Add Delta decompressor

README.md

@@ -16,6 +16,6 @@ Current status:
 * Handles password-protected versions of both of the above (`7za a -mhc=on|off -mhe=on -ppassword test.7z ...`).
 * Handles archives split into multiple volumes, (`7za a -v100m test.7z ...`).
 * Validates CRC values as it parses the file.
-* Supports BCJ2, Bzip2, Deflate, Copy, LZMA and LZMA2 methods.
+* Supports BCJ2, Bzip2, Copy, Deflate, Delta, LZMA and LZMA2 methods.
 
 More examples of 7-zip archives are needed to test all of the different combinations/algorithms possible.

internal/delta/reader.go

@@ -0,0 +1,72 @@
+package delta
+
+import (
+	"errors"
+	"io"
+)
+
+const (
+	stateSize = 256
+)
+
+type readCloser struct {
+	rc    io.ReadCloser
+	state [stateSize]byte
+	delta int
+}
+
+func (rc *readCloser) Close() (err error) {
+	if rc.rc != nil {
+		err = rc.rc.Close()
+		rc.rc = nil
+	}
+	return
+}
+
+func (rc *readCloser) Read(p []byte) (int, error) {
+	if rc.rc == nil {
+		return 0, errors.New("delta: Read after Close")
+	}
+
+	n, err := rc.rc.Read(p)
+	if err != nil {
+		return n, err
+	}
+
+	var buffer [stateSize]byte
+	copy(buffer[:], rc.state[:rc.delta])
+
+	var j int
+	for i := 0; i < n; {
+		for j = 0; j < rc.delta && i < n; i++ {
+			p[i] = buffer[j] + p[i]
+			buffer[j] = p[i]
+			j++
+		}
+	}
+
+	if j == rc.delta {
+		j = 0
+	}
+
+	copy(rc.state[:], buffer[j:rc.delta])
+	copy(rc.state[rc.delta-j:], buffer[:j])
+
+	return n, nil
+}
+
+// NewReader returns a new Delta io.ReadCloser.
+func NewReader(p []byte, _ uint64, readers []io.ReadCloser) (io.ReadCloser, error) {
+	if len(readers) != 1 {
+		return nil, errors.New("delta: need exactly one reader")
+	}
+
+	if len(p) != 1 {
+		return nil, errors.New("delta: not enough properties")
+	}
+
+	return &readCloser{
+		rc:    readers[0],
+		delta: int(p[0] + 1),
+	}, nil
+}

reader_test.go

@@ -125,6 +125,10 @@ func BenchmarkDeflate(b *testing.B) {
 	benchmarkArchive("deflate.7z", b)
 }
 
+func BenchmarkDelta(b *testing.B) {
+	benchmarkArchive("delta.7z", b)
+}
+
 func BenchmarkLZMA(b *testing.B) {
 	benchmarkArchive("lzma.7z", b)
 }

register.go

@@ -9,6 +9,7 @@ import (
 	"github.com/bodgit/sevenzip/internal/bcj2"
 	"github.com/bodgit/sevenzip/internal/bzip2"
 	"github.com/bodgit/sevenzip/internal/deflate"
+	"github.com/bodgit/sevenzip/internal/delta"
 	"github.com/bodgit/sevenzip/internal/lzma"
 	"github.com/bodgit/sevenzip/internal/lzma2"
 )
@@ -30,6 +31,8 @@ func init() {
 		}
 		return readers[0], nil
 	}))
+	// Delta
+	RegisterDecompressor([]byte{0x03}, Decompressor(delta.NewReader))
 	// LZMA
 	RegisterDecompressor([]byte{0x03, 0x01, 0x01}, Decompressor(lzma.NewReader))
 	// BCJ2