add a test to make sure the recordingResponseWriter preserves interfa…

…ces implemented by the wrapped writer

go.mod

@@ -4,6 +4,7 @@ go 1.14
 
 require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/gorilla/mux v1.8.0 // indirect
 	github.com/kr/pretty v0.1.0 // indirect
 	go.opentelemetry.io/otel v0.12.0
 	gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15 // indirect

go.sum

@@ -3,6 +3,8 @@ github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/google/go-cmp v0.5.2 h1:X2ev0eStA3AbceY54o37/0PQ/UWqKEiiO2dKL5OPaFM=
 github.com/google/go-cmp v0.5.2/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
+github.com/gorilla/mux v1.8.0 h1:i40aqfkR1h2SlN9hojwV5ZA91wcXFOvkdNIeFDP5koI=
+github.com/gorilla/mux v1.8.0/go.mod h1:DVbg23sWSpFRCP0SfiEN6jmj59UnW/n46BH5rLB71So=
 github.com/kr/pretty v0.1.0 h1:L/CwN0zerZDmRFUapSPitk6f+Q3+0za1rQkzVuMiMFI=
 github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORNo=
 github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=

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

@@ -15,7 +15,10 @@
 package otelmux
 
 import (
+	"bufio"
 	"context"
+	"io"
+	"net"
 	"net/http"
 	"net/http/httptest"
 	"testing"
@@ -183,3 +186,65 @@ func TestPropagationWithCustomPropagators(t *testing.T) {
 
 	router.ServeHTTP(w, r)
 }
+
+type testResponseWriter struct {
+	writer http.ResponseWriter
+}
+
+func (rw *testResponseWriter) Header() http.Header {
+	return rw.writer.Header()
+}
+func (rw *testResponseWriter) Write(b []byte) (int, error) {
+	return rw.writer.Write(b)
+}
+func (rw *testResponseWriter) WriteHeader(statusCode int) {
+	rw.writer.WriteHeader(statusCode)
+}
+
+// implement Hijacker
+func (rw *testResponseWriter) Hijack() (net.Conn, *bufio.ReadWriter, error) {
+	return nil, nil, nil
+}
+
+// implement Pusher
+func (rw *testResponseWriter) Push(target string, opts *http.PushOptions) error {
+	return nil
+}
+
+// implement CloseNotifier
+func (rw *testResponseWriter) CloseNotify() <-chan bool {
+	return nil
+}
+
+// implement Flusher
+func (rw *testResponseWriter) Flush() {
+}
+
+// implement io.ReaderFrom
+func (rw *testResponseWriter) ReadFrom(r io.Reader) (n int64, err error) {
+	return 0, nil
+}
+
+
+func TestResponseWriterInterfaces(t *testing.T) {
+	// make sure the recordingResponseWriter preserves interfaces implemented by the wrapped writer
+	provider, _ := mocktrace.NewTracerProviderAndTracer(tracerName)
+
+	router := mux.NewRouter()
+	router.Use(Middleware("foobar", WithTracerProvider(provider)))
+	router.HandleFunc("/user/{id}", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		assert.Implements(t, (*http.Hijacker)(nil), w)
+		assert.Implements(t, (*http.Pusher)(nil), w)
+		assert.Implements(t, (*http.CloseNotifier)(nil), w)
+		assert.Implements(t, (*http.Flusher)(nil), w)
+		assert.Implements(t, (*io.ReaderFrom)(nil), w)
+		w.WriteHeader(http.StatusOK)
+	}))
+
+	r := httptest.NewRequest("GET", "/user/123", nil)
+	w := &testResponseWriter{
+		writer: httptest.NewRecorder(),
+	}
+
+	router.ServeHTTP(w, r)
+}