Split from #276 (see ticket:276#comment:15): OSX clients receive the token and the data at the same time, we should tell the server about client-side direction settings so that the server can avoid sending that data. This could be considered a security issue: when clients request "to-server" only, they don't expect server clipboard data to travel in the other direction at all...
The "can_send" and "can_receive" flags would have to be split between client and server side settings, with the former being changed at runtime through a new clipboard packet type (new capability). Tricky.
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/1329