mozlz4.go

// Copyright (c) 2024 cions
// Licensed under the MIT License. See LICENSE for details.

package mozlz4

import (
	"bytes"
	"encoding/binary"
	"errors"
	"fmt"

	"github.com/pierrec/lz4/v4"
)

var HEADER = []byte("mozLz40\x00")

var ErrInvalid = errors.New("not a mozlz4 file")

func Compress(data []byte) ([]byte, error) {
	buf := make([]byte, 0, len(HEADER)+4+lz4.CompressBlockBound(len(data)))

	buf = append(buf, HEADER...)

	buf, err := binary.Append(buf, binary.LittleEndian, uint32(len(data)))
	if err != nil {
		return nil, err
	}

	if len(data) != 0 {
		var c lz4.Compressor
		n, err := c.CompressBlock(data, buf[len(buf):cap(buf)])
		if err != nil {
			return nil, err
		}
		buf = buf[:len(buf)+n]
	}

	return buf, nil
}

func Decompress(data []byte) ([]byte, error) {
	data, found := bytes.CutPrefix(data, HEADER)
	if !found {
		return nil, ErrInvalid
	}

	var size uint32
	if n, err := binary.Decode(data, binary.LittleEndian, &size); err != nil {
		return nil, ErrInvalid
	} else {
		data = data[n:]
	}

	if size == 0 {
		return []byte{}, nil
	}

	buf := make([]byte, size)
	if n, err := lz4.UncompressBlock(data, buf); err != nil {
		return nil, err
	} else if uint32(n) != size {
		return nil, fmt.Errorf("uncompressed size mismatch: expected %v, but got %v", size, n)
	}

	return buf, nil
}