act_runner_debian_packing/dpkg/compression.go

package dpkg

import (
	"bytes"
	"io"
)

func compressExt(r io.Reader) (string, io.Reader, error) {
	// Read fist bytes to detect file compression
	buf := make([]byte, 15)
	if _, err := r.Read(buf); err != nil {
		return "", r, err
	}

	// Concat read bytes
	r = io.MultiReader(bytes.NewReader(buf), r)

	switch {
	// Gzip
	case bytes.HasPrefix(buf, []byte{0x1F, 0x8B, 0x08}):
		return ".gz", r, nil

	// BZip2
	case bytes.HasPrefix(buf, []byte{0x5A, 0x42}):
		return ".bz2", r, nil

	// XZ
	case bytes.HasPrefix(buf, []byte{0xFD, 0x37, 0x7A, 0x58, 0x5A, 0x00}):
		return ".xz", r, nil

	// Zstd
	case bytes.HasPrefix(buf, []byte{0xB5, 0x28, 0xFD, 0x2F}):
		return ".zst", r, nil
	}
	return "", r, nil
}