XTLS/Xray-core · warning

set deadline: %w

Error message

set deadline: %w

What it means

serverConn.handshake fails when connectionDeadlines.beginHandshake cannot apply the 2-minute handshake read/write deadline to the underlying net.Conn (deadline.go:24-35 applies both deadlines via applyLocked). This means SetReadDeadline or SetWriteDeadline on the raw connection returned an error — typically because the connection is already closed or the wrapped conn type does not support deadlines.

Source

Thrown at transport/internet/finalmask/xmc/server.go:55

	profiles        []loginProfile
	password        string
	rsaPrivateKey   *rsa.PrivateKey
	rsaPublicKey    []byte
	paddingSchedule []paddingTurn
	packet          *packetStream
	deadlines       *connectionDeadlines
}

func (c *serverConn) handshake() error {
	c.handshakeLock.Lock()
	defer c.handshakeLock.Unlock()

	if c.state != serverStateHandshake {
		return nil
	}

	if err := c.deadlines.beginHandshake(); err != nil {
		return fmt.Errorf("set deadline: %w", err)
	}
	defer func() { _ = c.deadlines.endHandshake() }()

	var (
		protocolVersion Varint
		serverAddress   String
		serverPort      UnsignedShort
		nextState       Varint
	)

	// handshake packet

	pkt, err := readPacket(c.reader)
	if err != nil {
		return fmt.Errorf("read handshake packet: %w", err)
	}

	if pkt.packetID != 0 {

View on GitHub (pinned to 7d214f8b09)

Solutions

1. Check whether the peer disconnected immediately (scanner/health-check traffic) — usually harmless noise to log at debug level
2. Verify the net.Conn supplied to the server actually supports deadlines and is not already closed
3. Ensure no concurrent Close() races with handshake start in the connection accept loop
4. If wrapping conns in the inbound chain, forward SetReadDeadline/SetWriteDeadline correctly

if tc, ok := conn.(*net.TCPConn); ok {\n\t_ = tc.SetDeadline(time.Now().Add(time.Minute)) // probe deadline support early\n}

func supportsDeadlines(c net.Conn) bool {\n\treturn c.SetReadDeadline(time.Now()) == nil && c.SetReadDeadline(time.Time{}) == nil\n}

if err := conn.handshake(); err != nil && strings.Contains(err.Error(), "set deadline") {\n\t// conn is dead or deadline-unsupported: nothing to negotiate\n\tlog.Debug("xmc: connection unusable before handshake: ", err)\n\t_ = conn.Close()\n}

When it happens

Trigger: A client connects and the server begins the Minecraft handshake while the underlying net.Conn is closed (peer hung up immediately) or is a wrapped connection whose SetDeadline returns an error (e.g. a pipe, TLS conn after Close, or a custom net.Conn wrapper).

Common situations: Port scanners opening and instantly closing TCP connections to the proxy port; health checks that RST immediately; middleboxes or custom inbound wrappers in Xray that don't propagate deadlines; connections closed by a prior goroutine race.

Related errors

• set deadline: %w
• write handshake packet: %w
• write login start: %w
• read encryption request: %w
• bad encrypt request packet id

AI-assisted analysis of XTLS/Xray-core@7d214f8b09 (2026-08-15). Data as JSON: /api/errors/ba460125f4b9f437. Report an issue: GitHub.