archive: support using lz4 legacy (MR 36)

fixes: https://gitlab.com/postmarketOS/postmarketos-mkinitfs/-/issues/27

go.mod

@@ -5,6 +5,7 @@ go 1.20
 require (
 	github.com/cavaliercoder/go-cpio v0.0.0-20180626203310-925f9528c45e
 	github.com/klauspost/compress v1.15.12
+	github.com/pierrec/lz4/v4 v4.1.17
 	github.com/ulikunitz/xz v0.5.10
 	golang.org/x/sys v0.0.0-20210630005230-0f9fa26af87c
 )

go.sum

@@ -2,6 +2,8 @@ github.com/cavaliercoder/go-cpio v0.0.0-20180626203310-925f9528c45e h1:hHg27A0RS
 github.com/cavaliercoder/go-cpio v0.0.0-20180626203310-925f9528c45e/go.mod h1:oDpT4efm8tSYHXV5tHSdRvBet/b/QzxZ+XyyPehvm3A=
 github.com/klauspost/compress v1.15.12 h1:YClS/PImqYbn+UILDnqxQCZ3RehC9N318SU3kElDUEM=
 github.com/klauspost/compress v1.15.12/go.mod h1:QPwzmACJjUTFsnSHH934V6woptycfrDDJnH7hvFVbGM=
+github.com/pierrec/lz4/v4 v4.1.17 h1:kV4Ip+/hUBC+8T6+2EgburRtkE9ef4nbY3f4dFhGjMc=
+github.com/pierrec/lz4/v4 v4.1.17/go.mod h1:gZWDp/Ze/IJXGXf23ltt2EXimqmTUXEy0GFuRQyBid4=
 github.com/ulikunitz/xz v0.5.10 h1:t92gobL9l3HE202wg3rlk19F6X+JOxl9BBrCCMYEYd8=
 github.com/ulikunitz/xz v0.5.10/go.mod h1:nbz6k7qbPmH4IRqmfOplQw/tblSgqTqBwxkY0oWt/14=
 golang.org/x/sys v0.0.0-20210630005230-0f9fa26af87c h1:F1jZWGFhYfh0Ci55sIpILtKKK8p3i2/krTr0H1rg74I=

internal/archive/archive.go

@@ -18,6 +18,7 @@ import (
 
 	"github.com/cavaliercoder/go-cpio"
 	"github.com/klauspost/compress/zstd"
+	"github.com/pierrec/lz4/v4"
 	"github.com/ulikunitz/xz"
 	"gitlab.com/postmarketOS/postmarketos-mkinitfs/internal/filelist"
 	"gitlab.com/postmarketOS/postmarketos-mkinitfs/internal/osutil"
@@ -28,6 +29,7 @@ type CompressFormat string
 const (
 	FormatGzip CompressFormat = "gzip"
 	FormatLzma CompressFormat = "lzma"
+	FormatLz4  CompressFormat = "lz4"
 	FormatZstd CompressFormat = "zstd"
 	FormatNone CompressFormat = "none"
 )
@@ -104,6 +106,7 @@ func ExtractFormatLevel(s string) (format CompressFormat, level CompressLevel) {
 	case FormatLzma:
 		log.Println("Format lzma doesn't support a compression level, using default settings")
 		level = LevelDefault
+	case FormatLz4:
 	case FormatNone:
 	case FormatZstd:
 	default:
@@ -348,6 +351,23 @@ func (archive *Archive) writeCompressed(path string, mode os.FileMode) (err erro
 		if err != nil {
 			return err
 		}
+	case FormatLz4:
+		// The default compression for the lz4 library is Fast, and
+		// they don't define a Default level otherwise
+		level := lz4.Fast
+		switch archive.compress_level {
+		case LevelBest:
+			level = lz4.Level9
+		case LevelFast:
+			level = lz4.Fast
+		}
+
+		var writer = lz4.NewWriter(fd)
+		err = writer.Apply(lz4.LegacyOption(true), lz4.CompressionLevelOption(level))
+		if err != nil {
+			return err
+		}
+		compressor = writer
 	case FormatNone:
 		compressor = fd
 	case FormatZstd:

internal/archive/archive_test.go

@@ -249,6 +249,12 @@ func TestExtractFormatLevel(t *testing.T) {
 			expectedFormat: FormatLzma,
 			expectedLevel:  LevelDefault,
 		},
+		{
+			name:           "lz4, fast",
+			in:             "lz4:fast",
+			expectedFormat: FormatLz4,
+			expectedLevel:  LevelFast,
+		},
 		{
 			name:           "none",
 			in:             "none",