net/http: don't cancel Request.Context on pipelined Server requests

See big comment in code.

Fixes #23921

Change-Id: I2dbd1acc2e9da07a71f9e0640aafe0c59a335627
Reviewed-on: https://go-review.googlesource.com/123875
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/net/http/serve_test.go

@@ -3175,25 +3175,32 @@ For:
 	ts.Close()
 }
 
-// Tests that a pipelined request causes the first request's Handler's CloseNotify
+// Tests that a pipelined request does not cause the first request's
-// channel to fire. Previously it deadlocked.
+// Handler's CloseNotify channel to fire.
 //
-// Issue 13165
+// Issue 13165 (where it used to deadlock), but behavior changed in Issue 23921.
 func TestCloseNotifierPipelined(t *testing.T) {
+	setParallel(t)
 	defer afterTest(t)
 	gotReq := make(chan bool, 2)
 	sawClose := make(chan bool, 2)
 	ts := httptest.NewServer(HandlerFunc(func(rw ResponseWriter, req *Request) {
 		gotReq <- true
 		cc := rw.(CloseNotifier).CloseNotify()
-		<-cc
+		select {
+		case <-cc:
+			t.Error("unexpected CloseNotify")
+		case <-time.After(100 * time.Millisecond):
+		}
 		sawClose <- true
 	}))
+	defer ts.Close()
 	conn, err := net.Dial("tcp", ts.Listener.Addr().String())
 	if err != nil {
 		t.Fatalf("error dialing: %v", err)
 	}
 	diec := make(chan bool, 1)
+	defer close(diec)
 	go func() {
 		const req = "GET / HTTP/1.1\r\nConnection: keep-alive\r\nHost: foo\r\n\r\n"
 		_, err = io.WriteString(conn, req+req) // two requests
@@ -3206,27 +3213,23 @@ func TestCloseNotifierPipelined(t *testing.T) {
 	}()
 	reqs := 0
 	closes := 0
-For:
 	for {
 		select {
 		case <-gotReq:
 			reqs++
 			if reqs > 2 {
 				t.Fatal("too many requests")
-			} else if reqs > 1 {
-				diec <- true
 			}
 		case <-sawClose:
 			closes++
 			if closes > 1 {
-				break For
+				return
 			}
 		case <-time.After(5 * time.Second):
 			ts.CloseClientConnections()
 			t.Fatal("timeout")
 		}
 	}
-	ts.Close()
 }
 
 func TestCloseNotifierChanLeak(t *testing.T) {
@@ -5796,31 +5799,23 @@ func TestServerHijackGetsBackgroundByte(t *testing.T) {
 		// Tell the client to send more data after the GET request.
 		inHandler <- true
 
-		// Wait until the HTTP server sees the extra data
-		// after the GET request. The HTTP server fires the
-		// close notifier here, assuming it's a pipelined
-		// request, as documented.
-		select {
-		case <-w.(CloseNotifier).CloseNotify():
-		case <-time.After(5 * time.Second):
-			t.Error("timeout")
-			return
-		}
-
 		conn, buf, err := w.(Hijacker).Hijack()
 		if err != nil {
 			t.Error(err)
 			return
 		}
 		defer conn.Close()
-		n := buf.Reader.Buffered()
+
-		if n != 1 {
-			t.Errorf("buffered data = %d; want 1", n)
-		}
 		peek, err := buf.Reader.Peek(3)
 		if string(peek) != "foo" || err != nil {
 			t.Errorf("Peek = %q, %v; want foo, nil", peek, err)
 		}
+
+		select {
+		case <-r.Context().Done():
+			t.Error("context unexpectedly canceled")
+		default:
+		}
 	}))
 	defer ts.Close()
 
@@ -5861,17 +5856,6 @@ func TestServerHijackGetsBackgroundByte_big(t *testing.T) {
 	ts := httptest.NewServer(HandlerFunc(func(w ResponseWriter, r *Request) {
 		defer close(done)
 
