1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
|
package compression
import (
"bytes"
"encoding/binary"
)
const (
zstdMagicSkippableStart = 0x184D2A50
zstdMagicSkippableMask = 0xFFFFFFF0
)
var (
bzip2Magic = []byte{0x42, 0x5A, 0x68}
gzipMagic = []byte{0x1F, 0x8B, 0x08}
xzMagic = []byte{0xFD, 0x37, 0x7A, 0x58, 0x5A, 0x00}
zstdMagic = []byte{0x28, 0xb5, 0x2f, 0xfd}
)
type matcher = func([]byte) bool
// Detect detects the compression algorithm of the source.
func Detect(source []byte) Compression {
compressionMap := map[Compression]matcher{
Bzip2: magicNumberMatcher(bzip2Magic),
Gzip: magicNumberMatcher(gzipMagic),
Xz: magicNumberMatcher(xzMagic),
Zstd: zstdMatcher(),
}
for _, compression := range []Compression{Bzip2, Gzip, Xz, Zstd} {
fn := compressionMap[compression]
if fn(source) {
return compression
}
}
return None
}
func magicNumberMatcher(m []byte) matcher {
return func(source []byte) bool {
return bytes.HasPrefix(source, m)
}
}
// zstdMatcher detects zstd compression algorithm.
// Zstandard compressed data is made of one or more frames.
// There are two frame formats defined by Zstandard: Zstandard frames and Skippable frames.
// See https://datatracker.ietf.org/doc/html/rfc8878#section-3 for more details.
func zstdMatcher() matcher {
return func(source []byte) bool {
if bytes.HasPrefix(source, zstdMagic) {
// Zstandard frame
return true
}
// skippable frame
if len(source) < 8 {
return false
}
// magic number from 0x184D2A50 to 0x184D2A5F.
if binary.LittleEndian.Uint32(source[:4])&zstdMagicSkippableMask == zstdMagicSkippableStart {
return true
}
return false
}
}
|
