bionic (3) mongoc_gridfs_t.3.gz

NAME

       mongoc_gridfs_t - mongoc_gridfs_t

SYNOPSIS

          #include <mongoc.h>

          typedef struct _mongoc_gridfs_t mongoc_gridfs_t;

DESCRIPTION

       mongoc_gridfs_t  provides  a  MongoDB  gridfs  implementation. The system as a whole is made up of gridfs
       objects, which contain gridfs_files and gridfs_file_lists.  Essentially, a basic file system API.

       There are extensive caveats about the kind of use cases gridfs  is  practical  for.  In  particular,  any
       writing  after  initial  file  creation  is  likely  to  both  break  any concurrent readers and be quite
       expensive. That said, this implementation does allow for arbitrary writes to existing gridfs object, just
       use them with caution.

       mongoc_gridfs  also  integrates  tightly  with  the  mongoc_stream_t  abstraction,  which  provides  some
       convenient wrapping for file creation and reading/writing.  It can be used without, but its worth looking
       to see if your problem can fit that model.

       WARNING:
          mongoc_gridfs_t  does not support read preferences. In a replica set, GridFS queries are always routed
          to the primary.

THREAD SAFETY

       mongoc_gridfs_t is  NOT  thread-safe  and  should  only  be  used  in  the  same  thread  as  the  owning
       mongoc_client_t.

LIFECYCLE

       It is an error to free a mongoc_gridfs_t before freeing all related instances of mongoc_gridfs_file_t and
       mongoc_gridfs_file_list_t.

EXAMPLE

       example-gridfs.c.INDENT 0.0

          #include <assert.h>
          #include <mongoc.h>
          #include <stdio.h>
          #include <stdlib.h>
          #include <fcntl.h>

          int
          main (int argc, char *argv[])
          {
             mongoc_gridfs_t *gridfs;
             mongoc_gridfs_file_t *file;
             mongoc_gridfs_file_list_t *list;
             mongoc_gridfs_file_opt_t opt = {0};
             mongoc_client_t *client;
             mongoc_stream_t *stream;
             bson_t filter;
             bson_t opts;
             bson_t child;
             bson_error_t error;
             ssize_t r;
             char buf[4096];
             mongoc_iovec_t iov;
             const char *filename;
             const char *command;
             bson_value_t id;

             if (argc < 2) {
                fprintf (stderr, "usage - %s command ...\n", argv[0]);
                return 1;
             }

             mongoc_init ();

             iov.iov_base = (void *) buf;
             iov.iov_len = sizeof buf;

             /* connect to localhost client */
             client =
                mongoc_client_new ("mongodb://127.0.0.1:27017/?appname=gridfs-example");
             assert (client);
             mongoc_client_set_error_api (client, 2);

             /* grab a gridfs handle in test prefixed by fs */
             gridfs = mongoc_client_get_gridfs (client, "test", "fs", &error);
             assert (gridfs);

             command = argv[1];
             filename = argv[2];

             if (strcmp (command, "read") == 0) {
                if (argc != 3) {
                   fprintf (stderr, "usage - %s read filename\n", argv[0]);
                   return 1;
                }
                file = mongoc_gridfs_find_one_by_filename (gridfs, filename, &error);
                assert (file);

                stream = mongoc_stream_gridfs_new (file);
                assert (stream);

                for (;;) {
                   r = mongoc_stream_readv (stream, &iov, 1, -1, 0);

                   assert (r >= 0);

                   if (r == 0) {
                      break;
                   }

                   if (fwrite (iov.iov_base, 1, r, stdout) != r) {
                      MONGOC_ERROR ("Failed to write to stdout. Exiting.\n");
                      exit (1);
                   }
                }

                mongoc_stream_destroy (stream);
                mongoc_gridfs_file_destroy (file);
             } else if (strcmp (command, "list") == 0) {
                bson_init (&filter);

                bson_init (&opts);
                bson_append_document_begin (&opts, "sort", -1, &child);
                BSON_APPEND_INT32 (&child, "filename", 1);
                bson_append_document_end (&opts, &child);

                list = mongoc_gridfs_find_with_opts (gridfs, &filter, &opts);

                bson_destroy (&filter);
                bson_destroy (&opts);

                while ((file = mongoc_gridfs_file_list_next (list))) {
                   const char *name = mongoc_gridfs_file_get_filename (file);
                   printf ("%s\n", name ? name : "?");

                   mongoc_gridfs_file_destroy (file);
                }

                mongoc_gridfs_file_list_destroy (list);
             } else if (strcmp (command, "write") == 0) {
                if (argc != 4) {
                   fprintf (stderr, "usage - %s write filename input_file\n", argv[0]);
                   return 1;
                }

                stream = mongoc_stream_file_new_for_path (argv[3], O_RDONLY, 0);
                assert (stream);

                opt.filename = filename;

                /* the driver generates a file_id for you */
                file = mongoc_gridfs_create_file_from_stream (gridfs, stream, &opt);
                assert (file);

                id.value_type = BSON_TYPE_INT32;
                id.value.v_int32 = 1;

                /* optional: the following method specifies a file_id of any
                   BSON type */
                if (!mongoc_gridfs_file_set_id (file, &id, &error)) {
                   fprintf (stderr, "%s\n", error.message);
                   return 1;
                }

                mongoc_gridfs_file_save (file);
                mongoc_gridfs_file_destroy (file);
             } else {
                fprintf (stderr, "Unknown command");
                return 1;
             }

             mongoc_gridfs_destroy (gridfs);
             mongoc_client_destroy (client);

             mongoc_cleanup ();

             return 0;
          }

AUTHOR

       MongoDB, Inc

COPYRIGHT

       2018, MongoDB, Inc