Allow setting custom metric attributes in otelhttp transport

CHANGELOG.md

@@ -24,6 +24,7 @@ The next release will require at least [Go 1.22].
   This module provides an OpenTelemetry logging bridge for `github.com/rs/zerolog`. (#5405)
 - Add `WithGinFilter` filter parameter in `go.opentelemetry.io/contrib/instrumentation/github.com/gin-gonic/gin/otelgin` to allow filtering requests with `*gin.Context`. (#5743)
 - Support [Go 1.23]. (#6017)
+- Add the `WithMetricsAttributesFn` option to allow setting dynamic, per-request metric attributes in `go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp`. (#5876)
 
 ### Removed
 

instrumentation/net/http/otelhttp/config.go

@@ -8,6 +8,8 @@ import (
 	"net/http"
 	"net/http/httptrace"
 
+	"go.opentelemetry.io/otel/attribute"
+
 	"go.opentelemetry.io/otel"
 	"go.opentelemetry.io/otel/metric"
 	"go.opentelemetry.io/otel/propagation"
@@ -33,8 +35,9 @@ type config struct {
 	SpanNameFormatter func(string, *http.Request) string
 	ClientTrace       func(context.Context) *httptrace.ClientTrace
 
-	TracerProvider trace.TracerProvider
-	MeterProvider  metric.MeterProvider
+	TracerProvider     trace.TracerProvider
+	MeterProvider      metric.MeterProvider
+	MetricAttributesFn func(*http.Request) []attribute.KeyValue
 }
 
 // Option interface used for setting optional config properties.
@@ -194,3 +197,11 @@ func WithServerName(server string) Option {
 		c.ServerName = server
 	})
 }
+
+// WithMetricAttributesFn returns an Option to set a function that maps an HTTP request to a slice of attribute.KeyValue.
+// These attributes will be included in metrics for every request.
+func WithMetricAttributesFn(metricAttributesFn func(r *http.Request) []attribute.KeyValue) Option {
+	return optionFunc(func(c *config) {
+		c.MetricAttributesFn = metricAttributesFn
+	})
+}

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

@@ -507,11 +507,15 @@ func TestCustomAttributesHandling(t *testing.T) {
 	}))
 	defer ts.Close()
 
+	expectedAttributes := []attribute.KeyValue{
+		attribute.String("foo", "fooValue"),
+		attribute.String("bar", "barValue"),
+	}
+
 	r, err := http.NewRequest(http.MethodGet, ts.URL, nil)
 	require.NoError(t, err)
 	labeler := &otelhttp.Labeler{}
-	labeler.Add(attribute.String("foo", "fooValue"))
-	labeler.Add(attribute.String("bar", "barValue"))
+	labeler.Add(expectedAttributes...)
 	ctx = otelhttp.ContextWithLabeler(ctx, labeler)
 	r = r.WithContext(ctx)
 
@@ -534,30 +538,85 @@ func TestCustomAttributesHandling(t *testing.T) {
 			d, ok := m.Data.(metricdata.Sum[int64])
 			assert.True(t, ok)
 			assert.Len(t, d.DataPoints, 1)
-			attrSet := d.DataPoints[0].Attributes
-			fooAtrr, ok := attrSet.Value(attribute.Key("foo"))
-			assert.True(t, ok)
-			assert.Equal(t, "fooValue", fooAtrr.AsString())
-			barAtrr, ok := attrSet.Value(attribute.Key("bar"))
-			assert.True(t, ok)
-			assert.Equal(t, "barValue", barAtrr.AsString())
-			assert.False(t, attrSet.HasValue(attribute.Key("baz")))
+			containsAttributes(t, d.DataPoints[0].Attributes, expectedAttributes)
 		case clientDuration:
 			d, ok := m.Data.(metricdata.Histogram[float64])
 			assert.True(t, ok)
 			assert.Len(t, d.DataPoints, 1)
-			attrSet := d.DataPoints[0].Attributes
-			fooAtrr, ok := attrSet.Value(attribute.Key("foo"))
+			containsAttributes(t, d.DataPoints[0].Attributes, expectedAttributes)
+		}
+	}
+}
+
+func TestDefaultAttributesHandling(t *testing.T) {
+	var rm metricdata.ResourceMetrics
+	const (
+		clientRequestSize = "http.client.request.size"
+		clientDuration    = "http.client.duration"
+	)
+	ctx := context.TODO()
+	reader := sdkmetric.NewManualReader()
+	provider := sdkmetric.NewMeterProvider(sdkmetric.WithReader(reader))
+	defer func() {
+		err := provider.Shutdown(ctx)
+		if err != nil {
+			t.Errorf("Error shutting down provider: %v", err)
+		}
+	}()
+
+	defaultAttributes := []attribute.KeyValue{
+		attribute.String("defaultFoo", "fooValue"),
+		attribute.String("defaultBar", "barValue"),
+	}
+
+	transport := otelhttp.NewTransport(
+		http.DefaultTransport, otelhttp.WithMeterProvider(provider),
+		otelhttp.WithMetricAttributesFn(func(_ *http.Request) []attribute.KeyValue {
+			return defaultAttributes
+		}))
+	client := http.Client{Transport: transport}
+
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer ts.Close()
+
+	r, err := http.NewRequest(http.MethodGet, ts.URL, nil)
+	require.NoError(t, err)
+
+	_, err = client.Do(r)
+	require.NoError(t, err)
+
+	err = reader.Collect(ctx, &rm)
+	assert.NoError(t, err)
+
+	// http.client.response.size is not recorded so the assert.Len
+	// above should be 2 instead of 3(test bonus)
+	assert.Len(t, rm.ScopeMetrics[0].Metrics, 2)
+	for _, m := range rm.ScopeMetrics[0].Metrics {
+		switch m.Name {
+		case clientRequestSize:
+			d, ok := m.Data.(metricdata.Sum[int64])
 			assert.True(t, ok)
-			assert.Equal(t, "fooValue", fooAtrr.AsString())
-			barAtrr, ok := attrSet.Value(attribute.Key("bar"))
+			assert.Len(t, d.DataPoints, 1)
+			containsAttributes(t, d.DataPoints[0].Attributes, defaultAttributes)
+		case clientDuration:
+			d, ok := m.Data.(metricdata.Histogram[float64])
 			assert.True(t, ok)
-			assert.Equal(t, "barValue", barAtrr.AsString())
-			assert.False(t, attrSet.HasValue(attribute.Key("baz")))
+			assert.Len(t, d.DataPoints, 1)
+			containsAttributes(t, d.DataPoints[0].Attributes, defaultAttributes)
 		}
 	}
 }
 
