lz4decompress.go

package dtx

import (
	"encoding/binary"

	"github.com/pierrec/lz4"
)

const bv41 = 0x62763431

// https://discuss.appium.io/t/how-to-parse-trace-file-to-get-cpu-performance-usage-data-for-ios-apps/35334/2
func Decompress(data []byte) ([]byte, error) {
	// no idea what the first four bytes mean
	totalUncompressedSize := binary.LittleEndian.Uint32(data)
	data = data[4:]

	var magic uint32
	magic = binary.BigEndian.Uint32(data)
	compressedAgg := make([]byte, 0)
	for magic == bv41 {
		// uncompressedSize := binary.LittleEndian.Uint32(data[4:])
		compressedSize := binary.LittleEndian.Uint32(data[8:])
		chunk := data[12 : 12+compressedSize]
		// log.Infof("chunk: %x", chunk)
		data = data[12+compressedSize:]

		compressedAgg = append(compressedAgg, chunk...)
		magic = binary.BigEndian.Uint32(data)
	}
	uncompressedData := make([]byte, totalUncompressedSize+100)
	n, err := lz4.UncompressBlock(compressedAgg, uncompressedData)
	if err != nil {
		return []byte{}, err
	}
	// log.Infof("uncompressed lz4 data of %d bytes", len(uncompressedData[:n]))
	return uncompressedData[:n], nil
}