Deprecate otel plugin: route tagging is now built into the Goa muxer

otel/README.md

@@ -1,97 +1,28 @@
-# OpenTelemetry Plugin
-
-The `otel` plugin is a [Goa](https://github.com/goadesign/goa/tree/v3) plugin that instruments
-HTTP endpoints with OpenTelemetry configuring it with the endpoint route pattern. This
-plugin is used in conjunction with the [Clue](https://github.com/goadesign/clue) project to
-instrument services with OpenTelemetry.
-
-## Usage
-
-Simply import the plugin in the service design package. Use the blank identifier `_` as explicit
-package name:
-
-```go
-package design
-
-import . "goa.design/goa/v3/dsl"
-import _ "goa.design/plugins/v3/otel" # Enables the otel plugin
-
-var _ = API("...
-```
-
-and generate as usual:
-
-```bash
-goa gen PACKAGE
-```
-
-where `PACKAGE` is the Go import path of the design package.
-
-## Effects of the Plugin
-
-Importing the `otel` package changes the behavior of the `gen` command of the
-`goa` tool. The `gen` command output is modified so that the generated HTTP
-handlers are wrapped with a call to the `otelhttp.WithRouteTag`.
-
-That is the code generated in `gen/http/<service>/server/server.go` that
-mounts an endpoint handler onto the HTTP mux changes from:
-
-```go
-mux.Handle("<VERB>", "<PATH>", f)
-```
-
-to:
-
-```go
-mux.Handle("<VERB>", otelhttp.WithRouteTag("<PATH>", f).ServeHTTP))
-```
-
-## OpenTelemetry Configuration
-
-For the code generated by the plugin to work the OpenTelemetry SDK must be
-initialized. This can be done by importing the `clue` package and calling
-`clue.ConfigureOpenTelemetry` in the `main` function of the service:
-
-```go
-package main
-
-import (
-	"context"
-	"net/http"
-
-	"go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"
-	"go.opentelemetry.io/otel/exporters/stdout/stdoutmetric"
-	"go.opentelemetry.io/otel/exporters/stdout/stdouttrace"
-	"goa.design/clue/clue"
-	"goa.design/clue/log"
-)
-
-func main() {
-	// Create OpenTelemetry metric and span exporters
-	// Use stdout exporters for demo.
-	metricExporter, err := stdoutmetric.New()
-	if err != nil {
-		panic(err)
-	}
-	spanExporter, err := stdouttrace.New()
-	if err != nil {
-		panic(err)
-	}
-
-	// Configure OpenTelemetry.
-	ctx := log.Context(context.Background())
-	cfg, err := clue.NewConfig(ctx, "service", "1.0.0", metricExporter, spanExporter)
-	if err != nil {
-		panic(err)
-	}
-	clue.ConfigureOpenTelemetry(ctx, cfg)
-
-	// Create HTTP handler and start server.
-	var handler http.Handler = http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		w.Write([]byte("Hello, World!"))
-	})
-	handler = otelhttp.NewHandler(handler, "service") // Instrument handler.
-	http.ListenAndServe(":8080", handler)
-}
-```
-
+# OpenTelemetry Plugin (Deprecated)
+
+> **Deprecated**: This plugin is no longer necessary and will be removed in a
+> future release. The Goa HTTP muxer now sets `r.Pattern` on every matched
+> request (using the Go 1.22+ convention), which `otelhttp` v0.65.0+ reads
+> automatically to tag spans and metrics with the matched route.
+>
+> **Migration**: Remove the blank import from your design package and
+> regenerate:
+>
+> ```diff
+> - import _ "goa.design/plugins/v3/otel"
+> ```
+>
+> No other changes are needed — route tagging now happens automatically in
+> the Goa muxer.
+
+## Background
+
+The `otel` plugin was a [Goa](https://github.com/goadesign/goa/tree/v3) plugin
+that wrapped generated HTTP handlers with `otelhttp.WithRouteTag` to set the
+`http.route` attribute on OpenTelemetry spans and metrics.
+
+`otelhttp.WithRouteTag` was
+[removed](https://github.com/open-telemetry/opentelemetry-go-contrib/pull/8268)
+in `otelhttp` v0.65.0 because `otelhttp` now reads `r.Pattern` (added in Go
+1.22) to obtain the route automatically. Goa's muxer has been updated to set
+`r.Pattern` on every dispatched request, making this plugin unnecessary.

