minor #12340 [Messenger] Added an implementation to the TransportInterface (Nyholm)

This PR was submitted for the master branch but it was squashed and merged into the 4.3 branch instead (closes #12340).

Discussion
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[Messenger] Added an implementation to the TransportInterface

This will fix #12230

This is basically a much simpler `DoctrineTransport` with easy query builders and no real error handling.

Commits
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e1c669b [Messenger] Added an implementation to the TransportInterface

Author: javiereguiluz

messenger/custom-transport.rst

@@ -31,33 +31,109 @@ DSN. You will need a transport factory::
 The transport object needs to implement the
 :class:`Symfony\\Component\\Messenger\\Transport\\TransportInterface`
 (which combines the :class:`Symfony\\Component\\Messenger\\Transport\\Sender\\SenderInterface`
-and :class:`Symfony\\Component\\Messenger\\Transport\\Receiver\\ReceiverInterface`)::
+and :class:`Symfony\\Component\\Messenger\\Transport\\Receiver\\ReceiverInterface`).
+Here is a simplified example of a database transport::
 
+    use Ramsey\Uuid\Uuid;
     use Symfony\Component\Messenger\Envelope;
+    use Symfony\Component\Messenger\Stamp\TransportMessageIdStamp;
+    use Symfony\Component\Messenger\Transport\Serialization\PhpSerializer;
+    use Symfony\Component\Messenger\Transport\Serialization\SerializerInterface;
+    use Symfony\Component\Messenger\Transport\TransportInterface;
 
     class YourTransport implements TransportInterface
     {
+        private $db;
+        private $serializer;
+
+        /**
+         * @param FakeDatabase $db is used for demo purposes. It is not a real class.
+         */
+        public function __construct(FakeDatabase $db, SerializerInterface $serializer = null)
+        {
+            $this->db = $db;
+            $this->serializer = $serializer ?? new PhpSerializer();
+        }
+
         public function get(): iterable
         {
-            // ...
+            // Get a message from "my_queue"
+            $row = $this->db->createQueryBuilder()
+                ->from('my_queue')
+                ->where('delivered_at is null OR delivered_at < :redeliver_timeout')
+                ->andWhere('handled = :false')
+                ->setParameter('redeliver_timeout', new DateTimeImmutable('-5minutes'))
+                ->setParameter('false', false)
+                ->getOneOrNullResult();
+
+            if (null === $row) {
+                return [];
+            }
+
+            $envelope = $this->serializer->decode([
+                'body' => $row['envelope'],
+            ]);
+
+            return [$envelope->with(new TransportMessageIdStamp($row['id']))];
         }
 
         public function ack(Envelope $envelope): void
         {
-            // ...
+            $stamp = $envelope->last(TransportMessageIdStamp::class);
+            if (!$stamp instanceof TransportMessageIdStamp) {
+                throw new \LogicException('No TransportMessageIdStamp found on the Envelope.');
+            }
+
+            // Mark the message as "handled"
+            $this->db->createQueryBuilder()
+                ->update('my_queue')
+                ->setValues([
+                    'handled' => true
+                ])
+                ->where('id = :id')
+                ->setParameter('id', $stamp->getId())
+                ->execute();
         }
 
         public function reject(Envelope $envelope): void
         {
-            // ...
+            $stamp = $envelope->last(TransportMessageIdStamp::class);
+            if (!$stamp instanceof TransportMessageIdStamp) {
+                throw new \LogicException('No TransportMessageIdStamp found on the Envelope.');
+            }
+
+            // Delete the message from the "my_queue" table
+            $this->db->createQueryBuilder()
+                ->delete('my_queue')
+                ->where('id = :id')
+                ->setParameter('id', $stamp->getId())
+                ->execute();
         }
 
         public function send(Envelope $envelope): Envelope
         {
-            // ...
+            $encodedMessage = $this->serializer->encode($envelope);
+            $uuid = Uuid::uuid4()->toString();
+
+            // Add a message to the "my_queue" table
+            $this->db->createQueryBuilder()
+                ->insert('my_queue')
+                ->values([
+                    'id' => $uuid,
+                    'envelope' => $encodedMessage['body'],
+                    'delivered_at' => null,
+                    'handled' => false,
+                ]);
+
+            return $envelope->with(new TransportMessageIdStamp($uuid));
         }
     }
 
+The implementation above is not runnable code but illustrates how a
+:class:`Symfony\\Component\\Messenger\\Transport\\TransportInterface` could
+be implemented. For real implementations see :class:`Symfony\\Component\\Messenger\\Transport\\InMemoryTransport`
+and :class:`Symfony\\Component\\Messenger\\Transport\\Doctrine\\DoctrineReceiver`.
+
 Register your Factory
 ---------------------