Enrich error

[kazu-yamamoto]

Trying to implement #609.

@khibino This is PoC. The error of bind is change from:

Network.Socket.bind: resource busy (Address already in use)

to

Network.Socket.bind: resource busy (Address already in use (EADDRINUSE) <socket: 14>)

The current problem is there are no way to show SocketAddress sa.

[kazu-yamamoto]

Breaking backward compatibility but just adding Show to bind:

Network.Socket.bind: resource busy (Address already in use (EADDRINUSE) <socket: 13> [::1]:53)

[kazu-yamamoto]

@khibino I guess this PR is ready for reviewing.
Backward compatibility is kept, yay!

[vdukhovni]

Breaking backward compatibility but just adding Show to bind:

Network.Socket.bind: resource busy (Address already in use (EADDRINUSE) <socket: 13> [::1]:53)

Adding the associated address for connect, bind, sendTo, ... is quite useful.
Perhaps also for already connected TCP sockets, when a connection breaks, or I/O times out, ... a getpeername() may be able to recover the peer address, so it can be reported.

But, FWIW, I am not sure that reporting the socket file descriptor number is useful, it does not tell the user much. If the user could "decorate" the socket with custom info about its purpose/role in the application to be reported on error, that'd work better, but may not be warranted.

[kazu-yamamoto]

Labeling sockets sounds a good idea.

[sjakobi]

I saw your message on Haskell Cafe:

In my opinion, Show IOException should display errno. Why doesn't it display?

I don't know why the instance is this way, but the problem has been noticed before. See https://gitlab.haskell.org/ghc/ghc/-/issues/16048.

[kazu-yamamoto]

An accepted socket (in the server side) is now labeled as:

<socket: 14 [::1]:58926>

[kazu-yamamoto]

@vdukhovni I fully re-implemented this scheme.
Now we have labelSocket and socketLabel
A connected socket is labeled as "sock 13 [::1]:8080 [::1]:60708", for instance.

[kazu-yamamoto]

I should merge #602 first then this PR next.