 1) {
          fprintf (stderr, "usage: %s FILE...\n", argv[0]);
          return 1;
       }

       /*
        * Process command line arguments expecting each to be a filename.
        */
       for (i = 1; i < argc; i++) {
          filename = argv[i];

          /*
           * Open the filename provided in command line arguments.
           */
          if (0 == strcmp (filename, "-")) {
             reader = bson_json_reader_new_from_fd (STDIN_FILENO, false);
          } else {
             if (!(reader = bson_json_reader_new_from_file (filename, &error))) {
                fprintf (
                   stderr, "Failed to open \"%s\": %s\n", filename, error.message);
                continue;
             }
          }

          /*
           * Convert each incoming document to BSON and print to stdout.
           */
          while ((b = bson_json_reader_read (reader, &doc, &error))) {
             if (b < 0) {
                fprintf (stderr, "Error in json parsing:\n%s\n", error.message);
                abort ();
             }

             if (fwrite (bson_get_data (&doc), 1, doc.len, stdout) != doc.len) {
                fprintf (stderr, "Failed to write to stdout, exiting.\n");
                exit (1);
             }
             bson_reinit (&doc);
          }

          bson_json_reader_destroy (reader);
          bson_destroy (&doc);
       }

       return 0;
    }

## Examples

The following example reads BSON documents from `stdin` and prints them to `stdout` as JSON.

    /*
     * Copyright 2013 MongoDB, Inc.
     *
     * Licensed under the Apache License, Version 2.0 (the "License");
     * you may not use this file except in compliance with the License.
     * You may obtain a copy of the License at
     *
     *   http://www.apache.org/licenses/LICENSE-2.0
     *
     * Unless required by applicable law or agreed to in writing, software
     * distributed under the License is distributed on an "AS IS" BASIS,
     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     * See the License for the specific language governing permissions and
     * limitations under the License.
     */

    /*
     * This program will print each BSON document contained in the provided files
     * as a JSON string to STDOUT.
     */

    #include <bson/bson.h>
    #include <stdio.h>

    int
    main (int argc, char *argv[])
    {
       bson_reader_t *reader;
       const bson_t *b;
       bson_error_t error;
       const char *filename;
       char *str;
       int i;

       /*
        * Print program usage if no arguments are provided.
        */
       if (argc == 1) {
          fprintf (stderr, "usage: %s [FILE | -]...\nUse - for STDIN.\n", argv[0]);
          return 1;
       }

       /*
        * Process command line arguments expecting each to be a filename.
        */
       for (i = 1; i < argc; i++) {
          filename = argv[i];

          if (strcmp (filename, "-") == 0) {
             reader = bson_reader_new_from_fd (STDIN_FILENO, false);
          } else {
             if (!(reader = bson_reader_new_from_file (filename, &error))) {
                fprintf (
                   stderr, "Failed to open \"%s\": %s\n", filename, error.message);
                continue;
             }
          }

          /*
           * Convert each incoming document to JSON and print to stdout.
           */
          while ((b = bson_reader_read (reader, NULL))) {
             str = bson_as_canonical_extended_json (b, NULL);
             fprintf (stdout, "%s\n", str);
             bson_free (str);
          }

          /*
           * Cleanup after our reader, which closes the file descriptor.
           */
          bson_reader_destroy (reader);
       }

       return 0;
    }