The regular ping packets are passed through the proxy server unmodified so that client and server can use them to derive latency values. But this means that the proxy cannot use its own ping packets to verify that the connection is still alive and well (see also #2405). We can enhance the ping and ping-echo packets with a source-id which can then be used to identify and filter out ping packets that originated from the proxy server.
TODO: close both connections if pings timeout.
r23778 will drop the connections if pings timeout:
server requested disconnect: server shutdown disconnect from server client ping timeout
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/2408