net/http: fix data race in TestTransportResponseHeaderTimeout

Fixes #7264

LGTM=dvyukov
R=dvyukov
CC=golang-codereviews
https://golang.org/cl/87970045

src/pkg/net/http/httptest/server_test.go

@@ -5,7 +5,6 @@
 package httptest
 
 import (
-	"flag"
 	"io/ioutil"
 	"net/http"
 	"testing"
@@ -30,15 +29,13 @@ func TestServer(t *testing.T) {
 	}
 }
 
-var testIssue7264 = flag.Bool("issue7264", false, "enable failing test for issue 7264")
-
 func TestIssue7264(t *testing.T) {
-	if !*testIssue7264 {
-		t.Skip("skipping failing test for issue 7264")
-	}
 	for i := 0; i < 1000; i++ {
 		func() {
-			ts := NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {}))
+			inHandler := make(chan bool, 1)
+			ts := NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				inHandler <- true
+			}))
 			defer ts.Close()
 			tr := &http.Transport{
 				ResponseHeaderTimeout: time.Nanosecond,
@@ -46,6 +43,7 @@ func TestIssue7264(t *testing.T) {
 			defer tr.CloseIdleConnections()
 			c := &http.Client{Transport: tr}
 			res, err := c.Get(ts.URL)
+			<-inHandler
 			if err == nil {
 				res.Body.Close()
 			}

src/pkg/net/http/transport_test.go

@@ -1250,9 +1250,13 @@ func TestTransportResponseHeaderTimeout(t *testing.T) {
 	if testing.Short() {
 		t.Skip("skipping timeout test in -short mode")
 	}
+	inHandler := make(chan bool, 1)
 	mux := NewServeMux()
-	mux.HandleFunc("/fast", func(w ResponseWriter, r *Request) {})
+	mux.HandleFunc("/fast", func(w ResponseWriter, r *Request) {
+		inHandler <- true
+	})
 	mux.HandleFunc("/slow", func(w ResponseWriter, r *Request) {
+		inHandler <- true
 		time.Sleep(2 * time.Second)
 	})
 	ts := httptest.NewServer(mux)
@@ -1275,6 +1279,12 @@ func TestTransportResponseHeaderTimeout(t *testing.T) {
 	}
 	for i, tt := range tests {
 		res, err := c.Get(ts.URL + tt.path)
+		select {
+		case <-inHandler:
+		case <-time.After(5 * time.Second):
+			t.Errorf("never entered handler for test index %d, %s", i, tt.path)
+			continue
+		}
 		if err != nil {
 			uerr, ok := err.(*url.Error)
 			if !ok {