vendor: github.com/moby/go-archive v0.1.0

full diff: https://github.com/moby/go-archive/compare/21f3f3385ab7...v0.1.0

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

vendor/github.com/moby/go-archive/compression/compression_detect.go

@@ -0,0 +1,65 @@
+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
+	}
+}