fix: avoid infinite recursion of openedx-event (#312)

Prevent event bus recursion: #79

CHANGELOG.rst

@@ -13,6 +13,13 @@ Change Log
 
 Unreleased
 ----------
+
+[9.5.1] - 2024-02-12
+--------------------
+Changed
+~~~~~~~
+* Fixed recursion error when consuming events on the same service that produced them.
+
 [9.5.0] - 2024-02-07
 --------------------
 Added

openedx_events/__init__.py

@@ -5,4 +5,4 @@
 more information about the project.
 """
 
-__version__ = "9.5.0"
+__version__ = "9.5.1"

openedx_events/apps.py

@@ -1,13 +1,16 @@
 """
 openedx_events Django application initialization.
 """
+import logging
 
 from django.apps import AppConfig
 from django.conf import settings
 
 from openedx_events.event_bus import get_producer
 from openedx_events.exceptions import ProducerConfigurationError
-from openedx_events.tooling import OpenEdxPublicSignal, load_all_signals
+from openedx_events.tooling import SIGNAL_PROCESSED_FROM_EVENT_BUS, OpenEdxPublicSignal, load_all_signals
+
+logger = logging.getLogger(__name__)
 
 
 def general_signal_handler(sender, signal, **kwargs):  # pylint: disable=unused-argument
@@ -20,6 +23,13 @@ def general_signal_handler(sender, signal, **kwargs):  # pylint: disable=unused-
     #        "topic_a": { "event_key_field": "my.key.field", "enabled": True },
     #        "topic_b": { "event_key_field": "my.key.field", "enabled": False }
     # }"
+    if kwargs.get(SIGNAL_PROCESSED_FROM_EVENT_BUS) is True:
+        logger.debug(
+            "Declining to send signal to the Event Bus since that's "
+            f"where it was sent from: {signal.event_type} (preventing recursion)"
+        )
+        return
+
     event_data = {key: kwargs.get(key) for key in signal.init_data}
 
     for topic in event_type_producer_configs.keys():

openedx_events/tests/test_producer_config.py

@@ -55,6 +55,29 @@ def test_enabled_disabled_events(self, mock_producer):
             call_args
         )
 
+    @patch("openedx_events.apps.logger")
+    @patch('openedx_events.apps.get_producer')
+    def test_send_events_with_custom_metadata_not_replayed_by_handler(self, mock_producer, mock_logger):
+        """
+        Check wheter XBLOCK_PUBLISHED is connected to the handler and the handler
+        do not send any events as the signal is marked "from_event_bus".
+
+        Args:
+            mock_producer: mock get_producer to inspect the arguments.
+            mock_logger: mock logger to inspect the arguments.
+        """
+        mock_send = Mock()
+        mock_producer.return_value = mock_send
+        metadata = XBLOCK_PUBLISHED.generate_signal_metadata()
+
+        XBLOCK_PUBLISHED.send_event_with_custom_metadata(metadata, xblock_info=self.xblock_info)
+
+        mock_send.send.assert_not_called()
+        mock_logger.debug.assert_called_once_with(
+            "Declining to send signal to the Event Bus since that's "
+            f"where it was sent from: {XBLOCK_PUBLISHED.event_type} (preventing recursion)"
+        )
+
     @patch('openedx_events.apps.get_producer')
     @override_settings(EVENT_BUS_PRODUCER_CONFIG={})
     def test_events_not_in_config(self, mock_producer):

openedx_events/tests/test_tooling.py

@@ -179,6 +179,7 @@ def test_send_event_allow_failure_successfully(self, send_mock, fake_metadata):
             sender=None,
             user=self.user_mock,
             metadata=expected_metadata,
+            from_event_bus=False,
         )
 
     @patch("openedx_events.tooling.OpenEdxPublicSignal.generate_signal_metadata")
@@ -198,7 +199,8 @@ def test_send_robust_event_successfully(self, format_responses_mock, log_mock, f
             self.public_signal.send_event(user=self.user_mock)
 
         self.ok_receiver.assert_called_once_with(
-            signal=self.public_signal, sender=None, user=self.user_mock, metadata=expected_metadata
+            signal=self.public_signal, sender=None, user=self.user_mock, metadata=expected_metadata,
+            from_event_bus=False
         )
         # format_responses is mocked out because its output is
         # complicated enough to warrant its own set of tests.
@@ -253,7 +255,7 @@ def test_send_event_with_custom_metadata(self, mock_send_event_with_metadata):
 
         assert response == expected_response
         mock_send_event_with_metadata.assert_called_once_with(
-            metadata=metadata, send_robust=True, foo="bar",
+            metadata=metadata, send_robust=True, foo="bar", from_event_bus=True
         )
 
     @ddt.data(

openedx_events/tooling.py

@@ -30,6 +30,8 @@
     "org.openedx.learning.course.notification.requested.v1",
 ]
 
+SIGNAL_PROCESSED_FROM_EVENT_BUS = "from_event_bus"
+
 
 class OpenEdxPublicSignal(Signal):
     """
@@ -115,7 +117,7 @@ def generate_signal_metadata(self, time=None):
             time=time,
         )
 
-    def _send_event_with_metadata(self, metadata, send_robust=True, **kwargs):
+    def _send_event_with_metadata(self, metadata, send_robust=True, from_event_bus=False, **kwargs):
         """
         Send events to all connected receivers with the provided metadata.
 
@@ -124,6 +126,10 @@ def _send_event_with_metadata(self, metadata, send_robust=True, **kwargs):
         Arguments:
             metadata (EventsMetadata): The metadata to be sent with the signal.
             send_robust (bool): Defaults to True. See Django signal docs.
+            from_event_bus (bool): Defaults to False. If True, the signal is
+                being sent from the event bus. This is used to prevent infinite
+                loops when the event bus is consuming events. It should not be
+                used when sending events from the application.
 
         See ``send_event`` docstring for more details on its usage and behavior.
         """
@@ -163,6 +169,7 @@ def validate_sender():
         validate_sender()
 
         kwargs["metadata"] = metadata
+        kwargs[SIGNAL_PROCESSED_FROM_EVENT_BUS] = from_event_bus
 
         if self._allow_send_event_failure or settings.DEBUG or not send_robust:
             return super().send(sender=None, **kwargs)
@@ -234,7 +241,9 @@ def send_event_with_custom_metadata(
         See ``send_event`` docstring for more details.
 
         """
-        return self._send_event_with_metadata(metadata=metadata, send_robust=send_robust, **kwargs)
+        return self._send_event_with_metadata(
+            metadata=metadata, send_robust=send_robust, from_event_bus=True, **kwargs
+        )
 
     def send(self, sender, **kwargs):  # pylint: disable=unused-argument
         """