Makes streaming Subscription iterable (#751)

* Make Streaming Subscription iterable

Signed-off-by: Elena Kolevska <[email protected]>

* Adds iter for async client

Signed-off-by: Elena Kolevska <[email protected]>

* linter and updates docs

Signed-off-by: Elena Kolevska <[email protected]>

---------

Signed-off-by: Elena Kolevska <[email protected]>

Author: elena-kolevska

dapr/aio/clients/grpc/client.py

@@ -534,13 +534,14 @@ async def subscribe_with_handler(
         async def stream_messages(sub: Subscription):
             while True:
                 try:
-                    message = await sub.next_message()
-                    if message:
-                        response = await handler_fn(message)
-                        if response:
-                            await subscription.respond(message, response.status)
-                    else:
-                        continue
+                    async for message in subscription:
+                        if message:
+                            response = await handler_fn(message)
+                            if response:
+                                await subscription.respond(message, response.status)
+                        else:
+                            continue
+
                 except StreamInactiveError:
                     break
 

dapr/aio/clients/grpc/subscription.py

@@ -114,3 +114,10 @@ async def close(self):
                     raise Exception(f'Error while closing stream: {e}')
             except Exception as e:
                 raise Exception(f'Error while closing stream: {e}')
+
+    def __aiter__(self):
+        """Make the subscription async iterable."""
+        return self
+
+    async def __anext__(self):
+        return await self.next_message()

dapr/clients/grpc/client.py

@@ -45,6 +45,7 @@
 from dapr.clients.grpc.interceptors import DaprClientInterceptor, DaprClientTimeoutInterceptor
 from dapr.clients.health import DaprHealth
 from dapr.clients.retry import RetryPolicy
+from dapr.common.pubsub.subscription import StreamCancelledError
 from dapr.conf import settings
 from dapr.proto import api_v1, api_service_v1, common_v1
 from dapr.proto.runtime.v1.dapr_pb2 import UnsubscribeConfigurationResponse
@@ -535,17 +536,20 @@ def subscribe_with_handler(
         def stream_messages(sub):
             while True:
                 try:
-                    message = sub.next_message()
-                    if message:
-                        # Process the message
-                        response = handler_fn(message)
-                        if response:
-                            subscription.respond(message, response.status)
-                    else:
-                        # No message received
-                        continue
+                    for message in sub:
+                        if message:
+                            # Process the message
+                            response = handler_fn(message)
+                            if response:
+                                subscription.respond(message, response.status)
+                        else:
+                            # No message received
+                            continue
+
                 except StreamInactiveError:
                     break
+                except StreamCancelledError:
+                    break
 
         def close_subscription():
             subscription.close()

dapr/clients/grpc/subscription.py

@@ -143,3 +143,9 @@ def close(self):
                     raise Exception(f'Error while closing stream: {e}')
             except Exception as e:
                 raise Exception(f'Error while closing stream: {e}')
+
+    def __iter__(self):
+        return self
+
+    def __next__(self):
+        return self.next_message()

daprdocs/content/en/python-sdk-docs/python-client.md

@@ -260,8 +260,8 @@ def mytopic_important(event: v1.Event) -> None:
 You can create a streaming subscription to a PubSub topic using either the `subscribe`
 or `subscribe_handler` methods.
 
-The `subscribe` method returns a `Subscription` object, which allows you to pull messages from the
-stream by
+The `subscribe` method returns an iterable `Subscription` object, which allows you to pull messages from the
+stream by using a `for` loop (ex. `for message in subscription`) or by 
 calling the `next_message` method. This will block on the main thread while waiting for messages.
 When done, you should call the close method to terminate the
 subscription and stop receiving messages.
@@ -281,7 +281,7 @@ Here's an example of using the `subscribe` method:
 import time
 
 from dapr.clients import DaprClient
-from dapr.clients.grpc.subscription import StreamInactiveError
+from dapr.clients.grpc.subscription import StreamInactiveError, StreamCancelledError
 
 counter = 0
 
@@ -303,30 +303,35 @@ def main():
         )
 
         try:
-            while counter < 5:
-                try:
-                    message = subscription.next_message()
+            for message in subscription:
+                if message is None:
+                    print('No message received. The stream might have been cancelled.')
+                    continue
 
-                except StreamInactiveError as e:
+                try:
+                    response_status = process_message(message)
+
+                    if response_status == 'success':
+                        subscription.respond_success(message)
+                    elif response_status == 'retry':
+                        subscription.respond_retry(message)
+                    elif response_status == 'drop':
+                        subscription.respond_drop(message)
+
+                    if counter >= 5:
+                        break
+                except StreamInactiveError:
                     print('Stream is inactive. Retrying...')
                     time.sleep(1)
                     continue
-                if message is None:
-                    print('No message received within timeout period.')
-                    continue
-
-                # Process the message
-                response_status = process_message(message)
-
-                if response_status == 'success':
-                    subscription.respond_success(message)
-                elif response_status == 'retry':
-                    subscription.respond_retry(message)
-                elif response_status == 'drop':
-                    subscription.respond_drop(message)
+                except StreamCancelledError:
+                    print('Stream was cancelled')
+                    break
+                except Exception as e:
+                    print(f'Error occurred during message processing: {e}')
 
         finally:
-            print("Closing subscription...")
+            print('Closing subscription...')
             subscription.close()
 
