network: move Version sending to the tcp transport

We have a race between reader and writer goroutines for the same connection
that leads to handshake failures when reader is faster to read the incoming
version (and try to reply to it) than writer is to write our own Version:

WARN[0000] peer disconnected                             addr="172.200.0.4:20334" peerCount=5 reason="invalid handshake: tried to send VersionAck, but didn't send Version yet

Fix it by moving Version sending before the reader loop starts.

pkg/network/server.go

@@ -200,12 +200,6 @@ func (s *Server) run() {
 			}
 			return
 		case p := <-s.register:
-			// When a new peer is connected we send out our version immediately.
-			if err := s.sendVersion(p); err != nil {
-				log.WithFields(log.Fields{
-					"addr": p.RemoteAddr(),
-				}).Error(err)
-			}
 			s.lock.Lock()
 			s.peers[p] = true
 			s.lock.Unlock()

pkg/network/tcp_transport.go

@@ -78,6 +78,12 @@ func (t *TCPTransport) handleConn(conn net.Conn) {
 
 	t.server.register <- p
 
+	// When a new peer is connected we send out our version immediately.
+	if err := t.server.sendVersion(p); err != nil {
+		log.WithFields(log.Fields{
+			"addr": p.RemoteAddr(),
+		}).Error(err)
+	}
 	r := io.NewBinReaderFromIO(p.conn)
 	for {
 		msg := &Message{}