package packfile
import (
"bytes"
"compress/zlib"
"encoding/binary"
"errors"
"fmt"
"io"
"io/ioutil"
)
const MaxObjectsLimit = 1000000
type PackfileReader struct {
r io.Reader
objects map[string]packfileObject
offsets map[int]string
deltas []packfileDelta
// The give back logic is explained in the giveBack method.
startedGivingBack bool
givebackBuffer []byte
givenBack io.Reader
contentCallback ContentCallback
}
// Sometimes, after reading an object from a packfile, there will be
// a few bytes with garbage data before the next object comes by.
// There is no way of reliably noticing this until when trying to read the
// next object and failing because zlib parses an invalid header. We can't
// notice before, because parsing the object's header (size, type, etc.)
// doesn't fail.
//
// At that point, we want to give back to the reader the bytes we've read
// since the last object, shift the input by one byte, and try again. That's
// why we save the bytes we read on each object and, if it fails in the middle
// of parsing it, those bytes will be read the next times you call Read() on
// a objectReader derived from a PackfileReader.readObject, until they run out.
func (pr *PackfileReader) giveBack() {
pr.givenBack = bytes.NewReader(pr.givebackBuffer)
pr.givebackBuffer = nil
}
type packfileObject struct {
bytes []byte
typ int8
}
type packfileDelta struct {
hash string
delta []byte
}
func NewPackfileReader(r io.Reader, contentCallback ContentCallback) (*PackfileReader, error) {
return &PackfileReader{
r: r,
objects: map[string]packfileObject{},
offsets: map[int]string{},
contentCallback: contentCallback,
}, nil
}
func (p *PackfileReader) Read() (*Packfile, error) {
packfile := NewPackfile()
if err := p.validateSignature(); err != nil {
if err == io.EOF {
// This is an empty repo. It's OK.
return packfile, nil
}
return nil, err
}
var err error
ver, err := p.readInt32()
if err != nil {
return nil, err
}
count, err := p.readInt32()
if err != nil {
return nil, err
}
packfile.Version = uint32(ver)
packfile.ObjectCount = int(count)
if packfile.ObjectCount > MaxObjectsLimit {
return nil, NewError("too many objects (%d)", packfile.ObjectCount)
}
if err := p.readObjects(packfile); err != nil {
return nil, err
}
return packfile, nil
}
func (p *PackfileReader) validateSignature() error {
var signature = make([]byte, 4)
if _, err := p.r.Read(signature); err != nil {
return err
}
if !bytes.Equal(signature, []byte{'P', 'A', 'C', 'K'}) {
return NewError("Pack file does not start with 'PACK'")
}
return nil
}
func (p *PackfileReader) readInt32() (uint32, error) {
var value uint32
if err := binary.Read(p.r, binary.BigEndian, &value); err != nil {
fmt.Println(err)
return 0, err
}
return value, nil
}
func (p *PackfileReader) readObjects(packfile *Packfile) error {
p.startedGivingBack = true
offset := 12
for i := 0; i < packfile.ObjectCount; i++ {
r, err := p.readObject(packfile, offset)
if err != nil && err != io.EOF {
return err
}
p.offsets[offset] = r.hash
offset += r.counter + 4
unknownForBytes := make([]byte, 4)
p.r.Read(unknownForBytes)
if err == io.EOF {
break
}
}
return nil
}
const (
OBJ_COMMIT = 1
OBJ_TREE = 2
OBJ_BLOB = 3
OBJ_TAG = 4
OBJ_OFS_DELTA = 6
OBJ_REF_DELTA = 7
)
const SIZE_LIMIT uint64 = 1 << 32 //4GB
type objectReader struct {
pr *PackfileReader
pf *Packfile
offset int
hash string
typ int8
size uint64
counter int
}
func (p *PackfileReader) readObject(packfile *Packfile, offset int) (*objectReader, error) {
o, err := newObjectReader(p, packfile, offset)
if err != nil {
return nil, err
}
switch o.typ {
case OBJ_REF_DELTA:
err = o.readREFDelta()
case OBJ_OFS_DELTA:
err = o.readOFSDelta()
case OBJ_COMMIT, OBJ_TREE, OBJ_BLOB, OBJ_TAG:
err = o.readObject()
default:
err = NewError("Invalid git object tag %q", o.typ)
}
if err == ErrZlibHeader {
p.giveBack()
io.CopyN(ioutil.Discard, p.r, 1)
return p.readObject(packfile, offset)
}
return o, err
}
