fix(flags): remove lower() when evaluating feature flag payloads – these payloads are case-sensitive!

posthog/client.py

@@ -822,7 +822,7 @@ def get_feature_flag_payload(
                     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)
+                payload = responses_and_payloads["featureFlagPayloads"].get(str(key), None)
             except Exception as e:
                 self.log.exception(f"[FEATURE FLAGS] Unable to get feature flags and payloads: {e}")
 
@@ -855,10 +855,14 @@ def _compute_payload_locally(self, key, match_value):
         if self.feature_flags_by_key is None:
             return payload
 
-        flag_definition = self.feature_flags_by_key.get(key) or {}
-        flag_filters = flag_definition.get("filters") or {}
-        flag_payloads = flag_filters.get("payloads") or {}
-        payload = flag_payloads.get(str(match_value).lower(), None)
+        flag_definition = self.feature_flags_by_key.get(key)
+        if flag_definition:
+            flag_filters = flag_definition.get("filters") or {}
+            flag_payloads = flag_filters.get("payloads") or {}
+            # For boolean flags, convert True to "true"
+            # For multivariate flags, use the variant string as-is
+            lookup_value = "true" if isinstance(match_value, bool) and match_value else str(match_value)
+            payload = flag_payloads.get(lookup_value, None)
         return payload
 
     def get_all_flags(

posthog/test/test_feature_flags.py

@@ -4640,3 +4640,84 @@ def test_multivariate_flag_consistency(self, patch_get):
                 self.assertEqual(feature_flag_match, results[i])
             else:
                 self.assertFalse(feature_flag_match)
+
+    @mock.patch("posthog.client.decide")
+    def test_feature_flag_case_sensitive(self, mock_decide):
+        mock_decide.return_value = {"featureFlags": {}}  # Ensure decide returns empty flags
+
+        client = Client(api_key=FAKE_TEST_API_KEY, personal_api_key=FAKE_TEST_API_KEY)
+        client.feature_flags = [
+            {
+                "id": 1,
+                "key": "Beta-Feature",
+                "active": True,
+                "filters": {
+                    "groups": [{"properties": [], "rollout_percentage": 100}],
+                },
+            }
+        ]
+
+        # Test that flag evaluation is case-sensitive
+        self.assertTrue(client.feature_enabled("Beta-Feature", "user1"))
+        self.assertFalse(client.feature_enabled("beta-feature", "user1"))
+        self.assertFalse(client.feature_enabled("BETA-FEATURE", "user1"))
+
+    @mock.patch("posthog.client.decide")
+    def test_feature_flag_payload_case_sensitive(self, mock_decide):
+        mock_decide.return_value = {
+            "featureFlags": {"Beta-Feature": True},
+            "featureFlagPayloads": {"Beta-Feature": {"some": "value"}},
+        }
+
+        client = Client(api_key=FAKE_TEST_API_KEY, personal_api_key=FAKE_TEST_API_KEY)
+        client.feature_flags = [
+            {
+                "id": 1,
+                "key": "Beta-Feature",
+                "active": True,
+                "filters": {
+                    "groups": [{"properties": [], "rollout_percentage": 100}],
+                    "payloads": {
+                        "true": {"some": "value"},
+                    },
+                },
+            }
+        ]
+
+        # Test that payload retrieval is case-sensitive
+        self.assertEqual(client.get_feature_flag_payload("Beta-Feature", "user1"), {"some": "value"})
+        self.assertIsNone(client.get_feature_flag_payload("beta-feature", "user1"))
+        self.assertIsNone(client.get_feature_flag_payload("BETA-FEATURE", "user1"))
+
+    @mock.patch("posthog.client.decide")
+    def test_feature_flag_case_sensitive_consistency(self, mock_decide):
+        mock_decide.return_value = {
+            "featureFlags": {"Beta-Feature": True},
+            "featureFlagPayloads": {"Beta-Feature": {"some": "value"}},
+        }
+
+        client = Client(api_key=FAKE_TEST_API_KEY, personal_api_key=FAKE_TEST_API_KEY)
+        client.feature_flags = [
+            {
+                "id": 1,
+                "key": "Beta-Feature",
+                "active": True,
+                "filters": {
+                    "groups": [{"properties": [], "rollout_percentage": 100}],
+                    "payloads": {
+                        "true": {"some": "value"},
+                    },
+                },
+            }
+        ]
+
+        # Test that flag evaluation and payload retrieval are consistently case-sensitive
+        # Only exact match should work
+        self.assertTrue(client.feature_enabled("Beta-Feature", "user1"))
+        self.assertEqual(client.get_feature_flag_payload("Beta-Feature", "user1"), {"some": "value"})
+
+        # Different cases should not match
+        test_cases = ["beta-feature", "BETA-FEATURE", "bEtA-FeAtUrE"]
+        for case in test_cases:
+            self.assertFalse(client.feature_enabled(case, "user1"))
+            self.assertIsNone(client.get_feature_flag_payload(case, "user1"))