net/http: add new Server benchmark

The new BenchmarkServer avoids profiling the client code
by running it in a child process.

R=rsc
CC=golang-dev
https://golang.org/cl/6260053

src/pkg/net/http/serve_test.go

@@ -20,7 +20,9 @@ import (
 	"net/http/httputil"
 	"net/url"
 	"os"
+	"os/exec"
 	"reflect"
+	"strconv"
 	"strings"
 	"syscall"
 	"testing"
@@ -1262,3 +1264,56 @@ func BenchmarkClientServer(b *testing.B) {
 
 	b.StopTimer()
 }
+
+// A benchmark for profiling the server without the HTTP client code.
+// The client code runs in a subprocess.
+//
+// For use like:
+//   $ go test -c
+//   $ ./http.test -test.run=XX -test.bench=Benchmarktime=15 -test.cpuprofile=http.prof
+//   $ go tool pprof http.test http.prof
+//   (pprof) web
+func BenchmarkServer(b *testing.B) {
+	// Child process mode;
+	if url := os.Getenv("TEST_BENCH_SERVER_URL"); url != "" {
+		n, err := strconv.Atoi(os.Getenv("TEST_BENCH_CLIENT_N"))
+		if err != nil {
+			panic(err)
+		}
+		for i := 0; i < n; i++ {
+			res, err := Get(url)
+			if err != nil {
+				log.Panicf("Get:", err)
+			}
+			all, err := ioutil.ReadAll(res.Body)
+			if err != nil {
+				log.Panicf("ReadAll:", err)
+			}
+			body := string(all)
+			if body != "Hello world.\n" {
+				log.Panicf("Got body:", body)
+			}
+		}
+		os.Exit(0)
+		return
+	}
+
+	var res = []byte("Hello world.\n")
+	b.StopTimer()
+	ts := httptest.NewServer(HandlerFunc(func(rw ResponseWriter, r *Request) {
+		rw.Header().Set("Content-Type", "text/html; charset=utf-8")
+		rw.Write(res)
+	}))
+	defer ts.Close()
+	b.StartTimer()
+
+	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),
+	}, os.Environ()...)
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		b.Errorf("Test failure: %v, with output: %s", err, out)
+	}
+}