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|
package packfile
import (
"io/ioutil"
"gopkg.in/src-d/go-git.v4/plumbing"
)
// See https://github.com/jelmer/dulwich/blob/master/dulwich/pack.py and
// https://github.com/tarruda/node-git-core/blob/master/src/js/delta.js
// for more info
const (
maxCopyLen = 0xffff
)
// GetDelta returns an EncodedObject of type OFSDeltaObject. Base and Target object,
// will be loaded into memory to be able to create the delta object.
// 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) {
br, err := base.Reader()
if err != nil {
return nil, err
}
tr, err := target.Reader()
if err != nil {
return nil, err
}
bb, err := ioutil.ReadAll(br)
if err != nil {
return nil, err
}
tb, err := ioutil.ReadAll(tr)
if err != nil {
return nil, err
}
db := DiffDelta(bb, tb)
delta := &plumbing.MemoryObject{}
_, err = delta.Write(db)
if err != nil {
return nil, err
}
delta.SetSize(int64(len(db)))
delta.SetType(plumbing.OFSDeltaObject)
return delta, nil
}
// DiffDelta returns the delta that transforms baseBuf into targetBuf.
func DiffDelta(baseBuf []byte, targetBuf []byte) []byte {
var outBuff []byte
outBuff = append(outBuff, deltaEncodeSize(len(baseBuf))...)
outBuff = append(outBuff, deltaEncodeSize(len(targetBuf))...)
sm := newMatcher(baseBuf, targetBuf)
for _, op := range sm.GetOpCodes() {
switch {
case op.Tag == tagEqual:
copyStart := op.I1
copyLen := op.I2 - op.I1
for {
if copyLen <= 0 {
break
}
var toCopy int
if copyLen < maxCopyLen {
toCopy = copyLen
} else {
toCopy = maxCopyLen
}
outBuff = append(outBuff, encodeCopyOperation(copyStart, toCopy)...)
copyStart += toCopy
copyLen -= toCopy
}
case op.Tag == tagReplace || op.Tag == tagInsert:
s := op.J2 - op.J1
o := op.J1
for {
if s <= 127 {
break
}
outBuff = append(outBuff, byte(127))
outBuff = append(outBuff, targetBuf[o:o+127]...)
s -= 127
o += 127
}
outBuff = append(outBuff, byte(s))
outBuff = append(outBuff, targetBuf[o:o+s]...)
}
}
return outBuff
}
func deltaEncodeSize(size int) []byte {
var ret []byte
c := size & 0x7f
size >>= 7
for {
if size == 0 {
break
}
ret = append(ret, byte(c|0x80))
c = size & 0x7f
size >>= 7
}
ret = append(ret, byte(c))
return ret
}
func encodeCopyOperation(offset, length int) []byte {
code := 0x80
var opcodes []byte
var i uint
for i = 0; i < 4; i++ {
f := 0xff << (i * 8)
if offset&f != 0 {
opcodes = append(opcodes, byte(offset&f>>(i*8)))
code |= 0x01 << i
}
}
for i = 0; i < 3; i++ {
f := 0xff << (i * 8)
if length&f != 0 {
opcodes = append(opcodes, byte(length&f>>(i*8)))
code |= 0x10 << i
}
}
return append([]byte{byte(code)}, opcodes...)
}
|
