/
pack.go
364 lines (319 loc) · 7.7 KB
/
pack.go
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package git
import (
"bufio"
"bytes"
"compress/flate"
"compress/zlib"
"crypto/sha1"
"encoding/binary"
"errors"
"fmt"
"hash"
"io"
"io/ioutil"
"github.com/gitchain/gitchain/util"
)
const (
OBJ_COMMIT = 1
OBJ_TREE = 2
OBJ_BLOB = 3
OBJ_TAG = 4
OBJ_OFS_DELTA = 6
OBJ_REF_DELTA = 7
)
type Delta struct {
Hash []byte
Delta []byte
}
type Packfile struct {
Version uint32
Objects []Object
Checksum []byte
Deltas []Delta
offsets map[int]int
hashes map[string]int
}
func (r *Packfile) ObjectByHash(hash []byte) Object {
index, exists := r.hashes[string(hash)]
if !exists {
return nil
}
return r.Objects[index]
}
func (r *Packfile) ObjectByOffset(offset int) Object {
index, exists := r.offsets[offset]
if !exists {
return nil
}
return r.Objects[index]
}
func (r *Packfile) PutObject(o Object) {
r.Objects = append(r.Objects, o)
r.hashes[string(o.Hash())] = len(r.Objects) - 1
}
func readMSBEncodedSize(reader io.Reader, initialOffset uint) uint64 {
var b byte
var sz uint64
shift := initialOffset
sz = 0
for {
binary.Read(reader, binary.BigEndian, &b)
sz += (uint64(b) &^ 0x80) << shift
shift += 7
if (b & 0x80) == 0 {
break
}
}
return sz
}
func inflate(reader io.Reader, sz int) ([]byte, error) {
zr, err := zlib.NewReader(reader)
if err != nil {
return nil, fmt.Errorf("error opening packfile's object zlib: %v", err)
}
buf := make([]byte, sz)
n, err := zr.Read(buf)
if err != nil {
return nil, err
}
if n != sz {
return nil, fmt.Errorf("inflated size mismatch, expected %d, got %d", sz, n)
}
zr.Close()
return buf, nil
}
func readEntry(packfile *Packfile, reader flate.Reader, offset int) error {
var b, typ uint8
var sz uint64
binary.Read(reader, binary.BigEndian, &b)
typ = (b &^ 0x8f) >> 4
sz = uint64(b &^ 0xf0)
switch typ {
case OBJ_REF_DELTA:
if (b & 0x80) != 0 {
sz += readMSBEncodedSize(reader, 4)
}
ref := make([]byte, 20)
reader.Read(ref)
buf, err := inflate(reader, int(sz))
if err != nil {
return err
}
referenced := packfile.ObjectByHash(ref)
if referenced == nil {
packfile.Deltas = append(packfile.Deltas, Delta{Hash: ref, Delta: buf})
} else {
patched := PatchDelta(referenced.Bytes(), buf)
if patched == nil {
return fmt.Errorf("error while patching %x", ref)
}
newObject := referenced.New()
err = newObject.SetBytes(patched)
if err != nil {
return err
}
packfile.PutObject(newObject)
}
case OBJ_OFS_DELTA:
if (b & 0x80) != 0 {
sz += readMSBEncodedSize(reader, 4)
}
// read negative offset
binary.Read(reader, binary.BigEndian, &b)
var noffset int = int(b & 0x7f)
for (b & 0x80) != 0 {
noffset += 1
binary.Read(reader, binary.BigEndian, &b)
noffset = (noffset << 7) + int(b&0x7f)
}
buf, err := inflate(reader, int(sz))
if err != nil {
return err
}
referenced := packfile.ObjectByOffset(offset - noffset)
if referenced == nil {
return fmt.Errorf("can't find a pack entry at %d", offset-noffset)
} else {
patched := PatchDelta(referenced.Bytes(), buf)
if patched == nil {
return fmt.Errorf("error while patching %x", referenced.Hash())
}
newObject := referenced.New()
err = newObject.SetBytes(patched)
if err != nil {
return err
}
packfile.PutObject(newObject)
}
case OBJ_COMMIT, OBJ_TREE, OBJ_BLOB, OBJ_TAG:
if (b & 0x80) != 0 {
sz += readMSBEncodedSize(reader, 4)
}
buf, err := inflate(reader, int(sz))
if err != nil {
return err
}
var obj Object
switch typ {
case OBJ_COMMIT:
obj = &Commit{}
case OBJ_TREE:
obj = &Tree{}
case OBJ_BLOB:
obj = &Blob{}
case OBJ_TAG:
obj = &Tag{}
}
obj.SetBytes(buf)
packfile.PutObject(obj)
default:
return fmt.Errorf("Invalid git object tag %03b", typ)
}
return nil
}
func ReadPackfile(r io.Reader) (*Packfile, error) {
buffer, err := ioutil.ReadAll(r)
contentChecksum := util.SHA160(buffer[0 : len(buffer)-20])
