Fix listening on a port after it was closed not working

[t4lz]

closes #1526

The bug is that when the app closes a socket it listens to, we don't remove it from our set of Listen objects, and if it then listens again on the same port, we don't update the Listen object, which results in the local port (the port mirrord connects to) not to be updated, so mirrord tries to connect to the local port from the first time the app listened on the same requested port.

The quick fix is to replace the Listen object if the app listens again. But maybe we want to handle socket closes (remove requested port from ports set, notify agent so that the agent stops listening...).

[aviramha]

@meowjesty just changed it in PR #1123 that we won't let user double bind - doesn't this (re)introduce the weird side effect? (from the code change hard to tell)
I think the more proper solution would be notify remote on close, since we already hook that?

[t4lz]

@meowjesty just changed it in PR #1123 that we won't let user double bind - doesn't this (re)introduce the weird side effect? (from the code change hard to tell) I think the more proper solution would be notify remote on close, since we already hook that?

This does not reintroduce that bug because we still make sure the socket is not bound and that there is no other bound socket with the same requested address.

Yes, I agree that the proper solution is to notify the TCP handler about the close, and I opened an issue for that.

The value of this PR would be the regression test and the temporary fix (the fix is only 2 lines). I can instead add the proper close handling in this PR if you're fine with that, or if it's going to be prioritized soon we can close this PR.

[t4lz]

Sorry wrong issue links in my comments, fixing

[aviramha]

okay I understand, sounds good.