Use felixge/httpsnoop approach to preserve additional interfaces (#26)

* Add overhead benchmark

* Use snoopwrap

* Use opencensus method for status code tracking

It's more efficient than using httpsnoop.

* Do not build status code tracker for go1.7

* Add remove support for http.Pusher in go1.7

* Adjust travis version range

Add up to go 1.11.

* Correct build tags

.travis.yml

@@ -4,6 +4,8 @@ go:
   - 1.7.x
   - 1.8.x
   - 1.9.x
+  - 1.10.x
+  - 1.11.x
   - tip
 
 script:

nethttp/server.go

@@ -9,16 +9,6 @@ import (
 	"github.com/opentracing/opentracing-go/ext"
 )
 
-type statusCodeTracker struct {
-	http.ResponseWriter
-	status int
-}
-
-func (w *statusCodeTracker) WriteHeader(status int) {
-	w.status = status
-	w.ResponseWriter.WriteHeader(status)
-}
-
 type mwOptions struct {
 	opNameFunc    func(r *http.Request) string
 	spanFilter    func(r *http.Request) bool
@@ -122,12 +112,12 @@ func MiddlewareFunc(tr opentracing.Tracer, h http.HandlerFunc, options ...MWOpti
 		}
 		ext.Component.Set(sp, componentName)
 
-		w = &statusCodeTracker{w, 200}
+		sct := &statusCodeTracker{w, 200}
 		r = r.WithContext(opentracing.ContextWithSpan(r.Context(), sp))
 
-		h(w, r)
+		h(sct.wrappedResponseWriter(), r)
 
-		ext.HTTPStatusCode.Set(sp, uint16(w.(*statusCodeTracker).status))
+		ext.HTTPStatusCode.Set(sp, uint16(sct.status))
 		sp.Finish()
 	}
 	return http.HandlerFunc(fn)

nethttp/server_test.go

@@ -160,3 +160,25 @@ func TestSpanFilterOption(t *testing.T) {
 		})
 	}
 }
+
+func BenchmarkStatusCodeTrackingOverhead(b *testing.B) {
+	mux := http.NewServeMux()
+	mux.HandleFunc("/root", func(w http.ResponseWriter, r *http.Request) {})
+	tr := &mocktracer.MockTracer{}
+	mw := Middleware(tr, mux)
+	srv := httptest.NewServer(mw)
+	defer srv.Close()
+
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			resp, err := http.Get(srv.URL)
+			if err != nil {
+				b.Fatalf("server returned error: %v", err)
+			}
+			err = resp.Body.Close()
+			if err != nil {
+				b.Fatalf("failed to close response: %v", err)
+			}
+		}
+	})
+}

nethttp/status-code-tracker-old.go

@@ -0,0 +1,135 @@
+// +build go1.7,!go1.8
+
+package nethttp
+
+import (
+	"io"
+	"net/http"
+)
+
+type statusCodeTracker struct {
+	http.ResponseWriter
+	status int
+}
+
+func (w *statusCodeTracker) WriteHeader(status int) {
+	w.status = status
+	w.ResponseWriter.WriteHeader(status)
+}
+
+// wrappedResponseWriter returns a wrapped version of the original
+// ResponseWriter and only implements the same combination of additional
+// interfaces as the original.  This implementation is based on
+// https://github.com/felixge/httpsnoop.
+func (w *statusCodeTracker) wrappedResponseWriter() http.ResponseWriter {
+	var (
+		hj, i0 = w.ResponseWriter.(http.Hijacker)
+		cn, i1 = w.ResponseWriter.(http.CloseNotifier)
+		fl, i3 = w.ResponseWriter.(http.Flusher)
+		rf, i4 = w.ResponseWriter.(io.ReaderFrom)
+	)
+	i2 := false
+
+	switch {
+	case !i0 && !i1 && !i2 && !i3 && !i4:
+		return struct {
+			http.ResponseWriter
+		}{w}
+	case !i0 && !i1 && !i2 && !i3 && i4:
+		return struct {
+			http.ResponseWriter
+			io.ReaderFrom
+		}{w, rf}
+	case !i0 && !i1 && !i2 && i3 && !i4:
+		return struct {
+			http.ResponseWriter
+			http.Flusher
+		}{w, fl}
+	case !i0 && !i1 && !i2 && i3 && i4:
+		return struct {
+			http.ResponseWriter
+			http.Flusher
+			io.ReaderFrom
+		}{w, fl, rf}
+	case !i0 && i1 && !i2 && !i3 && !i4:
+		return struct {
+			http.ResponseWriter
+			http.CloseNotifier
+		}{w, cn}
+	case !i0 && i1 && !i2 && !i3 && i4:
+		return struct {
+			http.ResponseWriter
+			http.CloseNotifier
+			io.ReaderFrom
+		}{w, cn, rf}
+	case !i0 && i1 && !i2 && i3 && !i4:
+		return struct {
+			http.ResponseWriter
+			http.CloseNotifier
+			http.Flusher
+		}{w, cn, fl}
+	case !i0 && i1 && !i2 && i3 && i4:
+		return struct {
+			http.ResponseWriter
+			http.CloseNotifier
+			http.Flusher
+			io.ReaderFrom
+		}{w, cn, fl, rf}
+	case i0 && !i1 && !i2 && !i3 && !i4:
+		return struct {
+			http.ResponseWriter
+			http.Hijacker
+		}{w, hj}
+	case i0 && !i1 && !i2 && !i3 && i4:
+		return struct {
+			http.ResponseWriter
+			http.Hijacker
+			io.ReaderFrom
+		}{w, hj, rf}
+	case i0 && !i1 && !i2 && i3 && !i4:
+		return struct {
+			http.ResponseWriter
+			http.Hijacker
+			http.Flusher
+		}{w, hj, fl}
+	case i0 && !i1 && !i2 && i3 && i4:
+		return struct {
+			http.ResponseWriter
+			http.Hijacker
+			http.Flusher
+			io.ReaderFrom
+		}{w, hj, fl, rf}
+	case i0 && i1 && !i2 && !i3 && !i4:
+		return struct {
+			http.ResponseWriter
+			http.Hijacker
+			http.CloseNotifier
+		}{w, hj, cn}
+	case i0 && i1 && !i2 && !i3 && i4:
+		return struct {
+			http.ResponseWriter
+			http.Hijacker
+			http.CloseNotifier
+			io.ReaderFrom
+		}{w, hj, cn, rf}
+	case i0 && i1 && !i2 && i3 && !i4:
+		return struct {
+			http.ResponseWriter
+			http.Hijacker
+			http.CloseNotifier
+			http.Flusher
+		}{w, hj, cn, fl}
+	case i0 && i1 && !i2 && i3 && i4:
+		return struct {
+			http.ResponseWriter
+			http.Hijacker
+			http.CloseNotifier
+			http.Flusher
+			io.ReaderFrom
+		}{w, hj, cn, fl, rf}
+	default:
+		return struct {
+			http.ResponseWriter
+		}{w}
+	}
+}