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Support for WPD infrastructure (WpdServiceSampleDriverSample)

The WPD infrastructure is command driven. When a WPD application calls one of the methods in a given interface, the WPD serializer (an in-process COM server) converts the method call into one or more commands that it sends to the driver. The driver, in turn, processes these commands and then returns a response. For more information about the infrastructure, see the Architecture Overview topic.

The following image of the WpdMon.exe tool shows the result of an application calling the IPortableDeviceServiceMethods::Invoke method to invoke the BeginSync method that is supported by the sample driver:

the wpd monitor.

In the previous image, the WPD serializer converted the Invoke call into the WPD_COMMAND_SERVICE_METHODS_START_INVOKE command and the corresponding parameters. The driver processed this command and issued two responses to the WPD API. The first response is the result of WPD_COMMAND_SERVICE_METHODS_START_INVOKE to indicate that the StartInvokecommand was successful and that the method started running on the device. The second response is the WPD_EVENT_SERVICE_METHOD_COMPLETE event that the driver sent when the method completed. The driver sent WPD_EVENT_SERVICE_METHOD_COMPLETE so that the WPD API could perform the necessary method completion and cleanup. For the sample driver, the two responses followed immediately with no time delay; on an actual device, there can be a delay between the two responses, if a method takes a long time to complete.

The WPD_COMMAND_SERVICE_METHODS_START_INVOKE command is first handled in the WpdService::DispatchWpdMessage method. This method, in turn, invokes the WpdServiceMethod::OnStartInvoke method. The first method is found in the file WpdService.cpp; the second is found in the file WpdServiceMethod.cpp.

The following excerpt from the WpdService::DispatchWpdMessage method in WpdService.cpp shows the call to the WpdServiceMethod::OnStartInvoke handler. The DispatchWpdMessage method passes the command parameters to the handler. These command parameters consist of a pointer to the parameters for the Invoke method as well as a pointer to the pResults variable that receives the method results:

HRESULT WpdService::DispatchWpdMessage(
            REFPROPERTYKEY         Command,
    __in    IPortableDeviceValues* pParams,
    __out   IPortableDeviceValues* pResults)
{
    HRESULT     hr                  = S_OK;
    LPWSTR      pszRequestFilename  = NULL;

    // Get the request filename to process the service message
    hr = pParams->GetStringValue(PRIVATE_SAMPLE_DRIVER_REQUEST_FILENAME, &pszRequestFilename);
    if (FAILED(hr))
    {
        hr = E_INVALIDARG;
        CHECK_HR(hr, "Failed to get the required requested filename");
    }

    if (hr == S_OK)
    {    
        hr = CheckRequestFilename(pszRequestFilename);
        CHECK_HR(hr, "Unknown request filename %ws received", pszRequestFilename);
    }

    if (hr == S_OK)
    {
     …
        else if (IsEqualPropertyKey(Command, WPD_COMMAND_SERVICE_METHODS_START_INVOKE))
        {
            hr = m_ServiceMethods.OnStartInvoke(pParams, pResults);
        }
        …
    return hr;
}

The WpdServiceSampleDriverSample

The WPD Driver Samples

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