Wrong PixelFormat if Server only Supports 8bit

[kieferei]

I am using noVnc 1.5.0. The VNC Server is inside a B&R PLC.

The VNC Server send the following information:

websock.js:304 >> WebSock.onopen
rfb.js:703 Starting VNC handshake
websock.js:309 << WebSock.onopen
rfb.js:1446 Server ProtocolVersion: 003.003
rfb.js:1487 Sent ProtocolVersion: 003.003
rfb.js:1551 Authenticating using scheme: 1
rfb.js:2182 Screen: 1024x768, bpp: 8, depth: 8, bigEndian: 0, trueColor: 0, redMax: 7, greenMax: 7, blueMax: 3, redShift: 0, greenShift: 3, blueShift: 6
display.js:150 Setting viewport to full display region

Based on this information noVnc is setting Pixelformat to the Server.
I didn't recive any Display data.

I see a "unknown pixelformat"-Error in the logging of the B&R PLC.

Suggestion:
When I look at the code (rfb.js line 2190) I see:

  this._fbDepth = 24;
  if (this._fbName === "Intel(r) AMT KVM") {
    Log.Warn("Intel AMT KVM only supports 8/16 bit depths. Using low color mode.");
    this._fbDepth = 8;
  }
  RFB.messages.pixelFormat(this._sock, this._fbDepth, true);

In my understanding it should be:

  this._fbDepth = depth

because than the pixelFormat is calculated based on the values from the server.

[CendioOssman]

Pixel format in VNC is ultimately decided by the client. It is unfortunately common with embedded VNC servers being buggy and not handling this correctly. It sounds like this is the case here.

As you can see, there is a hacky workaround for some Intel chips there. It might be possible to do the same for your B&R PLC, but only if there is a reliable way to detect them. The VNC protocol generally doesn't send over any identification info.

Have you contacted B&R about this and see what they have to say?