net/http: TimeoutHandler should start timer when serving request

TimeoutHandler was starting the Timer when the handler was created,
instead of when serving a request. It also was sharing it between
multiple requests, which is incorrect, as the requests might start
at different times.

Store the timeout duration and create the Timer when ServeHTTP is
called. Different requests will have different timers.

The testing plumbing was simplified to store the channel used to
control when timeout happens. It overrides the regular timer.

Fixes #14568.

Change-Id: I4bd51a83f412396f208682d3ae5e382db5f8dc81
Reviewed-on: https://go-review.googlesource.com/20046
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/net/http/export_test.go

@@ -60,8 +60,8 @@ func SetTestHookServerServe(fn func(*Server, net.Listener)) { testHookServerServ
 func NewTestTimeoutHandler(handler Handler, ch <-chan time.Time) Handler {
 	return &timeoutHandler{
 		handler:     handler,
-		timeout: func() <-chan time.Time { return ch },
-		// (no body and nil cancelTimer)
+		testTimeout: ch,
+		// (no body)
 	}
 }
 

src/net/http/serve_test.go

@@ -1888,6 +1888,32 @@ func TestTimeoutHandlerRaceHeaderTimeout(t *testing.T) {
 	}
 }
 
+// Issue 14568.
+func TestTimeoutHandlerStartTimerWhenServing(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping sleeping test in -short mode")
+	}
+	defer afterTest(t)
+	var handler HandlerFunc = func(w ResponseWriter, _ *Request) {
+		w.WriteHeader(StatusNoContent)
+	}
+	timeout := 300 * time.Millisecond
+	ts := httptest.NewServer(TimeoutHandler(handler, timeout, ""))
+	defer ts.Close()
+	// Issue was caused by the timeout handler starting the timer when
+	// was created, not when the request. So wait for more than the timeout
+	// to ensure that's not the case.
+	time.Sleep(2 * timeout)
+	res, err := Get(ts.URL)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer res.Body.Close()
+	if res.StatusCode != StatusNoContent {
+		t.Errorf("got res.StatusCode %d, want %v", res.StatusCode, StatusNoContent)
+	}
+}
+
 // Verifies we don't path.Clean() on the wrong parts in redirects.
 func TestRedirectMunging(t *testing.T) {
 	req, _ := NewRequest("GET", "http://example.com/", nil)

src/net/http/server.go

@@ -2309,15 +2309,10 @@ func (srv *Server) onceSetNextProtoDefaults() {
 // TimeoutHandler buffers all Handler writes to memory and does not
 // support the Hijacker or Flusher interfaces.
 func TimeoutHandler(h Handler, dt time.Duration, msg string) Handler {
-	t := time.NewTimer(dt)
 	return &timeoutHandler{
 		handler: h,
 		body:    msg,
-
-		// Effectively storing a *time.Timer, but decomposed
-		// for testing:
-		timeout:     func() <-chan time.Time { return t.C },
-		cancelTimer: t.Stop,
+		dt:      dt,
 	}
 }
 
@@ -2328,12 +2323,11 @@ var ErrHandlerTimeout = errors.New("http: Handler timeout")
 type timeoutHandler struct {
 	handler Handler
 	body    string
+	dt      time.Duration
 
-	// timeout returns the channel of a *time.Timer and
-	// cancelTimer cancels it. They're stored separately for
-	// testing purposes.
-	timeout     func() <-chan time.Time // returns channel producing a timeout
-	cancelTimer func() bool             // optional
+	// When set, no timer will be created and this channel will
+	// be used instead.
+	testTimeout <-chan time.Time
 }
 
 func (h *timeoutHandler) errorBody() string {
@@ -2344,6 +2338,12 @@ func (h *timeoutHandler) errorBody() string {
 }
 
 func (h *timeoutHandler) ServeHTTP(w ResponseWriter, r *Request) {
+	var t *time.Timer
+	timeout := h.testTimeout
+	if timeout == nil {
+		t = time.NewTimer(h.dt)
+		timeout = t.C
+	}
 	done := make(chan struct{})
 	tw := &timeoutWriter{
 		w: w,
@@ -2363,10 +2363,10 @@ func (h *timeoutHandler) ServeHTTP(w ResponseWriter, r *Request) {
 		}
 		w.WriteHeader(tw.code)
 		w.Write(tw.wbuf.Bytes())
-		if h.cancelTimer != nil {
-			h.cancelTimer()
+		if t != nil {
+			t.Stop()
 		}
-	case <-h.timeout():
+	case <-timeout:
 		tw.mu.Lock()
 		defer tw.mu.Unlock()
 		w.WriteHeader(StatusServiceUnavailable)