Shutting down is a formality two peers can do before closing their connections. It's not required, but it can help assert your I/O procedures, so it's useful.
If writing is shut down, trying to send will result in a pipe error, and the remote peer will read an empty string after receiving all other pending data.
If reading is shut down, trying to receive will return an empty string, and the remote peer will get a pipe error if they try to send.
Writing should be shut down first between two peers. Remaining data should then be read and handled. If anything is sent at this point it should be a "goodbye" (nothing that requires the remote peer to write back to you). Finally, reading can be shut down.
Selection on a shut down channel will always succeed. Similarly, the remote peer will always succeed at selecting the opposite channel.
