Connection probems with RealVNC Server 6.7.2

[Martin Schneckenreiter]

Hi there,

I am using noVNC already on Raspberry 3 devices with websockify as websocket proxy. All devices work like a charm.

But now I installed it on a Raspberry 4 device with a RealVNC Server 6.7.2.

Connection and password prompt is working. Also Websocket-Connection is established, but after ~13 data packages (each 12kb size), I get following message in my console:

Failed while connected: Error decoding rect: Error: Illegal hextile subencoding (subencoding: 94)

_fail @ rfb.js:808

_handleDataRect @ rfb.js:2473

_handleRect @ rfb.js:2208

_framebufferUpdate @ rfb.js:2160

_normalMsg @ rfb.js:2076

_handleMessage @ rfb.js:847

(anonymous) @ rfb.js:236

_recvMessage @ websock.js:283

websock.js:214 Closing WebSocket connection

websock.js:185 WebSocket connection to 'ws://10.0.0.60:6080/websockify' failed: Received a broken close frame containing a reserved status code.

open @ websock.js:185

_connect @ rfb.js:511

_updateConnectionState @ rfb.js:773

rfb.js:282 WebSocket on-error event

Any ideas?

Thanks.

[Pierre Ossman]

On 21/10/2020 23:56, 'Martin Schneckenreiter' via noVNC wrote:
> Hi there,
>
> I am using noVNC already on Raspberry 3 devices with websockify as
> websocket proxy. All devices work like a charm.
>
> But now I installed it on a Raspberry 4 device with a RealVNC Server 6.7.2.
>
> Connection and password prompt is working. Also Websocket-Connection is
> established, but after ~13 data packages (each 12kb size), I get following
> message in my console:
>
> Failed while connected: Error decoding rect: Error: Illegal hextile
> subencoding (subencoding: 94)

This indicates a bug in either noVNC or RealVNC. Do you think you can
get a network recording of this so we can see what might be broken?

Regards
--
Pierre Ossman Software Development
Cendio AB https://cendio.com
Teknikringen 8 https://twitter.com/ThinLinc
583 30 Linköping https://facebook.com/ThinLinc
Phone: +46-13-214600

A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?

[Martin Schneckenreiter]

Hi there,

thanks for your quick response. Please find websocket traffic via following link:
https://drive.google.com/file/d/12GqD3dp1M2h3T7PId3nZ-LOxLI293tGB/view?usp=sharing

I also setup a test device in a separate vlan, which is accessible via internet. If you like, I can send you url and password via email.

Thanks for your support.

Regards

[Pierre Ossman]

On 22/10/2020 21:18, 'Martin Schneckenreiter' via noVNC wrote:
> Hi there,
>

> thanks for your quick response. Please find websocket traffic via following
> link:
> https://drive.google.com/file/d/12GqD3dp1M2h3T7PId3nZ-LOxLI293tGB/view?usp=sharing
>

Unfortunately that didn't save the WebSocket traffic. Do you think you
could run something like tcpdump or wireshark? Or if you are using
websockify then you can use its record option.

[Martin Schneckenreiter]

Hi there,

I captured tcp traffic with tcpdump in pcap format (so it should be readable by Wireshark):

https://drive.google.com/file/d/13loB-OMEtMZ7CctuKytMBIhw-esuMaxw/view?usp=sharing

Just let me know, if you need further details.

Thank you

[Pierre Ossman]

On 25/10/2020 18:51, 'Martin Schneckenreiter' via noVNC wrote:
> Hi there,
>

> I captured tcp traffic with tcpdump in pcap format (so it should be
> readable by Wireshark):
> https://drive.google.com/file/d/13loB-OMEtMZ7CctuKytMBIhw-esuMaxw/view?usp=sharing
>
> Just let me know, if you need further details.
>

Great, thanks. Did your log show the same error here? I.e. "Illegal
hextile subencoding (subencoding: 94)" ?

Regards
--
Pierre Ossman Software Development

Cendio AB http://cendio.com
Teknikringen 8 http://twitter.com/ThinLinc
583 30 Linköping http://facebook.com/ThinLinc
Phone: +46-13-214600 http://plus.google.com/+CendioThinLinc

[Martin Schneckenreiter]

Hi there,

yes that is correct. I receive similiar error messages, e.g.:

rfb.js:808 Failed while connected: Error decoding rect: Error: Illegal hextile subencoding (subencoding: 255)

rfb.js:808 Failed while connected: Error decoding rect: Error: Illegal hextile subencoding (subencoding: 34)

rfb.js:808 Failed while connected: Error decoding rect: Error: Illegal hextile subencoding (subencoding: 160)

Only values for subencoding differs (even if I start vnc session on the same device 3 times in a row).

Thanks for your support.

Regards

[Pierre Ossman]

Ah,

It seems you are hit by this bug:

https://github.com/novnc/websockify/pull/455

Please use a released version of websockify or apply the patch on that
PR and things should work better for you.

Regards
--
Pierre Ossman Software Development

Cendio AB https://cendio.com
Teknikringen 8 https://twitter.com/ThinLinc
583 30 Linköping https://facebook.com/ThinLinc
Phone: +46-13-214600

[Martin Schneckenreiter]

Hi there,

thank you very much. After applying the patch, noVNC works again with RealVNC. Will test it tomorrow with another device.

Will the patch be included in the master branch within the next weeks?

For the moment, thanks for your great support. I am happy that noVNC is working again.

Best regards

[Pierre Ossman]

On 28/10/2020 21:56, 'Martin Schneckenreiter' via noVNC wrote:
> Hi there,
>
> thank you very much. After applying the patch, noVNC works again with
> RealVNC. Will test it tomorrow with another device.
>
> Will the patch be included in the master branch within the next weeks?
>

Hopefully. I'm waiting to see if we can get a unit test for the bug as well.