On Wed, Jan 25, 2017 at 12:23:35PM -0500, Frediano Ziglio wrote: > > > > When used with QEMU at least, both SPICE and VNC live in the same port > > range (5900+). It is thus not entirely uncommon for a user to mistakenly > > connect to a SPICE server with a VNC client, or vica-verca. > > > > When connecting to VNC server with a SPICE client, you quickly get an > > error. This is because the VNC server sends its short greeting and then > > sees the RedLinkMess from the SPICE client, realizes its garbage and > > drops the connection. > > > > When connecting to a SPICE server with a VNC client though, you get an > > indefinite hang. The VNC client is waiting for the VNC greeting, which > > the SPICE server will never send. The SPICE server is waiting for the > > RedLinkMess which the VNC client will never send. > > > > Since VNC is a server sends first protocol and SPICE is a client sends > > first protocol, it would seem this problem is impossible to fix, but > > I think it is possible to tweak things so it can be more gracefully > > handled. > > > > In VNC the protocol starts with the follow data sent: > > > > Server: "RFB 003.008\n" > > Client: "RFB 003.008\n" > > > > What I'm thinking is that we could easily change the VNC client so that > > it will send some bytes first. eg > > > > Client: "RFB " > > Server: "RFB 003.008\n" > > Client: "003.008\n" > > > > From the VNC server POV, it'll still be receiving the same 12 bytes from > > the client - it just happens that 4 of them might arrive a tiny bit > > earlier than the other 8 of them. IOW nothing should break in the VNC > > server from this change. > > > > I tried this, but we still get a hang in the SPICE server. The problem > > is that the SPICE server code is waiting for the full RedLinkMess > > message to be received before checking its content. > > > > Can we change the SPICE server so that it reads the 'uint32 magic' first, > > validates that, and then reads the remainder of RedLinkMess ? > > > > This would solve the problem, as the SPICE server would see 'RFB ' as the > > magic, realize it was garbage and so close the connection. The VNC client > > which is waiting for the VNC greeting will thus terminate rather than > > hanging > > forever. > > > > Regards, > > Daniel > > Perhaps another solution would be to add a timeout to spice server so > after, say, 2/3 seconds it would close the connection. > > This would work even without changing the VNC client.
I'm not a fan of timeouts because this could negatively impact on genuine spice clients which hit a latency spike on the network for whatever reason. The incremental read of RedLinkMess by constrast is guaranteed to not have any chance of negative impact on spice clients. Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://entangle-photo.org -o- http://search.cpan.org/~danberr/ :| _______________________________________________ Spice-devel mailing list Spice-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/spice-devel
