Regular CI failures with `Could not bind to 'host:port'`

[ysbaddaden]

The socket related specs (TCP, HTTP, ...) regularly fail on CI with a Could not bind to host:port exception.

These don't happen much on Linux, but they happen frequently enough on Windows that they got annoying and a waste of time to figure out it's unimportant and re-running the failed job(s).

[ysbaddaden]

I'm suspicious of the unused_local_port helper method. It starts a TCP server on port 0, grabs the actual port number, closes the TCP server and returns the port number.

Specs then go on to immediately start a server on that port.

I believe closing the socket on the port doesn't necessarily happen fast enough in the system (or asynchronously), so when we try to bind a new socket on the port, that fails.

Whenever possible we should instead start the server on port 0 and use server.port if we need to connect a client to that port, as we do this in a few places already.

If there are cases where we can't do the above, then we might want to introduce a retry mechanism, with some delay, before failing after a few attempts.

[HertzDevil]

This happens almost always for Windows UDP sockets only. After reading this StackOverflow answer I believe this is due to Windows reserving different port ranges between TCP and UDP:

>netsh int ip show excludedportrange protocol=tcp

Protocol tcp Port Exclusion Ranges

Start Port    End Port
----------    --------
     28385       28385
     28390       28390
     50000       50059     *
     53652       53751
     53752       53851
     53952       54051
     54052       54151
     54152       54251
     54252       54351
     54974       55073

* - Administered port exclusions.

>netsh int ip show excludedportrange protocol=udp

Protocol udp Port Exclusion Ranges

Start Port    End Port
----------    --------
     50000       50059     *
     63056       63155
     63948       64047
     64048       64147
     64248       64347
     64348       64447
     64448       64547
     64548       64647

* - Administered port exclusions.

::unused_local_port uses TCP, but there is no guarantee the same port number is available for UDP.