A delta encoding library heavily inspired by rdiff.
signature(basis-file) -> sig-file
delta(sig-file, new-file) -> delta-file
patch(basis-file, delta-file) -> recreated-file
The idea of rolling checksum algorithm (rollsum) was taken from librsync.
package diff
var (
ByteOrder = binary.BigEndian
NewHash = md5.New
)- Signature
type (
Signature struct {
signatureHeader
signatureChecksum
}
signatureHeader struct {
BlockSize uint32
StrongSize byte
}
signatureChecksum struct {
weak map[uint32]int
strong [][]byte
}
)
diff.WriteSignature(basisReader io.Reader, signatureWriter io.Writer, blockSize uint32, strongSize byte) (*diff.Signature, error)
diff.ReadSignature(signatureReader io.Reader) (*diff.Signature, error)
func (sig *Signature) Lookup(weak uint32) (strong []byte, offset uint64, blockSize uint32, ok bool)File spec.:
// header
{block size: 4 bytes, strong checksum size: 1 byte}
// checksum
{weak checksum: 4 bytes, strong checksum: StrongSize bytes}
{weak checksum: 4 bytes, strong checksum: StrongSize bytes}
...
{weak checksum: 4 bytes, strong checksum: StrongSize bytes}
- Delta
const (
FromOld = byte(0x0)
FromNew = byte(0x1)
)
type (
Delta = []*DeltaInstruction
DeltaInstruction struct {
DeltaInstructionHeader
Data []byte
}
DeltaInstructionHeader struct {
From byte
Offset uint64
Size uint64
}
)
diff.WriteDelta(signature *diff.Signature, newReader io.Reader, deltaWriter io.Writer) error
diff.ReadDelta(r io.Reader) (delta diff.Delta, err error)
diff.ReadDeltaInstructionHeader(r io.Reader) (header diff.DeltaInstructionHeader, err error)File spec.:
// instruction
{from: 1 byte, offset: 8 bytes, size: 8 bytes}
// data
...
// instruction
{from: 1 byte, offset: 8 bytes, size: 8 bytes}
// data
...
- Patch
diff.Patch(basisReaderSeeker io.ReadSeeker, deltaReader io.Reader, newWriter io.Writer) errorgo build ./cmd/signature
./signature [-b block size] [-s strong size] old-file signature-file
go build ./cmd/delta
./delta signature-file new-file delta-file
go build ./cmd/patch
./patch old-file delta-file new-file