src/Handler/SyncConsumerHandler.php
private function handleSyncMessage(Message $message, $returnValue)
    {
        self::checkMessageIsSync($message);

        $this->logger->debug(
            'Send return value back!',
            [
                'returnValue' => $returnValue,
                'correlationId' => $message->getCorrelationId(),
                'replyTo' => $message->getReplyTo()
            ]
        );

        $this->driver->publish(
            '',
            new Message(
                $returnValue,
                $message->getReplyTo(),
                $message->getHeaders(),
                $message->getCorrelationId()
            )
        );
    }
private function handleSyncMessage(Message $message, $returnValue)
    {
        self::checkMessageIsSync($message);

        $this->logger->debug(
            'Send return value back!',
            [
                'returnValue' => $returnValue,
                'correlationId' => $message->getCorrelationId(),
                'replyTo' => $message->getReplyTo()
            ]
        );

        $this->driver->publish(
            '',
            new Message(
                $returnValue,
                $message->getReplyTo(),
                $message->getHeaders(),
                $message->getCorrelationId()
            )
        );
    }
Handle the return value.

@param Message $message
@param string  $returnValue

@throws ConsumerException
@throws AssertionFailedException
@throws \InvalidArgumentException