Why ActiveMQ delivers duplicate messages to my PHP consumer over Stomp? - php

Question

I am not sure whether this question is related to stomp-php or ActiveMQ Docker (running with defaults).
I have a simple Queue helper class written in PHP that handles both sending the message to the queue (Queue::push), as well as consumes it (Queue::fetch). See code below.
As you can see, fetch() should subscribe to the queue, read one message and unsubscribe. The message should be acknowledged automatically (\Stomp\StatefulStomp::subscribe(), 3rd. argument).
For some reason, about 5-7% of the messages are received by the customer twice or even three times. Why messages are delivered multiple times and how to avoid it?
Publisher (pushing 1000 messages):
$mq = new Queue('tcp://activemq:61613','test');
for ($msgCount = 0; $msgCount < 1000; $msgCount++) {
$mq->push('Message #' . $msgCount);
}
Consumer (receiving ~1070 messages):
$mq = new Queue('tcp://activemq:61613','test');
$received = 0;
while (true) {
$message = $mq->fetch();
if (null === $message) { break; }
$received++;
}
Queue class code:
use Stomp\Client;
use Stomp\Network\Connection;
use Stomp\SimpleStomp;
use Stomp\StatefulStomp;
use Stomp\Transport\Message;
class Queue
{
/**
* #var \Stomp\StatefulStomp
*/
private $stomp;
private $queue;
public function __construct($uri, $queue) {
$connection = new Connection('tcp://activemq:61613');
$this->stomp = new StatefulStomp(new Client($connection));
$connection->setReadTimeout(1);
$this->queue = $queue;
}
public function push($body) {
$message = new Message($body, ['activemq.maximumRedeliveries' => 0]);
$this->stomp->send('/queue/' . $this->queue, $message);
}
public function fetch() {
$subscriptionId = $this->stomp->subscribe('/queue/' . $this->queue, null, 'auto', ['activemq.prefetchSize' => 1]);
$msg = $this->stomp->read();
$this->stomp->unsubscribe($subscriptionId);
return $msg;
}
}