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package binarydist
import (
"bytes"
"compress/bzip2"
"encoding/binary"
"errors"
"io"
"io/ioutil"
)
var ErrCorrupt = errors.New("corrupt patch")
// Patch applies patch to old, according to the bspatch algorithm,
// and writes the result to new.
func Patch(old io.Reader, new io.Writer, patch io.Reader) error {
var hdr header
err := binary.Read(patch, signMagLittleEndian{}, &hdr)
if err != nil {
return err
}
if hdr.Magic != magic {
return ErrCorrupt
}
if hdr.CtrlLen < 0 || hdr.DiffLen < 0 || hdr.NewSize < 0 {
return ErrCorrupt
}
ctrlbuf := make([]byte, hdr.CtrlLen)
_, err = io.ReadFull(patch, ctrlbuf)
if err != nil {
return err
}
cpfbz2 := bzip2.NewReader(bytes.NewReader(ctrlbuf))
diffbuf := make([]byte, hdr.DiffLen)
_, err = io.ReadFull(patch, diffbuf)
if err != nil {
return err
}
dpfbz2 := bzip2.NewReader(bytes.NewReader(diffbuf))
// The entire rest of the file is the extra block.
epfbz2 := bzip2.NewReader(patch)
obuf, err := ioutil.ReadAll(old)
if err != nil {
return err
}
nbuf := make([]byte, hdr.NewSize)
var oldpos, newpos int64
for newpos < hdr.NewSize {
var ctrl struct{ Add, Copy, Seek int64 }
err = binary.Read(cpfbz2, signMagLittleEndian{}, &ctrl)
if err != nil {
return err
}
// Sanity-check
if newpos+ctrl.Add > hdr.NewSize {
return ErrCorrupt
}
// Read diff string
_, err = io.ReadFull(dpfbz2, nbuf[newpos:newpos+ctrl.Add])
if err != nil {
return ErrCorrupt
}
// Add old data to diff string
for i := int64(0); i < ctrl.Add; i++ {
if oldpos+i >= 0 && oldpos+i < int64(len(obuf)) {
nbuf[newpos+i] += obuf[oldpos+i]
}
}
// Adjust pointers
newpos += ctrl.Add
oldpos += ctrl.Add
// Sanity-check
if newpos+ctrl.Copy > hdr.NewSize {
return ErrCorrupt
}
// Read extra string
_, err = io.ReadFull(epfbz2, nbuf[newpos:newpos+ctrl.Copy])
if err != nil {
return ErrCorrupt
}
// Adjust pointers
newpos += ctrl.Copy
oldpos += ctrl.Seek
}
// Write the new file
for len(nbuf) > 0 {
n, err := new.Write(nbuf)
if err != nil {
return err
}
nbuf = nbuf[n:]
}
return nil
}