XTLS/Xray-core · error

unsupported padding placement:

Error message

unsupported padding placement: 

What it means

SplitHTTPConfig.Build() validates "xPaddingPlacement" in a switch at transport_method.go:346-352. Empty defaults to "queryInHeader"; only "cookie", "header", "query", "queryInHeader" are accepted; anything else appends the bad value to this error.

Source

Thrown at infra/conf/transport_method.go:351

	if c.XPaddingBytes != (Int32Range{}) && (c.XPaddingBytes.From <= 0 || c.XPaddingBytes.To <= 0) {
		return nil, errors.New("xPaddingBytes cannot be disabled")
	}

	if c.XPaddingKey == "" {
		c.XPaddingKey = "x_padding"
	}

	if c.XPaddingHeader == "" {
		c.XPaddingHeader = "X-Padding"
	}

	switch c.XPaddingPlacement {
	case "":
		c.XPaddingPlacement = "queryInHeader"
	case "cookie", "header", "query", "queryInHeader":
	default:
		return nil, errors.New("unsupported padding placement: " + c.XPaddingPlacement)
	}

	switch c.XPaddingMethod {
	case "":
		c.XPaddingMethod = "repeat-x"
	case "repeat-x", "tokenish":
	default:
		return nil, errors.New("unsupported padding method: " + c.XPaddingMethod)
	}

	switch c.UplinkDataPlacement {
	case "":
		c.UplinkDataPlacement = splithttp.PlacementAuto
	case splithttp.PlacementAuto, splithttp.PlacementBody:
	case splithttp.PlacementCookie, splithttp.PlacementHeader:
		if c.Mode != "packet-up" {
			return nil, errors.New("UplinkDataPlacement can be " + c.UplinkDataPlacement + " only in packet-up mode")
		}

View on GitHub (pinned to 7d214f8b09)

Solutions

1. Use one of: "cookie", "header", "query", "queryInHeader" (exact camelCase)
2. Omit "xPaddingPlacement" to accept the "queryInHeader" default

Example fix

// before
"xPaddingPlacement": "query-in-header"
// after
"xPaddingPlacement": "queryInHeader"

func validXPaddingPlacement(p string) bool {
	switch p {
	case "", "cookie", "header", "query", "queryInHeader":
		return true
	}
	return false
}

When it happens

Trigger: "xPaddingPlacement": "query-in-header" (hyphenated instead of camelCase), "body", "none", or any string outside the four allowed values in splithttp transportSettings. Note the default is queryInHeader — writing an invalid value explicitly is the only way to hit this.

Common situations: Guessing placement names from the padding docs instead of the enum; using hyphenated forms consistent with mode names ("packet-up") which don't apply here; stale third-party config generators.

Related errors

• xPaddingBytes cannot be disabled
• unsupported padding method:
• not a Service.
• Dispatcher: Invalid destination.
• FakeDNSEngine is not initialized, but such a sniffer is used

AI-assisted analysis of XTLS/Xray-core@7d214f8b09 (2026-08-15). Data as JSON: /api/errors/0cffc8aaff6dd365. Report an issue: GitHub.