App service desktop bridge for Edge native messaging does not work

Question

I am developing native messaging between a WebExtension in Edge and a desktop app. But the communication with the desktop app via desktopBridge does not work. In the code below, the message box Success is shown, but not the message box Test.

AppServiceResponse desktopBridgeResponse = await this.desktopBridgeConnection.SendMessageAsync(testValueSet); runs into the exception "Object reference not set to an instance of an object".

// AppService.cs
public async void Run(IBackgroundTaskInstance taskInstance)
{
    if (appService.CallerPackageFamilyName == "Microsoft.MicrosoftEdge_8wekyb3d8bbwe") // App service connection from Edge
    {
        appServiceconnection = details.AppServiceConnection;
        appServiceconnection.RequestReceived += OnRequestReceived;

        try
        {
            // Make sure the DesktopApp.exe is in your AppX folder, if not rebuild the solution
            await Windows.ApplicationModel.FullTrustProcessLauncher.LaunchFullTrustProcessForCurrentAppAsync();
        }
        catch (Exception)
        {
            MessageDialog dialog = new MessageDialog("Rebuild the solution and make sure the DesktopApp.exe is in your AppX folder");
            await dialog.ShowAsync();
        }
    }
    else (appService.CallerPackageFamilyName == Windows.ApplicationModel.Package.Current.Id.FamilyName) // App service connection from desktopBridge App
    {
        desktopBridgeConnection = details.AppServiceConnection;
    }
}

private async void OnRequestReceived(AppServiceConnection sender, AppServiceRequestReceivedEventArgs args)
{
    try
    {
        AppServiceResponse desktopBridgeResponse = await this.desktopBridgeConnection.SendMessageAsync(testValueSet);
    }
    catch (Exception e)
    {
        var errorMessage = e.Message;
    }
}

// DesktopApp.cs
[STAThread]
static void Main()
{
    Thread appServiceThread = new Thread(new ThreadStart(InitializeAppServiceConnection));
    appServiceThread.Start();
    Application.Run();
}

static async void InitializeAppServiceConnection()
{
    connection = new AppServiceConnection();
    connection.AppServiceName = "example";
    connection.PackageFamilyName = Package.Current.Id.FamilyName;
    connection.RequestReceived += Connection_RequestReceived;

    AppServiceConnectionStatus status = await connection.OpenAsync();
    if (status != AppServiceConnectionStatus.Success)
    {
        // something went wrong ...
        MessageBox.Show(status.ToString());
    }
    else
    {
        MessageBox.Show("Success");
    }
}

private static void Connection_RequestReceived(AppServiceConnection sender, AppServiceRequestReceivedEventArgs args)
{
    MessageBox.Show("Test");

    string key = args.Request.Message.First().Key;
    string value = args.Request.Message.First().Value.ToString();

}

According to Secure Input it should work.

Why is Connection_RequestReceived() not entered, although the connection to the app service has been established successfully?

Any help will be appreciated, thanks!

Update: Through debugging I found the following out: When the app service receives a message from Edge, the Run() method runs into the "Edge connection branch". Next, OnRequestReceived() is executed in which a message is sent to desktopBridge await this.desktopBridgeConnection.SendMessageAsync(testValueSet), but this failes. Then, Run() is executed again and runs into the "DesktopBridge connection branch". At this point, the desktopBridgeConnection is defined, but it is too late.

I need to define desktopBridgeConnection before OnRequestReceived() is entered so that I can use it within OnRequestReceived(). But I don't know how to implement this.

I suggest you to close your solution in Visual Studio. Try to move your project folder to trusted location. Again try to open the solution from trusted location. make sure all the projects in the solution are loaded. Than try to run the solution to check whether it runs successfully or not. — Deepak-MSFT
@Deepak-MSFT Can you explain what exactly a trusted location is? How can I determine if a folder is a trusted location? Can I define the folder where my project currently resides as a trusted location so that I don't need to move it? When I search for it, I only find something about trusted locations in context with Microsoft Office applications. — Ronquam
@Deepak-MSFT In Visual Studio under Tools -> Options... -> Environment -> Trust Settings are no trusted paths listed. File and folder trust settings are both set to No verification. Do you mean this setting? — Ronquam
Yes, I was talking about this option. Actually, If you are using an API or invoking methods that may return null then this error can occur. So you can try to debug your code to check what cause this issue. — Deepak-MSFT
@Deepak-MSFT I added the parent directory of the .sln and the path to DesktopApp.exe to the list of trusted paths but the problem remains. I cannot debug DesktopApp.exe in VS because breakpoints will not be hit. This is the reason why I use the MessageBoxes there. Any other suggestions? — Ronquam

AliShahi AliShahi · Accepted Answer · 2019-10-24T09:01:56

You need to move the code that launches the fulltrust process inside OnRequestRecived() and wait for the launched process to connect via the AppServiceConnection. Then send the command to the launched process and get the response and send it back to the page.

Please see my question and the solution I devised here.

Essentially, I use a non-persistent connection. So, you need to remove all the code for connect/disconnect from content.js and background.js. This makes it a sessionless "synchronous" call all the way down and back.

And good luck!

App service desktop bridge for Edge native messaging does not work

1 Answers