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package packfile
import (
"bytes"
"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 (
// Standard chunk size used to generate fingerprints
s = 16
// https://github.com/git/git/blob/f7466e94375b3be27f229c78873f0acf8301c0a5/diff-delta.c#L428
// Max size of a copy operation (64KB)
maxCopySize = 64 * 1024
)
// 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) {
return getDelta(new(deltaIndex), base, target)
}
func getDelta(index *deltaIndex, base, target plumbing.EncodedObject) (plumbing.EncodedObject, error) {
br, err := base.Reader()
if err != nil {
return nil, err
}
defer br.Close()
tr, err := target.Reader()
if err != nil {
return nil, err
}
defer tr.Close()
bb := bufPool.Get().(*bytes.Buffer)
bb.Reset()
defer bufPool.Put(bb)
_, err = bb.ReadFrom(br)
if err != nil {
return nil, err
}
tb := bufPool.Get().(*bytes.Buffer)
tb.Reset()
defer bufPool.Put(tb)
_, err = tb.ReadFrom(tr)
if err != nil {
return nil, err
}
db := diffDelta(index, bb.Bytes(), tb.Bytes())
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 src into tgt.
func DiffDelta(src, tgt []byte) []byte {
return diffDelta(new(deltaIndex), src, tgt)
}
func diffDelta(index *deltaIndex, src []byte, tgt []byte) []byte {
buf := bufPool.Get().(*bytes.Buffer)
buf.Reset()
buf.Write(deltaEncodeSize(len(src)))
buf.Write(deltaEncodeSize(len(tgt)))
if len(index.entries) == 0 {
index.init(src)
}
ibuf := bufPool.Get().(*bytes.Buffer)
ibuf.Reset()
for i := 0; i < len(tgt); i++ {
offset, l := index.findMatch(src, tgt, i)
if l == 0 {
// couldn't find a match, just write the current byte and continue
ibuf.WriteByte(tgt[i])
} else if l < 0 {
// src is less than blksz, copy the rest of the target to avoid
// calls to findMatch
for ; i < len(tgt); i++ {
ibuf.WriteByte(tgt[i])
}
} else if l < s {
// remaining target is less than blksz, copy what's left of it
// and avoid calls to findMatch
for j := i; j < i+l; j++ {
ibuf.WriteByte(tgt[j])
}
i += l - 1
} else {
encodeInsertOperation(ibuf, buf)
rl := l
aOffset := offset
for rl > 0 {
if rl < maxCopySize {
buf.Write(encodeCopyOperation(aOffset, rl))
break
}
buf.Write(encodeCopyOperation(aOffset, maxCopySize))
rl -= maxCopySize
aOffset += maxCopySize
}
i += l - 1
}
}
encodeInsertOperation(ibuf, buf)
bytes := buf.Bytes()
bufPool.Put(buf)
bufPool.Put(ibuf)
return bytes
}
func encodeInsertOperation(ibuf, buf *bytes.Buffer) {
if ibuf.Len() == 0 {
return
}
b := ibuf.Bytes()
s := ibuf.Len()
o := 0
for {
if s <= 127 {
break
}
buf.WriteByte(byte(127))
buf.Write(b[o : o+127])
s -= 127
o += 127
}
buf.WriteByte(byte(s))
buf.Write(b[o : o+s])
ibuf.Reset()
}
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...)
}
|
