ensure consuming only occurs once per queue

a Queue can act as a consumer in QAMQP, but previously we did no checks
to ensure that a Queue sent a request to consume only once. This commit
adds API for checking and ensuring that this is the case. Also, I reverted
the changes to allow multiple consumer tags because this was incorrect.
Also included is a new signal "consuming" to notify when consumption occurs,
and auto tests have been updated to use this, as well as verify that it
can only occur once per-consumer

src/amqp_queue.cpp

@@ -15,7 +15,8 @@ QueuePrivate::QueuePrivate(Queue *q)
       delayedDeclare(false),
       declared(false),
       noAck(true),
-      recievingMessage(false)
+      recievingMessage(false),
+      consuming(false)
 {
 }
 
@@ -190,12 +191,14 @@ void QueuePrivate::getOk(const Frame::Method &frame)
 
 void QueuePrivate::consumeOk(const Frame::Method &frame)
 {
+    Q_Q(Queue);
     qAmqpDebug() << "consume ok: " << name;
     QByteArray data = frame.arguments();
     QDataStream stream(&data, QIODevice::ReadOnly);
-    QString consumerTag = Frame::readField('s',stream).toString();
+    consumerTag = Frame::readField('s',stream).toString();
     qAmqpDebug("consumer tag = %s", qPrintable(consumerTag));
-    consumerTags.append(consumerTag);
+    consuming = true;
+    Q_EMIT q->consuming(consumerTag);
 }
 
 void QueuePrivate::deliver(const Frame::Method &frame)
@@ -204,7 +207,7 @@ void QueuePrivate::deliver(const Frame::Method &frame)
     QByteArray data = frame.arguments();
     QDataStream in(&data, QIODevice::ReadOnly);
     QString consumer = Frame::readField('s',in).toString();
-    if (!consumerTags.contains(consumer)) {
+    if (consumerTag != consumer) {
         qAmqpDebug() << Q_FUNC_INFO << "invalid consumer tag: " << consumer;
         return;
     }
@@ -411,12 +414,17 @@ void Queue::unbind(const QString &exchangeName, const QString &key)
     d->sendFrame(frame);
 }
 
-void Queue::consume(int options)
+bool Queue::consume(int options)
 {
     Q_D(Queue);
     if (!d->opened) {
         qAmqpDebug() << Q_FUNC_INFO << "queue is not open";
-        return;
+        return false;
+    }
+
+    if (d->consuming) {
+        qAmqpDebug() << Q_FUNC_INFO << "already consuming with tag: " << d->consumerTag;
+        return false;
     }
 
     Frame::Method frame(Frame::fcBasic, QueuePrivate::bmConsume);
@@ -427,25 +435,32 @@ void Queue::consume(int options)
 
     out << qint16(0);   //reserved 1
     Frame::writeField('s', out, d->name);
-    Frame::writeField('s', out, d->explicitConsumerTag);
+    Frame::writeField('s', out, d->consumerTag);
 
     out << qint8(options);
     Frame::writeField('F', out, Frame::TableField());
 
     frame.setArguments(arguments);
     d->sendFrame(frame);
+    return true;
 }
 
 void Queue::setConsumerTag(const QString &consumerTag)
 {
     Q_D(Queue);
-    d->explicitConsumerTag = consumerTag;
+    d->consumerTag = consumerTag;
 }
 
 QString Queue::consumerTag() const
 {
     Q_D(const Queue);
-    return d->explicitConsumerTag;
+    return d->consumerTag;
+}
+
+bool Queue::isConsuming() const
+{
+    Q_D(const Queue);
+    return d->consuming;
 }
 
 void Queue::get()

src/amqp_queue.h

@@ -55,6 +55,8 @@ public:
 
     ~Queue();
 
+    bool isConsuming() const;
+
     void setConsumerTag(const QString &consumerTag);
     QString consumerTag() const;
 
@@ -71,7 +73,7 @@ public:
     void remove(int options = roIfUnused|roIfEmpty|roNoWait);
 
     // AMQP Basic
-    void consume(int options = NoOptions);
+    bool consume(int options = NoOptions);
     void get();
     void ack(const Message &message);
 
@@ -83,6 +85,7 @@ Q_SIGNALS:
     void messageReceived();
     void empty();
     void purged(int messageCount);
+    void consuming(const QString &consumerTag);
 
 protected:
     // reimp Channel

src/amqp_queue_p.h

@@ -45,11 +45,11 @@ public:
     bool delayedDeclare;
     bool declared;
     bool noAck;
-    QString explicitConsumerTag;
-    QStringList consumerTags;
+    QString consumerTag;
     QQueue<QPair<QString, QString> > delayedBindings;
     bool recievingMessage;
     Message currentMessage;
+    bool consuming;
 
     Q_DECLARE_PUBLIC(Queue)
 

tests/auto/qamqpqueue/tst_qamqpqueue.cpp

@@ -30,6 +30,7 @@ private Q_SLOTS:
     void removeIfEmpty();
     void unbind();
     void purge();
+    void canOnlyStartConsumingOnce();
 
 private:
     QScopedPointer<Client> client;
@@ -56,7 +57,8 @@ void tst_QAMQPQueue::defaultExchange()
     Queue *queue = client->createQueue("test-default-exchange");
     queue->declare();
     QVERIFY(waitForSignal(queue, SIGNAL(declared())));
-    queue->consume();
+    QVERIFY(queue->consume());
+    QVERIFY(waitForSignal(queue, SIGNAL(consuming(QString))));
 