-		// Wait until the HTTP server sees the extra data
-		// after the GET request. The HTTP server fires the
-		// close notifier here, assuming it's a pipelined
-		// request, as documented.
-		select {
-		case <-w.(CloseNotifier).CloseNotify():
-		case <-time.After(5 * time.Second):
-			t.Error("timeout")
-			return
-		}
-
 		conn, buf, err := w.(Hijacker).Hijack()
 		if err != nil {
 			t.Error(err)

src/net/http/server.go

@@ -203,6 +203,9 @@ type Hijacker interface {
 //
 // This mechanism can be used to cancel long operations on the server
 // if the client has disconnected before the response is ready.
+//
+// Deprecated: the CloseNotifier interface predates Go's context package.
+// New code should use Request.Context instead.
 type CloseNotifier interface {
 	// CloseNotify returns a channel that receives at most a
 	// single value (true) when the client connection has gone
@@ -674,10 +677,28 @@ func (cr *connReader) backgroundRead() {
 	cr.lock()
 	if n == 1 {
 		cr.hasByte = true
-		// We were at EOF already (since we wouldn't be in a
+		// We were past the end of the previous request's body already
-		// background read otherwise), so this is a pipelined
+		// (since we wouldn't be in a background read otherwise), so
-		// HTTP request.
+		// this is a pipelined HTTP request. Prior to Go 1.11 we used to
-		cr.closeNotifyFromPipelinedRequest()
+		// send on the CloseNotify channel and cancel the context here,
+		// but the behavior was documented as only "may", and we only
+		// did that because that's how CloseNotify accidentally behaved
+		// in very early Go releases prior to context support. Once we
+		// added context support, people used a Handler's
+		// Request.Context() and passed it along. Having that context
+		// cancel on pipelined HTTP requests caused problems.
+		// Fortunately, almost nothing uses HTTP/1.x pipelining.
+		// Unfortunately, apt-get does, or sometimes does.
+		// New Go 1.11 behavior: don't fire CloseNotify or cancel
+		// contexts on pipelined requests. Shouldn't affect people, but
+		// fixes cases like Issue 23921. This does mean that a client
+		// closing their TCP connection after sending a pipelined
+		// request won't cancel the context, but we'll catch that on any
+		// write failure (in checkConnErrorWriter.Write).
+		// If the server never writes, yes, there are still contrived
+		// server & client behaviors where this fails to ever cancel the
+		// context, but that's kinda why HTTP/1.x pipelining died
+		// anyway.
 	}
 	if ne, ok := err.(net.Error); ok && cr.aborted && ne.Timeout() {
 		// Ignore this error. It's the expected error from
@@ -724,19 +745,6 @@ func (cr *connReader) handleReadError(_ error) {
 	cr.closeNotify()
 }
 
-// closeNotifyFromPipelinedRequest simply calls closeNotify.
-//
-// This method wrapper is here for documentation. The callers are the
-// cases where we send on the closenotify channel because of a
-// pipelined HTTP request, per the previous Go behavior and
-// documentation (that this "MAY" happen).
-//
-// TODO: consider changing this behavior and making context
-// cancelation and closenotify work the same.
-func (cr *connReader) closeNotifyFromPipelinedRequest() {
-	cr.closeNotify()
-}
-
 // may be called from multiple goroutines.
 func (cr *connReader) closeNotify() {
 	res, _ := cr.conn.curReq.Load().(*response)
@@ -1834,9 +1842,6 @@ func (c *conn) serve(ctx context.Context) {
 		if requestBodyRemains(req.Body) {
 			registerOnHitEOF(req.Body, w.conn.r.startBackgroundRead)
 		} else {
-			if w.conn.bufr.Buffered() > 0 {
-				w.conn.r.closeNotifyFromPipelinedRequest()
-			}
 			w.conn.r.startBackgroundRead()
 		}