compression: add support for the zstd algorithm

zstd is a compression algorithm that has a very fast decoder, while
providing also good compression ratios.  The fast decoder makes it
suitable for container images, as decompressing the tarballs is a very
expensive operation.  This is a first step at supporting zstd as we We
don't yet generate zstd layers.

In my testing, copying the Fedora image from a local dir: repository,
the wall clock time passed from ~8s with gzip compression to ~4.5s
with zstd.

Signed-off-by: Giuseppe Scrivano <[email protected]>

pkg/archive/archive.go

@@ -98,6 +98,8 @@ const (
 	Gzip
 	// Xz is xz compression algorithm.
 	Xz
+	// Zstd is zstd compression algorithm.
+	Zstd
 )
 
 const (
@@ -141,6 +143,7 @@ func DetectCompression(source []byte) Compression {
 		Bzip2: {0x42, 0x5A, 0x68},
 		Gzip:  {0x1F, 0x8B, 0x08},
 		Xz:    {0xFD, 0x37, 0x7A, 0x58, 0x5A, 0x00},
+		Zstd:  {0x28, 0xb5, 0x2f, 0xfd},
 	} {
 		if len(source) < len(m) {
 			logrus.Debug("Len too short")
@@ -200,6 +203,8 @@ func DecompressStream(archive io.Reader) (io.ReadCloser, error) {
 			<-chdone
 			return readBufWrapper.Close()
 		}), nil
+	case Zstd:
+		return zstdReader(buf)
 	default:
 		return nil, fmt.Errorf("Unsupported compression format %s", (&compression).Extension())
 	}
@@ -217,6 +222,8 @@ func CompressStream(dest io.Writer, compression Compression) (io.WriteCloser, er
 		gzWriter := gzip.NewWriter(dest)
 		writeBufWrapper := p.NewWriteCloserWrapper(buf, gzWriter)
 		return writeBufWrapper, nil
+	case Zstd:
+		return zstdWriter(dest)
 	case Bzip2, Xz:
 		// archive/bzip2 does not support writing, and there is no xz support at all
 		// However, this is not a problem as docker only currently generates gzipped tars
@@ -324,6 +331,8 @@ func (compression *Compression) Extension() string {
 		return "tar.gz"
 	case Xz:
 		return "tar.xz"
+	case Zstd:
+		return "tar.zst"
 	}
 	return ""
 }

pkg/archive/archive_cgo.go

@@ -0,0 +1,17 @@
+// +build cgo
+
+package archive
+
+import (
+	"io"
+
+	"github.com/DataDog/zstd"
+)
+
+func zstdReader(buf io.Reader) (io.ReadCloser, error) {
+	return zstd.NewReader(buf), nil
+}
+
+func zstdWriter(dest io.Writer) (io.WriteCloser, error) {
+	return zstd.NewWriter(dest), nil
+}

pkg/archive/archive_nocgo.go

@@ -0,0 +1,16 @@
+// +build !cgo
+
+package archive
+
+import (
+	"fmt"
+	"io"
+)
+
+func zstdReader(buf io.Reader) (io.ReadCloser, error) {
+	return nil, fmt.Errorf("zstd not supported on this platform")
+}
+
+func zstdWriter(dest io.Writer) (io.WriteCloser, error) {
+	return nil, fmt.Errorf("zstd not supported on this platform")
+}

vendor.conf

@@ -26,3 +26,4 @@ golang.org/x/net 7dcfb8076726a3fdd9353b6b8a1f1b6be6811bd6
 golang.org/x/sys 07c182904dbd53199946ba614a412c61d3c548f5
 gotest.tools master
 github.com/google/go-cmp master
+github.com/DataDog/zstd 1.x