Deep copy message in ServeMux (#54)

message.go

@@ -0,0 +1,36 @@
+// Copyright 2019 The mqtt-go authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package mqtt
+
+// Message represents MQTT message.
+type Message struct {
+	Topic   string
+	ID      uint16
+	QoS     QoS
+	Retain  bool
+	Dup     bool
+	Payload []byte
+}
+
+func (m *Message) clone() *Message {
+	return &Message{
+		Topic:   string([]byte(m.Topic)),
+		QoS:     m.QoS,
+		Retain:  m.Retain,
+		Payload: append([]byte{}, m.Payload...),
+		Dup:     m.Dup,
+		ID:      m.ID,
+	}
+}

mqtt.go

@@ -30,16 +30,6 @@ const (
 	SubscribeFailure QoS = 0x80 // Rejected to subscribe
 )
 
-// Message represents MQTT message.
-type Message struct {
-	Topic   string
-	ID      uint16
-	QoS     QoS
-	Retain  bool
-	Dup     bool
-	Payload []byte
-}
-
 // Subscription represents MQTT subscription target.
 type Subscription struct {
 	Topic string

servemux.go

@@ -47,7 +47,7 @@ func (m *ServeMux) Handle(filter string, handler Handler) error {
 func (m *ServeMux) Serve(message *Message) {
 	for _, h := range m.handlers {
 		if h.filter.Match(message.Topic) {
-			h.handler.Serve(message)
+			h.handler.Serve(message.clone())
 		}
 	}
 }