XTLS/Xray-core · error

Can not use "downloadSettings" in "stream-one" mode.

Error message

Can not use "downloadSettings" in "stream-one" mode.

What it means

At the end of SplitHTTPConfig.Build(), a present "downloadSettings" (a *StreamConfig, i.e. a full separate transport stream settings for the downlink) is rejected when mode is "stream-one" (transport_method.go:499-502). stream-one uses a single bidirectional HTTP connection, so a separate download transport is contradictory by definition.

Source

Thrown at infra/conf/transport_method.go:501

		ScMinPostsIntervalMs: newRangeConfig(c.ScMinPostsIntervalMs),
		ScMaxBufferedPosts:   c.ScMaxBufferedPosts,
		ScStreamUpServerSecs: newRangeConfig(c.ScStreamUpServerSecs),
		ServerMaxHeaderBytes: c.ServerMaxHeaderBytes,
		SessionIDTable:       c.SessionIDTable,
		SessionIDLength:      newRangeConfig(c.SessionIDLength),
		Xmux: &splithttp.XmuxConfig{
			MaxConcurrency:   newRangeConfig(c.Xmux.MaxConcurrency),
			MaxConnections:   newRangeConfig(c.Xmux.MaxConnections),
			CMaxReuseTimes:   newRangeConfig(c.Xmux.CMaxReuseTimes),
			HMaxRequestTimes: newRangeConfig(c.Xmux.HMaxRequestTimes),
			HMaxReusableSecs: newRangeConfig(c.Xmux.HMaxReusableSecs),
			HKeepAlivePeriod: c.Xmux.HKeepAlivePeriod,
		},
	}

	if c.DownloadSettings != nil {
		if c.Mode == "stream-one" {
			return nil, errors.New(`Can not use "downloadSettings" in "stream-one" mode.`)
		}
		var err error
		if config.DownloadSettings, err = c.DownloadSettings.Build(); err != nil {
			return nil, errors.New(`Failed to build "downloadSettings".`).Base(err)
		}
	}

	return config, nil
}

func roomSize(tableSize int, min, max int32) *big.Int {
	base := big.NewInt(int64(tableSize))
	sum := new(big.Int)
	term := new(big.Int)
	for k := min; k <= max; k++ {
		term.Exp(base, big.NewInt(int64(k)), nil)
		sum.Add(sum, term)
	}

View on GitHub (pinned to 7d214f8b09)

Solutions

1. Delete the "downloadSettings" block when using "mode": "stream-one"
2. Or keep downloadSettings and switch mode to "packet-up"/"stream-up"/"auto"

Example fix

// before
"mode": "stream-one", "downloadSettings": { "transportSettings": { "transport": "tcp" } }
// after
"mode": "stream-one"

// Go: stream-one has no separate download transport
if cfg.DownloadSettings != nil && cfg.Mode == "stream-one" {
	return errors.New("remove downloadSettings for stream-one mode")
}

When it happens

Trigger: "mode": "stream-one" together with a "downloadSettings": {"transportSettings": ...} block in the same splithttp transportSettings. Common when converting a stream-up config (where downloadSettings is the normal way to split up/down transports) to stream-one without removing the block.

Common situations: Migrating from splithttp/stream-up asymmetric-CDN setups to stream-one; templates that always include downloadSettings; clientside configs generated for stream-up reused with the mode line changed.

Related errors

• unsupported mode:
• UplinkDataPlacement can be only in packet-up mode
• uplinkHTTPMethod can be GET only in packet-up mode
• Failed to build "downloadSettings".
• Failed to unmarshal "extra".

AI-assisted analysis of XTLS/Xray-core@7d214f8b09 (2026-08-15). Data as JSON: /api/errors/14cc715a096d0103. Report an issue: GitHub.