otel/generate.go

@@ -1,9 +1,16 @@
+// Package otel was a Goa plugin that instrumented HTTP handlers with
+// otelhttp.WithRouteTag to set the http.route attribute on spans and metrics.
+//
+// Deprecated: As of Goa v3.x.x the default HTTP muxer sets r.Pattern on every
+// matched request, which otelhttp (v0.65.0+) reads automatically to tag spans
+// and metrics with the matched route. This plugin is no longer necessary and
+// will be removed in a future release. Remove the blank import from your
+// design package:
+//
+//	import _ "goa.design/plugins/v3/otel" // ← delete this line
 package otel
 
 import (
-	"path/filepath"
-	"strings"
-
 	"goa.design/goa/v3/codegen"
 	"goa.design/goa/v3/eval"
 )
@@ -13,27 +20,10 @@ func init() {
 	codegen.RegisterPluginLast("otel", "gen", nil, Generate)
 }
 
-// Generate generates the call to otelhttp.WithRouteTag
-func Generate(genpkg string, roots []eval.Root, files []*codegen.File) ([]*codegen.File, error) {
-	for _, f := range files {
-		if filepath.Base(f.Path) == "server.go" {
-			for _, s := range f.SectionTemplates {
-				if s.Name == "server-handler" {
-					s.Source = strings.Replace(
-						s.Source,
-						`mux.Handle("{{ .Verb }}", "{{ .Path }}", f)`,
-						`mux.Handle("{{ .Verb }}", "{{ .Path }}", otelhttp.WithRouteTag("{{ .Path }}", f).ServeHTTP)`,
-						1,
-					)
-				}
-			}
-			imports := f.SectionTemplates[0].Data.(map[string]any)["Imports"].([]*codegen.ImportSpec)
-			imports = append(imports, &codegen.ImportSpec{
-				Path: "go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp",
-				Name: "otelhttp",
-			})
-			f.SectionTemplates[0].Data.(map[string]any)["Imports"] = imports
-		}
-	}
+// Generate is a no-op kept for backward compatibility. The Goa HTTP muxer now
+// sets r.Pattern on every request, making explicit route tagging unnecessary.
+//
+// Deprecated: Remove the otel plugin import from your design package.
+func Generate(_ string, _ []eval.Root, files []*codegen.File) ([]*codegen.File, error) {
 	return files, nil
 }

otel/generate_test.go

@@ -37,6 +37,10 @@ func TestOtel(t *testing.T) {
 			fs, err := Generate("", []eval.Root{root}, serverFiles)
 			assert.NoError(t, err)
 			require.Len(t, fs, 2)
+			// Generate is a no-op: the returned files must be identical
+			// to the input server files.
+			assert.Same(t, serverFiles[0], fs[0])
+			assert.Same(t, serverFiles[1], fs[1])
 			sections := fs[0].Section("server-handler")
 			require.Len(t, sections, 1)
 			section := sections[0]

otel/testdata/multiple routes.golden

@@ -1,4 +1,3 @@
-
 // MountMethodHandler configures the mux to serve the "Service2" service
 // "Method" endpoint.
 func MountMethodHandler(mux goahttp.Muxer, h http.Handler) {
@@ -8,6 +7,6 @@ func MountMethodHandler(mux goahttp.Muxer, h http.Handler) {
 			h.ServeHTTP(w, r)
 		}
 	}
-	mux.Handle("GET", "/", otelhttp.WithRouteTag("/", f).ServeHTTP)
-	mux.Handle("GET", "/other", otelhttp.WithRouteTag("/other", f).ServeHTTP)
+	mux.Handle("GET", "/", f)
+	mux.Handle("GET", "/other", f)
 }

otel/testdata/one route.golden

@@ -1,4 +1,3 @@
-
 // MountMethodHandler configures the mux to serve the "Service" service
 // "Method" endpoint.
 func MountMethodHandler(mux goahttp.Muxer, h http.Handler) {
@@ -8,5 +7,5 @@ func MountMethodHandler(mux goahttp.Muxer, h http.Handler) {
 			h.ServeHTTP(w, r)
 		}
 	}
-	mux.Handle("GET", "/", otelhttp.WithRouteTag("/", f).ServeHTTP)
+	mux.Handle("GET", "/", f)
 }