// Make takes a message as a byte slice, along with the expected loss rate and
// target reliability and produces the packets for that message. The packets are
// returned as a slice of byte-slices.
func (p *Packeter) Make(msg []byte, loss, reliability float64) [][]byte {
l := uint32(len(msg) + 4)
msk := uint32(255)
lb := []byte{
byte(l & msk),
byte((l >> 8) & msk),
byte((l >> 16) & msk),
byte((l >> 24) & msk),
}
msg = append(lb, msg...)
dataShards, parityShards := findRedundancy(len(msg), Packetlength, loss, reliability)
if parityShards < 1 {
// reedsolomon.Encoder cannot have 0 parity shards
// at some point I want to change this so it doesn't use reedsolomon in this
// case
parityShards = 1
}
shards := dataShards + parityShards
var data [][]byte
if enc, e := reedsolomon.New(dataShards, parityShards); err.Warn(e) {
if data, e = enc.Split(msg); err.Warn(e) {
err.Warn(enc.Encode(data))
}
} else {
return nil
}
idArr := make([]byte, 4)
rand.Read(idArr)
id := uint32(idArr[0]) + uint32(idArr[1])<<8 + uint32(idArr[2])<<16 + uint32(idArr[3])<<24
pk := Packet{}
pks := make([][]byte, shards)
pk.MessageId = id
pk.ParityShards = uint32(parityShards)
for i := 0; i < shards; i++ {
pk.PacketId = uint32(i<<16) + uint32(shards)
pk.Data = data[i]
if d, e := proto.Marshal(&pk); err.Log(e) {
pks[i] = d
} else {
return nil
}
}
return pks
}
// Receive collects packets. When exactly enough packets have been recovered to
// reconstruct the message, the message is returned as a byte slice. Otherwise
// nil is returned. Receive can continue to collect packets after the message
// has been constructed for reliability statistics.
func (p Packeter) Receive(b []byte) []byte {
var pk Packet
if err.Log(proto.Unmarshal(b, &pk)) {
return nil
}
mid, pid, dataShards, parityShards := pk.MetaData()
clctr, ok := p[mid]
if !ok {
clctr = &collector{
data: make([][]byte, dataShards+parityShards),
collected: make(map[uint32]bool),
complete: false,
}
p[mid] = clctr
}
clctr.collected[pid] = true
if clctr.complete {
return nil
}
clctr.data[pid] = pk.Data
if uint32(len(clctr.collected)) >= dataShards {
clctr.complete = true
if enc, e := reedsolomon.New(int(dataShards), int(parityShards)); err.Warn(e) {
if err.Log(enc.Reconstruct(clctr.data)) {
//maybe should take out as an arg
ln := int(clctr.data[0][0]) + int(clctr.data[0][1])<<8 + int(clctr.data[0][2])<<16 + int(clctr.data[0][2])<<24
var out bytes.Buffer
err.Warn(enc.Join(&out, clctr.data, ln))
clctr.data = nil
return out.Bytes()[4:]
}
}
}
return nil
}