r = bytes.NewBuffer(buffer)
magic := make([]byte, 4)
r.Read(magic)
if bytes.Compare(magic, []byte("PACK")) != 0 {
return nil, errors.New("not a packfile")
}
packfile := &Packfile{offsets: make(map[int]int), hashes: make(map[string]int)}
var objects uint32
binary.Read(r, binary.BigEndian, &packfile.Version)
binary.Read(r, binary.BigEndian, &objects)
content, err := ioutil.ReadAll(r)
if err != nil {
return nil, err
}
offset := 12
for i := 0; i < int(objects); i++ {
peReader := &packEntryReader{reader: bytes.NewBuffer(content)}
err := readEntry(packfile, peReader, offset)
if err != nil {
return packfile, err
}
packfile.offsets[offset] = len(packfile.Objects) - 1
offset += peReader.Counter + 4
content = content[peReader.Counter+4:]
}
var unresolvedDeltas []Delta
for i := range packfile.Deltas {
ref := packfile.ObjectByHash(packfile.Deltas[i].Hash)
if ref == nil {
unresolvedDeltas = append(unresolvedDeltas, packfile.Deltas[i])
} else {
patched := PatchDelta(ref.Bytes(), packfile.Deltas[i].Delta)
newObject := ref.New()
err = newObject.SetBytes(patched)
if err != nil {
return packfile, err
}
packfile.Objects = append(packfile.Objects, newObject)
}
}
packfile.Deltas = unresolvedDeltas
packfile.Checksum = make([]byte, 20)
bytes.NewBuffer(content).Read(packfile.Checksum)
if bytes.Compare(contentChecksum, packfile.Checksum) != 0 {
return packfile, errors.New(fmt.Sprintf("checksum mismatch: expected %x got %x",
packfile.Checksum, contentChecksum))
}
return packfile, nil
}
// This byte-counting hack is here to work around the fact that both zlib
// and flate use bufio and are very eager to read more data than they need.
// The counter in this reader allows us to know the length of the header +
// packed data read and therefore readjust the offset
type packEntryReader struct {
Counter int
reader io.Reader
}
func (r *packEntryReader) Read(p []byte) (int, error) {
r.Counter += (len(p))
return r.reader.Read(p)
}
func (r *packEntryReader) ReadByte() (byte, error) {
b := make([]byte, 1)
_, err := r.Read(b)
if err != nil {
return 0, err
}
return b[0], nil
}
func NewPackfile(objects []Object) *Packfile {
return &Packfile{Version: 2, Objects: objects, offsets: make(map[int]int), hashes: make(map[string]int)}
}
func writeEntry(w io.Writer, o Object) (err error) {
var t byte
t |= 0x80
switch o.Type() {
case "commit":
t |= OBJ_COMMIT << 4
case "tree":
t |= OBJ_TREE << 4
case "blob":
t |= OBJ_BLOB << 4
case "tag":
t |= OBJ_TAG << 4
}
t |= byte(uint64(len(o.Bytes())) &^ 0xfffffffffffffff0)
sz := len(o.Bytes()) >> 4
szb := make([]byte, 16)
n := binary.PutUvarint(szb, uint64(sz))
szb = szb[0:n]
w.Write(append([]byte{t}, szb...))
zw := zlib.NewWriter(w)
_, err = zw.Write(o.Bytes())
defer zw.Close()
if err != nil {
return err
}
zw.Flush()
return
}
func WritePackfile(writer io.Writer, p *Packfile) (err error) {
cw := newSHA160checksumWriter(writer)
w := bufio.NewWriterSize(cw, 65519)
err = binary.Write(w, binary.BigEndian, []byte("PACK"))
if err != nil {
return
}
err = binary.Write(w, binary.BigEndian, p.Version)
if err != nil {
return
}
err = binary.Write(w, binary.BigEndian, uint32(len(p.Objects)))
if err != nil {
return
}
w.Flush()
for i := range p.Objects {
err = writeEntry(w, p.Objects[i])
if err != nil {
return err
}
w.Flush()
}
w.Flush()
p.Checksum = cw.Sum()
err = binary.Write(w, binary.BigEndian, p.Checksum)
w.Flush()
return
}
type checksumWriter struct {
hash hash.Hash
writer io.Writer
}
func newSHA160checksumWriter(w io.Writer) *checksumWriter {
return &checksumWriter{hash: sha1.New(), writer: w}
}
func (w *checksumWriter) Write(p []byte) (n int, err error) {
w.hash.Write(p)
return w.writer.Write(p)
}
func (w *checksumWriter) Sum() []byte {
return w.hash.Sum(nil)
}