net/http: use cancellation instead of a timeout in TestTransportProxyHTTPSConnectTimeout

The use of a timeout in this test caused it to be flaky: if the
timeout occurred before the connection was attempted, then the Accept
call on the Listener could hang indefinitely, and its goroutine would
not exit until that Listener was closed. That caused the test to fail.

A longer timeout would make the test less flaky, but it would become
even slower and would still be sensitive to timing.

Instead, replace the timeout with an explicit Context cancellation
after the CONNECT request has been read. That not only ensures that
the cancellation occurs at the appropriate point, but also makes the
test much faster: a test run with -count=1000 now executes in less
than 2s on my machine, whereas before it took upwards of 50s.

Fixes #36082
Updates #28012

Change-Id: I00c20d87365fd3d257774422f39d2acc8791febd
Reviewed-on: https://go-review.googlesource.com/c/go/+/210857
Run-TryBot: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/net/http/transport_test.go

@@ -1444,9 +1444,13 @@ func TestTransportProxy(t *testing.T) {
 
 // Issue 28012: verify that the Transport closes its TCP connection to http proxies
 // when they're slow to reply to HTTPS CONNECT responses.
-func TestTransportProxyHTTPSConnectTimeout(t *testing.T) {
+func TestTransportProxyHTTPSConnectLeak(t *testing.T) {
 	setParallel(t)
 	defer afterTest(t)
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
 	ln := newLocalListener(t)
 	defer ln.Close()
 	listenerDone := make(chan struct{})
@@ -1469,8 +1473,11 @@ func TestTransportProxyHTTPSConnectTimeout(t *testing.T) {
 			t.Errorf("unexpected method %q", cr.Method)
 			return
 		}
-		// now hang and never write a response; wait for the client to give up on us and
-		// close (prior to Issue 28012 being fixed, we never closed)
+
+		// Now hang and never write a response; instead, cancel the request and wait
+		// for the client to close.
+		// (Prior to Issue 28012 being fixed, we never closed.)
+		cancel()
 		var buf [1]byte
 		_, err = br.Read(buf[:])
 		if err != io.EOF {
@@ -1478,23 +1485,27 @@ func TestTransportProxyHTTPSConnectTimeout(t *testing.T) {
 		}
 		return
 	}()
-	tr := &Transport{
-		Proxy: func(*Request) (*url.URL, error) {
-			return url.Parse("http://" + ln.Addr().String())
+
+	c := &Client{
+		Transport: &Transport{
+			Proxy: func(*Request) (*url.URL, error) {
+				return url.Parse("http://" + ln.Addr().String())
+			},
 		},
 	}
-	c := &Client{Transport: tr, Timeout: 50 * time.Millisecond}
-	_, err := c.Get("https://golang.fake.tld/")
+	req, err := NewRequestWithContext(ctx, "GET", "https://golang.fake.tld/", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	_, err = c.Do(req)
 	if err == nil {
 		t.Errorf("unexpected Get success")
 	}
-	timer := time.NewTimer(5 * time.Second)
-	defer timer.Stop()
-	select {
-	case <-listenerDone:
-	case <-timer.C:
-		t.Errorf("timeout waiting for Transport to close its connection to the proxy")
-	}
+
+	// Wait unconditionally for the listener goroutine to exit: this should never
+	// hang, so if it does we want a full goroutine dump — and that's exactly what
+	// the testing package will give us when the test run times out.
+	<-listenerDone
 }
 
 // Issue 16997: test transport dial preserves typed errors