Better handling for topic alias of a received message

* for received PUBLISH, check for Client-to-Server Maximum Topic Alias
  preference, not Server-to-Client one
* fire ProtocolViolation on topicAlias == 0
* return earlier on errors

Change-Id: Ia371b7a4e05704d07caab6c0d67b9180f590f1fc
Reviewed-by: Maurice Kalinowski <maurice.kalinowski@qt.io>

1 files changed, 9 insertions, 6 deletions

diff --git a/src/mqtt/qmqttconnection.cpp b/src/mqtt/qmqttconnection.cpp
index 59d29eb..b8ab752 100644
--- a/src/mqtt/qmqttconnection.cpp
+++ b/src/mqtt/qmqttconnection.cpp
@@ -1531,18 +1531,21 @@ void QMqttConnection::finalize_publish()
     if (m_clientPrivate->m_protocolVersion == QMqttClient::MQTT_5_0)
         readPublishProperties(publishProperties);
 
-    const quint16 topicAlias = publishProperties.topicAlias();
-    if (topicAlias > 0) {
-        if (topicAlias > m_clientPrivate->m_serverConnectionProperties.maximumTopicAlias()) {
+    if (publishProperties.availableProperties() & QMqttPublishProperties::TopicAlias) {
+        const quint16 topicAlias = publishProperties.topicAlias();
+        if (topicAlias == 0 || topicAlias > m_clientPrivate->m_connectionProperties.maximumTopicAlias()) {
             qCDebug(lcMqttConnection) << "TopicAlias receive: overflow.";
             closeConnection(QMqttClient::ProtocolViolation);
-        } else if (topicLength == 0) { // New message on existing topic alias
-            if (m_receiveAliases.at(topicAlias - 1).name().isEmpty()) {
+            return;
+        }
+        if (topicLength == 0) { // New message on existing topic alias
+            topic = m_receiveAliases.at(topicAlias - 1);
+            if (topic.name().isEmpty()) {
                 qCDebug(lcMqttConnection) << "TopicAlias receive: alias for unknown topic.";
                 closeConnection(QMqttClient::ProtocolViolation);
+                return;
             }
             qCDebug(lcMqttConnectionVerbose) << "TopicAlias receive: Using " << topicAlias;
-            topic = m_receiveAliases.at(topicAlias - 1);
         } else { // Resetting a topic alias
             qCDebug(lcMqttConnection) << "TopicAlias receive: Resetting:" << topic.name() << " : " << topicAlias;
             m_receiveAliases[topicAlias - 1] = topic;