XTLS/Xray-core · error

write remaining bytes: %w

Error message

write remaining bytes: %w

What it means

RestBytes.writeTo writes the raw trailing bytes to the io.Writer and wraps any Write failure. As with the other write wrappers, the encoding cannot fail; this is an underlying connection/buffer error while flushing the tail of a packet.

Source

Thrown at transport/internet/finalmask/xmc/protocol.go:348

	*v = append([]byte(*v), buf...)

	return nil
}

type RestBytes []byte

func (v *RestBytes) readFrom(r io.Reader) error {
	buf, err := io.ReadAll(r)
	if err != nil {
		return fmt.Errorf("read remaining bytes: %w", err)
	}
	*v = append((*v)[:0], buf...)
	return nil
}

func (v *RestBytes) writeTo(w io.Writer) error {
	if _, err := w.Write(*v); err != nil {
		return fmt.Errorf("write remaining bytes: %w", err)
	}
	return nil
}

func (v *Bytes) writeTo(w io.Writer) error {
	length := Varint(len(*v))
	err := length.writeTo(w)
	if err != nil {
		return fmt.Errorf("write bytes length: %w", err)
	}

	_, err = w.Write(*v)
	if err != nil {
		return fmt.Errorf("write bytes: %w", err)
	}

	return nil
}

View on GitHub (pinned to 7d214f8b09)

Solutions

1. Unwrap and classify: ErrConnClosed/broken pipe => peer gone, skip further writes; timeout => deadline too tight or network stalled.
2. Serialize all writes through one writer goroutine/channel so close-vs-write races cannot happen.
3. Once any write fails, abandon the connection instead of attempting more packet writes.
4. Tune write deadlines to the expected RTT and payload size.

if err := rest.writeTo(w); err != nil {
    if errors.Is(err, net.ErrClosed) || isBrokenPipe(err) {
        stopWriterLoop()
        return nil // peer gone; nothing more to flush
    }
    return err
}

When it happens

Trigger: Sending a packet with a RestBytes payload after the peer disconnected; write deadline exceeded; underlying conn already closed by another goroutine or by error handling elsewhere.

Common situations: Writing a final close/flush packet after the remote already went away; races between a watchdog closing the conn and the encoder still writing; outbound proxy failure beneath the transport.

Related errors

• write boolean: %w
• write UUID: %w
• read bytes: %w
• read remaining bytes: %w
• write bytes length: %w

AI-assisted analysis of XTLS/Xray-core@7d214f8b09 (2026-08-15). Data as JSON: /api/errors/3af8d25356e10ca4. Report an issue: GitHub.