     Exchange *defaultExchange = client->createExchange();
     defaultExchange->publish("first message", "test-default-exchange");
@@ -85,8 +87,9 @@ void tst_QAMQPQueue::standardExchanges()
     Queue *queue = client->createQueue(queueName);
     queue->declare();
     QVERIFY(waitForSignal(queue, SIGNAL(declared())));
-    queue->consume();   // required because AutoDelete will not delete if
-                        // there was never a consumer
+    QVERIFY(queue->consume());   // required because AutoDelete will not delete if
+                                 // there was never a consumer
+    QVERIFY(waitForSignal(queue, SIGNAL(consuming(QString))));
 
     queue->bind(exchange, routingKey);
     QVERIFY(waitForSignal(queue, SIGNAL(bound())));
@@ -126,7 +129,8 @@ void tst_QAMQPQueue::invalidBind()
     Queue *queue = client->createQueue("test-invalid-bind");
     queue->declare();
     QVERIFY(waitForSignal(queue, SIGNAL(declared())));
-    queue->consume();   // for autodelete
+    QVERIFY(queue->consume());   // for autodelete
+    QVERIFY(waitForSignal(queue, SIGNAL(consuming(QString))));
 
     queue->bind("non-existant-exchange", "routingKey");
     QVERIFY(waitForSignal(queue, SIGNAL(error(QAMQP::Error))));
@@ -138,7 +142,8 @@ void tst_QAMQPQueue::unnamed()
     Queue *queue = client->createQueue();
     queue->declare();
     QVERIFY(waitForSignal(queue, SIGNAL(declared())));
-    queue->consume();
+    QVERIFY(queue->consume());
+    QVERIFY(waitForSignal(queue, SIGNAL(consuming(QString))));
 
     QVERIFY(!queue->name().isEmpty());
 }
@@ -204,7 +209,8 @@ void tst_QAMQPQueue::removeIfUnused()
     Queue *queue = client->createQueue("test-remove-if-unused");
     queue->declare();
     QVERIFY(waitForSignal(queue, SIGNAL(declared())));
-    queue->consume();
+    QVERIFY(queue->consume());
+    QVERIFY(waitForSignal(queue, SIGNAL(consuming(QString))));
 
     queue->remove(Queue::roIfUnused);
     QVERIFY(waitForSignal(queue, SIGNAL(error(QAMQP::Error))));
@@ -249,8 +255,9 @@ void tst_QAMQPQueue::unbind()
     Queue *queue = client->createQueue("test-unbind");
     queue->declare();
     QVERIFY(waitForSignal(queue, SIGNAL(declared())));
-    queue->consume();   // required because AutoDelete will not delete if
-                        // there was never a consumer
+    QVERIFY(queue->consume());   // required because AutoDelete will not delete if
+                                 // there was never a consumer
+    QVERIFY(waitForSignal(queue, SIGNAL(consuming(QString))));
 
     queue->bind("amq.topic", "routingKey");
     QVERIFY(waitForSignal(queue, SIGNAL(bound())));
@@ -294,5 +301,19 @@ void tst_QAMQPQueue::purge()
     QVERIFY(waitForSignal(queue, SIGNAL(removed())));
 }
 
+void tst_QAMQPQueue::canOnlyStartConsumingOnce()
+{
+    Queue *queue = client->createQueue("test-single-consumer");
+    queue->declare();
+    QVERIFY(waitForSignal(queue, SIGNAL(declared())));
+    QVERIFY(queue->consume());
+    QSignalSpy spy(queue, SIGNAL(consuming(QString)));
+    QVERIFY(waitForSignal(queue, SIGNAL(consuming(QString))));
+    QVERIFY(queue->isConsuming());
+    QList<QVariant> arguments = spy.takeFirst();
+    QCOMPARE(arguments.at(0).toString(), queue->consumerTag());
+    QCOMPARE(queue->consume(), false);
+}
+
 QTEST_MAIN(tst_QAMQPQueue)
 #include "tst_qamqpqueue.moc"

tutorials/routing/receive_logs_direct/main.cpp

@@ -30,7 +30,6 @@ private Q_SLOTS:
     void exchangeDeclared() {
         Queue *temporaryQueue = m_client.createQueue();
         connect(temporaryQueue, SIGNAL(declared()), this, SLOT(queueDeclared()));
-        connect(temporaryQueue, SIGNAL(bound()), this, SLOT(queueBound()));
         connect(temporaryQueue, SIGNAL(messageReceived()), this, SLOT(messageReceived()));
         temporaryQueue->declare(Queue::Exclusive);
     }
@@ -40,18 +39,14 @@ private Q_SLOTS:
         if (!temporaryQueue)
             return;
 
+        // start consuming
+        temporaryQueue->consume(Queue::coNoAck);
+
         foreach (QString severity, m_severities)
             temporaryQueue->bind("direct_logs", severity);
         qDebug() << " [*] Waiting for logs. To exit press CTRL+C";
     }
 
-    void queueBound() {
-        Queue *temporaryQueue = qobject_cast<Queue*>(sender());
-        if (!temporaryQueue)
-            return;
-        temporaryQueue->consume(Queue::coNoAck);
-    }
-
     void messageReceived() {
         Queue *temporaryQueue = qobject_cast<Queue*>(sender());
         if (!temporaryQueue)