feat: Make message_id encode a PublishMetadata which includes the partition

google/cloud/pubsublite/cloudpubsub/internal/make_subscriber.py

@@ -17,6 +17,11 @@
 
 from google.api_core.client_options import ClientOptions
 from google.auth.credentials import Credentials
+
+from google.cloud.pubsublite.cloudpubsub.message_transforms import (
+    to_cps_subscribe_message,
+    add_id_to_cps_subscribe_transformer,
+)
 from google.cloud.pubsublite.types import FlowControlSettings
 from google.cloud.pubsublite.cloudpubsub.internal.ack_set_tracker_impl import (
     AckSetTrackerImpl,
@@ -28,10 +33,7 @@
 from google.cloud.pubsublite.cloudpubsub.internal.single_partition_subscriber import (
     SinglePartitionSingleSubscriber,
 )
-from google.cloud.pubsublite.cloudpubsub.message_transformer import (
-    MessageTransformer,
-    DefaultMessageTransformer,
-)
+from google.cloud.pubsublite.cloudpubsub.message_transformer import MessageTransformer
 from google.cloud.pubsublite.cloudpubsub.nack_handler import (
     NackHandler,
     DefaultNackHandler,
@@ -149,7 +151,7 @@ def cursor_connection_factory(
             flow_control_settings,
             ack_set_tracker,
             nack_handler,
-            message_transformer,
+            add_id_to_cps_subscribe_transformer(partition, message_transformer),
         )
 
     return factory
@@ -200,7 +202,7 @@ def make_async_subscriber(
     if nack_handler is None:
         nack_handler = DefaultNackHandler()
     if message_transformer is None:
-        message_transformer = DefaultMessageTransformer()
+        message_transformer = MessageTransformer.of_callable(to_cps_subscribe_message)
     partition_subscriber_factory = _make_partition_subscriber_factory(
         subscription,
         transport,

google/cloud/pubsublite/cloudpubsub/message_transformer.py

@@ -13,12 +13,11 @@
 # limitations under the License.
 
 from abc import ABC, abstractmethod
+from typing import Callable
 
 from google.pubsub_v1 import PubsubMessage
+from overrides import overrides
 
-from google.cloud.pubsublite.cloudpubsub.message_transforms import (
-    to_cps_subscribe_message,
-)
 from google.cloud.pubsublite_v1 import SequencedMessage
 
 
@@ -39,7 +38,11 @@ def transform(self, source: SequencedMessage) -> PubsubMessage:
     """
         pass
 
+    @staticmethod
+    def of_callable(transformer: Callable[[SequencedMessage], PubsubMessage]):
+        class CallableTransformer(MessageTransformer):
+            @overrides
+            def transform(self, source: SequencedMessage) -> PubsubMessage:
+                return transformer(source)
 
-class DefaultMessageTransformer(MessageTransformer):
-    def transform(self, source: SequencedMessage) -> PubsubMessage:
-        return to_cps_subscribe_message(source)
+        return CallableTransformer()

google/cloud/pubsublite/cloudpubsub/message_transforms.py

@@ -18,6 +18,8 @@
 from google.protobuf.timestamp_pb2 import Timestamp
 from google.pubsub_v1 import PubsubMessage
 
+from google.cloud.pubsublite.cloudpubsub import MessageTransformer
+from google.cloud.pubsublite.types import Partition, PublishMetadata
 from google.cloud.pubsublite_v1 import AttributeValues, SequencedMessage, PubSubMessage
 
 PUBSUB_LITE_EVENT_TIME = "x-goog-pubsublite-event-time"
@@ -52,9 +54,23 @@ def _parse_attributes(values: AttributeValues) -> str:
         )
 
 
+def add_id_to_cps_subscribe_transformer(
+    partition: Partition, transformer: MessageTransformer
+) -> MessageTransformer:
+    def add_id_to_message(source: SequencedMessage):
+        message: PubsubMessage = transformer.transform(source)
+        if message.message_id:
+            raise InvalidArgument(
+                "Message after transforming has the message_id field set."
+            )
+        message.message_id = PublishMetadata(partition, source.cursor).encode()
+        return message
+
+    return MessageTransformer.of_callable(add_id_to_message)
+
+
 def to_cps_subscribe_message(source: SequencedMessage) -> PubsubMessage:
     message: PubsubMessage = to_cps_publish_message(source.message)
-    message.message_id = str(source.cursor.offset)
     message.publish_time = source.publish_time
     return message
 

google/cloud/pubsublite/cloudpubsub/subscriber_client.py

@@ -74,7 +74,7 @@ def __init__(
         Args:
             executor: A ThreadPoolExecutor to use. The client will shut it down on __exit__. If provided a single threaded executor, messages will be ordered per-partition, but take care that the callback does not block for too long as it will impede forward progress on all subscriptions.
             nack_handler: A handler for when `nack()` is called. The default NackHandler raises an exception and fails the subscribe stream.
-            message_transformer: A transformer from Pub/Sub Lite messages to Cloud Pub/Sub messages.
+            message_transformer: A transformer from Pub/Sub Lite messages to Cloud Pub/Sub messages. This may not return a message with "message_id" set.
             credentials: If provided, the credentials to use when connecting.
             transport: The transport to use. Must correspond to an asyncio transport.
             client_options: The client options to use when connecting. If used, must explicitly set `api_endpoint`.
@@ -151,7 +151,7 @@ def __init__(
 
