fix encoding of negative offsets

Author: kr

encoding.go

@@ -0,0 +1,39 @@
+package binarydist
+
+// SMLE is the numeric encoding used by the bsdiff tools.
+// It implements binary.ByteOrder using a sign-magnitude format
+// and little-endian byte order. Only methods Uint64, String,
+// and GoString have been written; the rest panic.
+var SMLE smle
+
+type smle struct{}
+
+func (smle) Uint16(b []byte) uint16 { panic("unimplemented") }
+
+func (smle) PutUint16(b []byte, v uint16) { panic("unimplemented") }
+
+func (smle) Uint32(b []byte) uint32 { panic("unimplemented") }
+
+func (smle) PutUint32(b []byte, v uint32) { panic("unimplemented") }
+
+func (smle) Uint64(b []byte) uint64 {
+	y := int64(b[0]) |
+		int64(b[1])<<8 |
+		int64(b[2])<<16 |
+		int64(b[3])<<24 |
+		int64(b[4])<<32 |
+		int64(b[5])<<40 |
+		int64(b[6])<<48 |
+		int64(b[7]&0x7f)<<56
+
+	if b[7]&0x80 != 0 {
+		y = -y
+	}
+	return uint64(y)
+}
+
+func (smle) PutUint64(b []byte, v uint64) { panic("unimplemented") }
+
+func (smle) String() string { return "SMLE" }
+
+func (smle) GoString() string { return "binarydist.SMLE" }

patch.go

@@ -37,7 +37,7 @@ func Patch(old io.Reader, new io.Writer, patch io.Reader) error {
 		DiffLen int64
 		NewSize int64
 	}
-	err := binary.Read(patch, binary.LittleEndian, &header)
+	err := binary.Read(patch, SMLE, &header)
 	if err != nil {
 		return err
 	}
@@ -75,7 +75,7 @@ func Patch(old io.Reader, new io.Writer, patch io.Reader) error {
 	var oldpos, newpos int64
 	for newpos < header.NewSize {
 		var ctrl struct{ Add, Copy, Seek int64 }
-		err = binary.Read(cpfbz2, binary.LittleEndian, &ctrl)
+		err = binary.Read(cpfbz2, SMLE, &ctrl)
 		if err != nil {
 			return err
 		}

patch_test.go

@@ -37,3 +37,26 @@ func TestPatch(t *testing.T) {
 		t.Fatalf("produced different output at pos %d", n)
 	}
 }
+
+func TestPatchHk(t *testing.T) {
+	got, err := ioutil.TempFile("/tmp", "bspatch.")
+	if err != nil {
+		panic(err)
+	}
+	os.Remove(got.Name())
+
+	err = Patch(mustOpen("testdata/sample.old"), got, mustOpen("testdata/sample.patch"))
+	if err != nil {
+		t.Fatal("err", err)
+	}
+
+	ref, err := got.Seek(0, 2)
+	if err != nil {
+		panic(err)
+	}
+
+	t.Logf("got %d bytes", ref)
+	if n := fileCmp(got, mustOpen("testdata/sample.new")); n > -1 {
+		t.Fatalf("produced different output at pos %d", n)
+	}
+}