// DownloadFile retrieves the erasure-coded segments corresponding to a given file from a quorum.
// It reconstructs the original file from the segments using erasure.RebuildSector().
func DownloadFile(mr common.MessageRouter, fileHash crypto.Hash, length int, k int, quorum [common.QuorumSize]common.Address) (fileData []byte, err error) {
// spawn a separate thread for each segment
for i := range quorum {
go func() {
// send request
m := new(common.Message)
m.Destination = quorum[i]
m.Payload = []byte{0x01}
m.Payload = append(m.Payload, fileHash[:]...)
mr.SendMessage(m)
// wait for response
}()
}
return
}
// TestTCPDownloadFile tests the NewTCPServer and DownloadFile functions.
// NewTCPServer must properly initialize a TCP server.
// UploadFile splits a file into erasure-coded segments and distributes them across a quorum.
// k is the number of non-redundant segments.
// The file is padded to satisfy the erasure-coding requirements that:
// len(fileData) = k*bytesPerSegment, and:
// bytesPerSegment % 64 = 0
func UploadFile(mr common.MessageRouter, file *os.File, k int, quorum [common.QuorumSize]common.Address) (bytesPerSegment int, err error) {
// read file
fileInfo, err := file.Stat()
if err != nil {
return
}
if fileInfo.Size() > int64(common.QuorumSize*common.MaxSegmentSize) {
err = fmt.Errorf("File exceeds maximum per-quorum size")
return
}
fileData := make([]byte, fileInfo.Size())
_, err = io.ReadFull(file, fileData)
if err != nil {
return
}
// calculate EncodeRing parameters, padding file if necessary
bytesPerSegment = len(fileData) / k
if bytesPerSegment%64 != 0 {
bytesPerSegment += 64 - (bytesPerSegment % 64)
padding := k*bytesPerSegment - len(fileData)
fileData = append(fileData, bytes.Repeat([]byte{0x00}, padding)...)
}
// create erasure-coded segments
segments, err := erasure.EncodeRing(k, bytesPerSegment, fileData)
if err != nil {
return
}
// for now we just send segment i to node i
// this may need to be randomized for security
for i := range quorum {
m := new(common.Message)
m.Destination = quorum[i]
m.Payload = append([]byte{byte(i)}, []byte(segments[i])...)
err = mr.SendMessage(m)
if err != nil {
return
}
}
return
}