fix deadlock when handling packets

packet_handler_map.go

@@ -162,8 +162,6 @@ func (h *packetHandlerMap) listen() {
 }
 
 func (h *packetHandlerMap) handlePacket(addr net.Addr, data []byte) error {
-	rcvTime := time.Now()
-
 	r := bytes.NewReader(data)
 	hdr, err := wire.ParseHeader(r, h.connIDLen)
 	// drop the packet if we can't parse the header
@@ -171,22 +169,29 @@ func (h *packetHandlerMap) handlePacket(addr net.Addr, data []byte) error {
 		return fmt.Errorf("error parsing header: %s", err)
 	}
 
-	h.mutex.RLock()
+	p := &receivedPacket{
-	handlerEntry, handlerFound := h.handlers[string(hdr.DestConnectionID)]
+		remoteAddr: addr,
-	server := h.server
+		hdr:        hdr,
+		data:       data,
+		rcvTime:    time.Now(),
+	}
+
+	h.mutex.RLock()
+	defer h.mutex.RUnlock()
+
+	handlerEntry, handlerFound := h.handlers[string(hdr.DestConnectionID)]
 
-	var handlePacket func(*receivedPacket)
 	if handlerFound { // existing session
-		handler := handlerEntry.handler
+		handlerEntry.handler.handlePacket(p)
-		handlePacket = handler.handlePacket
+		return nil
-	} else { // no session found
+	}
-		// this might be a stateless reset
+	// No session found.
+	// This might be a stateless reset.
 	if !hdr.IsLongHeader {
 		if len(data) >= protocol.MinStatelessResetSize {
 			var token [16]byte
 			copy(token[:], data[len(data)-16:])
 			if sess, ok := h.resetTokens[token]; ok {
-					h.mutex.RUnlock()
 				sess.destroy(errors.New("received a stateless reset"))
 				return nil
 			}
@@ -194,19 +199,9 @@ func (h *packetHandlerMap) handlePacket(addr net.Addr, data []byte) error {
 		// TODO(#943): send a stateless reset
 		return fmt.Errorf("received a short header packet with an unexpected connection ID %s", hdr.DestConnectionID)
 	}
-		if server == nil { // no server set
+	if h.server == nil { // no server set
-			h.mutex.RUnlock()
 		return fmt.Errorf("received a packet with an unexpected connection ID %s", hdr.DestConnectionID)
 	}
-		handlePacket = server.handlePacket
+	h.server.handlePacket(p)
-	}
-	h.mutex.RUnlock()
-
-	handlePacket(&receivedPacket{
-		remoteAddr: addr,
-		hdr:        hdr,
-		data:       data,
-		rcvTime:    rcvTime,
-	})
 	return nil
 }