fix(flags): correctly emit feature flag events with the FF response on get_feature_flag_payload calls (#143)

* this is the fix, needs tests

* fix test

* tests

* yeah

* please work

* ran the formatter

* code review feedback

* how'd this get here

* bump version add changelog

* Update CHANGELOG.md

Co-authored-by: David Newell <[email protected]>

---------

Co-authored-by: David Newell <[email protected]>

Author: dmarticus

CHANGELOG.md

@@ -1,3 +1,7 @@
+## 3.7.4 - 2024-11-25
+
+1. Fix bug where this SDK incorrectly sent feature flag events with null values when calling `get_feature_flag_payload`.
+
 ## 3.7.3 - 2024-11-25
 
 1. Use personless mode when sending an exception without a provided `distinct_id`.

posthog/client.py

@@ -173,6 +173,15 @@ def get_feature_payloads(
         resp_data = self.get_decide(distinct_id, groups, person_properties, group_properties, disable_geoip)
         return resp_data["featureFlagPayloads"]
 
+    def get_feature_flags_and_payloads(
+        self, distinct_id, groups=None, person_properties=None, group_properties=None, disable_geoip=None
+    ):
+        resp_data = self.get_decide(distinct_id, groups, person_properties, group_properties, disable_geoip)
+        return {
+            "featureFlags": resp_data["featureFlags"],
+            "featureFlagPayloads": resp_data["featureFlagPayloads"],
+        }
+
     def get_decide(self, distinct_id, groups=None, person_properties=None, group_properties=None, disable_geoip=None):
         require("distinct_id", distinct_id, ID_TYPES)
 
@@ -746,23 +755,52 @@ def get_feature_flag_payload(
                 groups=groups,
                 person_properties=person_properties,
                 group_properties=group_properties,
-                send_feature_flag_events=send_feature_flag_events,
-                only_evaluate_locally=True,
+                send_feature_flag_events=False,
+                # Disable automatic sending of feature flag events because we're manually handling event dispatch.
+                # This prevents sending events with empty data when `get_feature_flag` cannot be evaluated locally.
+                only_evaluate_locally=True,  # Enable local evaluation of feature flags to avoid making multiple requests to `/decide`.
                 disable_geoip=disable_geoip,
             )
 
         response = None
+        payload = None
 
         if match_value is not None:
-            response = self._compute_payload_locally(key, match_value)
+            payload = self._compute_payload_locally(key, match_value)
+
+        flag_was_locally_evaluated = payload is not None
+        if not flag_was_locally_evaluated and not only_evaluate_locally:
+            try:
+                responses_and_payloads = self.get_feature_flags_and_payloads(
+                    distinct_id, groups, person_properties, group_properties, disable_geoip
+                )
+                response = responses_and_payloads["featureFlags"].get(key, None)
+                payload = responses_and_payloads["featureFlagPayloads"].get(str(key).lower(), None)
+            except Exception as e:
+                self.log.exception(f"[FEATURE FLAGS] Unable to get feature flags and payloads: {e}")
 
-        if response is None and not only_evaluate_locally:
-            decide_payloads = self.get_feature_payloads(
-                distinct_id, groups, person_properties, group_properties, disable_geoip
+        feature_flag_reported_key = f"{key}_{str(response)}"
+
+        if (
+            feature_flag_reported_key not in self.distinct_ids_feature_flags_reported[distinct_id]
+            and send_feature_flag_events  # noqa: W503
+        ):
+            self.capture(
+                distinct_id,
+                "$feature_flag_called",
+                {
+                    "$feature_flag": key,
+                    "$feature_flag_response": response,
+                    "$feature_flag_payload": payload,
+                    "locally_evaluated": flag_was_locally_evaluated,
+                    f"$feature/{key}": response,
+                },
+                groups=groups,
+                disable_geoip=disable_geoip,
             )
-            response = decide_payloads.get(str(key).lower(), None)
+            self.distinct_ids_feature_flags_reported[distinct_id].add(feature_flag_reported_key)
 
-        return response
+        return payload
 
     def _compute_payload_locally(self, key, match_value):
         payload = None

posthog/test/test_feature_flags.py

@@ -1632,9 +1632,10 @@ def test_boolean_feature_flag_payloads_local(self, patch_decide):
         )
         self.assertEqual(patch_decide.call_count, 0)
 
