Add Labeler and instrumentation integration for custom attribute addition to HTTP request duration metrics (Flask, Django, Falcon, WSGI, ASGI)

CHANGELOG.md

@@ -57,6 +57,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   ([#4141](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/4141))
 - `opentelemetry-instrumentation-pyramid`: pass request attributes at span creation
   ([#4139](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/4139))
+- `opentelemetry-instrumentation`, `opentelemetry-instrumentation-flask`, `opentelemetry-instrumentation-wsgi`, `opentelemetry-instrumentation-django`, `opentelemetry-instrumentation-falcon`, `opentelemetry-instrumentation-asgi`: Add Labeler utility. Add FalconInstrumentor, FlaskInstrumentor, DjangoInstrumentor, WsgiInstrumentor, AsgiInstrumentor support of custom attributes merging for HTTP duration metrics.
+  ([#3689](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/3689))
 
 ### Fixed
 - `opentelemetry-instrumentation-mysql`: Refactor MySQL integration test mocks to use concrete DBAPI connection attributes, reducing noisy attribute type warnings.

instrumentation/opentelemetry-instrumentation-asgi/src/opentelemetry/instrumentation/asgi/__init__.py

@@ -204,6 +204,46 @@ def client_response_hook(span: Span, scope: Scope, message: dict[str, Any]):
 Note:
     The environment variable names used to capture HTTP headers are still experimental, and thus are subject to change.
 
+Custom Metrics Attributes using Labeler
+***************************************
+The ASGI instrumentation reads from a labeler utility that supports adding custom
+attributes to HTTP duration metrics at record time. The custom attributes are
+stored only within the context of an instrumented request or operation. The
+instrumentor does not overwrite base attributes that exist at the same keys as
+any custom attributes.
+
+
+.. code-block:: python
+
+    .. code-block:: python
+
+    from quart import Quart
+    from opentelemetry.instrumentation._labeler import get_labeler
+    from opentelemetry.instrumentation.asgi import OpenTelemetryMiddleware
+
+    app = Quart(__name__)
+    app.asgi_app = OpenTelemetryMiddleware(app.asgi_app)
+
+    @app.route("/users/<user_id>/")
+    async def user_profile(user_id):
+        # Get the labeler for the current request
+        labeler = get_labeler()
+
+        # Add custom attributes to ASGI instrumentation metrics
+        labeler.add("user_id", user_id)
+        labeler.add("user_type", "registered")
+
+        # Or, add multiple attributes at once
+        labeler.add_attributes({
+            "feature_flag": "new_ui",
+            "experiment_group": "control"
+        })
+
+        return f"User profile for {user_id}"
+
+    if __name__ == "__main__":
+        app.run(debug=True)
+
 API
 ---
 """
@@ -220,6 +260,10 @@ def client_response_hook(span: Span, scope: Scope, message: dict[str, Any]):
 from asgiref.compatibility import guarantee_single_callable
 
 from opentelemetry import context, trace
+from opentelemetry.instrumentation._labeler import (
+    enrich_metric_attributes,
+    get_labeler,
+)
 from opentelemetry.instrumentation._semconv import (
     HTTP_DURATION_HISTOGRAM_BUCKETS_NEW,
     _filter_semconv_active_request_count_attr,
@@ -744,6 +788,9 @@ async def __call__(
             receive: An awaitable callable yielding dictionaries
             send: An awaitable callable taking a single dictionary as argument.
         """
+        # Required to create new instance for custom attributes in async context
+        _ = get_labeler()
+
         start = default_timer()
         if scope["type"] not in ("http", "websocket"):
             return await self.app(scope, receive, send)
@@ -825,11 +872,19 @@ async def __call__(
                 duration_attrs_old = _parse_duration_attrs(
                     attributes, _StabilityMode.DEFAULT
                 )
+                # Enhance attributes with any custom labeler attributes
+                duration_attrs_old = enrich_metric_attributes(
+                    duration_attrs_old
+                )
                 if target:
                     duration_attrs_old[HTTP_TARGET] = target
                 duration_attrs_new = _parse_duration_attrs(
                     attributes, _StabilityMode.HTTP
                 )
+                # Enhance attributes with any custom labeler attributes
+                duration_attrs_new = enrich_metric_attributes(
+                    duration_attrs_new
+                )
                 span_ctx = set_span_in_context(span)
                 if self.duration_histogram_old:
                     self.duration_histogram_old.record(