//Verify checks res is codeward in the server.
func Verify(res []byte, fnum int, key []byte, n int, loc []int) (bool, error) {
p := &prf{key: key, fnum: fnum}
for _, l := range loc {
res[len(res)-1] ^= p.rand(l)
}
enc, err := reedsolomon.NewAN(nServerBlock-1, 1, p.perm())
if err != nil {
log.Println(err)
return false, err
}
data := make([][]byte, nServerBlock)
for i := 0; i < nServerBlock; i++ {
data[i] = make([]byte, 1)
data[i][0] = res[i]
}
ok, err := enc.Verify(data)
if err != nil {
log.Println(err)
return false, err
}
return ok, nil
}
//Build builds shards for servers with reed solomon coding
//and (255,1) redundant codes for each servers for challenge/response.
func Build(m, n int, fname string) ([]string, []byte, error) {
key := make([]byte, 32)
if _, err := rand.Read(key); err != nil {
log.Fatal(err)
}
prf := &prf{key: key}
enc, err := reedsolomon.New(n, m)
if err != nil {
log.Println(err)
return nil, nil, err
}
data := make([][]byte, m+n)
rs, err := rmmap(fname)
if err != nil {
log.Println(err)
return nil, nil, err
}
defer rs.Close()
shardSize, err := size(rs.f, n)
if err != nil {
return nil, nil, err
}
serverBlockSize := blocks(shardSize, nServerBlock-1)
ss := make([]*smap, m+n)
name := parseName(fname)
outfiles := make([]string, m+n)
for i := 0; i < m+n; i++ {
outfiles[i] = name.rename(i)
ss[i], err = wmmap(outfiles[i], int64(serverBlockSize)*nServerBlock)
if err != nil {
log.Println(err)
return nil, nil, err
}
data[i] = ss[i].bytes()[:shardSize]
}
defer func() {
for i := 0; i < m+n; i++ {
ss[i].Close()
}
}()
for i := 0; i < n; i++ {
end := (i + 1) * shardSize
if end > len(rs.bytes()) {
end = len(rs.bytes())
}
copy(data[i], rs.bytes()[i*shardSize:end])
}
if err != nil {
log.Println(err)
return nil, nil, err
}
if err = enc.Encode(data); err != nil {
log.Println(err)
return nil, nil, err
}
encServer, err := reedsolomon.NewAN(nServerBlock-1, 1, prf.perm())
if err != nil {
log.Println(err)
return nil, nil, err
}
for i := 0; i < m+n; i++ {
prf.fnum = i
if err := serverEncode(ss[i].bytes(), prf, serverBlockSize, encServer); err != nil {
log.Println(err)
return nil, nil, err
}
}
return outfiles, key, err
}