XTLS/Xray-core · error

padding turn %d has an invalid write chunk range: %d-%d

Error message

padding turn %d has an invalid write chunk range: %d-%d

What it means

validatePaddingSchedule rejected turn i's generated write-chunk parameters: writeChunkMinLength is negative, writeChunkLength < writeChunkMinLength, or writeChunkLength exceeds maxPaddingChunkLength (48 KiB). These bound the random chunk sizes used when the turn writes padding without explicit variants.

Source

Thrown at transport/internet/finalmask/xmc/padding.go:95

	if firstTurnPrefixLength < 0 {
		return fmt.Errorf("negative first turn prefix length: %d", firstTurnPrefixLength)
	}
	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)
			}
		}

View on GitHub (pinned to 7d214f8b09)

Solutions

1. Set 0 <= writeChunkMinLength <= writeChunkLength <= 48*1024
2. Leave both zero to use the default 16 KiB paddingBufferLength chunking
3. Clamp externally supplied chunk sizes to maxPaddingChunkLength before building the turn

Example fix

// before
writeChunkMinLength: 32 * 1024, writeChunkLength: 64 * 1024 // > 48 KiB cap

// after
writeChunkMinLength: 32 * 1024, writeChunkLength: 48 * 1024

func validWriteChunkRange(minLen, length int) bool {
    return minLen >= 0 && length >= minLen && length <= 48*1024
}

When it happens

Trigger: A turn with writeChunkMinLength < 0, a min greater than the fixed length, or a writeChunkLength above 49152; setting writeChunkLength without clamping to the 48 KiB cap.

Common situations: Forks tuning chunk sizes for different Minecraft versions; config values expressed in the wrong unit (bits vs bytes); off-by-one conversions at the 48 KiB boundary.

Related errors

• empty padding schedule
• negative first turn prefix length: %d
• first prefixed padding turn is not client-to-server
• padding turn %d has invalid direction: %d
• padding turn %d has an invalid start delay: %w

AI-assisted analysis of XTLS/Xray-core@7d214f8b09 (2026-08-15). Data as JSON: /api/errors/228254b11ce19614. Report an issue: GitHub.