confighttp: route-based span naming for ServeMux

If the handler supplied to ToServer is an *http.ServeMux,
use its Handler method to determine the matching pattern
and use that to name the span as described at
https://opentelemetry.io/docs/specs/semconv/http/http-spans/#name
If there is no matching pattern, fall back to "unknown route".

Fixes
open-telemetry#12468

Author: axw

.chloggen/confighttp-server-spanname.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. otlpreceiver)
+component: confighttp
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Use low-cardinality route pattern for confighttp server span names
+
+# One or more tracking issues or pull requests related to the change
+issues: [12468]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext: |
+  For components that route HTTP requests using a net/http.ServeMux, such as otlpreceiver,
+  server spans will now be given low-cardinality span names based on the route pattern.
+
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: [api, user]

config/confighttp/confighttp.go

@@ -410,7 +410,13 @@ func WithDecoder(key string, dec func(body io.ReadCloser) (io.ReadCloser, error)
 	})
 }
 
-// ToServer creates an http.Server from settings object.
+// ToServer creates an http.Server, serving requests with the given handler.
+//
+// If handler is an *http.ServeMux, then its Handler method will be used to
+// determine the matching route pattern to format the span name according to
+// https://opentelemetry.io/docs/specs/semconv/http/http-spans/#name. For
+// backwards compatibility, if handler is NOT an *http.ServeMux, then the
+// span name will be the URL path.
 func (hss *ServerConfig) ToServer(_ context.Context, host component.Host, settings component.TelemetrySettings, handler http.Handler, opts ...ToServerOption) (*http.Server, error) {
 	serverOpts := &toServerOptions{}
 	serverOpts.Apply(opts...)
@@ -423,6 +429,7 @@ func (hss *ServerConfig) ToServer(_ context.Context, host component.Host, settin
 		hss.CompressionAlgorithms = defaultCompressionAlgorithms
 	}
 
+	mux, handlerIsMux := handler.(*http.ServeMux)
 	handler = httpContentDecompressor(
 		handler,
 		hss.MaxRequestBodySize,
@@ -461,20 +468,38 @@ func (hss *ServerConfig) ToServer(_ context.Context, host component.Host, settin
 		handler = responseHeadersHandler(handler, hss.ResponseHeaders)
 	}
 
+	spanNameFormatter := func(_ string, r *http.Request) string {
+		return r.URL.Path
+	}
+	if handlerIsMux {
+		spanNameFormatter = func(_ string, r *http.Request) string {
+			target := r.Pattern
+			if target == "" {
+				target = "unknown route"
+			}
+			return fmt.Sprintf("%s %s", r.Method, target)
+		}
+	}
+
 	otelOpts := append(
 		[]otelhttp.Option{
 			otelhttp.WithTracerProvider(settings.TracerProvider),
 			otelhttp.WithPropagators(otel.GetTextMapPropagator()),
-			otelhttp.WithSpanNameFormatter(func(_ string, r *http.Request) string {
-				return r.URL.Path
-			}),
+			otelhttp.WithSpanNameFormatter(spanNameFormatter),
 			otelhttp.WithMeterProvider(settings.MeterProvider),
 		},
 		serverOpts.OtelhttpOpts...)
 
 	// Enable OpenTelemetry observability plugin.
 	handler = otelhttp.NewHandler(handler, "", otelOpts...)
 
+	// We need to ensure Request.Pattern is set prior to instrumentation.
+	// This is set by ServeMux.ServeHTTP, but that won't be invoked until
+	// after the otelhttp instrumentation.
+	if handlerIsMux {
+		handler = &muxPatternHandler{next: handler, mux: mux}
+	}
+
 	// wrap the current handler in an interceptor that will add client.Info to the request's context
 	handler = &clientInfoHandler{
 		next:            handler,
@@ -498,6 +523,16 @@ func (hss *ServerConfig) ToServer(_ context.Context, host component.Host, settin
 	return server, err
 }
 
+type muxPatternHandler struct {
+	next http.Handler
+	mux  *http.ServeMux
+}
+
+func (h *muxPatternHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	_, r.Pattern = h.mux.Handler(r)
+	h.next.ServeHTTP(w, r)
+}
+
 func responseHeadersHandler(handler http.Handler, headers map[string]configopaque.String) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		h := w.Header()

config/confighttp/confighttp_test.go

@@ -21,6 +21,8 @@ import (
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+	"go.opentelemetry.io/otel/sdk/trace"
+	"go.opentelemetry.io/otel/sdk/trace/tracetest"
 	"go.uber.org/zap"
 
