// EncodeRing takes a Sector and encodes it as a Ring: a set of common.QuorumSize Segments that include redundancy.
// The encoding parameters are stored in params.
// k is the number of non-redundant segments, and b is the size of each segment. b is calculated from k.
// The erasure-coding algorithm requires that the original data must be k*b in size, so it is padded here as needed.
//
// The return value is a Ring.
// The first k Segments of the Ring are the original data split up.
// The remaining Segments are newly generated redundant data.
func EncodeRing(sec *common.Sector, params *common.EncodingParams) (ring [common.QuorumSize]common.Segment, err error) {
k, b, length := params.GetValues()
// check for legal size of k
if k <= 0 || k >= common.QuorumSize {
err = fmt.Errorf("k must be greater than 0 and smaller than %v", common.QuorumSize)
return
}
// check for legal size of b
if b < common.MinSegmentSize || b > common.MaxSegmentSize {
err = fmt.Errorf("b must be greater than %v and smaller than %v", common.MinSegmentSize, common.MaxSegmentSize)
return
}
// check for legal size of length
if length != len(sec.Data) {
err = fmt.Errorf("length mismatch: sector length %v != parameter length %v", len(sec.Data), length)
return
} else if length > common.MaxSegmentSize*common.QuorumSize {
err = fmt.Errorf("length must be smaller than %v", common.MaxSegmentSize*common.QuorumSize)
}
// pad data as needed
padding := k*b - len(sec.Data)
paddedData := append(sec.Data, bytes.Repeat([]byte{0x00}, padding)...)
// call the encoding function
m := common.QuorumSize - k
redundantChunk := C.encodeRedundancy(C.int(k), C.int(m), C.int(b), (*C.char)(unsafe.Pointer(&paddedData[0])))
redundantBytes := C.GoBytes(unsafe.Pointer(redundantChunk), C.int(m*b))
// split paddedData into ring
for i := 0; i < k; i++ {
ring[i] = common.Segment{
paddedData[i*b : (i+1)*b],
uint8(i),
}
}
// split redundantString into ring
for i := k; i < common.QuorumSize; i++ {
ring[i] = common.Segment{
redundantBytes[(i-k)*b : (i-k+1)*b],
uint8(i),
}
}
// free the memory allocated by the C file
C.free(unsafe.Pointer(redundantChunk))
return
}
// EncodeRing takes data and produces a set of common.QuorumSize pieces that include redundancy.
// 'k' indiciates the number of non-redundant segments, and 'bytesPerSegment' indicates the size of each segment.
// 'originalData' must be 'k' * 'bytesPerSegment' in size, and should be padded before calling 'EncodeRing'.
//
// The return value is a set of strings common.QuorumSize in length.
// Each string is bytesPerSegment large.
// The first 'k' strings are the original data split up.
// The remaining strings are newly generated redundant data.
func EncodeRing(k int, bytesPerSegment int, originalData []byte) (segmentdData []string, err error) {
// check that 'k' is legal
if k <= 0 || k >= common.QuorumSize {
err = fmt.Errorf("k must be greater than 0 and smaller than %v", common.QuorumSize)
return
}
// check that bytesPerSegment is not too big or small
if bytesPerSegment < common.MinSliceSize || bytesPerSegment > common.MaxSliceSize {
err = fmt.Errorf("bytesPerSegment must be greater than %v and smaller than %v", common.MinSliceSize, common.MaxSliceSize)
return
}
// check that bytesPerSegment is divisible by 8
if bytesPerSegment%8 != 0 {
err = fmt.Errorf("bytesPerSegment must be divisible by 8")
return
}
// check that originalData is the correct size
if len(originalData) != bytesPerSegment*k {
err = fmt.Errorf("originalData incorrectly padded, must be of size 'bytesPerSegment' * %v - 'm'", common.QuorumSize)
return
}
// call c library to encode data
m := common.QuorumSize - k
redundantChunk := C.encodeRedundancy(C.int(k), C.int(m), C.int(bytesPerSegment), (*C.char)(unsafe.Pointer(&originalData[0])))
redundantString := C.GoStringN(redundantChunk, C.int(m*bytesPerSegment))
segmentdData = make([]string, common.QuorumSize)
// split originalData into segmentdData
for i := 0; i < k; i++ {
segmentdData[i] = string(originalData[i*bytesPerSegment : i*bytesPerSegment+bytesPerSegment])
}
// split redundantString into segmentdData
for i := k; i < common.QuorumSize; i++ {
segmentdData[i] = redundantString[(i-k)*bytesPerSegment : ((i-k)*bytesPerSegment)+bytesPerSegment]
}
// free the memory allocated by the C file
C.free(unsafe.Pointer(redundantChunk))
return
}