What causes "decompress an empty input" in juicedata/juicefs?

Check for empty input before decompressing and handle it as a valid empty payload (or skip).

decompress an empty input

Error message

decompress an empty input

What it means

Returned by LZ4.Decompress when the input buffer is empty. LZ4 has no representation for zero-length compressed data, so decompressing nothing is treated as invalid input rather than returning zero bytes.

Source

Thrown at pkg/compress/compress.go:122

// LZ4 implements Compressor using LZ4 library
type LZ4 struct{}

// Name returns name of the algorithm LZ4
func (l LZ4) Name() string { return "LZ4" }

// CompressBound max size of compressed data
func (l LZ4) CompressBound(size int) int { return lz4.CompressBound(size) }

// Compress using LZ4 algorithm
func (l LZ4) Compress(dst, src []byte) (int, error) {
	return lz4.CompressDefault(src, dst)
}

// Decompress using LZ4 algorithm
func (l LZ4) Decompress(dst, src []byte) (int, error) {
	if len(src) == 0 {
		return 0, fmt.Errorf("decompress an empty input")
	}
	return lz4.DecompressSafe(src, dst)
}

View on GitHub (pinned to c9a67b23e8)

Solutions

Check for empty input before decompressing and handle it as a valid empty payload (or skip).
Investigate why a 0-byte compressed block exists: verify the object in object storage, re-upload or repair the block.
Use `juicefs gc`/fsck-style tooling to find and clean corrupt or empty blocks.

Example fix

// before
n, err := comp.Decompress(dst, src) // panics/errors when src empty

// after
if len(src) == 0 {
    return 0, nil // empty payload is valid
}
n, err := comp.Decompress(dst, src)

Defensive patterns

Strategy: validation

Validate before calling

if len(src) == 0 { /* treat as empty payload; skip decompress */ }

Try / catch

n, err := comp.Decompress(dst, src)
if err != nil && strings.Contains(err.Error(), "empty input") {
    return handleEmptyBlock() // or flag corrupt block for repair
}

Prevention

Guard len(src)==0 before decompressing
Investigate any 0-byte compressed objects in storage — they indicate corrupt/truncated uploads
Enable integrity checks on upload paths

When it happens

Trigger: Calling LZ4.Decompress(dst, src) with len(src) == 0 — e.g. a zero-length compressed block read from object storage or cache, or passing an empty/nil slice directly.

Common situations: Corrupt or truncated uploads producing 0-byte blocks; volume formatted with lz4 compression but a block was stored empty; bugs in callers that skip empty-data checks before decompressing.

Understand the failure class

Background: "must not be empty", "cannot be empty" — required-field validation errors across open-source libraries — this error's family across 41 libraries.

Related errors

AI-assisted analysis of juicedata/juicefs@c9a67b23e8 (2026-09-06). Data as JSON: /api/errors/1aaa138ada84fcbe. Report an issue: GitHub.