XTLS/Xray-core · error

padding turn %d combines variants with generated write chunk

Error message

padding turn %d combines variants with generated write chunks

What it means

validatePaddingSchedule rejected turn i because it defines both explicit variants (pre-shaped chunk lists) and a non-zero writeChunkLength (randomly generated chunks). A turn must choose one shaping mode: variant-based or generator-based; combining them is ambiguous.

Source

Thrown at transport/internet/finalmask/xmc/padding.go:98

	if firstTurnPrefixLength > 0 && schedule[0].direction != paddingClientToServer {
		return fmt.Errorf("first prefixed padding turn is not client-to-server")
	}

	for i, turn := range schedule {
		if turn.direction != paddingClientToServer && turn.direction != paddingServerToClient {
			return fmt.Errorf("padding turn %d has invalid direction: %d", i, turn.direction)
		}
		if err := validatePaddingDelayRange(turn.startDelay); err != nil {
			return fmt.Errorf("padding turn %d has an invalid start delay: %w", i, err)
		}
		if err := validatePaddingDelayRange(turn.chunkDelay); err != nil {
			return fmt.Errorf("padding turn %d has an invalid chunk delay: %w", i, err)
		}
		if turn.writeChunkMinLength < 0 || turn.writeChunkLength < turn.writeChunkMinLength || turn.writeChunkLength > maxPaddingChunkLength {
			return fmt.Errorf("padding turn %d has an invalid write chunk range: %d-%d", i, turn.writeChunkMinLength, turn.writeChunkLength)
		}
		if len(turn.variants) > 0 && turn.writeChunkLength != 0 {
			return fmt.Errorf("padding turn %d combines variants with generated write chunks", i)
		}

		minLength, maxLength, err := paddingTurnBounds(turn)
		if err != nil {
			return fmt.Errorf("padding turn %d: %w", i, err)
		}
		hasSendRange := turn.sendMinLength != 0 || turn.sendMaxLength != 0
		if hasSendRange {
			if len(turn.variants) > 0 {
				return fmt.Errorf("padding turn %d combines variants with a send range", i)
			}
			if turn.sendMinLength < minLength || turn.sendMaxLength < turn.sendMinLength || turn.sendMaxLength > maxLength {
				return fmt.Errorf("padding turn %d has an invalid send range: %d-%d", i, turn.sendMinLength, turn.sendMaxLength)
			}
		}
		if i == 0 && minLength-firstTurnPrefixLength < 1 {
			return fmt.Errorf("padding turn 0 is too short for %d prefix bytes", firstTurnPrefixLength)
		}

View on GitHub (pinned to 7d214f8b09)

Solutions

1. If using variants, leave writeChunkLength (and writeChunkMinLength) at 0
2. If using generated chunks, remove the variants list
3. Enforce mutual exclusion in the schedule builder so this cannot compile/configure its way into runtime

Example fix

// before
turn := paddingTurn{variants: vs, writeChunkLength: 8 * 1024}

// after
turn := paddingTurn{variants: vs} // generated chunks disabled

func variantsExclusive(turn paddingTurn) bool {
    return !(len(turn.variants) > 0 && turn.writeChunkLength != 0)
}

When it happens

Trigger: A hand-authored turn that copies a variant list and also sets writeChunkLength for tuning; merging two schedule profiles without clearing one field.

Common situations: Forks extending schedules; config formats where both fields are optional and both get filled; schedule merge/refactor mistakes.

Related errors

• first prefixed padding turn is not client-to-server
• padding turn %d has invalid direction: %d
• padding turn %d: %w
• unexpected client IP length
• empty padding schedule

AI-assisted analysis of XTLS/Xray-core@7d214f8b09 (2026-08-15). Data as JSON: /api/errors/0c9303503314e854. Report an issue: GitHub.