net/http2: send WINDOW_UPDATE on a body's write failure

When the body.Write fails during processData, the connection flow
control must be updated to account for the data received. The connection's
WINDOW_UPDATE should reflect the amount of data that was not successfully
written. The stream is about to be closed, so no update is required.

Fixes golang/go#40423

Change-Id: I546597cedf3715e6617babcb3b62140bf1857a27
Reviewed-on: https://go-review.googlesource.com/c/net/+/245158
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Emmanuel Odeke <emm.odeke@gmail.com>

http2/server.go

@@ -1694,6 +1694,7 @@ func (sc *serverConn) processData(f *DataFrame) error {
 		if len(data) > 0 {
 			wrote, err := st.body.Write(data)
 			if err != nil {
+				sc.sendWindowUpdate(nil, int(f.Length)-wrote)
 				return streamError(id, ErrCodeStreamClosed)
 			}
 			if wrote != len(data) {

http2/server_test.go

@@ -4209,3 +4209,62 @@ func TestContentEncodingNoSniffing(t *testing.T) {
 		})
 	}
 }
+
+func TestServerWindowUpdateOnBodyClose(t *testing.T) {
+	const content = "12345678"
+	blockCh := make(chan bool)
+	errc := make(chan error, 1)
+	st := newServerTester(t, func(w http.ResponseWriter, r *http.Request) {
+		buf := make([]byte, 4)
+		n, err := io.ReadFull(r.Body, buf)
+		if err != nil {
+			errc <- err
+			return
+		}
+		if n != len(buf) {
+			errc <- fmt.Errorf("too few bytes read: %d", n)
+			return
+		}
+		blockCh <- true
+		<-blockCh
+		errc <- nil
+	})
+	defer st.Close()
+
+	st.greet()
+	st.writeHeaders(HeadersFrameParam{
+		StreamID: 1, // clients send odd numbers
+		BlockFragment: st.encodeHeader(
+			":method", "POST",
+			"content-length", strconv.Itoa(len(content)),
+		),
+		EndStream:  false, // to say DATA frames are coming
+		EndHeaders: true,
+	})
+	st.writeData(1, false, []byte(content[:5]))
+	<-blockCh
+	st.stream(1).body.CloseWithError(io.EOF)
+	st.writeData(1, false, []byte(content[5:]))
+	blockCh <- true
+
+	increments := len(content)
+	for {
+		f, err := st.readFrame()
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			t.Fatal(err)
+		}
+		if wu, ok := f.(*WindowUpdateFrame); ok && wu.StreamID == 0 {
+			increments -= int(wu.Increment)
+			if increments == 0 {
+				break
+			}
+		}
+	}
+
+	if err := <-errc; err != nil {
+		t.Error(err)
+	}
+}