net/http: add client benchmark

BenchmarkClient is intended for profiling
the client without the HTTP server code.
The server code runs in a subprocess.

Change-Id: I9aa128604d0d4e94dc5c0372dc86f962282ed6e8
Reviewed-on: https://go-review.googlesource.com/3164Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/http/serve_test.go

@@ -2891,7 +2891,7 @@ func BenchmarkServer(b *testing.B) {
 	defer ts.Close()
 	b.StartTimer()
 
-	cmd := exec.Command(os.Args[0], "-test.run=XXXX", "-test.bench=BenchmarkServer")
+	cmd := exec.Command(os.Args[0], "-test.run=XXXX", "-test.bench=BenchmarkServer$")
 	cmd.Env = append([]string{
 		fmt.Sprintf("TEST_BENCH_CLIENT_N=%d", b.N),
 		fmt.Sprintf("TEST_BENCH_SERVER_URL=%s", ts.URL),
@@ -2902,6 +2902,83 @@ func BenchmarkServer(b *testing.B) {
 	}
 }
 
+// A benchmark for profiling the client without the HTTP server code.
+// The server code runs in a subprocess.
+func BenchmarkClient(b *testing.B) {
+	b.ReportAllocs()
+	b.StopTimer()
+	port := os.Getenv("TEST_BENCH_SERVER_PORT") // can be set by user
+	if port == "" {
+		port = "39207"
+	}
+	var data = []byte("Hello world.\n")
+	if server := os.Getenv("TEST_BENCH_SERVER"); server != "" {
+		// Server process mode.
+		HandleFunc("/", func(w ResponseWriter, r *Request) {
+			r.ParseForm()
+			if r.Form.Get("stop") != "" {
+				os.Exit(0)
+			}
+			w.Header().Set("Content-Type", "text/html; charset=utf-8")
+			w.Write(data)
+		})
+		log.Fatal(ListenAndServe(":"+port, nil))
+	}
+
+	// Start server process.
+	cmd := exec.Command(os.Args[0], "-test.run=XXXX", "-test.bench=BenchmarkClient$")
+	cmd.Env = append(os.Environ(), "TEST_BENCH_SERVER=yes")
+	if err := cmd.Start(); err != nil {
+		b.Fatalf("subprocess failed to start: %v", err)
+	}
+	defer cmd.Process.Kill()
+	done := make(chan error)
+	go func() {
+		done <- cmd.Wait()
+	}()
+
+	// Wait for the server process to respond.
+	url := "http://localhost:" + port + "/"
+	for i := 0; i < 100; i++ {
+		time.Sleep(50 * time.Millisecond)
+		if _, err := Get(url); err == nil {
+			break
+		}
+		if i == 99 {
+			b.Fatalf("subprocess does not respond")
+		}
+	}
+
+	// Do b.N requests to the server.
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		res, err := Get(url)
+		if err != nil {
+			b.Fatalf("Get: %v", err)
+		}
+		body, err := ioutil.ReadAll(res.Body)
+		res.Body.Close()
+		if err != nil {
+			b.Fatalf("ReadAll: %v", err)
+		}
+		if bytes.Compare(body, data) != 0 {
+			b.Fatalf("Got body: %q", body)
+		}
+	}
+	b.StopTimer()
+
+	// Instruct server process to stop.
+	Get(url + "?stop=yes")
+	select {
+	case err := <-done:
+		if err != nil {
+			b.Fatalf("subprocess failed: %v", err)
+		}
+	case <-time.After(5 * time.Second):
+		b.Fatalf("subprocess did not stop")
+	}
+}
+
 func BenchmarkServerFakeConnNoKeepAlive(b *testing.B) {
 	b.ReportAllocs()
 	req := reqBytes(`GET / HTTP/1.0