Allow empty will messages

A will message is allowed to be empty. Hence, check whether a will topic
exists to identify incorporating the last will to the connect message.

Task-number: QTBUG-76783
Change-Id: Ifb7f5467e8e7e70c6d9c050b36a35df2419f4171
Reviewed-by: hjk <hjk@qt.io>

2 files changed, 15 insertions, 4 deletions

diff --git a/src/mqtt/qmqttconnection.cpp b/src/mqtt/qmqttconnection.cpp
index bbad0bd..e3beb56 100644
--- a/src/mqtt/qmqttconnection.cpp
+++ b/src/mqtt/qmqttconnection.cpp
@@ -253,7 +253,7 @@ bool QMqttConnection::sendControlConnect()
     if (m_clientPrivate->m_cleanSession)
         flags |= 1 << 1;
 
-    if (!m_clientPrivate->m_willMessage.isEmpty()) {
+    if (!m_clientPrivate->m_willTopic.isEmpty()) {
         flags |= 1 << 2;
         if (m_clientPrivate->m_willQoS > 2) {
             qCDebug(lcMqttConnection) << "Invalid Will QoS specified.";
@@ -290,7 +290,7 @@ bool QMqttConnection::sendControlConnect()
         packet.append(char(0));
     }
 
-    if (!m_clientPrivate->m_willMessage.isEmpty()) {
+    if (!m_clientPrivate->m_willTopic.isEmpty()) {
         if (m_clientPrivate->m_protocolVersion == QMqttClient::MQTT_5_0)
             packet.appendRaw(writeLastWillProperties());
 
diff --git a/tests/auto/qmqttclient/tst_qmqttclient.cpp b/tests/auto/qmqttclient/tst_qmqttclient.cpp
index c4da40d..21bd512 100644
--- a/tests/auto/qmqttclient/tst_qmqttclient.cpp
+++ b/tests/auto/qmqttclient/tst_qmqttclient.cpp
@@ -263,14 +263,25 @@ void Tst_QMqttClient::retainMessage()
     publisher.disconnect();
 }
 
-DefaultVersionTestData(Tst_QMqttClient::willMessage_data)
+void Tst_QMqttClient::willMessage_data()
+{
+    QTest::addColumn<QMqttClient::ProtocolVersion>("mqttVersion");
+    QTest::addColumn<QByteArray>("willMessage");
+
+    QList<QMqttClient::ProtocolVersion> versions{QMqttClient::MQTT_3_1_1, QMqttClient::MQTT_5_0};
+
+    for (int i = 0; i < 2; ++i) {
+        QTest::newRow(qPrintable(QString::number(versions[i]) + ":simple")) << versions[i] << QByteArray("The client connection is gone.");
+        QTest::newRow(qPrintable(QString::number(versions[i]) + ":empty")) << versions[i] << QByteArray();
+    }
+}
 
 void Tst_QMqttClient::willMessage()
 {
     QFETCH(QMqttClient::ProtocolVersion, mqttVersion);
+    QFETCH(QByteArray, willMessage);
 
     const QString willTopic = QLatin1String("Qt/QMqttClient/will/topic");
-    const QByteArray willMessage("The client died....");
 
     // Client A connects
     VersionClient(mqttVersion, client1);