add support for sending error codes on stream reset

const.go

@@ -57,6 +57,27 @@ func (e *GoAwayError) Is(target error) bool {
 	return false
 }
 
+// A StreamError is used for errors returned from Read and Write calls after the stream is Reset
+type StreamError struct {
+	ErrorCode uint32
+	Remote    bool
+}
+
+func (s *StreamError) Error() string {
+	if s.Remote {
+		return fmt.Sprintf("stream reset by remote, error code: %d", s.ErrorCode)
+	}
+	return fmt.Sprintf("stream reset, error code: %d", s.ErrorCode)
+}
+
+func (s *StreamError) Is(target error) bool {
+	if target == ErrStreamReset {
+		return true
+	}
+	e, ok := target.(*StreamError)
+	return ok && *e == *s
+}
+
 var (
 	// ErrInvalidVersion means we received a frame with an
 	// invalid version

session_test.go

@@ -16,6 +16,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
@@ -1571,6 +1572,56 @@ func TestStreamResetRead(t *testing.T) {
 	wc.Wait()
 }
 
+func TestStreamResetWithError(t *testing.T) {
+	client, server := testClientServer()
+	defer client.Close()
+	defer server.Close()
+
+	wc := new(sync.WaitGroup)
+	wc.Add(2)
+	go func() {
+		defer wc.Done()
+		stream, err := server.AcceptStream()
+		if err != nil {
+			t.Error(err)
+		}
+
+		se := &StreamError{}
+		_, err = io.ReadAll(stream)
+		if !errors.As(err, &se) {
+			t.Errorf("exptected StreamError, got type:%T, err: %s", err, err)
+			return
+		}
+		expected := &StreamError{Remote: true, ErrorCode: 42}
+		assert.Equal(t, se, expected)
+	}()
+
+	stream, err := client.OpenStream(context.Background())
+	if err != nil {
+		t.Error(err)
+	}
+
+	go func() {
+		defer wc.Done()
+
+		se := &StreamError{}
+		_, err = io.ReadAll(stream)
+		if !errors.As(err, &se) {
+			t.Errorf("exptected StreamError, got type:%T, err: %s", err, err)
+			return
+		}
+		expected := &StreamError{Remote: false, ErrorCode: 42}
+		assert.Equal(t, se, expected)
+	}()
+
+	time.Sleep(1 * time.Second)
+	err = stream.ResetWithError(42)
+	if err != nil {
+		t.Fatal(err)
+	}
+	wc.Wait()
+}
+
 func TestLotsOfWritesWithStreamDeadline(t *testing.T) {
 	config := testConf()
 	config.EnableKeepAlive = false
@@ -1809,7 +1860,7 @@ func TestMaxIncomingStreams(t *testing.T) {
 	require.NoError(t, err)
 	str.SetDeadline(time.Now().Add(time.Second))
 	_, err = str.Read([]byte{0})
-	require.EqualError(t, err, "stream reset")
+	require.ErrorIs(t, err, ErrStreamReset)
 
 	// Now close one of the streams.
 	// This should then allow the client to open a new stream.

stream.go

@@ -42,6 +42,7 @@ type Stream struct {
 	state                 streamState
 	writeState, readState halfStreamState
 	stateLock             sync.Mutex
+	resetErr              *StreamError
 
 	recvBuf segmentedBuffer
 
@@ -101,7 +102,7 @@ START:
 		}
 		// Closed, but we have data pending -> read.
 	case halfReset:
-		return 0, ErrStreamReset
+		return 0, s.resetErr
 	default:
 		panic("unknown state")
 	}
@@ -155,7 +156,7 @@ START:
 	case halfClosed:
 		return 0, ErrStreamClosed
 	case halfReset:
-		return 0, ErrStreamReset
+		return 0, s.resetErr
 	default:
 		panic("unknown state")
 	}
@@ -251,12 +252,20 @@ func (s *Stream) sendClose() error {
 
 // sendReset is used to send a RST
 func (s *Stream) sendReset() error {
-	hdr := encode(typeWindowUpdate, flagRST, s.id, 0)
+	code := uint32(0)
+	if s.resetErr != nil {
+		code = s.resetErr.ErrorCode
+	}
+	hdr := encode(typeWindowUpdate, flagRST, s.id, code)
 	return s.session.sendMsg(hdr, nil, nil)
 }
 
 // Reset resets the stream (forcibly closes the stream)
 func (s *Stream) Reset() error {
+	return s.ResetWithError(0)
+}
+
+func (s *Stream) ResetWithError(errCode uint32) error {
 	sendReset := false
 	s.stateLock.Lock()
 	switch s.state {
@@ -281,6 +290,7 @@ func (s *Stream) Reset() error {
 		s.readState = halfReset
 	}
 	s.state = streamFinished
+	s.resetErr = &StreamError{Remote: false, ErrorCode: errCode}
 	s.notifyWaiting()
 	s.stateLock.Unlock()
 	if sendReset {
@@ -382,7 +392,7 @@ func (s *Stream) cleanup() {
 
 // processFlags is used to update the state of the stream
 // based on set flags, if any. Lock must be held
-func (s *Stream) processFlags(flags uint16) {
+func (s *Stream) processFlags(flags uint16, hdr header) {
 	// Close the stream without holding the state lock
 	var closeStream bool
 	defer func() {
@@ -425,6 +435,10 @@ func (s *Stream) processFlags(flags uint16) {
 			s.writeState = halfReset
 		}
 		s.state = streamFinished
+		// Length in a window update frame with RST flag encodes an error code.
+		if hdr.MsgType() == typeWindowUpdate && s.resetErr == nil {
+			s.resetErr = &StreamError{Remote: true, ErrorCode: hdr.Length()}
+		}
 		s.stateLock.Unlock()
 		closeStream = true
 		s.notifyWaiting()
@@ -439,15 +453,15 @@ func (s *Stream) notifyWaiting() {
 
 // incrSendWindow updates the size of our send window
 func (s *Stream) incrSendWindow(hdr header, flags uint16) {
-	s.processFlags(flags)
+	s.processFlags(flags, hdr)
 	// Increase window, unblock a sender
 	atomic.AddUint32(&s.sendWindow, hdr.Length())
 	asyncNotify(s.sendNotifyCh)
 }
 
 // readData is used to handle a data frame
 func (s *Stream) readData(hdr header, flags uint16, conn io.Reader) error {
-	s.processFlags(flags)
+	s.processFlags(flags, hdr)
 
 	// Check that our recv window is not exceeded
 	length := hdr.Length()