Feature Request: give ability to drop connection before greeting about go-smtp

[emersion]

You can pass your own net.Listener wrapper to go-smtp, and drop connections before go-smtp handles them.

[aine-etke]

Thank you for suggestion!
Unfortunately, it doesn't solve the mentioned issue, because go-smtp server will crash completely if net.Listener.Accept() returns error and/or nil connection. You have to return something that won't crash it.

We managed that by implying the following workaround:

// Accept waits for and returns the next connection to the listener.
func (l *Listener) Accept() (net.Conn, error) {
	conn, err := l.listener.Accept()
	if err != nil {
		return conn, err
	}
	if l.isBanned(conn.RemoteAddr()) {
		conn.Close()
		l.log.Info("rejected connection from %q (already banned)", conn.RemoteAddr())
		return &net.TCPConn{}, nil
	}

	return conn, nil
}

but as you can see, it's not ideal.

May I ask you to re-open the issue, please? Right now there is no straitforward way without forging connection to actually drop it. If you don't want to implement a hook, could you perform error check without crashing the whole server (latest release/git tag) or stopping the whole server (master branch), please?

[emersion]

You can just loop until you get a non-nil connection.