net/http: Set a timeout on Request.Context when using TimeoutHandler

In TimeoutHandler, use a request whose context has been configured with
the handler's timeout

Fixes #20712

Change-Id: Ie670148f85fdad46841ff29232042309e15665ae
Reviewed-on: https://go-review.googlesource.com/46412
Run-TryBot: Tom Bergan <tombergan@google.com>
Reviewed-by: Tom Bergan <tombergan@google.com>

src/net/http/export_test.go

@@ -63,9 +63,14 @@ func SetPendingDialHooks(before, after func()) {
 func SetTestHookServerServe(fn func(*Server, net.Listener)) { testHookServerServe = fn }
 
 func NewTestTimeoutHandler(handler Handler, ch <-chan time.Time) Handler {
+	ctx, cancel := context.WithCancel(context.Background())
+	go func() {
+		<-ch
+		cancel()
+	}()
 	return &timeoutHandler{
 		handler:     handler,
-		testTimeout: ch,
+		testContext: ctx,
 		// (no body)
 	}
 }

src/net/http/server.go

@@ -3032,9 +3032,9 @@ type timeoutHandler struct {
 	body    string
 	dt      time.Duration
 
-	// When set, no timer will be created and this channel will
+	// When set, no context will be created and this context will
 	// be used instead.
-	testTimeout <-chan time.Time
+	testContext context.Context
 }
 
 func (h *timeoutHandler) errorBody() string {
@@ -3045,12 +3045,13 @@ 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
+	ctx := h.testContext
+	if ctx == nil {
+		var cancelCtx context.CancelFunc
+		ctx, cancelCtx = context.WithTimeout(r.Context(), h.dt)
+		defer cancelCtx()
 	}
+	r = r.WithContext(ctx)
 	done := make(chan struct{})
 	tw := &timeoutWriter{
 		w: w,
@@ -3073,10 +3074,7 @@ func (h *timeoutHandler) ServeHTTP(w ResponseWriter, r *Request) {
 		}
 		w.WriteHeader(tw.code)
 		w.Write(tw.wbuf.Bytes())
-		if t != nil {
-			t.Stop()
-		}
-	case <-timeout:
+	case <-ctx.Done():
 		tw.mu.Lock()
 		defer tw.mu.Unlock()
 		w.WriteHeader(StatusServiceUnavailable)