XTLS/Xray-core · error

0-RTT is not allowed

Error message

0-RTT is not allowed

What it means

Error "0-RTT is not allowed" thrown in XTLS/Xray-core.

Source

Thrown at proxy/vless/encryption/server.go:200

	if fallback != nil {
		*fallback = append(*fallback, encryptedLength...)
	}
	decryptedLength := make([]byte, 2)
	if _, err := nfsAEAD.Open(decryptedLength[:0], nil, encryptedLength, nil); err != nil {
		c.UseAES = !c.UseAES
		nfsAEAD = NewAEAD(iv, nfsKey, c.UseAES)
		if _, err := nfsAEAD.Open(decryptedLength[:0], nil, encryptedLength, nil); err != nil {
			return nil, err
		}
	}
	if fallback != nil {
		*fallback = nil
	}
	length := DecodeLength(decryptedLength)

	if length == 32 {
		if i.SecondsFrom == 0 && i.SecondsTo == 0 {
			return nil, errors.New("0-RTT is not allowed")
		}
		encryptedTicket := make([]byte, 32)
		if _, err := io.ReadFull(conn, encryptedTicket); err != nil {
			return nil, err
		}
		ticket, err := nfsAEAD.Open(nil, nil, encryptedTicket, nil)
		if err != nil {
			return nil, err
		}
		i.RWLock.RLock()
		s := i.Sessions[[16]byte(ticket)]
		i.RWLock.RUnlock()
		if s == nil {
			noises := make([]byte, crypto.RandBetween(1279, 2279)) // matches 1-RTT's server hello length for "random", though it is not important, just for example
			var err error
			for err == nil {
				rand.Read(noises)
				_, err = DecodeHeader(noises)

View on GitHub (pinned to 7d214f8b09)

When it happens

Trigger: Thrown at proxy/vless/encryption/server.go:200 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/7537d03b3fe87e21. Report an issue: GitHub.