XTLS/Xray-core · error

customTable produced empty padding pool

Error message

customTable produced empty padding pool

What it means

Thrown inside customLayout when generating the padding-byte pool for a custom table: it enumerates candidate encodings with at least 5 of 8 bits set and collects distinct results, and the resulting pool is empty. This means the given bit layout cannot produce any valid padding byte, an internal inconsistency between the pattern and the encoder.

Source

Thrown at transport/internet/finalmask/sudoku/table.go:341

	paddingSet := make(map[byte]struct{}, 64)
	padding := make([]byte, 0, 64)
	for drop := range xBits {
		for val := byte(0); val < 4; val++ {
			for pos := byte(0); pos < 16; pos++ {
				group := (val << 4) | pos
				b := encodeGroupWithDropX(group, drop)
				if bits.OnesCount8(b) >= 5 {
					if _, exists := paddingSet[b]; !exists {
						paddingSet[b] = struct{}{}
						padding = append(padding, b)
					}
				}
			}
		}
	}
	sort.Slice(padding, func(i, j int) bool { return padding[i] < padding[j] })
	if len(padding) == 0 {
		return nil, fmt.Errorf("customTable produced empty padding pool")
	}

	decodeGroup := func(b byte) (byte, bool) {
		if (b & xMask) != xMask {
			return 0, false
		}

		var val, pos byte
		if b&(1<<pBits[0]) != 0 {
			val |= 0x02
		}
		if b&(1<<pBits[1]) != 0 {
			val |= 0x01
		}
		for i, bit := range vBits {
			if b&(1<<bit) != 0 {
				pos |= 1 << (3 - uint8(i))
			}

View on GitHub (pinned to 7d214f8b09)

Solutions

1. Switch to the default layout by clearing customTable (mode prefer_entropy) and retest.
2. Try a known-good pattern such as "xxppvvvv".
3. If a specific pattern is required, report it upstream so the padding pool rule can be adjusted for that layout.

Example fix

// before
"customTable": "vvxxppvv"
// after
"customTable": ""

layout, err := resolveLayout(mode, customTable)
if err != nil {
	if strings.Contains(err.Error(), "empty padding pool") {
		layout, err = resolveLayout("prefer_entropy", "") // fall back to default
	}
	if err != nil {
		return err
	}
}

When it happens

Trigger: A customTable whose x/p bit positions make encodeGroupWithDropX never return a byte with popcount >= 5 across all enumerated groups. This is layout-dependent; most 2/2/4 patterns work, so hitting it indicates an exotic arrangement or a code change in the candidate enumeration.

Common situations: Experimenting with unusual permutations of the 8-slot pattern; upgrading the finalmask transport where the padding-generation rules changed while keeping an old custom pattern.

Related errors

• decode key collision for byte %d and %d
• invalid sudoku ascii mode: %s
• customTable must be 8 chars, got %d
• customTable has invalid char %q
• customTable must contain exactly 2 x, 2 p and 4 v

AI-assisted analysis of XTLS/Xray-core@7d214f8b09 (2026-08-15). Data as JSON: /api/errors/2e38987bf15ccb96. Report an issue: GitHub.