Add support for the WithMetricAttributesFn option for otelhttp middlewares

CHANGELOG.md

@@ -27,6 +27,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - Added SNS instrumentation in `go.opentelemetry.io/contrib/instrumentation/github.com/aws/aws-sdk-go-v2/otelaws`. (#6388)
 - Use a `sync.Pool` for metric options in `go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp`. (#6394)
 - Added support for configuring `Certificate` field when configuring OTLP exporters in `go.opentelemetry.io/contrib/config`. (#6376)
+- Added support for the `WithMetricAttributesFn` option to middlewares in `go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp`. (#6542)
 
 ### Changed
 

instrumentation/net/http/otelhttp/handler.go

@@ -12,6 +12,7 @@ import (
 	"go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp/internal/request"
 	"go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp/internal/semconv"
 	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/attribute"
 	"go.opentelemetry.io/otel/propagation"
 	"go.opentelemetry.io/otel/trace"
 )
@@ -21,15 +22,16 @@ type middleware struct {
 	operation string
 	server    string
 
-	tracer            trace.Tracer
-	propagators       propagation.TextMapPropagator
-	spanStartOptions  []trace.SpanStartOption
-	readEvent         bool
-	writeEvent        bool
-	filters           []Filter
-	spanNameFormatter func(string, *http.Request) string
-	publicEndpoint    bool
-	publicEndpointFn  func(*http.Request) bool
+	tracer             trace.Tracer
+	propagators        propagation.TextMapPropagator
+	spanStartOptions   []trace.SpanStartOption
+	readEvent          bool
+	writeEvent         bool
+	filters            []Filter
+	spanNameFormatter  func(string, *http.Request) string
+	publicEndpoint     bool
+	publicEndpointFn   func(*http.Request) bool
+	metricAttributesFn func(*http.Request) []attribute.KeyValue
 
 	semconv semconv.HTTPServer
 }
@@ -79,6 +81,7 @@ func (h *middleware) configure(c *config) {
 	h.publicEndpointFn = c.PublicEndpointFn
 	h.server = c.ServerName
 	h.semconv = semconv.NewHTTPServer(c.Meter)
+	h.metricAttributesFn = c.MetricAttributesFn
 }
 
 // serveHTTP sets up tracing and calls the given next http.Handler with the span
@@ -189,21 +192,31 @@ func (h *middleware) serveHTTP(w http.ResponseWriter, r *http.Request, next http
 	// Use floating point division here for higher precision (instead of Millisecond method).
 	elapsedTime := float64(time.Since(requestStartTime)) / float64(time.Millisecond)
 
+	metricAttributes := semconv.MetricAttributes{
+		Req:                  r,
+		StatusCode:           statusCode,
+		AdditionalAttributes: append(labeler.Get(), h.metricAttributesFromRequest(r)...),
+	}
+
 	h.semconv.RecordMetrics(ctx, semconv.ServerMetricData{
-		ServerName:   h.server,
-		ResponseSize: bytesWritten,
-		MetricAttributes: semconv.MetricAttributes{
-			Req:                  r,
-			StatusCode:           statusCode,
-			AdditionalAttributes: labeler.Get(),
-		},
+		ServerName:       h.server,
+		ResponseSize:     bytesWritten,
+		MetricAttributes: metricAttributes,
 		MetricData: semconv.MetricData{
 			RequestSize: bw.BytesRead(),
 			ElapsedTime: elapsedTime,
 		},
 	})
 }
 
+func (h *middleware) metricAttributesFromRequest(r *http.Request) []attribute.KeyValue {
+	var attributeForRequest []attribute.KeyValue
+	if h.metricAttributesFn != nil {
+		attributeForRequest = h.metricAttributesFn(r)
+	}
+	return attributeForRequest
+}
+
 // WithRouteTag annotates spans and metrics with the provided route name
 // with HTTP route attribute.
 func WithRouteTag(route string, h http.Handler) http.Handler {

instrumentation/net/http/otelhttp/test/handler_test.go

@@ -577,6 +577,78 @@ func TestWithRouteTag(t *testing.T) {
 	}
 }
 
+func TestHandlerWithMetricAttributesFn(t *testing.T) {
+	const (
+		serverRequestSize  = "http.server.request.size"
+		serverResponseSize = "http.server.response.size"
+		serverDuration     = "http.server.duration"
+	)
+	testCases := []struct {
+		name                        string
+		fn                          func(r *http.Request) []attribute.KeyValue
+		expectedAdditionalAttribute []attribute.KeyValue
+	}{
+		{
+			name:                        "With a nil function",
+			fn:                          nil,
+			expectedAdditionalAttribute: []attribute.KeyValue{},
+		},
+		{
+			name: "With a function that returns an additional attribute",
+			fn: func(r *http.Request) []attribute.KeyValue {
+				return []attribute.KeyValue{
+					attribute.String("fooKey", "fooValue"),
+					attribute.String("barKey", "barValue"),
+				}
+			},
+			expectedAdditionalAttribute: []attribute.KeyValue{
+				attribute.String("fooKey", "fooValue"),
+				attribute.String("barKey", "barValue"),
+			},
+		},
+	}
+
+	for _, tc := range testCases {
+		reader := sdkmetric.NewManualReader()
+		meterProvider := sdkmetric.NewMeterProvider(sdkmetric.WithReader(reader))
+
+		h := otelhttp.NewHandler(
+			http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				w.WriteHeader(http.StatusOK)
+			}), "test_handler",
+			otelhttp.WithMeterProvider(meterProvider),
+			otelhttp.WithMetricAttributesFn(tc.fn),
+		)
+
+		r, err := http.NewRequest(http.MethodGet, "http://localhost/", nil)
+		require.NoError(t, err)
+		rr := httptest.NewRecorder()
+		h.ServeHTTP(rr, r)
+
+		rm := metricdata.ResourceMetrics{}
+		err = reader.Collect(context.Background(), &rm)
+		require.NoError(t, err)
+		require.Len(t, rm.ScopeMetrics, 1)
+		assert.Len(t, rm.ScopeMetrics[0].Metrics, 3)
+
+		// Verify that the additional attribute is present in the metrics.
+		for _, m := range rm.ScopeMetrics[0].Metrics {
+			switch m.Name {
+			case serverRequestSize, serverResponseSize:
+				d, ok := m.Data.(metricdata.Sum[int64])
+				assert.True(t, ok)
+				assert.Len(t, d.DataPoints, 1)
+				containsAttributes(t, d.DataPoints[0].Attributes, testCases[0].expectedAdditionalAttribute)
+			case serverDuration:
+				d, ok := m.Data.(metricdata.Histogram[float64])
+				assert.True(t, ok)
+				assert.Len(t, d.DataPoints, 1)
+				containsAttributes(t, d.DataPoints[0].Attributes, testCases[0].expectedAdditionalAttribute)
+			}
+		}
+	}
+}
+
 func BenchmarkHandlerServeHTTP(b *testing.B) {
 	tp := sdktrace.NewTracerProvider()
 	mp := sdkmetric.NewMeterProvider()