unexpected response version. Expecting %d but actually %d

Error message

unexpected response version. Expecting %d but actually %d

What it means

Error "unexpected response version. Expecting %d but actually %d" thrown in XTLS/Xray-core.

Source

Thrown at proxy/vless/encoding/encoding.go:164

	if _, err := writer.Write(buffer.Bytes()); err != nil {
		return errors.New("failed to write response header").Base(err)
	}

	return nil
}

// DecodeResponseHeader decodes and returns (if successful) a ResponseHeader from an input stream.
func DecodeResponseHeader(reader io.Reader, request *protocol.RequestHeader) (*Addons, error) {
	buffer := buf.StackNew()
	defer buffer.Release()

	if _, err := buffer.ReadFullFrom(reader, 1); err != nil {
		return nil, errors.New("failed to read response version").Base(err)
	}

	if buffer.Byte(0) != request.Version {
		return nil, errors.New("unexpected response version. Expecting ", int(request.Version), " but actually ", int(buffer.Byte(0)))
	}

	responseAddons, err := DecodeHeaderAddons(&buffer, reader)
	if err != nil {
		return nil, errors.New("failed to decode response header addons").Base(err)
	}

	return responseAddons, nil
}

// XtlsRead can switch to splice copy
func XtlsRead(reader buf.Reader, writer buf.Writer, timer *signal.ActivityTimer, conn net.Conn, trafficState *proxy.TrafficState, isUplink bool, ctx context.Context) error {
	err := func() error {
		for {
			if isUplink && trafficState.Inbound.UplinkReaderDirectCopy || !isUplink && trafficState.Outbound.DownlinkReaderDirectCopy {
				var writerConn net.Conn
				var inTimer *signal.ActivityTimer
				if inbound := session.InboundFromContext(ctx); inbound != nil && inbound.Conn != nil {

View on GitHub (pinned to 7d214f8b09)

When it happens

Trigger: Thrown at proxy/vless/encoding/encoding.go:164 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of XTLS/Xray-core@7d214f8b09 (2026-08-15). Data as JSON: /api/errors/f9d72b09755dd9f1. Report an issue: GitHub.