func newObjectReader(pr *PackfileReader, pf *Packfile, offset int) (*objectReader, error) {
o := &objectReader{pr: pr, pf: pf, offset: offset}
buf := make([]byte, 1)
if _, err := o.Read(buf); err != nil {
return nil, err
}
o.typ = int8((buf[0] >> 4) & 7)
o.size = uint64(buf[0] & 15)
var shift uint = 4
for buf[0]&0x80 == 0x80 {
if _, err := o.Read(buf); err != nil {
return nil, err
}
o.size += uint64(buf[0]&0x7f) << shift
shift += 7
}
return o, nil
}
func (o *objectReader) readREFDelta() error {
ref := make([]byte, 20)
o.Read(ref)
buf, err := o.inflate()
if err != nil {
return err
}
refhash := fmt.Sprintf("%x", ref)
referenced, ok := o.pr.objects[refhash]
if !ok {
o.pr.deltas = append(o.pr.deltas, packfileDelta{hash: refhash, delta: buf})
} else {
patched := PatchDelta(referenced.bytes, buf)
if patched == nil {
return NewError("error while patching %x", ref)
}
o.typ = referenced.typ
err = o.addObject(patched)
if err != nil {
return err
}
}
return nil
}
func (o *objectReader) readOFSDelta() error {
// read negative offset
var b uint8
binary.Read(o, binary.BigEndian, &b)
var noffset int = int(b & 0x7f)
for (b & 0x80) != 0 {
noffset += 1
binary.Read(o, binary.BigEndian, &b)
noffset = (noffset << 7) + int(b&0x7f)
}
buf, err := o.inflate()
if err != nil {
return err
}
refhash := o.pr.offsets[o.offset-noffset]
referenced, ok := o.pr.objects[refhash]
if !ok {
return NewError("can't find a pack entry at %d", o.offset-noffset)
} else {
patched := PatchDelta(referenced.bytes, buf)
if patched == nil {
return NewError("error while patching %x", refhash)
}
o.typ = referenced.typ
err = o.addObject(patched)
if err != nil {
return err
}
}
return nil
}
func (o *objectReader) readObject() error {
buf, err := o.inflate()
if err != nil {
return err
}
return o.addObject(buf)
}
func (o *objectReader) addObject(bytes []byte) error {
var hash string
switch o.typ {
case OBJ_COMMIT:
c, err := NewCommit(bytes)
if err != nil {
return err
}
o.pf.Commits[c.Hash()] = c
hash = c.Hash()
case OBJ_TREE:
c, err := NewTree(bytes)
if err != nil {
return err
}
o.pf.Trees[c.Hash()] = c
hash = c.Hash()
case OBJ_BLOB:
c, err := NewBlob(bytes)
if err != nil {
return err
}
o.pf.Blobs[c.Hash()] = c
hash = c.Hash()
if o.pr.contentCallback != nil {
o.pr.contentCallback(hash, bytes)
}
}
o.pr.objects[hash] = packfileObject{bytes: bytes, typ: o.typ}
o.hash = hash
return nil
}
func (o *objectReader) inflate() ([]byte, error) {
//Quick fix "Invalid git object tag '\x00'" when the length of a object is 0
if o.size == 0 {
buf := make([]byte, 4)
if _, err := o.Read(buf); err != nil {
return nil, err
}
return nil, nil
}
zr, err := zlib.NewReader(o)
if err != nil {
if err.Error() == "zlib: invalid header" {
return nil, ErrZlibHeader
} else {
return nil, NewError("error opening packfile's object zlib: %v", err)
}
}
defer zr.Close()
if o.size > SIZE_LIMIT {
return nil, NewError("the object size exceeed the allowed limit: %d", o.size)
}
buf := make([]byte, o.size)
read := 0
for read < int(o.size) {
n, err := zr.Read(buf[read:])
if err != nil {
return nil, err
}
read += n
}
if read != int(o.size) {
return nil, NewError("inflated size mismatch, expected %d, got %d", o.size, read)
}
return buf, nil
}
func (o *objectReader) Read(p []byte) (int, error) {
i := 0
if o.pr.givenBack != nil {
i1, err := o.pr.givenBack.Read(p)
if err == nil {
i += i1
} else {
o.pr.givenBack = nil
}
}
i2, err := o.pr.r.Read(p[i:])
i += i2
o.counter += i
if err == nil && o.pr.startedGivingBack {
o.pr.givebackBuffer = append(o.pr.givebackBuffer, p[:i]...)
}
return i, err
}
func (o *objectReader) ReadByte() (byte, error) {
var c byte
if err := binary.Read(o, binary.BigEndian, &c); err != nil {
return 0, err
}
return c, nil
}
type ReaderError struct {
Msg string // description of error
}
func NewError(format string, args ...interface{}) error {
return &ReaderError{Msg: fmt.Sprintf(format, args...)}
}
func (e *ReaderError) Error() string { return e.Msg }
var ErrZlibHeader = errors.New("zlib: invalid header")
