stateful sockets (ssl, ssh) cannot be serialized

[totaamwin32]

Causes problems with the proxy server.

Options:

• keep the socket open on the proxy server side and relay all packets using a queue: problem is that this will use CPU time and make the processes more brittle
• somehow get the client to re-open the connection? closing the ssl layer and then re-creating it, so that the handshake will be handled by the proxy instance

[totaamwin32]

Upstream ticket: ​python.org issue 30829 : 'Cannot serialize socket object' after ssl.wrap_socket.

[Antoine Martin]

On Linux, this manifested itself as a [Errno 32] Broken pipe exception.

Fixes in:

• r23698 split the fake glib scheduler into its own module
• r23700 + r23701 + r23704 + r23706: proxy instance refactoring
• r23702 split pure proxy instance methods into a separate module (+r23703)
• r23705 proxy server refactoring
• r23707 new threaded implementation, used when needed (ssl, wss or ssh socket type) or when XPRA_PROXY_INSTANCE_THREADED=1

Example proxy output:

using threaded mode for ssl client connection
started threaded proxy instance
 for client ssl socket: 192.168.1.9:14500 <- 192.168.1.9:53892
 and server unix-domain socket:  <- /run/user/1000/xpra/localhost.localdomain-2

TODO:

• unit test for the queue scheduler module
• ensure there are no leaks: timeout connection, threads, etc

[Antoine Martin]

Updates:

• r23728 move module
• r23730 adds unit tests, found:
• r23729 scheduler bug
• r23731 fixes, + try harder to ensure we always reap proxy instances
• r23734 logging tweaks

Will follow up in #2405 with better unit tests.

[migration script]

this ticket has been moved to: ​https://github.com/Xpra-org/xpra/issues/2399