Fix client metrics recording on round trip error

CHANGELOG.md

@@ -75,6 +75,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 - Fix data race when writing log entries with `context.Context` fields in `go.opentelemetry.io/contrib/bridges/otelzap`. (#7368)
 - Fix nil pointer dereference when `ClientTracer` did not have a span in `go.opentelemetry.io/contrib/instrumentation/net/http/httptrace/otelhttptrace`. (#7464)
+- Record all non-failure metrics on transport round trip errors in `go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp`. (#7146)
 
 <!-- Released section -->
 <!-- Don't change this section unless doing release -->

instrumentation/net/http/otelhttp/transport.go

@@ -129,6 +129,41 @@ func (t *Transport) RoundTrip(r *http.Request) (*http.Response, error) {
 	t.propagators.Inject(ctx, propagation.HeaderCarrier(r.Header))
 
 	res, err := t.rt.RoundTrip(r)
+
+	// Defer metrics recording function to record the metrics on error or no error.
+	defer func() {
+		metricAttributes := semconv.MetricAttributes{
+			Req:                  r,
+			AdditionalAttributes: append(labeler.Get(), t.metricAttributesFromRequest(r)...),
+		}
+
+		if err == nil {
+			metricAttributes.StatusCode = res.StatusCode
+		}
+
+		metricOpts := t.semconv.MetricOptions(metricAttributes)
+
+		metricData := semconv.MetricData{
+			RequestSize: bw.BytesRead(),
+		}
+
+		if err == nil {
+			// For handling response bytes we leverage a callback when the client reads the http response
+			readRecordFunc := func(n int64) {
+				t.semconv.RecordResponseSize(ctx, n, metricOpts)
+			}
+
+			res.Body = newWrappedBody(span, readRecordFunc, res.Body)
+		}
+
+		// Use floating point division here for higher precision (instead of Millisecond method).
+		elapsedTime := float64(time.Since(requestStartTime)) / float64(time.Millisecond)
+
+		metricData.ElapsedTime = elapsedTime
+
+		t.semconv.RecordMetrics(ctx, metricData, metricOpts)
+	}()
+
 	if err != nil {
 		// set error type attribute if the error is part of the predefined
 		// error types.
@@ -141,35 +176,14 @@ func (t *Transport) RoundTrip(r *http.Request) (*http.Response, error) {
 
 		span.SetStatus(codes.Error, err.Error())
 		span.End()
-		return res, err
-	}
 
-	// metrics
-	metricOpts := t.semconv.MetricOptions(semconv.MetricAttributes{
-		Req:                  r,
-		StatusCode:           res.StatusCode,
-		AdditionalAttributes: append(labeler.Get(), t.metricAttributesFromRequest(r)...),
-	})
-
-	// For handling response bytes we leverage a callback when the client reads the http response
-	readRecordFunc := func(n int64) {
-		t.semconv.RecordResponseSize(ctx, n, metricOpts)
+		return res, err
 	}
 
 	// traces
 	span.SetAttributes(t.semconv.ResponseTraceAttrs(res)...)
 	span.SetStatus(t.semconv.Status(res.StatusCode))
 
-	res.Body = newWrappedBody(span, readRecordFunc, res.Body)
-
-	// Use floating point division here for higher precision (instead of Millisecond method).
-	elapsedTime := float64(time.Since(requestStartTime)) / float64(time.Millisecond)
-
-	t.semconv.RecordMetrics(ctx, semconv.MetricData{
-		RequestSize: bw.BytesRead(),
-		ElapsedTime: elapsedTime,
-	}, metricOpts)
-
 	return res, nil
 }
 

instrumentation/net/http/otelhttp/transport_test.go

@@ -1171,6 +1171,43 @@ func TestCustomAttributesHandling(t *testing.T) {
 	}
 }
 
+func TestMetricsExistenceOnRequestError(t *testing.T) {
+	var rm metricdata.ResourceMetrics
+
+	ctx := context.Background()
+	reader := sdkmetric.NewManualReader()
+	provider := sdkmetric.NewMeterProvider(sdkmetric.WithReader(reader))
+	defer func() {
+		err := provider.Shutdown(ctx)
+		assert.NoError(t, err)
+	}()
+
+	transport := NewTransport(http.DefaultTransport, WithMeterProvider(provider))
+	client := http.Client{Transport: transport}
+
+	// simulate an error by closing the server
+	// before the request is made
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {}))
+	ts.Close()
+
+	r, err := http.NewRequest(http.MethodGet, ts.URL, nil)
+	require.NoError(t, err)
+
+	resp, err := client.Do(r)
+	if err == nil {
+		e := resp.Body.Close()
+		assert.NoError(t, e)
+	}
+
+	require.Error(t, err)
+
+	err = reader.Collect(ctx, &rm)
+	require.NoError(t, err)
+
+	// make sure client request size and duration metrics is recorded
+	assert.Len(t, rm.ScopeMetrics[0].Metrics, 2, "should record client request size and duration metrics")
+}
+
 func TestDefaultAttributesHandling(t *testing.T) {
 	var rm metricdata.ResourceMetrics
 	const (