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package packfile
import (
"compress/zlib"
"crypto"
"fmt"
"io"
"github.com/go-git/go-git/v5/plumbing"
"github.com/go-git/go-git/v5/plumbing/hash"
"github.com/go-git/go-git/v5/plumbing/storer"
"github.com/go-git/go-git/v5/utils/binary"
"github.com/go-git/go-git/v5/utils/ioutil"
)
// Encoder gets the data from the storage and write it into the writer in PACK
// format
type Encoder struct {
selector *deltaSelector
w *offsetWriter
zw *zlib.Writer
hasher plumbing.Hasher
useRefDeltas bool
}
// NewEncoder creates a new packfile encoder using a specific Writer and
// EncodedObjectStorer. By default deltas used to generate the packfile will be
// OFSDeltaObject. To use Reference deltas, set useRefDeltas to true.
func NewEncoder(w io.Writer, s storer.EncodedObjectStorer, useRefDeltas bool) *Encoder {
h := plumbing.Hasher{
Hash: hash.New(crypto.SHA1),
}
mw := io.MultiWriter(w, h)
ow := newOffsetWriter(mw)
zw := zlib.NewWriter(mw)
return &Encoder{
selector: newDeltaSelector(s),
w: ow,
zw: zw,
hasher: h,
useRefDeltas: useRefDeltas,
}
}
// Encode creates a packfile containing all the objects referenced in
// hashes and writes it to the writer in the Encoder. `packWindow`
// specifies the size of the sliding window used to compare objects
// for delta compression; 0 turns off delta compression entirely.
func (e *Encoder) Encode(
hashes []plumbing.Hash,
packWindow uint,
) (plumbing.Hash, error) {
objects, err := e.selector.ObjectsToPack(hashes, packWindow)
if err != nil {
return plumbing.ZeroHash, err
}
return e.encode(objects)
}
func (e *Encoder) encode(objects []*ObjectToPack) (plumbing.Hash, error) {
if err := e.head(len(objects)); err != nil {
return plumbing.ZeroHash, err
}
for _, o := range objects {
if err := e.entry(o); err != nil {
return plumbing.ZeroHash, err
}
}
return e.footer()
}
func (e *Encoder) head(numEntries int) error {
return binary.Write(
e.w,
signature,
int32(VersionSupported),
int32(numEntries),
)
}
func (e *Encoder) entry(o *ObjectToPack) (err error) {
if o.WantWrite() {
// A cycle exists in this delta chain. This should only occur if a
// selected object representation disappeared during writing
// (for example due to a concurrent repack) and a different base
// was chosen, forcing a cycle. Select something other than a
// delta, and write this object.
e.selector.restoreOriginal(o)
o.BackToOriginal()
}
if o.IsWritten() {
return nil
}
o.MarkWantWrite()
if err := e.writeBaseIfDelta(o); err != nil {
return err
}
// We need to check if we already write that object due a cyclic delta chain
if o.IsWritten() {
return nil
}
o.Offset = e.w.Offset()
if o.IsDelta() {
if err := e.writeDeltaHeader(o); err != nil {
return err
}
} else {
if err := e.entryHead(o.Type(), o.Size()); err != nil {
return err
}
}
e.zw.Reset(e.w)
defer ioutil.CheckClose(e.zw, &err)
or, err := o.Object.Reader()
if err != nil {
return err
}
defer ioutil.CheckClose(or, &err)
_, err = io.Copy(e.zw, or)
if err != nil {
return err
}
return nil
}
func (e *Encoder) writeBaseIfDelta(o *ObjectToPack) error {
if o.IsDelta() && !o.Base.IsWritten() {
// We must write base first
return e.entry(o.Base)
}
return nil
}
func (e *Encoder) writeDeltaHeader(o *ObjectToPack) error {
// Write offset deltas by default
t := plumbing.OFSDeltaObject
if e.useRefDeltas {
t = plumbing.REFDeltaObject
}
if err := e.entryHead(t, o.Object.Size()); err != nil {
return err
}
if e.useRefDeltas {
return e.writeRefDeltaHeader(o.Base.Hash())
} else {
return e.writeOfsDeltaHeader(o)
}
}
func (e *Encoder) writeRefDeltaHeader(base plumbing.Hash) error {
return binary.Write(e.w, base)
}
func (e *Encoder) writeOfsDeltaHeader(o *ObjectToPack) error {
// for OFS_DELTA, offset of the base is interpreted as negative offset
// relative to the type-byte of the header of the ofs-delta entry.
relativeOffset := o.Offset - o.Base.Offset
if relativeOffset <= 0 {
return fmt.Errorf("bad offset for OFS_DELTA entry: %d", relativeOffset)
}
return binary.WriteVariableWidthInt(e.w, relativeOffset)
}
func (e *Encoder) entryHead(typeNum plumbing.ObjectType, size int64) error {
t := int64(typeNum)
header := []byte{}
c := (t << firstLengthBits) | (size & maskFirstLength)
size >>= firstLengthBits
for {
if size == 0 {
break
}
header = append(header, byte(c|maskContinue))
c = size & int64(maskLength)
size >>= lengthBits
}
header = append(header, byte(c))
_, err := e.w.Write(header)
return err
}
func (e *Encoder) footer() (plumbing.Hash, error) {
h := e.hasher.Sum()
return h, binary.Write(e.w, h)
}
type offsetWriter struct {
w io.Writer
offset int64
}
func newOffsetWriter(w io.Writer) *offsetWriter {
return &offsetWriter{w: w}
}
func (ow *offsetWriter) Write(p []byte) (n int, err error) {
n, err = ow.w.Write(p)
ow.offset += int64(n)
return n, err
}
func (ow *offsetWriter) Offset() int64 {
return ow.offset
}
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