Basic Service Example

This sample registers a file store request callback with DXL as part of a "custom" service.

Following the instructions in the Running document, you can register a standalone File Transfer service with the DXL fabric. This example shows how you can, alternatively, add file storage capabilities to your own service — avoiding the need to register a separate, standalone service with the DXL fabric.

The standalone File Transfer service has its own Service Configuration File for managing file storage settings — for example, the root directory under which files are stored. With the "custom" service approach, you pass the desired configuration values directly into the dxlfiletransferservice.requesthandlers.FileStoreRequestCallback instance during construction. If you want to give end users the ability to configure these settings, you could expose them as part of your service's own configuration file.

The sample uses a client application wrapper to send a file via the DXL fabric to the request callback for storage. The progress and result of the file storage operation are displayed to the console.



Modify the example to include the storage directory under which the service should store files sent to it.

For example:

STORAGE_DIR = "C:\\dxl-file-store"

Note that the service would need to have write permissions to the directory which is provided. If the directory does not exist when the service first starts up, the service attempts to create the directory, including any intermediate subdirectories in the path which may not yet exist.


To run this sample execute the sample/basic/ script with the path to the file to be sent to the service as a parameter. For example, to send a file named C:\test.exe to the service, you could run the sample as follows:

python sample/basic/ C:\test.exe

As the file is being sent, a "Percent complete" indicator -- moving from 0% to 100% -- should be updated:

Percent complete: 5%

After the file has been uploaded completely, the response from the service and some summary information for the file store operation should be printed out. For example:

Percent complete: 100%
    "file_id": "7b89f71d-f348-45ee-aef3-4ac2555e92f8",
    "hashes": {
        "sha256": "a2e52129a28feec1ee3f22f5aaf9bdecbb02d51af6da408ace0a2ac2e0365c8b"
    "size": 89579672
Elapsed time (ms): 89546.39649391174

The service stores files under the directory configured for the STORAGE_DIR constant. For example, if the STORAGE_DIR constant were set to C:\\dxl-file-store and the base name of the file supplied as a parameter to the script were test.exe, the file would be stored at the following location:


If a second parameter is passed to the example when run, the extra parameter is used as the name of the subdirectory under which the file should be stored. For example, the following command could be run:

python sample/basic/ C:\test.exe storesub1/storesub2

Assuming the storage directory setting on the server were specified as C:\\dxl-file-store, the file would be stored at the following location:



The majority of the sample code is shown below:

# The topic for the service to respond to
SERVICE_TOPIC = "/file-transfer-sample/basic-service"


# Create the client
with DxlClient(config) as dxl_client:

    # Connect to the fabric
    dxl_client.connect()"Connected to DXL fabric.")

    # Create service registration object
    info = ServiceRegistrationInfo(dxl_client, "myService")

    # Add a topic for the service to respond to
                   FileStoreRequestCallback(dxl_client, STORAGE_DIR))

    # Register the service with the fabric (wait up to 10 seconds for
    # registration to complete)
    dxl_client.register_service_sync(info, 10)

    # Create client wrapper
    file_transfer_client = FileTransferClient(dxl_client, SERVICE_TOPIC)

    start = time.time()

    # Invoke the send file request method to store the file on the server
    resp = file_transfer_client.send_file_request(
            STORE_FILE_DIR, os.path.basename(STORE_FILE_NAME)),

    # Print out the response (convert dictionary to JSON for pretty printing)
        MessageUtils.dict_to_json(resp.to_dict(), pretty_print=True)))

    print("Elapsed time (ms): {}".format((time.time() - start) * 1000))

The value for the SERVICE_TOPIC constant is used as a topic name on the DXL fabric, both for registering a request callback and for file storage requests made from a client.

After connecting to the DXL fabric, a service is registered. The service registration associates an instance of the dxlfiletransferservice.requesthandlers.FileStoreRequestCallback class with the SERVICE_TOPIC. The root directory under which the request callback should store files is supplied to the callback, the STORAGE_DIR constant.

The next step is to create a FileTransferClient, including the SERVICE_TOPIC constant as the name of the topic to use when sending to the DXL fabric the segments of the file to store.

The final step is to invoke the send_file_request method on the FileTransferClient instance. This call sends the file contents to the DXL fabric. As the FileStoreRequestCallback request handler (registered with the DXL fabric above) receives DXL request messages with the file segments, the segments are reassembled into a single file which is stored to the file system.

Assuming the file store operation is successful, the last response from the service is printed to the console output. The response contains a sha256 hash and size of the file bytes which were stored on the server.