+func containsAttributes(t *testing.T, attrSet attribute.Set, expected []attribute.KeyValue) {
+	for _, att := range expected {
+		actualValue, ok := attrSet.Value(att.Key)
+		assert.True(t, ok)
+		assert.Equal(t, att.Value.AsString(), actualValue.AsString())
+	}
+}
+
 func BenchmarkTransportRoundTrip(b *testing.B) {
 	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		fmt.Fprint(w, "Hello World")

instrumentation/net/http/otelhttp/transport.go

@@ -28,13 +28,14 @@ import (
 type Transport struct {
 	rt http.RoundTripper
 
-	tracer            trace.Tracer
-	meter             metric.Meter
-	propagators       propagation.TextMapPropagator
-	spanStartOptions  []trace.SpanStartOption
-	filters           []Filter
-	spanNameFormatter func(string, *http.Request) string
-	clientTrace       func(context.Context) *httptrace.ClientTrace
+	tracer             trace.Tracer
+	meter              metric.Meter
+	propagators        propagation.TextMapPropagator
+	spanStartOptions   []trace.SpanStartOption
+	filters            []Filter
+	spanNameFormatter  func(string, *http.Request) string
+	clientTrace        func(context.Context) *httptrace.ClientTrace
+	metricAttributesFn func(*http.Request) []attribute.KeyValue
 
 	semconv              semconv.HTTPClient
 	requestBytesCounter  metric.Int64Counter
@@ -80,6 +81,7 @@ func (t *Transport) applyConfig(c *config) {
 	t.filters = c.Filters
 	t.spanNameFormatter = c.SpanNameFormatter
 	t.clientTrace = c.ClientTrace
+	t.metricAttributesFn = c.MetricAttributesFn
 }
 
 func (t *Transport) createMeasures() {
@@ -175,7 +177,7 @@ func (t *Transport) RoundTrip(r *http.Request) (*http.Response, error) {
 	}
 
 	// metrics
-	metricAttrs := append(labeler.Get(), semconvutil.HTTPClientRequestMetrics(r)...)
+	metricAttrs := append(append(labeler.Get(), semconvutil.HTTPClientRequestMetrics(r)...), t.metricAttributesFromRequest(r)...)
 	if res.StatusCode > 0 {
 		metricAttrs = append(metricAttrs, semconv.HTTPStatusCode(res.StatusCode))
 	}
@@ -201,6 +203,14 @@ func (t *Transport) RoundTrip(r *http.Request) (*http.Response, error) {
 	return res, err
 }
 
+func (t *Transport) metricAttributesFromRequest(r *http.Request) []attribute.KeyValue {
+	var attributeForRequest []attribute.KeyValue
+	if t.metricAttributesFn != nil {
+		attributeForRequest = t.metricAttributesFn(r)
+	}
+	return attributeForRequest
+}
+
 // newWrappedBody returns a new and appropriately scoped *wrappedBody as an
 // io.ReadCloser. If the passed body implements io.Writer, the returned value
 // will implement io.ReadWriteCloser.