+    @mock.patch.object(Client, "capture")
     @mock.patch("posthog.client.decide")
-    def test_boolean_feature_flag_payload_decide(self, patch_decide):
-        patch_decide.return_value = {"featureFlagPayloads": {"person-flag": 300}}
+    def test_boolean_feature_flag_payload_decide(self, patch_decide, patch_capture):
+        patch_decide.return_value = {"featureFlags": {"person-flag": True}, "featureFlagPayloads": {"person-flag": 300}}
         self.assertEqual(
             self.client.get_feature_flag_payload(
                 "person-flag", "some-distinct-id", person_properties={"region": "USA"}
@@ -1649,6 +1650,8 @@ def test_boolean_feature_flag_payload_decide(self, patch_decide):
             300,
         )
         self.assertEqual(patch_decide.call_count, 2)
+        self.assertEqual(patch_capture.call_count, 1)
+        patch_capture.reset_mock()
 
     @mock.patch("posthog.client.decide")
     def test_multivariate_feature_flag_payloads(self, patch_decide):
@@ -2334,6 +2337,88 @@ def test_capture_is_called(self, patch_decide, patch_capture):
             disable_geoip=None,
         )
 
+    @mock.patch.object(Client, "capture")
+    @mock.patch("posthog.client.decide")
+    def test_capture_is_called_in_get_feature_flag_payload(self, patch_decide, patch_capture):
+        patch_decide.return_value = {
+            "featureFlags": {"person-flag": True},
+            "featureFlagPayloads": {"person-flag": 300},
+        }
+        client = Client(api_key=FAKE_TEST_API_KEY, personal_api_key=FAKE_TEST_API_KEY)
+
+        client.feature_flags = [
+            {
+                "id": 1,
+                "name": "Beta Feature",
+                "key": "person-flag",
+                "is_simple_flag": False,
+                "active": True,
+                "filters": {
+                    "groups": [
+                        {
+                            "properties": [{"key": "region", "value": "USA"}],
+                            "rollout_percentage": 100,
+                        }
+                    ],
+                },
+            }
+        ]
+
+        # Call get_feature_flag_payload with match_value=None to trigger get_feature_flag
+        client.get_feature_flag_payload(
+            key="person-flag", distinct_id="some-distinct-id", person_properties={"region": "USA", "name": "Aloha"}
+        )
+
+        # Assert that capture was called once, with the correct parameters
+        self.assertEqual(patch_capture.call_count, 1)
+        patch_capture.assert_called_with(
+            "some-distinct-id",
+            "$feature_flag_called",
+            {
+                "$feature_flag": "person-flag",
+                "$feature_flag_response": True,
+                "$feature_flag_payload": 300,
+                "locally_evaluated": False,
+                "$feature/person-flag": True,
+            },
+            groups={},
+            disable_geoip=None,
+        )
+
+        # Reset mocks for further tests
+        patch_capture.reset_mock()
+        patch_decide.reset_mock()
+
+        # Call get_feature_flag_payload again for the same user; capture should not be called again because we've already reported an event for this distinct_id + flag
+        client.get_feature_flag_payload(
+            key="person-flag", distinct_id="some-distinct-id", person_properties={"region": "USA", "name": "Aloha"}
+        )
+
+        self.assertEqual(patch_capture.call_count, 0)
+        patch_capture.reset_mock()
+
+        # Call get_feature_flag_payload for a different user; capture should be called
+        client.get_feature_flag_payload(
+            key="person-flag", distinct_id="some-distinct-id2", person_properties={"region": "USA", "name": "Aloha"}
+        )
+
+        self.assertEqual(patch_capture.call_count, 1)
+        patch_capture.assert_called_with(
+            "some-distinct-id2",
+            "$feature_flag_called",
+            {
+                "$feature_flag": "person-flag",
+                "$feature_flag_response": True,
+                "$feature_flag_payload": 300,
+                "locally_evaluated": False,
+                "$feature/person-flag": True,
+            },
+            groups={},
+            disable_geoip=None,
+        )
+
+        patch_capture.reset_mock()
+
     @mock.patch.object(Client, "capture")
     @mock.patch("posthog.client.decide")
     def test_disable_geoip_get_flag_capture_call(self, patch_decide, patch_capture):