fix: cause http2.serverConn.unackedSettings ack_mystery

buffer.go

@@ -29,6 +29,7 @@ type bufferedReader struct {
 	buffer     bytes.Buffer
 	bufferRead int
 	bufferSize int
+	stagePoint int
 	sniffing   bool
 	lastErr    error
 }
@@ -65,3 +66,11 @@ func (s *bufferedReader) reset(snif bool) {
 	s.bufferRead = 0
 	s.bufferSize = s.buffer.Len()
 }
+
+func (s *bufferedReader) newStage() {
+	s.stagePoint = s.buffer.Len()
+}
+
+func (s *bufferedReader) discard() {
+	s.buffer.Truncate(s.stagePoint)
+}

matchers.go

@@ -217,11 +217,28 @@ func matchHTTP1Field(r io.Reader, name string, matches func(string) bool) (match
 	return matches(req.Header.Get(name))
 }
 
+type stageReader interface {
+	io.Reader
+	newStage()
+	discard()
+}
+
+type nonStageReader struct{ io.Reader }
+
+func (nonStageReader) newStage() {}
+func (nonStageReader) discard()  {}
+
 func matchHTTP2Field(w io.Writer, r io.Reader, name string, matches func(string) bool) (matched bool) {
 	if !hasHTTP2Preface(r) {
 		return false
 	}
 
+	sr := (stageReader)(nil)
+	if sr, _ = r.(stageReader); sr == nil {
+		sr = nonStageReader{}
+	}
+
+	waitAcks := 0
 	done := false
 	framer := http2.NewFramer(w, r)
 	hdec := hpack.NewDecoder(uint32(4<<10), func(hf hpack.HeaderField) {
@@ -233,6 +250,7 @@ func matchHTTP2Field(w io.Writer, r io.Reader, name string, matches func(string)
 		}
 	})
 	for {
+		sr.newStage()
 		f, err := framer.ReadFrame()
 		if err != nil {
 			return false
@@ -243,11 +261,15 @@ func matchHTTP2Field(w io.Writer, r io.Reader, name string, matches func(string)
 			// Sender acknoweldged the SETTINGS frame. No need to write
 			// SETTINGS again.
 			if f.IsAck() {
+				// Avoid causing golang.org/x/net/http2.serverConn.unackedSettings PROTOCOL_ERROR
+				sr.discard()
+				waitAcks--
 				break
 			}
 			if err := framer.WriteSettings(); err != nil {
 				return false
 			}
+			waitAcks++
 		case *http2.ContinuationFrame:
 			if _, err := hdec.Write(f.HeaderBlockFragment()); err != nil {
 				return false
@@ -260,7 +282,7 @@ func matchHTTP2Field(w io.Writer, r io.Reader, name string, matches func(string)
 			done = done || f.FrameHeader.Flags&http2.FlagHeadersEndHeaders != 0
 		}
 
-		if done {
+		if done && waitAcks == 0 {
 			return matched
 		}
 	}