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此仓库是为了提升国内下载速度的镜像仓库,每日同步一次。 原始仓库: https://github.com/src-d/go-git
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decoder.go 8.15 KB
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ferhat elmas authored 2017-11-29 02:24 . all: simplification
package index
import (
"bytes"
"crypto/sha1"
"errors"
"hash"
"io"
"io/ioutil"
"strconv"
"time"
"gopkg.in/src-d/go-git.v4/plumbing"
"gopkg.in/src-d/go-git.v4/utils/binary"
)
var (
// DecodeVersionSupported is the range of supported index versions
DecodeVersionSupported = struct{ Min, Max uint32 }{Min: 2, Max: 4}
// ErrMalformedSignature is returned by Decode when the index header file is
// malformed
ErrMalformedSignature = errors.New("malformed index signature file")
// ErrInvalidChecksum is returned by Decode if the SHA1 hash missmatch with
// the read content
ErrInvalidChecksum = errors.New("invalid checksum")
errUnknownExtension = errors.New("unknown extension")
)
const (
entryHeaderLength = 62
entryExtended = 0x4000
entryValid = 0x8000
nameMask = 0xfff
intentToAddMask = 1 << 13
skipWorkTreeMask = 1 << 14
)
// A Decoder reads and decodes index files from an input stream.
type Decoder struct {
r io.Reader
hash hash.Hash
lastEntry *Entry
}
// NewDecoder returns a new decoder that reads from r.
func NewDecoder(r io.Reader) *Decoder {
h := sha1.New()
return &Decoder{
r: io.TeeReader(r, h),
hash: h,
}
}
// Decode reads the whole index object from its input and stores it in the
// value pointed to by idx.
func (d *Decoder) Decode(idx *Index) error {
var err error
idx.Version, err = validateHeader(d.r)
if err != nil {
return err
}
entryCount, err := binary.ReadUint32(d.r)
if err != nil {
return err
}
if err := d.readEntries(idx, int(entryCount)); err != nil {
return err
}
return d.readExtensions(idx)
}
func (d *Decoder) readEntries(idx *Index, count int) error {
for i := 0; i < count; i++ {
e, err := d.readEntry(idx)
if err != nil {
return err
}
d.lastEntry = e
idx.Entries = append(idx.Entries, e)
}
return nil
}
func (d *Decoder) readEntry(idx *Index) (*Entry, error) {
e := &Entry{}
var msec, mnsec, sec, nsec uint32
var flags uint16
flow := []interface{}{
&sec, &nsec,
&msec, &mnsec,
&e.Dev,
&e.Inode,
&e.Mode,
&e.UID,
&e.GID,
&e.Size,
&e.Hash,
&flags,
}
if err := binary.Read(d.r, flow...); err != nil {
return nil, err
}
read := entryHeaderLength
if sec != 0 || nsec != 0 {
e.CreatedAt = time.Unix(int64(sec), int64(nsec))
}
if msec != 0 || mnsec != 0 {
e.ModifiedAt = time.Unix(int64(msec), int64(mnsec))
}
e.Stage = Stage(flags>>12) & 0x3
if flags&entryExtended != 0 {
extended, err := binary.ReadUint16(d.r)
if err != nil {
return nil, err
}
read += 2
e.IntentToAdd = extended&intentToAddMask != 0
e.SkipWorktree = extended&skipWorkTreeMask != 0
}
if err := d.readEntryName(idx, e, flags); err != nil {
return nil, err
}
return e, d.padEntry(idx, e, read)
}
func (d *Decoder) readEntryName(idx *Index, e *Entry, flags uint16) error {
var name string
var err error
switch idx.Version {
case 2, 3:
len := flags & nameMask
name, err = d.doReadEntryName(len)
case 4:
name, err = d.doReadEntryNameV4()
default:
return ErrUnsupportedVersion
}
if err != nil {
return err
}
e.Name = name
return nil
}
func (d *Decoder) doReadEntryNameV4() (string, error) {
l, err := binary.ReadVariableWidthInt(d.r)
if err != nil {
return "", err
}
var base string
if d.lastEntry != nil {
base = d.lastEntry.Name[:len(d.lastEntry.Name)-int(l)]
}
name, err := binary.ReadUntil(d.r, '\x00')
if err != nil {
return "", err
}
return base + string(name), nil
}
func (d *Decoder) doReadEntryName(len uint16) (string, error) {
name := make([]byte, len)
if err := binary.Read(d.r, &name); err != nil {
return "", err
}
return string(name), nil
}
// Index entries are padded out to the next 8 byte alignment
// for historical reasons related to how C Git read the files.