 

examples/pubsub-streaming-async/subscriber-handler.py

@@ -18,7 +18,7 @@ async def process_message(message) -> TopicEventResponse:
     Asynchronously processes the message and returns a TopicEventResponse.
     """
 
-    print(f'Processing message: {message.data()} from {message.topic()}...')
+    print(f'Processing message: {message.data()} from {message.topic()}...', flush=True)
     global counter
     counter += 1
     return TopicEventResponse('success')

examples/pubsub-streaming-async/subscriber.py

@@ -19,7 +19,7 @@ def process_message(message):
     global counter
     counter += 1
     # Process the message here
-    print(f'Processing message: {message.data()} from {message.topic()}...')
+    print(f'Processing message: {message.data()} from {message.topic()}...', flush=True)
     return 'success'
 
 
@@ -31,32 +31,36 @@ async def main():
         )
 
         try:
-            while counter < 5:
+            async for message in subscription:
+                if message is None:
+                    print(
+                        'No message received within timeout period. '
+                        'The stream might have been cancelled.'
+                    )
+                    continue
+
                 try:
-                    message = await subscription.next_message()
-                    if message is None:
-                        print(
-                            'No message received within timeout period. '
-                            'The stream might have been cancelled.'
-                        )
-                        continue
+                    # Process the message
+                    response_status = process_message(message)
+
+                    # Respond based on the processing result
+                    if response_status == 'success':
+                        await subscription.respond_success(message)
+                    elif response_status == 'retry':
+                        await subscription.respond_retry(message)
+                    elif response_status == 'drop':
+                        await subscription.respond_drop(message)
+
+                    if counter >= 5:
+                        break
 
                 except StreamInactiveError:
                     print('Stream is inactive. Retrying...')
                     await asyncio.sleep(1)
                     continue
-                except StreamCancelledError as e:
+                except StreamCancelledError:
                     print('Stream was cancelled')
                     break
-                # Process the message
-                response_status = process_message(message)
-
-                if response_status == 'success':
-                    await subscription.respond_success(message)
-                elif response_status == 'retry':
-                    await subscription.respond_retry(message)
-                elif response_status == 'drop':
-                    await subscription.respond_drop(message)
 
         finally:
             print('Closing subscription...')

examples/pubsub-streaming/subscriber-handler.py

@@ -18,7 +18,7 @@ def process_message(message):
     # Process the message here
     global counter
     counter += 1
-    print(f'Processing message: {message.data()} from {message.topic()}...')
+    print(f'Processing message: {message.data()} from {message.topic()}...', flush=True)
     return TopicEventResponse('success')
 
 

examples/pubsub-streaming/subscriber.py

@@ -19,7 +19,7 @@ def process_message(message):
     global counter
     counter += 1
     # Process the message here
-    print(f'Processing message: {message.data()} from {message.topic()}...')
+    print(f'Processing message: {message.data()} from {message.topic()}...', flush=True)
     return 'success'
 
 
@@ -36,36 +36,32 @@ def main():
             return
 
         try:
-            while counter < 5:
+            for message in subscription:
+                if message is None:
+                    print('No message received. The stream might have been cancelled.')
+                    continue
+
                 try:
-                    message = subscription.next_message()
-                    if message is None:
-                        print(
-                            'No message received within timeout period. '
-                            'The stream might have been cancelled.'
-                        )
-                        continue
-
-                except StreamInactiveError as e:
+                    response_status = process_message(message)
+
+                    if response_status == 'success':
+                        subscription.respond_success(message)
+                    elif response_status == 'retry':
+                        subscription.respond_retry(message)
+                    elif response_status == 'drop':
+                        subscription.respond_drop(message)
+
+                    if counter >= 5:
+                        break
+                except StreamInactiveError:
                     print('Stream is inactive. Retrying...')
                     time.sleep(1)
                     continue
-                except StreamCancelledError as e:
+                except StreamCancelledError:
                     print('Stream was cancelled')
                     break
                 except Exception as e:
-                    print(f'Error occurred: {e}')
-                    pass
-
-                # Process the message
-                response_status = process_message(message)
-
-                if response_status == 'success':
-                    subscription.respond_success(message)
-                elif response_status == 'retry':
-                    subscription.respond_retry(message)
-                elif response_status == 'drop':
-                    subscription.respond_drop(message)
+                    print(f'Error occurred during message processing: {e}')
 
         finally:
             print('Closing subscription...')