samples: sample for receiving messages with exactly-once delivery ena…

…bled (#588)

* Add receive_messages_with_exactly_once_delivery_enabled sample with its own region tag

* Address Tianzi and Mahesh's comments.

* Add code for arg parsing / integrate sample with infra

* Add sample test

* Reformat and remove min lease extension period setting from sample

* Address Tianzi's comments.

* Fix import of subscriber exceptions.

samples/snippets/subscriber.py

@@ -580,6 +580,61 @@ def callback(message: pubsub_v1.subscriber.message.Message) -> None:
     # [END pubsub_subscriber_blocking_shutdown]
 
 
+def receive_messages_with_exactly_once_delivery_enabled(
+    project_id: str, subscription_id: str, timeout: Optional[float] = None
+) -> None:
+    """Receives messages from a pull subscription with exactly-once delivery enabled."""
+    # [START pubsub_subscriber_exactly_once]
+    from concurrent.futures import TimeoutError
+    from google.cloud import pubsub_v1
+    from google.cloud.pubsub_v1.subscriber import exceptions as sub_exceptions
+
+    # TODO(developer)
+    # project_id = "your-project-id"
+    # subscription_id = "your-subscription-id"
+    # Number of seconds the subscriber should listen for messages
+    # timeout = 5.0
+
+    subscriber = pubsub_v1.SubscriberClient()
+    # The `subscription_path` method creates a fully qualified identifier
+    # in the form `projects/{project_id}/subscriptions/{subscription_id}`
+    subscription_path = subscriber.subscription_path(project_id, subscription_id)
+
+    def callback(message: pubsub_v1.subscriber.message.Message) -> None:
+        print(f"Received {message}.")
+
+        # Use `ack_with_response()` instead of `ack()` to get a future that tracks
+        # the result of the acknowledge call. When exactly-once delivery is enabled
+        # on the subscription, the message is guaranteed to not be delivered again
+        # if the ack future succeeds.
+        ack_future = message.ack_with_response()
+
+        try:
+            # Block on result of acknowledge call.
+            # When `timeout` is not set, result() will block indefinitely,
+            # unless an exception is encountered first.
+            ack_future.result(timeout=timeout)
+            print(f"Ack for message {message.message_id} successful.")
+        except sub_exceptions.AcknowledgeError as e:
+            print(
+                f"Ack for message {message.message_id} failed with error: {e.error_code}"
+            )
+
+    streaming_pull_future = subscriber.subscribe(subscription_path, callback=callback)
+    print(f"Listening for messages on {subscription_path}..\n")
+
+    # Wrap subscriber in a 'with' block to automatically call close() when done.
+    with subscriber:
+        try:
+            # When `timeout` is not set, result() will block indefinitely,
+            # unless an exception is encountered first.
+            streaming_pull_future.result(timeout=timeout)
+        except TimeoutError:
+            streaming_pull_future.cancel()  # Trigger the shutdown.
+            streaming_pull_future.result()  # Block until the shutdown is complete.
+    # [END pubsub_subscriber_exactly_once]
+
+
 def synchronous_pull(project_id: str, subscription_id: str) -> None:
     """Pulling messages synchronously."""
     # [START pubsub_subscriber_sync_pull]
@@ -881,6 +936,17 @@ def callback(message: pubsub_v1.subscriber.message.Message) -> None:
         "timeout", default=None, type=float, nargs="?"
     )
 
+    receive_messages_with_exactly_once_delivery_enabled_parser = subparsers.add_parser(
+        "receive-messages-with-exactly-once-delivery-enabled",
+        help=receive_messages_with_exactly_once_delivery_enabled.__doc__,
+    )
+    receive_messages_with_exactly_once_delivery_enabled_parser.add_argument(
+        "subscription_id"
+    )
+    receive_messages_with_exactly_once_delivery_enabled_parser.add_argument(
+        "timeout", default=None, type=float, nargs="?"
+    )
+
     synchronous_pull_parser = subparsers.add_parser(
         "receive-synchronously", help=synchronous_pull.__doc__
     )
@@ -967,6 +1033,10 @@ def callback(message: pubsub_v1.subscriber.message.Message) -> None:
         receive_messages_with_blocking_shutdown(
             args.project_id, args.subscription_id, args.timeout
         )
+    elif args.command == "receive-messages-with-exactly-once-delivery-enabled":
+        receive_messages_with_exactly_once_delivery_enabled(
+            args.project_id, args.subscription_id, args.timeout
+        )
     elif args.command == "receive-synchronously":
         synchronous_pull(args.project_id, args.subscription_id)
     elif args.command == "receive-synchronously-with-lease":

samples/snippets/subscriber_test.py

@@ -624,6 +624,34 @@ def eventually_consistent_test() -> None:
     eventually_consistent_test()
 
 
+def test_receive_messages_with_exactly_once_delivery_enabled(
+    publisher_client: pubsub_v1.PublisherClient,
+    topic: str,
+    subscription_async: str,
+    capsys: CaptureFixture[str],
+) -> None:
+
+    typed_backoff = cast(
+        Callable[[C], C], backoff.on_exception(backoff.expo, Unknown, max_time=60),
+    )
+
+    @typed_backoff
+    def eventually_consistent_test() -> None:
+        _publish_messages(publisher_client, topic)
+
+        subscriber.receive_messages_with_exactly_once_delivery_enabled(
+            PROJECT_ID, SUBSCRIPTION_ASYNC, 10
+        )
+
+        out, _ = capsys.readouterr()
+        assert "Listening" in out
+        assert subscription_async in out
+        assert "Received" in out
+        assert "Ack" in out
+
+    eventually_consistent_test()
+
+
 def test_listen_for_errors(
     publisher_client: pubsub_v1.PublisherClient,
     topic: str,