Serving Files and Directories
-----------------------------

Build with ``UA_BUILD_EXAMPLES``, Method calls and a reduced or full
Namespace Zero.
This example serves a local directory and a separate read-only file through
the OPC UA Part 20 Methods.

Create a backend, construct its driver, then register it with the server.
Registration starts the driver if the server is already running; otherwise
it starts with the server. Shutdown stops drivers; deleting the server
frees them. For parameters and backend callbacks, see
:doc:`driver_file_transfer`. A custom in-memory backend is shown in
``examples/filetransfer/server_filetransfer_custom_backend.c``.

Serving a local directory
^^^^^^^^^^^^^^^^^^^^^^^^^

The default root Object is named "FileSystem". Its entries are mirrored on
start and refreshed periodically. Client Methods operate on storage directly.

.. code-block:: c

   
   static UA_StatusCode
   mountLocalDirectory(UA_Server *server, const char *rootPath) {
       UA_FileTransferBackend backend;
       UA_StatusCode res =
           UA_FileTransferBackend_localDirectory(UA_STRING((char*)(uintptr_t)rootPath),
                                                  &backend);
       if(res != UA_STATUSCODE_GOOD)
           return res;
   
       UA_Driver *ftd = NULL;
       res = UA_FileTransferDriver_newDirectory(server, &backend, NULL, NULL, &ftd);
       if(res != UA_STATUSCODE_GOOD) {
           backend.file.clear(&backend.file);
           return res;
       }
       res = UA_Server_addDriver(server, ftd);
       if(res != UA_STATUSCODE_GOOD)
           ftd->free(ftd);
       return res;
   }
   
Exposing a single file
^^^^^^^^^^^^^^^^^^^^^^

Individual files (a configuration file, a manual, a log) can be exposed as
standalone FileType Objects without mirroring a whole directory. Here the
file is served read-only: the Writable/UserWritable Properties are false
and opening the file for writing fails.

.. code-block:: c

   
   static UA_StatusCode
   addReadOnlyFile(UA_Server *server, const char *rootPath) {
       char filePath[512];
       int length = snprintf(filePath, sizeof(filePath), "%s/readme.txt", rootPath);
       if(length < 0 || (size_t)length >= sizeof(filePath))
           return UA_STATUSCODE_BADINVALIDARGUMENT;
       UA_FileTransferFileBackend backend;
       UA_StatusCode res =
           UA_FileTransferFileBackend_localFile(UA_STRING(filePath), &backend);
       if(res != UA_STATUSCODE_GOOD)
           return res;
   
       UA_Driver *ftd = NULL;
       UA_FileTransferNodeDescription description;
       memset(&description, 0, sizeof(description));
       description.browseName = UA_QUALIFIEDNAME(1, "ReadMe");
       res = UA_FileTransferDriver_newFile(server, &backend, UA_STRING_NULL,
                                          &description, NULL, &ftd);
       if(res != UA_STATUSCODE_GOOD) {
           backend.clear(&backend);
           return res;
       }
       /* Configure the driver before adding it: registration starts it immediately
        * when the server is already running. */
       UA_Boolean readOnly = true;
       res = UA_KeyValueMap_setScalar(&ftd->params, UA_QUALIFIEDNAME(0, "read-only"),
                                      &readOnly, &UA_TYPES[UA_TYPES_BOOLEAN]);
       if(res == UA_STATUSCODE_GOOD)
           res = UA_Server_addDriver(server, ftd);
       if(res != UA_STATUSCODE_GOOD)
           ftd->free(ftd);
       return res;
   }
   
   /* Prepare the served directory with demo content */
   static void
   prepareDemoDirectory(const char *rootPath) {