Re: Client server handshake and missing color maps

["Daniel P. Berrange" <dan berrange com>]

On Tue, Apr 22, 2014 at 06:57:27PM +0200, Marco Gidde wrote:
> Hello Daniel, hello list,
>
> I noticed and analyzed a gtk-vnc crash, via vinagre on ubuntu 13.10 and
> gvncviewer.py on an older SUSE release. The client tried to connect to
> an older proprietary VNCserver running on a PLC, RFB version 3.3, maybe
> some RealVNC derivative.
>
> It turned out that the server uses 8bit color depth with a color map and
> does not accept clients which request different color encodings or true
> color. On the other hand the server does not send the color entries
> unless the client explicitly sends the SetPixelFormat message.
>
> There is some code/comment in src/vncdisplay.c:1182:
>
> #if 0
>         /* TigerVNC always sends back the encoding even if
>            unchanged from what the server suggested. This
>            does not appear to matter, so lets save the bytes */
>         memcpy(&fmt, currentFormat, sizeof(fmt));
>         break;
> #else
>         return TRUE;
> #endif
>
> If I activate that code, the client connects successfully, so there
> might be a reason why TigerVNC always sends it :-)
>
> It's not entirely clear whether the client is required to always send
> SetPixelFormat - when using true color it is obviously superfluous. But
> in this case its main purpose is to instruct the server to send the
> color map. I couldn't find anything about this in the specification, but
> I only skimmed through it.

All a little bizarre. It has been a long time since I looked at the
colourmap handling code. In fact I'm not entirely sure it ever worked
right, since basically no one uses colourmaps since the late 1990's :-)
Thanks for the bug report though - I'll try to refamiliarize myself
with this code and see if the change you suggest makes sense.

Daniel
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