func (d *Decoder) padEntry(idx *Index, e *Entry, read int) error {
if idx.Version == 4 {
return nil
}
entrySize := read + len(e.Name)
padLen := 8 - entrySize%8
_, err := io.CopyN(ioutil.Discard, d.r, int64(padLen))
return err
}
func (d *Decoder) readExtensions(idx *Index) error {
// TODO: support 'Split index' and 'Untracked cache' extensions, take in
// count that they are not supported by jgit or libgit
var expected []byte
var err error
var header [4]byte
for {
expected = d.hash.Sum(nil)
var n int
if n, err = io.ReadFull(d.r, header[:]); err != nil {
if n == 0 {
err = io.EOF
}
break
}
err = d.readExtension(idx, header[:])
if err != nil {
break
}
}
if err != errUnknownExtension {
return err
}
return d.readChecksum(expected, header)
}
func (d *Decoder) readExtension(idx *Index, header []byte) error {
switch {
case bytes.Equal(header, treeExtSignature):
r, err := d.getExtensionReader()
if err != nil {
return err
}
idx.Cache = &Tree{}
d := &treeExtensionDecoder{r}
if err := d.Decode(idx.Cache); err != nil {
return err
}
case bytes.Equal(header, resolveUndoExtSignature):
r, err := d.getExtensionReader()
if err != nil {
return err
}
idx.ResolveUndo = &ResolveUndo{}
d := &resolveUndoDecoder{r}
if err := d.Decode(idx.ResolveUndo); err != nil {
return err
}
default:
return errUnknownExtension
}
return nil
}
func (d *Decoder) getExtensionReader() (io.Reader, error) {
len, err := binary.ReadUint32(d.r)
if err != nil {
return nil, err
}
return &io.LimitedReader{R: d.r, N: int64(len)}, nil
}
func (d *Decoder) readChecksum(expected []byte, alreadyRead [4]byte) error {
var h plumbing.Hash
copy(h[:4], alreadyRead[:])
if err := binary.Read(d.r, h[4:]); err != nil {
return err
}
if !bytes.Equal(h[:], expected) {
return ErrInvalidChecksum
}
return nil
}
func validateHeader(r io.Reader) (version uint32, err error) {
var s = make([]byte, 4)
if _, err := io.ReadFull(r, s); err != nil {
return 0, err
}
if !bytes.Equal(s, indexSignature) {
return 0, ErrMalformedSignature
}
version, err = binary.ReadUint32(r)
if err != nil {
return 0, err
}
if version < DecodeVersionSupported.Min || version > DecodeVersionSupported.Max {
return 0, ErrUnsupportedVersion
}
return
}
type treeExtensionDecoder struct {
r io.Reader
}
func (d *treeExtensionDecoder) Decode(t *Tree) error {
for {
e, err := d.readEntry()
if err != nil {
if err == io.EOF {
return nil
}
return err
}
if e == nil {
continue
}
t.Entries = append(t.Entries, *e)
}
}
func (d *treeExtensionDecoder) readEntry() (*TreeEntry, error) {
e := &TreeEntry{}
path, err := binary.ReadUntil(d.r, '\x00')
if err != nil {
return nil, err
}
e.Path = string(path)
count, err := binary.ReadUntil(d.r, ' ')
if err != nil {
return nil, err
}
i, err := strconv.Atoi(string(count))
if err != nil {
return nil, err
}
// An entry can be in an invalidated state and is represented by having a
// negative number in the entry_count field.
if i == -1 {
return nil, nil
}
e.Entries = i
trees, err := binary.ReadUntil(d.r, '\n')
if err != nil {
return nil, err
}
i, err = strconv.Atoi(string(trees))
if err != nil {
return nil, err
}
e.Trees = i
if err := binary.Read(d.r, &e.Hash); err != nil {
return nil, err
}
return e, nil
}
type resolveUndoDecoder struct {
r io.Reader
}
func (d *resolveUndoDecoder) Decode(ru *ResolveUndo) error {
for {
e, err := d.readEntry()
if err != nil {
if err == io.EOF {
return nil
}
return err
}
ru.Entries = append(ru.Entries, *e)
}
}
func (d *resolveUndoDecoder) readEntry() (*ResolveUndoEntry, error) {
e := &ResolveUndoEntry{
Stages: make(map[Stage]plumbing.Hash),
}
path, err := binary.ReadUntil(d.r, '\x00')
if err != nil {
return nil, err
}
e.Path = string(path)
for i := 0; i < 3; i++ {
if err := d.readStage(e, Stage(i+1)); err != nil {
return nil, err
}
}
for s := range e.Stages {
var hash plumbing.Hash
if err := binary.Read(d.r, hash[:]); err != nil {
return nil, err
}
e.Stages[s] = hash
}
return e, nil
}
func (d *resolveUndoDecoder) readStage(e *ResolveUndoEntry, s Stage) error {
ascii, err := binary.ReadUntil(d.r, '\x00')
if err != nil {
return err
}
stage, err := strconv.ParseInt(string(ascii), 8, 64)
if err != nil {
return err
}
if stage != 0 {
e.Stages[s] = plumbing.ZeroHash
}
return nil
}

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