         Args:
             nack_handler: A handler for when `nack()` is called. The default NackHandler raises an exception and fails the subscribe stream.
-            message_transformer: A transformer from Pub/Sub Lite messages to Cloud Pub/Sub messages.
+            message_transformer: A transformer from Pub/Sub Lite messages to Cloud Pub/Sub messages. This may not return a message with "message_id" set.
             credentials: If provided, the credentials to use when connecting.
             transport: The transport to use. Must correspond to an asyncio transport.
             client_options: The client options to use when connecting. If used, must explicitly set `api_endpoint`.

samples/snippets/subscriber_example.py

@@ -21,6 +21,10 @@
 
 import argparse
 
+from google.pubsub_v1 import PubsubMessage
+
+from google.cloud.pubsublite.types import PublishMetadata
+
 
 def receive_messages(
     project_number, cloud_region, zone_id, subscription_id, timeout=90
@@ -54,9 +58,10 @@ def receive_messages(
         bytes_outstanding=10 * 1024 * 1024,
     )
 
-    def callback(message):
+    def callback(message: PubsubMessage):
         message_data = message.data.decode("utf-8")
-        print(f"Received {message_data} of ordering key {message.ordering_key}.")
+        metadata = PublishMetadata.decode(message.message_id)
+        print(f"Received {message_data} of ordering key {message.ordering_key} with id {metadata}.")
         message.ack()
 
     # SubscriberClient() must be used in a `with` block or have __enter__() called before use.

tests/unit/pubsublite/cloudpubsub/message_transforms_test.py

@@ -19,12 +19,15 @@
 from google.protobuf.timestamp_pb2 import Timestamp
 from google.pubsub_v1 import PubsubMessage
 
+from google.cloud.pubsublite.cloudpubsub import MessageTransformer
 from google.cloud.pubsublite.cloudpubsub.message_transforms import (
     PUBSUB_LITE_EVENT_TIME,
     to_cps_subscribe_message,
     encode_attribute_event_time,
     from_cps_publish_message,
+    add_id_to_cps_subscribe_transformer,
 )
+from google.cloud.pubsublite.types import Partition, PublishMetadata
 from google.cloud.pubsublite_v1 import (
     SequencedMessage,
     Cursor,
@@ -104,7 +107,6 @@ def test_subscribe_transform_correct():
                 Timestamp(seconds=55).ToDatetime()
             ),
         },
-        message_id=str(10),
         publish_time=Timestamp(seconds=10),
     )
     result = to_cps_subscribe_message(
@@ -126,6 +128,66 @@ def test_subscribe_transform_correct():
     assert result == expected
 
 
+def test_wrapped_sets_id_error():
+    wrapped = add_id_to_cps_subscribe_transformer(
+        Partition(1),
+        MessageTransformer.of_callable(lambda x: PubsubMessage(message_id="a")),
+    )
+    with pytest.raises(InvalidArgument):
+        wrapped.transform(
+            SequencedMessage(
+                message=PubSubMessage(
+                    data=b"xyz",
+                    key=b"def",
+                    event_time=Timestamp(seconds=55),
+                    attributes={
+                        "x": AttributeValues(values=[b"abc"]),
+                        "y": AttributeValues(values=[b"abc"]),
+                    },
+                ),
+                publish_time=Timestamp(seconds=10),
+                cursor=Cursor(offset=10),
+                size_bytes=10,
+            )
+        )
+
+
+def test_wrapped_successful():
+    wrapped = add_id_to_cps_subscribe_transformer(
+        Partition(1), MessageTransformer.of_callable(to_cps_subscribe_message)
+    )
+    expected = PubsubMessage(
+        data=b"xyz",
+        ordering_key="def",
+        attributes={
+            "x": "abc",
+            "y": "abc",
+            PUBSUB_LITE_EVENT_TIME: encode_attribute_event_time(
+                Timestamp(seconds=55).ToDatetime()
+            ),
+        },
+        message_id=PublishMetadata(Partition(1), Cursor(offset=10)).encode(),
+        publish_time=Timestamp(seconds=10),
+    )
+    result = wrapped.transform(
+        SequencedMessage(
+            message=PubSubMessage(
+                data=b"xyz",
+                key=b"def",
+                event_time=Timestamp(seconds=55),
+                attributes={
+                    "x": AttributeValues(values=[b"abc"]),
+                    "y": AttributeValues(values=[b"abc"]),
+                },
+            ),
+            publish_time=Timestamp(seconds=10),
+            cursor=Cursor(offset=10),
+            size_bytes=10,
+        )
+    )
+    assert result == expected
+
+
 def test_publish_invalid_event_time():
     with pytest.raises(InvalidArgument):
         from_cps_publish_message(