Cleanup serve function (reland) (#667)

* Split central ServeDNS code out of (*Server).serve

* Add UDP and TCP specific (*Server).serve wrappers

* Move UDP serve functionality into serveUDPPacket

* Merge serve into serveTCPConn

* Cleanup serveTCPConn replacing goto with for

* defer Close in serveTCPConn

* Remove remoteAddr field from response struct

* Fix broken tsigSecret check in serveDNS

* Reorder serveDNS arguments

This makes it consistent with the ordering of arguments to
serveUDPPacket and serveTCPConn.

server.go

@@ -51,7 +51,6 @@ type response struct {
 	udp            *net.UDPConn      // i/o connection if UDP was used
 	tcp            net.Conn          // i/o connection if TCP was used
 	udpSession     *SessionUDP       // oob data to get egress interface right
-	remoteAddr     net.Addr          // address of the client
 	writer         Writer            // writer to output the raw DNS bits
 }
 
@@ -447,16 +446,10 @@ func (srv *Server) serveTCP(l net.Listener) error {
 		srv.NotifyStartedFunc()
 	}
 
-	reader := Reader(&defaultReader{srv})
-	if srv.DecorateReader != nil {
-		reader = srv.DecorateReader(reader)
-	}
-
 	handler := srv.Handler
 	if handler == nil {
 		handler = DefaultServeMux
 	}
-	rtimeout := srv.getReadTimeout()
 	// deadline is not used here
 	for {
 		rw, err := l.Accept()
@@ -472,14 +465,7 @@ func (srv *Server) serveTCP(l net.Listener) error {
 			}
 			return err
 		}
-		go func() {
-			m, err := reader.ReadTCP(rw, rtimeout)
-			if err != nil {
-				rw.Close()
-				return
-			}
-			srv.serve(rw.RemoteAddr(), handler, m, nil, nil, rw)
-		}()
+		go srv.serveTCPConn(handler, rw)
 	}
 }
 
@@ -520,80 +506,94 @@ func (srv *Server) serveUDP(l *net.UDPConn) error {
 		if len(m) < headerSize {
 			continue
 		}
-		go srv.serve(s.RemoteAddr(), handler, m, l, s, nil)
+		go srv.serveUDPPacket(handler, m, l, s)
 	}
 }
 
-// Serve a new connection.
-func (srv *Server) serve(a net.Addr, h Handler, m []byte, u *net.UDPConn, s *SessionUDP, t net.Conn) {
-	w := &response{tsigSecret: srv.TsigSecret, udp: u, tcp: t, remoteAddr: a, udpSession: s}
+// Serve a new TCP connection.
+func (srv *Server) serveTCPConn(h Handler, t net.Conn) {
+	reader := Reader(&defaultReader{srv})
+	if srv.DecorateReader != nil {
+		reader = srv.DecorateReader(reader)
+	}
+
+	w := &response{tsigSecret: srv.TsigSecret, tcp: t}
 	if srv.DecorateWriter != nil {
 		w.writer = srv.DecorateWriter(w)
 	} else {
 		w.writer = w
 	}
 
-	q := 0 // counter for the amount of TCP queries we get
+	defer func() {
+		if !w.hijacked {
+			w.Close()
+		}
+	}()
 
-	reader := Reader(&defaultReader{srv})
-	if srv.DecorateReader != nil {
-		reader = srv.DecorateReader(reader)
+	idleTimeout := tcpIdleTimeout
+	if srv.IdleTimeout != nil {
+		idleTimeout = srv.IdleTimeout()
 	}
-Redo:
+
+	timeout := srv.getReadTimeout()
+
+	// TODO(miek): make maxTCPQueries configurable?
+	for q := 0; q < maxTCPQueries; q++ {
+		m, err := reader.ReadTCP(t, timeout)
+		if err != nil {
+			// TODO(tmthrgd): handle error
+			break
+		}
+		srv.serveDNS(h, m, w)
+		if w.tcp == nil {
+			break // Close() was called
+		}
+		if w.hijacked {
+			break // client will call Close() themselves
+		}
+		// The first read uses the read timeout, the rest use the
+		// idle timeout.
+		timeout = idleTimeout
+	}
+}
+
+// Serve a new UDP request.
+func (srv *Server) serveUDPPacket(h Handler, m []byte, u *net.UDPConn, s *SessionUDP) {
+	w := &response{tsigSecret: srv.TsigSecret, udp: u, udpSession: s}
+	if srv.DecorateWriter != nil {
+		w.writer = srv.DecorateWriter(w)
+	} else {
+		w.writer = w
+	}
+	srv.serveDNS(h, m, w)
+}
+
+func (srv *Server) serveDNS(h Handler, m []byte, w *response) {
 	req := new(Msg)
 	err := req.Unpack(m)
 	if err != nil { // Send a FormatError back
 		x := new(Msg)
 		x.SetRcodeFormatError(req)
 		w.WriteMsg(x)
-		goto Exit
+		return
 	}
 	if !srv.Unsafe && req.Response {
-		goto Exit
+		return
 	}
 
 	w.tsigStatus = nil
 	if w.tsigSecret != nil {
 		if t := req.IsTsig(); t != nil {
-			secret := t.Hdr.Name
-			if _, ok := w.tsigSecret[secret]; !ok {
-				w.tsigStatus = ErrKeyAlg
+			if secret, ok := w.tsigSecret[t.Hdr.Name]; ok {
+				w.tsigStatus = TsigVerify(m, secret, "", false)
+			} else {
+				w.tsigStatus = ErrSecret
 			}
-			w.tsigStatus = TsigVerify(m, w.tsigSecret[secret], "", false)
 			w.tsigTimersOnly = false
 			w.tsigRequestMAC = req.Extra[len(req.Extra)-1].(*TSIG).MAC
 		}
 	}
 	h.ServeDNS(w, req) // Writes back to the client
-
-Exit:
-	if w.tcp == nil {
-		return
-	}
-	// TODO(miek): make this number configurable?
-	if q > maxTCPQueries { // close socket after this many queries
-		w.Close()
-		return
-	}
-
-	if w.hijacked {
-		return // client calls Close()
-	}
-	if u != nil { // UDP, "close" and return
-		w.Close()
-		return
-	}
-	idleTimeout := tcpIdleTimeout
-	if srv.IdleTimeout != nil {
-		idleTimeout = srv.IdleTimeout()
-	}
-	m, err = reader.ReadTCP(w.tcp, idleTimeout)
-	if err == nil {
-		q++
-		goto Redo
-	}
-	w.Close()
-	return
 }
 
 func (srv *Server) readTCP(conn net.Conn, timeout time.Duration) ([]byte, error) {
@@ -696,7 +696,12 @@ func (w *response) LocalAddr() net.Addr {
 }
 
 // RemoteAddr implements the ResponseWriter.RemoteAddr method.
-func (w *response) RemoteAddr() net.Addr { return w.remoteAddr }
+func (w *response) RemoteAddr() net.Addr {
+	if w.tcp != nil {
+		return w.tcp.RemoteAddr()
+	}
+	return w.udpSession.RemoteAddr()
+}
 
 // TsigStatus implements the ResponseWriter.TsigStatus method.
 func (w *response) TsigStatus() error { return w.tsigStatus }