 	"go.opentelemetry.io/collector/client"
@@ -1525,3 +1527,74 @@ func TestDefaultHTTPServerSettings(t *testing.T) {
 	assert.Equal(t, time.Duration(0), httpServerSettings.ReadTimeout)
 	assert.Equal(t, 1*time.Minute, httpServerSettings.ReadHeaderTimeout)
 }
+
+func TestServerTelemetry(t *testing.T) {
+	hss := ServerConfig{Endpoint: "localhost:0"}
+	exporter := tracetest.NewInMemoryExporter()
+	telemetry := componenttest.NewNopTelemetrySettings()
+	telemetry.TracerProvider = trace.NewTracerProvider(trace.WithSyncer(exporter))
+
+	nopHandler := http.HandlerFunc(func(http.ResponseWriter, *http.Request) {})
+	muxHandler := http.NewServeMux()
+	muxHandler.Handle("/a/{pattern}", nopHandler)
+	sendRequest := func(t *testing.T, url string, expectedCode int) {
+		t.Helper()
+		resp, err := http.Get(url) //nolint:gosec
+		require.NoError(t, err)
+		require.NoError(t, resp.Body.Close())
+		assert.Equal(t, expectedCode, resp.StatusCode)
+	}
+
+	t.Run("plain_handler", func(t *testing.T) {
+		withServer(t, hss, telemetry, nopHandler, func(_ *http.Server, url string) {
+			sendRequest(t, url+"/plain", http.StatusOK)
+			sendRequest(t, url+"/", http.StatusOK)
+		})
+		spans := exporter.GetSpans()
+		assert.Len(t, spans, 2)
+		assert.Equal(t, "/plain", spans[0].Name)
+		assert.Equal(t, "/", spans[1].Name)
+		exporter.Reset()
+	})
+	t.Run("mux", func(t *testing.T) {
+		withServer(t, hss, telemetry, muxHandler, func(_ *http.Server, url string) {
+			sendRequest(t, url+"/a/bc123", http.StatusOK)
+			sendRequest(t, url+"/", http.StatusNotFound)
+		})
+		spans := exporter.GetSpans()
+		assert.Len(t, spans, 2)
+		assert.Equal(t, "GET /a/{pattern}", spans[0].Name)
+		assert.Equal(t, "GET unknown route", spans[1].Name)
+		exporter.Reset()
+	})
+}
+
+func withServer(
+	t *testing.T,
+	cfg ServerConfig,
+	set component.TelemetrySettings,
+	h http.Handler,
+	f func(srv *http.Server, url string),
+) {
+	srv, err := cfg.ToServer(context.Background(), componenttest.NewNopHost(), set, h)
+	require.NoError(t, err)
+	defer func() {
+		assert.NoError(t, srv.Close())
+	}()
+
+	lis, err := cfg.ToListener(context.Background())
+	require.NoError(t, err)
+	done := make(chan struct{})
+	go func() {
+		defer close(done)
+		_ = srv.Serve(lis)
+	}()
+	defer func() {
+		err := srv.Shutdown(context.Background())
+		assert.NoError(t, err)
+		<-done
+	}()
+
+	u := &url.URL{Scheme: "http", Host: lis.Addr().String()}
+	f(srv, u.String())
+}

config/confighttp/go.mod

@@ -19,6 +19,7 @@ require (
 	go.opentelemetry.io/collector/extension/extensionauth/extensionauthtest v0.121.0
 	go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.59.0
 	go.opentelemetry.io/otel v1.34.0
+	go.opentelemetry.io/otel/sdk v1.34.0
 	go.uber.org/goleak v1.3.0
 	go.uber.org/zap v1.27.0
 	golang.org/x/net v0.35.0
@@ -37,7 +38,6 @@ require (
 	go.opentelemetry.io/collector/extension v1.27.0 // indirect
 	go.opentelemetry.io/collector/pdata v1.27.0 // indirect
 	go.opentelemetry.io/otel/metric v1.34.0 // indirect
-	go.opentelemetry.io/otel/sdk v1.34.0 // indirect
 	go.opentelemetry.io/otel/sdk/metric v1.34.0 // indirect
 	go.opentelemetry.io/otel/trace v1.34.0 // indirect
 	go.uber.org/multierr v1.11.0 // indirect