xpra shell

[totaam]

Using exec to make it easier to debug a client or server in real-time.
Not everything is available via xpra info or debug logging. (see also #2749)
This will allow runtime inspection and modification of the code.

[totaam]

Very useful, in particular for things like #2756.

[totaam]

xpra shell subcommand added in r26340, with server support only.

ie:

XPRA_SHELL=1 python3 /usr/bin/xpra start --start=xterm  --bind-tcp=0.0.0.0:10000 -d exec

xpra shell tcp://127.0.0.1:10000
> print(server.get_root_window_size())
(8192, 4096)
> exit

TODO:

• better output capture needed? only capture output coming from our exec thread (server could have debug enabled and printing lots of other unrelated stuff)
• support for client sockets
• replace environment variable with command line option, or socket option (or both)
• handle stdout / stderr write errors:

BlockingIOError: [Errno 11] write could not complete without blocking

• prompt is messy and asynchronous
• O_NONBLOCK on win32?
• compress shell-reply packet, use brotli?

[totaam]

r27425 allows individual server sockets to have the shell option enabled, ie:

xpra start :20 --bind-tcp=0.0.0.0:10000,shell=true --no-daemon --start=xterm

This will do for now, will follow up in #2872