naps2.sdk - problem with scanner in citrix environment

[tobiasoehler]

Describe the bug

I have tried to access a scanner via redirected Twain in Citrix using the NAPS2.Sdk and the examples. However, the process hangs and the scanner is then blocked via Twain.

Logging in first Scan:

Scanning with ScanDevice { Driver = Twain, ID = PaperStream IP SP-1125, Name = PaperStream IP SP-1125 }
Scan source: Duplex; bit depth: Color; dpi: 150; page size: 8.5x11 in
Using TWAIN DSM: C:\WINDOWS\twain_32.dll
NAPS2.TW - Opening session
NAPS2.TW - StateChanged (to 3)
NAPS2.TW - Finding source
NAPS2.TW - Opening source
NAPS2.TW - Name: PaperStream IP SP-1125; Manu: FUJITSU; Family: PaperStr; Version: 3.32 3.32.0.1361 Apr 23 2024; Protocol: 2.4
NAPS2.TW - StateChanged (to 4)
NAPS2.TW - Configuring source
NAPS2.TW - Enabling source
NAPS2.TW - StateChanged (to 5)

-> from here it does not go any further - it hangs

Logging in second Scan:

Scanning with ScanDevice { Driver = Twain, ID = PaperStream IP SP-1125, Name = PaperStream IP SP-1125 }
Scan source: Duplex; bit depth: Color; dpi: 150; page size: 8.5x11 in
Using TWAIN DSM: C:\WINDOWS\twain_32.dll
NAPS2.TW - Opening session
NAPS2.TW - StateChanged (to 3)
NAPS2.TW - Finding source
NAPS2.TW - Opening source
NAPS2.TW - Name: PaperStream IP SP-1125; Manu: FUJITSU; Family: PaperStr; Version: 3.32 3.32.0.1361 Apr 23 2024; Protocol: 2.4
NAPS2.TW - Finishing with error
Error: NAPS2.Scan.Exceptions.DeviceException: TWAIN error: MaxConnections

• OS: Laptop with Windows 10 accessing Window Server 2019 via Citrix and redirected Twain

Additional context

When using the Naps2 console application and the Naps2 exe, the scanner works without any problems.

[cyanfish]

Can you attach the debuglog from the NAPS2 exe for comparison?

Are you scanning using the worker (NAPS2.Sdk.Worker.Win32) or by running your main process as 32-bit? (You can also try the other to see if it makes a difference.)

[tobiasoehler]

The debug log is attached.
debuglog.txt

We have tried both. Both reacted in the same way.

[rothtobi]

Tobias is a colleague of mine, we can do a remote session together under a Citrix session to analyze/fix the bug.
Feel free to contact Tobias Oehler or me directly.

[cyanfish]

A couple more things you could try to narrow down the difference between the SDK and the NAPS2 application:

1. In the NAPS2 application, in your profile settings, under Advanced, under Twain Implementation, select "Old DSM". See if that causes any problems.
2. In your SDK project, try setting ScanOptions.DialogParent to a valid window handle (e.g. if you can run it as a WinForms application, then set it to form.Handle). See if that helps.

[tobiasoehler]

I apologize for my late response. “Old DSM” works without problems in NAPS2. If I start a Windows Forms application and call controller.Scan(options) with the option DialogParent = form.Handle I get the error message “This can only be created on the Windows Forms UI thread”.

[cyanfish]

Yes, you'll need to call form.Handle somewhere on the UI thread (e.g. in your form's Load or Shown event).

[tobiasoehler]

Sorry for my stupid questions. But unfortunately I'm not very familiar with Windows Forms. When starting the application, I registered the load event to get the handle.

form.Load += (object sender, System.EventArgs e) => {
    formHandle = form.Handle;
};

Then I click on a button to load the scanner and scan as in the example. I have tried both, using an async method and also invoking it.

Example async button click:

private async void button1_Click(object sender, EventArgs e)
{
    using var scanningContext = new ScanningContext(new GdiImageContext());
    var controller = new ScanController(scanningContext);

    ScanDevice device = (await controller.GetDeviceList(Driver.Twain)).First();

    var options = new ScanOptions
    {
        Device = device,
        DialogParent = Program.formHandle
    };

    await foreach (var image in controller.Scan(options))
    {
        MessageBox.Show("Scanned a page!");
    }
}

Example Invoke:

private void button1_Click(object sender, EventArgs e)
{
    this.Invoke(async () =>
    {
        using var scanningContext = new ScanningContext(new GdiImageContext());
        var controller = new ScanController(scanningContext);

        ScanDevice device = (await controller.GetDeviceList(Driver.Twain)).First();

        var options = new ScanOptions
        {
            Device = device,
            DialogParent = Program.formHandle
        };

        await foreach (var image in controller.Scan(options))
        {
            MessageBox.Show("Scanned a page!");
        }
    });
}

But in both cases I get the error message “This can only be created on the Windows Forms UI thread”.