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erasure.go
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/
erasure.go
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package renter
import (
"io"
"github.com/klauspost/reedsolomon"
"github.com/NebulousLabs/Sia/modules"
)
// rsCode is a Reed-Solomon encoder/decoder. It implements the
// modules.ErasureCoder interface.
type rsCode struct {
enc reedsolomon.Encoder
numPieces int
dataPieces int
}
// NumPieces returns the number of pieces returned by Encode.
func (rs *rsCode) NumPieces() int { return rs.numPieces }
// MinPieces return the minimum number of pieces that must be present to
// recover the original data.
func (rs *rsCode) MinPieces() int { return rs.dataPieces }
// Encode splits data into equal-length pieces, some containing the original
// data and some containing parity data.
func (rs *rsCode) Encode(data []byte) ([][]byte, error) {
pieces, err := rs.enc.Split(data)
if err != nil {
return nil, err
}
// err should not be possible if Encode is called on the result of Split,
// but no harm in checking anyway.
err = rs.enc.Encode(pieces)
if err != nil {
return nil, err
}
return pieces, nil
}
// Recover recovers the original data from pieces (including parity) and
// writes it to w. pieces should be identical to the slice returned by
// Encode (length and order must be preserved), but with missing elements
// set to nil.
func (rs *rsCode) Recover(pieces [][]byte, n uint64, w io.Writer) error {
err := rs.enc.Reconstruct(pieces)
if err != nil {
return err
}
return rs.enc.Join(w, pieces, int(n))
}
// NewRSCode creates a new Reed-Solomon encoder/decoder using the supplied
// parameters.
func NewRSCode(nData, nParity int) (modules.ErasureCoder, error) {
enc, err := reedsolomon.New(nData, nParity)
if err != nil {
return nil, err
}
return &rsCode{
enc: enc,
numPieces: nData + nParity,
dataPieces: nData,
}, nil
}