// RebuildSector takes a Ring and returns a Sector containing the original data.
// The encoding parameters are stored in params.
// k must be equal to the number of non-redundant segments when the file was originally built.
// Because recovery is just a bunch of matrix operations, there is no way to tell if the data has been corrupted
// or if an incorrect value of k has been chosen. This error checking must happen before calling RebuildSector.
// Each Segment's Data must have the correct Index from when it was encoded.
func RebuildSector(ring []common.Segment, params *common.EncodingParams) (sec *common.Sector, err error) {
k, b, length := params.GetValues()
if k == 0 && b == 0 {
err = fmt.Errorf("could not rebuild using uninitialized encoding parameters")
return
}
// check for legal size of k
if k > common.QuorumSize || k < 1 {
err = fmt.Errorf("k must be greater than 0 but 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 > common.MaxSegmentSize*common.QuorumSize {
err = fmt.Errorf("length must be smaller than %v", common.MaxSegmentSize*common.QuorumSize)
}
// check for correct number of segments
if len(ring) < k {
err = fmt.Errorf("insufficient segments: expected at least %v, got %v", k, len(ring))
return
}
// move all data into a single slice
var segmentData []byte
var segmentIndices []uint8
for i := 0; i < k; i++ {
// verify that each segment is the correct length
// TODO: skip bad segments and continue rebuilding if possible
if len(ring[i].Data) != b {
err = fmt.Errorf("at least 1 Segment's Data field is the wrong length")
return
}
segmentData = append(segmentData, ring[i].Data...)
segmentIndices = append(segmentIndices, ring[i].Index)
}
// call the recovery function
C.recoverData(C.int(k), C.int(common.QuorumSize-k), C.int(b), (*C.uchar)(unsafe.Pointer(&segmentData[0])), (*C.uchar)(unsafe.Pointer(&segmentIndices[0])))
// remove padding introduced by EncodeRing()
sec, err = common.NewSector(segmentData[:length])
return
}
// RebuildSector takes a set of 'k' strings, each 'bytesPerSegment' in size, and recovers the original data.
// 'k' must be equal to the number of non-redundant segments when the file was originally built.
// Because recovery is just a bunch of matrix operations, there is no way to tell if the data has been corrupted
// or if an incorrect value of 'k' has been chosen. This error checking must happen before calling RebuildSector.
// The set of 'untaintedSegments' will have corresponding indicies from when they were encoded.
// There is no way to tell what the indicies are, so they must be supplied in the 'segmentIndicies' slice.
// This must be a uint8 because the C library uses a char.
//
// The output is a single byteslice that is equivalent to the data used when initially calling EncodeRing()
func RebuildSector(k int, bytesPerSegment int, untaintedSegments []string, segmentIndicies []uint8) (originalData []byte, err error) {
// check for legal size of k and m
m := common.QuorumSize - k
if k > common.QuorumSize || k < 1 {
err = fmt.Errorf("k must be greater than 0 but smaller than %v", common.QuorumSize)
return
}
// check for legal size of bytesPerSegment
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 input data is correct number of slices.
if len(untaintedSegments) != k {
err = fmt.Errorf("there must be k elements in untaintedSegments")
return
}
// check that input indicies are correct number of indicies
if len(segmentIndicies) != k {
err = fmt.Errorf("there must be k elements in segmentIndicies")
return
}
// move all data into a single slice for C
originalData = make([]byte, 0, k*bytesPerSegment)
for _, segment := range untaintedSegments {
byteSlice := []byte(segment)
// verify that each string is the correct length
if len(byteSlice) != bytesPerSegment {
err = fmt.Errorf("at least 1 of 'untaintedSegments' is the wrong length")
return
}
originalData = append(originalData, byteSlice...)
}
// call the recovery option
C.recoverData(C.int(k), C.int(m), C.int(bytesPerSegment), (*C.uchar)(unsafe.Pointer(&originalData[0])), (*C.uchar)(unsafe.Pointer(&segmentIndicies[0])))
return
}
