otelmux: fix: Do not require calling Write nor WriteHeader

CHANGELOG.md

@@ -15,6 +15,9 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 ### Fixed
 
 - The `"go.opentelemetry.io/contrib/detector/aws/ecs".Detector` no longer errors if not running in ECS. (#1426, #1428)
+- `go.opentelemetry.io/contrib/instrumentation/github.com/gorilla/mux/otelmux`
+  does not require instrumented HTTP handlers to call `Write` nor
+  `WriteHeader` anymore. (#1443)
 
 ## [1.2.0/0.27.0] - 2021-11-15
 
@@ -46,7 +49,7 @@ Update dependency on the `go.opentelemetry.io/otel` project to `v1.1.0`.
 - Add instrumentation for the `github.com/aws/aws-lambda-go` package. (#983)
 - Add resource detector for AWS Lambda. (#983)
 - Add `WithTracerProvider` option for `otelhttptrace.NewClientTrace`. (#1128)
-- Add optional AWS X-Ray configuration module for AWS Lambda Instrumentation (#984)
+- Add optional AWS X-Ray configuration module for AWS Lambda Instrumentation. (#984)
 
 ### Fixed
 

instrumentation/github.com/gorilla/mux/otelmux/mux.go

@@ -83,13 +83,12 @@ var rrwPool = &sync.Pool{
 func getRRW(writer http.ResponseWriter) *recordingResponseWriter {
 	rrw := rrwPool.Get().(*recordingResponseWriter)
 	rrw.written = false
-	rrw.status = 0
+	rrw.status = http.StatusOK
 	rrw.writer = httpsnoop.Wrap(writer, httpsnoop.Hooks{
 		Write: func(next httpsnoop.WriteFunc) httpsnoop.WriteFunc {
 			return func(b []byte) (int, error) {
 				if !rrw.written {
 					rrw.written = true
-					rrw.status = http.StatusOK
 				}
 				return next(b)
 			}

instrumentation/github.com/gorilla/mux/otelmux/test/mux_test.go

@@ -30,9 +30,7 @@ import (
 	"go.opentelemetry.io/otel/trace"
 )
 
-func ok(w http.ResponseWriter, _ *http.Request) {
-	w.WriteHeader(http.StatusOK)
-}
+func ok(w http.ResponseWriter, _ *http.Request) {}
 
 func TestSDKIntegration(t *testing.T) {
 	sr := tracetest.NewSpanRecorder()