feat: implement OpenTelemetry traces hook

Signed-off-by: Federico Bond <[email protected]>

openfeature/contrib/hooks/otel.py

@@ -0,0 +1,44 @@
+import json
+
+from openfeature.flag_evaluation import FlagEvaluationDetails
+from openfeature.hook import Hook, HookContext
+from opentelemetry import trace
+
+
+OTEL_EVENT_NAME = "feature_flag"
+
+
+class EventAttributes:
+    FLAG_KEY = f"{OTEL_EVENT_NAME}.key"
+    FLAG_VARIANT = f"{OTEL_EVENT_NAME}.variant"
+    PROVIDER_NAME = f"{OTEL_EVENT_NAME}.provider_name"
+
+
+class OTelTracesHook(Hook):
+    def after(
+        self, hook_context: HookContext, details: FlagEvaluationDetails, hints: dict
+    ):
+        current_span = trace.get_current_span()
+
+        variant = details.variant
+        if variant is None:
+            if isinstance(details.value, str):
+                variant = str(details.value)
+            else:
+                variant = json.dumps(details.value)
+
+        event_attributes = {
+            EventAttributes.FLAG_KEY: details.flag_key,
+            EventAttributes.FLAG_VARIANT: variant,
+        }
+
+        if hook_context.provider_metadata:
+            event_attributes[
+                EventAttributes.PROVIDER_NAME
+            ] = hook_context.provider_metadata.name
+
+        current_span.add_event(OTEL_EVENT_NAME, event_attributes)
+
+    def error(self, hook_context: HookContext, exception: Exception, hints: dict):
+        current_span = trace.get_current_span()
+        current_span.record_exception(exception)

requirements-dev.in

@@ -8,3 +8,4 @@ flake8
 pytest-mock
 coverage
 openfeature-sdk
+opentelemetry-api

requirements-dev.txt

@@ -18,6 +18,8 @@ click==8.1.3
     #   pip-tools
 coverage==7.2.7
     # via -r requirements-dev.in
+deprecated==1.2.14
+    # via opentelemetry-api
 dill==0.3.4
     # via pylint
 distlib==0.3.4
@@ -28,6 +30,8 @@ flake8==4.0.1
     # via -r requirements-dev.in
 identify==2.5.0
     # via pre-commit
+importlib-metadata==6.8.0
+    # via opentelemetry-api
 iniconfig==1.1.1
     # via pytest
 isort==5.10.1
@@ -44,6 +48,8 @@ nodeenv==1.6.0
     # via pre-commit
 openfeature-sdk==0.3.1
     # via -r requirements-dev.in
+opentelemetry-api==1.19.0
+    # via -r requirements-dev.in
 packaging==21.3
     # via pytest
 pathspec==0.9.0
@@ -92,7 +98,11 @@ virtualenv==20.14.1
 wheel==0.37.1
     # via pip-tools
 wrapt==1.14.1
-    # via astroid
+    # via
+    #   astroid
+    #   deprecated
+zipp==3.16.2
+    # via importlib-metadata
 
 # The following packages are considered to be unsafe in a requirements file:
 # pip

tests/hooks/test_otel.py

@@ -0,0 +1,69 @@
+from unittest.mock import Mock
+
+import pytest
+from openfeature.contrib.hooks.otel import OTelTracesHook
+from openfeature.evaluation_context import EvaluationContext
+from openfeature.flag_evaluation import FlagEvaluationDetails, FlagType
+from openfeature.hook import HookContext
+from opentelemetry import trace
+from opentelemetry.trace import Span
+
+
+@pytest.fixture
+def mock_get_current_span(monkeypatch):
+    monkeypatch.setattr(trace, "get_current_span", Mock())
+
+
+def test_before(mock_get_current_span):
+    # Given
+    hook = OTelTracesHook()
+    hook_context = HookContext(
+        flag_key="flag_key",
+        flag_type=FlagType.BOOLEAN,
+        default_value=False,
+        evaluation_context=EvaluationContext(),
+    )
+    details = FlagEvaluationDetails(
+        flag_key="flag_key",
+        value=True,
+        variant="enabled",
+        reason=None,
+        error_code=None,
+        error_message=None,
+    )
+
+    mock_span = Mock(spec=Span)
+    trace.get_current_span.return_value = mock_span
+
+    # When
+    hook.after(hook_context, details, hints={})
+
+    # Then
+    mock_span.add_event.assert_called_once_with(
+        "feature_flag",
+        {
+            "feature_flag.key": "flag_key",
+            "feature_flag.variant": "enabled",
+        },
+    )
+
+
+def test_error(mock_get_current_span):
+    # Given
+    hook = OTelTracesHook()
+    hook_context = HookContext(
+        flag_key="flag_key",
+        flag_type=FlagType.BOOLEAN,
+        default_value=False,
+        evaluation_context=EvaluationContext(),
+    )
+    exception = Exception()
+
+    mock_span = Mock(spec=Span)
+    trace.get_current_span.return_value = mock_span
+
+    # When
+    hook.error(hook_context, exception, hints={})
+
+    # Then
+    mock_span.record_exception.assert_called_once_with(exception)