confighttp: make server span naming spec-compliant (#13088)

#### Description

Update the confighttp server span names to use the low-cardnality
request pattern, rather than the full client-specified path, as
described by the specification:
https://opentelemetry.io/docs/specs/semconv/http/http-spans/#name.

Requires
open-telemetry/opentelemetry-go-contrib#7192

#### Link to tracking issue

Fixes #12468

#### Testing

Added a unit test.

#### Documentation

None

---------

Co-authored-by: Alex Boten <[email protected]>

Author: axw

.chloggen/confighttp-server-pattern-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: enhancement
+
+# 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: Update the HTTP server span naming to use the HTTP method and route pattern instead of the path.
+
+# 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: |
+  The HTTP server span name will now be formatted as `<http.request.method> <http.route>`.
+  If a route pattern is not available, it will fall back to `<http.request.method>`.
+
+# 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: [user]

config/confighttp/confighttp.go

@@ -517,7 +517,17 @@ func (hss *ServerConfig) ToServer(ctx context.Context, host component.Host, sett
 			otelhttp.WithTracerProvider(settings.TracerProvider),
 			otelhttp.WithPropagators(otel.GetTextMapPropagator()),
 			otelhttp.WithSpanNameFormatter(func(_ string, r *http.Request) string {
-				return r.URL.Path
+				// https://opentelemetry.io/docs/specs/semconv/http/http-spans/#name:
+				//
+				//   "HTTP span names SHOULD be {method} {target} if there is a (low-cardinality) target available.
+				//   If there is no (low-cardinality) {target} available, HTTP span names SHOULD be {method}.
+				//   ...
+				//   Instrumentation MUST NOT default to using URI path as a {target}."
+				//
+				if r.Pattern != "" {
+					return r.Method + " " + r.Pattern
+				}
+				return r.Method
 			}),
 			otelhttp.WithMeterProvider(settings.MeterProvider),
 		},

config/confighttp/confighttp_test.go

@@ -1575,3 +1575,61 @@ func TestDefaultHTTPServerSettings(t *testing.T) {
 	assert.Equal(t, time.Duration(0), httpServerSettings.ReadTimeout)
 	assert.Equal(t, 1*time.Minute, httpServerSettings.ReadHeaderTimeout)
 }
+
+func TestHTTPServerTelemetry_Tracing(t *testing.T) {
+	// Create a pattern route. The server name the span after the
+	// pattern rather than the client-specified path.
+	mux := http.NewServeMux()
+	mux.HandleFunc("/b/{bucket}/o/{objectname...}", func(http.ResponseWriter, *http.Request) {})
+
+	type testcase struct {
+		handler          http.Handler
+		expectedSpanName string
+	}
+
+	for name, testcase := range map[string]testcase{
+		"pattern": {
+			handler:          mux,
+			expectedSpanName: "GET /b/{bucket}/o/{objectname...}",
+		},
+		"no_pattern": {
+			handler:          http.HandlerFunc(func(http.ResponseWriter, *http.Request) {}),
+			expectedSpanName: "GET",
+		},
+	} {
+		t.Run(name, func(t *testing.T) {
+			telemetry := componenttest.NewTelemetry()
+			config := NewDefaultServerConfig()
+			config.Endpoint = "localhost:0"
+			config.TLSSetting = nil
+			srv, err := config.ToServer(
+				context.Background(),
+				componenttest.NewNopHost(),
+				telemetry.NewTelemetrySettings(),
+				testcase.handler,
+			)
+			require.NoError(t, err)
+
+			done := make(chan struct{})
+			lis, err := config.ToListener(context.Background())
+			require.NoError(t, err)
+			go func() {
+				defer close(done)
+				_ = srv.Serve(lis)
+			}()
+			defer func() {
+				assert.NoError(t, srv.Close())
+				<-done
+			}()
+
+			resp, err := http.Get(fmt.Sprintf("http://%s/b/bucket123/o/object456/segment", lis.Addr()))
+			require.NoError(t, err)
+			require.Equal(t, http.StatusOK, resp.StatusCode)
+			resp.Body.Close()
+
+			spans := telemetry.SpanRecorder.Ended()
+			require.Len(t, spans, 1)
+			assert.Equal(t, testcase.expectedSpanName, spans[0].Name())
+		})
+	}
+}