Fix crash caused by Message::getTopicName when the message is a producer message (#503)

Author: BewareMyPower

lib/MessageImpl.cc

@@ -88,7 +88,10 @@ void MessageImpl::setTopicName(const std::shared_ptr<std::string>& topicName) {
     messageId.setTopicName(topicName);
 }
 
-const std::string& MessageImpl::getTopicName() { return *topicName_; }
+const std::string& MessageImpl::getTopicName() {
+    static const std::string emptyString = "";
+    return topicName_ ? *topicName_ : emptyString;
+}
 
 int MessageImpl::getRedeliveryCount() { return redeliveryCount_; }
 

tests/MessageTest.cc

@@ -147,3 +147,8 @@ TEST(MessageTest, testMessageImplKeyValuePayloadCovert) {
         ASSERT_EQ(deMsgImpl.keyValuePtr->getValueAsString(), valueContent);
     }
 }
+
+TEST(MessageTest, testGetTopicNameOnProducerMessage) {
+    auto msg = MessageBuilder().setContent("test").build();
+    ASSERT_TRUE(msg.getTopicName().empty());
+}