fs2-io is not closing ports when a DatagramChannel is used

[markehammons]

On fs2 3.13.0. I was testing usage of DatagramChannel with some code of mine in an integration test and noted that subsequent tests/suites would fail with the error java.net.BindException: Address already in use.

Attached is a minimal test case that shows the failure. It's not sufficient to merely create the DatagramChannel, it has to be used in a read/write. I believe the Selector registration may be at fault, it may not be being closed:

https://stackoverflow.com/questions/12977164/datagramchannel-close-keeps-port-open-on-windows

https://scastie.scala-lang.org/GD6QuczvSRitJaMBrLyZPw

[reardonj]

Note: Setting the options SocketOption.reusePort(true), SocketOption.reuseAddress(true) is not effective because options are not being set until after bind:

fs2/io/jvm/src/main/scala/fs2/io/net/SelectingIpDatagramSocketsProvider.scala

Lines 49 to 50 in 00814bf

	ch.bind(jAddr)
	options.foreach(opt => ch.setOption(opt.key, opt.value))

I'm going to see if I can get a fix together today.

[reardonj]

PR to fix this is out in #3764 , but even then, testing on some platforms still failed when trying to immediately reuse a port until I include the SocketOption.reuseAddress(true) option. This is probably necessary to be safe on all platforms. I don't think there is a good way for us to ever know when the port is actually available again (besides using it, which would be a bit circular).

Currently, using the options doesn't help because they aren't set early enough. The PR fixes this.