Add http.server.response.size metric to ASGI implementation.

CHANGELOG.md

@@ -27,6 +27,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   ([#1407](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/1407))
 - `opentelemetry-instrumentation-logging` Add `otelTraceSampled` to instrumetation-logging
   ([#1773](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/1773))
+- `opentelemetry-instrumentation-asgi` Add `http.server.response.size` metric
+  ([#1789](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/1789))
 
 
 ### Fixed

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

@@ -501,6 +501,11 @@ def __init__(
             unit="ms",
             description="measures the duration of the inbound HTTP request",
         )
+        self.server_response_size_histogram = self.meter.create_histogram(
+            name=MetricInstruments.HTTP_SERVER_RESPONSE_SIZE,
+            unit="By",
+            description="measures the size of HTTP response messages (compressed).",
+        )
         self.active_requests_counter = self.meter.create_up_down_counter(
             name=MetricInstruments.HTTP_SERVER_ACTIVE_REQUESTS,
             unit="requests",
@@ -615,6 +620,18 @@ def _get_otel_send(
     ):
         @wraps(send)
         async def otel_send(message):
+            if message.get("headers"):
+                headers = {
+                    _key.decode("utf8"): _value.decode("utf8")
+                    for (_key, _value) in message.get("headers")
+                }
+                if headers.get("content-length"):
+                    target = _collect_target_attribute(scope)
+                    if target:
+                        duration_attrs[SpanAttributes.HTTP_TARGET] = target
+                    self.server_response_size_histogram.record(
+                        int(headers.get("content-length")), duration_attrs
+                    )
             with self.tracer.start_as_current_span(
                 " ".join((server_span_name, scope["type"], "send"))
             ) as send_span:

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

@@ -46,10 +46,12 @@
 _expected_metric_names = [
     "http.server.active_requests",
     "http.server.duration",
+    "http.server.response.size",
 ]
 _recommended_attrs = {
     "http.server.active_requests": _active_requests_count_attrs,
     "http.server.duration": _duration_attrs,
+    "http.server.response.size": _duration_attrs,
 }
 
 
@@ -61,7 +63,10 @@ async def http_app(scope, receive, send):
             {
                 "type": "http.response.start",
                 "status": 200,
-                "headers": [[b"Content-Type", b"text/plain"]],
+                "headers": [
+                    [b"Content-Type", b"text/plain"],
+                    [b"content-length", b"1024"],
+                ],
             }
         )
         await send({"type": "http.response.body", "body": b"*"})
@@ -103,7 +108,10 @@ async def error_asgi(scope, receive, send):
             {
                 "type": "http.response.start",
                 "status": 200,
-                "headers": [[b"Content-Type", b"text/plain"]],
+                "headers": [
+                    [b"Content-Type", b"text/plain"],
+                    [b"content-length", b"1024"],
+                ],
             }
         )
         await send({"type": "http.response.body", "body": b"*"})
@@ -126,7 +134,8 @@ def validate_outputs(self, outputs, error=None, modifiers=None):
         # Check http response start
         self.assertEqual(response_start["status"], 200)
         self.assertEqual(
-            response_start["headers"], [[b"Content-Type", b"text/plain"]]
+            response_start["headers"],
+            [[b"Content-Type", b"text/plain"], [b"content-length", b"1024"]],
         )
 
         exc_info = self.scope.get("hack_exc_info")
@@ -352,6 +361,7 @@ def test_traceresponse_header(self):
             response_start["headers"],
             [
                 [b"Content-Type", b"text/plain"],
+                [b"content-length", b"1024"],
                 [b"traceresponse", f"{traceresponse}".encode()],
                 [b"access-control-expose-headers", b"traceresponse"],
             ],
@@ -575,9 +585,12 @@ def test_basic_metric_success(self):
                                 dict(point.attributes),
                             )
                             self.assertEqual(point.count, 1)
-                            self.assertAlmostEqual(
-                                duration, point.sum, delta=5
-                            )
+                            if metric.name == "http.server.duration":
+                                self.assertAlmostEqual(
+                                    duration, point.sum, delta=5
+                                )
+                            elif metric.name == "http.server.response.size":
+                                self.assertEqual(1024, point.sum)
                         elif isinstance(point, NumberDataPoint):
                             self.assertDictEqual(
                                 expected_requests_count_attributes,
@@ -602,13 +615,12 @@ async def target_asgi(scope, receive, send):
         app = otel_asgi.OpenTelemetryMiddleware(target_asgi)
         self.seed_app(app)
         self.send_default_request()
-
         metrics_list = self.memory_metrics_reader.get_metrics_data()
         assertions = 0
         for resource_metric in metrics_list.resource_metrics:
             for scope_metrics in resource_metric.scope_metrics:
                 for metric in scope_metrics.metrics:
-                    if metric.name != "http.server.duration":
+                    if metric.name == "http.server.active_requests":
                         continue
                     for point in metric.data.data_points:
                         if isinstance(point, HistogramDataPoint):
@@ -617,7 +629,7 @@ async def target_asgi(scope, receive, send):
                                 expected_target,
                             )
                             assertions += 1
-        self.assertEqual(assertions, 1)
+        self.assertEqual(assertions, 2)
 
     def test_no_metric_for_websockets(self):
         self.scope = {