# bson_reader_t

## Streaming BSON Document Reader

## Synopsis

    #include <bson.h>

    typedef struct _bson_reader_t bson_reader_t;

    bson_reader_t *bson_reader_new_from_handle (void *handle,
                                                bson_reader_read_func_t rf,
                                                bson_reader_destroy_func_t df);
    bson_reader_t *bson_reader_new_from_fd     (int fd,
                                                bool close_on_destroy);
    bson_reader_t *bson_reader_new_from_file   (const char *path,
                                                bson_error_t *error);
    bson_reader_t *bson_reader_new_from_data   (const uint8_t *data,
                                                size_t length);

    void           bson_reader_destroy         (bson_reader_t *reader);

## Description

bson_reader_t is a structure used for reading a sequence of BSON documents. The sequence can come from a file-descriptor, memory region, or custom callbacks.

## Example

### Convert a Sequence of BSON documents to 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.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_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;
    }