ZlibHex Error

W. Brian Blevins brian.blevins "at" tridia.com
Thu Mar 25 01:54:00 2004

Undoubtedly, James is correct about CotVNC becoming confused.  Likely
it is misinterpreting the length of a message and loosing "framing".  So,
probably attempts to interpret the start of a message in the wrong place
and the message type for ZlibHex (8) happens to be the value it finds.
ZlibHex itself may or may not be at fault.

From an immediate workaround point of view, it would be best to select a
specific encoding and have CotVNC stick with it.  (Viewers can change
encodings at any time in RFB/VNC, if so configured.)  If it is possible to

disable automatic encoding selection, that would be the first step of a
workaround.  Then try various encodings until you find the optimal one for

your applications and network connectivity.

Obviously feedback to the CotVNC team for a fix would be best.

Good luck,


> From: "James Weatherall"
> To: ,
> Subject: RE: ZlibHex Error
> Date: Tue, 23 Mar 2004 15:28:24 -0000
> Organization: RealVNC Ltd.
> > I am using "Chicken of the VNC" V. 1.3.6 on a Mac G5.  When I connect
> > to a WinXP machine on my local network using WinVNC V 3.3.7
> > server, the
> > system works perfectly.
> > However, the original purpose was to be able to run my mother WinXP
> > box.  When I try to connect over the Internet (using the same version
> > of the server),
> > I see a black screen for a few seconds and then a error
> > window appears
> > on my Mac that says "ZlibHex unknown subencoding error 300
> > encountered".
> ZlibHex isn't a standard part of the VNC protocol, so VNC Server 3.3.7 will
> not produce ZlibHex data.  The error you're seeing suggests that CotVNC is
> getting confused into intepreting incoming data as ZlibHex, even though it's
> not.
> The most likely cause for things working locally but not remotely is that
> CotVNC may be trying to switch to ZlibHex when it detects a slower network
> connection.
> Cheers,
> Wez @ RealVNC Ltd.
Brian Blevins

Tridia, Turning Downtime Into Uptime. (tm)

Tridia's Mission: To always exceed our customers' expectations by providing
the absolute best software products backed by outstanding technical support
and customer service.  Please let us know how we are doing:
brian . blevins @ tridia.com or ceo-hotline @ tridia.com.