66 lines
1.6 KiB
Go
66 lines
1.6 KiB
Go
package compression
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import (
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"bytes"
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"encoding/binary"
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)
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const (
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zstdMagicSkippableStart = 0x184D2A50
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zstdMagicSkippableMask = 0xFFFFFFF0
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)
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var (
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bzip2Magic = []byte{0x42, 0x5A, 0x68}
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gzipMagic = []byte{0x1F, 0x8B, 0x08}
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xzMagic = []byte{0xFD, 0x37, 0x7A, 0x58, 0x5A, 0x00}
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zstdMagic = []byte{0x28, 0xb5, 0x2f, 0xfd}
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)
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type matcher = func([]byte) bool
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// Detect detects the compression algorithm of the source.
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func Detect(source []byte) Compression {
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compressionMap := map[Compression]matcher{
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Bzip2: magicNumberMatcher(bzip2Magic),
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Gzip: magicNumberMatcher(gzipMagic),
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Xz: magicNumberMatcher(xzMagic),
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Zstd: zstdMatcher(),
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}
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for _, compression := range []Compression{Bzip2, Gzip, Xz, Zstd} {
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fn := compressionMap[compression]
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if fn(source) {
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return compression
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}
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}
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return None
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}
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func magicNumberMatcher(m []byte) matcher {
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return func(source []byte) bool {
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return bytes.HasPrefix(source, m)
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}
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}
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// zstdMatcher detects zstd compression algorithm.
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// Zstandard compressed data is made of one or more frames.
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// There are two frame formats defined by Zstandard: Zstandard frames and Skippable frames.
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// See https://datatracker.ietf.org/doc/html/rfc8878#section-3 for more details.
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func zstdMatcher() matcher {
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return func(source []byte) bool {
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if bytes.HasPrefix(source, zstdMagic) {
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// Zstandard frame
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return true
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}
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// skippable frame
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if len(source) < 8 {
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return false
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}
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// magic number from 0x184D2A50 to 0x184D2A5F.
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if binary.LittleEndian.Uint32(source[:4])&zstdMagicSkippableMask == zstdMagicSkippableStart {
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return true
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}
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return false
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}
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}
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