packfile: reuse delta indexes when possible

Signed-off-by: Miguel Molina <miguel@erizocosmi.co>

3 files changed, 22 insertions, 10 deletions

diff --git a/plumbing/format/packfile/delta_selector.go b/plumbing/format/packfile/delta_selector.go
index cc0ae0f..78b5733 100644
--- a/plumbing/format/packfile/delta_selector.go
+++ b/plumbing/format/packfile/delta_selector.go
@@ -172,6 +172,7 @@ func (dw *deltaSelector) sort(objectsToPack []*ObjectToPack) {
 }
 
 func (dw *deltaSelector) walk(objectsToPack []*ObjectToPack) error {
+	indexMap := make(map[plumbing.Hash]deltaIndex)
 	for i := 0; i < len(objectsToPack); i++ {
 		target := objectsToPack[i]
 
@@ -196,7 +197,7 @@ func (dw *deltaSelector) walk(objectsToPack []*ObjectToPack) error {
 				break
 			}
 
-			if err := dw.tryToDeltify(base, target); err != nil {
+			if err := dw.tryToDeltify(indexMap, base, target); err != nil {
 				return err
 			}
 		}
@@ -205,7 +206,7 @@ func (dw *deltaSelector) walk(objectsToPack []*ObjectToPack) error {
 	return nil
 }
 
-func (dw *deltaSelector) tryToDeltify(base, target *ObjectToPack) error {
+func (dw *deltaSelector) tryToDeltify(indexMap map[plumbing.Hash]deltaIndex, base, target *ObjectToPack) error {
 	// If the sizes are radically different, this is a bad pairing.
 	if target.Size() < base.Size()>>4 {
 		return nil
@@ -238,8 +239,12 @@ func (dw *deltaSelector) tryToDeltify(base, target *ObjectToPack) error {
 		return err
 	}
 
+	if _, ok := indexMap[base.Hash()]; !ok {
+		indexMap[base.Hash()] = make(deltaIndex)
+	}
+
 	// Now we can generate the delta using originals
-	delta, err := GetDelta(base.Original, target.Original)
+	delta, err := getDelta(indexMap[base.Hash()], base.Original, target.Original)
 	if err != nil {
 		return err
 	}
diff --git a/plumbing/format/packfile/delta_test.go b/plumbing/format/packfile/delta_test.go
index 42b777a..f6e93d2 100644
--- a/plumbing/format/packfile/delta_test.go
+++ b/plumbing/format/packfile/delta_test.go
@@ -84,7 +84,7 @@ func (s *DeltaSuite) TestAddDelta(c *C) {
 	for _, t := range s.testCases {
 		baseBuf := genBytes(t.base)
 		targetBuf := genBytes(t.target)
-		delta := DiffDelta(baseBuf, targetBuf)
+		delta := DiffDelta(make(deltaIndex), baseBuf, targetBuf)
 		result, err := PatchDelta(baseBuf, delta)
 
 		c.Log("Executing test case:", t.description)
@@ -98,7 +98,7 @@ func (s *DeltaSuite) TestIncompleteDelta(c *C) {
 		c.Log("Incomplete delta on:", t.description)
 		baseBuf := genBytes(t.base)
 		targetBuf := genBytes(t.target)
-		delta := DiffDelta(baseBuf, targetBuf)
+		delta := DiffDelta(make(deltaIndex), baseBuf, targetBuf)
 		delta = delta[:len(delta)-2]
 		result, err := PatchDelta(baseBuf, delta)
 		c.Assert(err, NotNil)
diff --git a/plumbing/format/packfile/diff_delta.go b/plumbing/format/packfile/diff_delta.go
index 7e9f822..d0db46b 100644
--- a/plumbing/format/packfile/diff_delta.go
+++ b/plumbing/format/packfile/diff_delta.go
@@ -26,6 +26,10 @@ const (
 // To generate target again, you will need the obtained object and "base" one.
 // Error will be returned if base or target object cannot be read.
 func GetDelta(base, target plumbing.EncodedObject) (plumbing.EncodedObject, error) {
+	return getDelta(make(deltaIndex), base, target)
+}
+
+func getDelta(index deltaIndex, base, target plumbing.EncodedObject) (plumbing.EncodedObject, error) {
 	br, err := base.Reader()
 	if err != nil {
 		return nil, err
@@ -45,7 +49,7 @@ func GetDelta(base, target plumbing.EncodedObject) (plumbing.EncodedObject, erro
 		return nil, err
 	}
 
-	db := DiffDelta(bb, tb)
+	db := DiffDelta(index, bb, tb)
 	delta := &plumbing.MemoryObject{}
 	_, err = delta.Write(db)
 	if err != nil {
@@ -59,13 +63,15 @@ func GetDelta(base, target plumbing.EncodedObject) (plumbing.EncodedObject, erro
 }
 
 // DiffDelta returns the delta that transforms src into tgt.
-func DiffDelta(src []byte, tgt []byte) []byte {
+func DiffDelta(sindex deltaIndex, src []byte, tgt []byte) []byte {
 	buf := bufPool.Get().(*bytes.Buffer)
 	buf.Reset()
 	buf.Write(deltaEncodeSize(len(src)))
 	buf.Write(deltaEncodeSize(len(tgt)))
 
-	sindex := initMatch(src)
+	if len(sindex) == 0 {
+		initMatch(sindex, src)
+	}
 
 	ibuf := bufPool.Get().(*bytes.Buffer)
 	ibuf.Reset()
@@ -126,9 +132,8 @@ func encodeInsertOperation(ibuf, buf *bytes.Buffer) {
 	ibuf.Reset()
 }
 
-func initMatch(src []byte) map[uint32]int {
+func initMatch(index map[uint32]int, src []byte) map[uint32]int {
 	i := 0
-	index := make(map[uint32]int)
 	for {
 		if i+s > len(src) {
 			break
@@ -213,3 +218,5 @@ func encodeCopyOperation(offset, length int) []byte {
 
 	return append([]byte{byte(code)}, opcodes...)
 }
+
+type deltaIndex map[uint32]int