fix(asgi): exclude background task duration from HTTP server metrics

.changelog/4656.fixed

@@ -0,0 +1 @@
+`opentelemetry-instrumentation-asgi`: Fix HTTP server duration metrics to exclude background task execution time

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

@@ -795,12 +795,14 @@ async def __call__(
                     span_name, scope, receive
                 )
 
+                response_complete_time: list[float] = []
                 otel_send = self._get_otel_send(
                     current_span,
                     span_name,
                     scope,
                     send,
                     attributes,
+                    response_complete_time,
                 )
 
                 await self.app(scope, otel_receive, otel_send)
@@ -816,7 +818,11 @@ async def __call__(
                         query,
                         self._sem_conv_opt_in_mode,
                     )
-                duration_s = default_timer() - start
+                duration_s = (
+                    response_complete_time[0] - start
+                    if response_complete_time
+                    else default_timer() - start
+                )
                 duration_attrs_old = _parse_duration_attrs(
                     attributes, _StabilityMode.DEFAULT
                 )
@@ -974,6 +980,7 @@ def _get_otel_send(
         scope,
         send,
         duration_attrs,
+        response_complete_time: list[float],
     ):
         expecting_trailers = False
 
@@ -1030,6 +1037,7 @@ async def otel_send(message: dict[str, Any]):
                 and message["type"] == "http.response.trailers"
                 and not message.get("more_trailers", False)
             ):
+                response_complete_time.append(default_timer())
                 server_span.end()
 
         return otel_send

instrumentation/opentelemetry-instrumentation-asgi/tests/test_asgi_middleware.py

@@ -702,6 +702,78 @@ def add_body_and_trailer_span(expected: list):
             _SIMULATED_BACKGROUND_TASK_EXECUTION_TIME_S * 10**9,
         )
 
+    async def test_background_execution_metrics_duration(self):
+        """Test that http.server.duration excludes background task time."""
+        app = otel_asgi.OpenTelemetryMiddleware(background_execution_asgi)
+        self.seed_app(app)
+        await self.send_default_request()
+        await self.get_all_output()
+
+        metrics = self.get_sorted_metrics(SCOPE)
+        duration_found = False
+        for metric in metrics:
+            if metric.name == "http.server.duration":
+                data_points = list(metric.data.data_points)
+                for point in data_points:
+                    if isinstance(point, HistogramDataPoint):
+                        duration_found = True
+                        self.assertLess(
+                            point.sum,
+                            _SIMULATED_BACKGROUND_TASK_EXECUTION_TIME_S * 1000,
+                        )
+        self.assertTrue(
+            duration_found, "http.server.duration metric not found"
+        )
+
+    async def test_background_execution_metrics_duration_new_semconv(self):
+        """Test that http.server.request.duration excludes background task time."""
+        app = otel_asgi.OpenTelemetryMiddleware(background_execution_asgi)
+        self.seed_app(app)
+        await self.send_default_request()
+        await self.get_all_output()
+
+        metrics = self.get_sorted_metrics(SCOPE)
+        duration_found = False
+        for metric in metrics:
+            if metric.name == "http.server.request.duration":
+                data_points = list(metric.data.data_points)
+                for point in data_points:
+                    if isinstance(point, HistogramDataPoint):
+                        duration_found = True
+                        self.assertLess(
+                            point.sum,
+                            _SIMULATED_BACKGROUND_TASK_EXECUTION_TIME_S,
+                        )
+        self.assertTrue(
+            duration_found,
+            "http.server.request.duration metric not found",
+        )
+
+    async def test_trailers_background_execution_metrics_duration(self):
+        """Test that http.server.duration excludes background task time for trailer responses."""
+        app = otel_asgi.OpenTelemetryMiddleware(
+            background_execution_trailers_asgi
+        )
+        self.seed_app(app)
+        await self.send_default_request()
+        await self.get_all_output()
+
+        metrics = self.get_sorted_metrics(SCOPE)
+        duration_found = False
+        for metric in metrics:
+            if metric.name == "http.server.duration":
+                data_points = list(metric.data.data_points)
+                for point in data_points:
+                    if isinstance(point, HistogramDataPoint):
+                        duration_found = True
+                        self.assertLess(
+                            point.sum,
+                            _SIMULATED_BACKGROUND_TASK_EXECUTION_TIME_S * 1000,
+                        )
+        self.assertTrue(
+            duration_found, "http.server.duration metric not found"
+        )
+
     async def test_override_span_name(self):
         """Test that default span_names can be overwritten by our callback function."""
         span_name = "Dymaxion"