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vendor.github.com.xtaci.kcp-go.v5.fec.go Maven / Gradle / Ivy
package kcp
import (
"encoding/binary"
"sync/atomic"
"github.com/klauspost/reedsolomon"
)
const (
fecHeaderSize = 6
fecHeaderSizePlus2 = fecHeaderSize + 2 // plus 2B data size
typeData = 0xf1
typeParity = 0xf2
fecExpire = 60000
rxFECMulti = 3 // FEC keeps rxFECMulti* (dataShard+parityShard) ordered packets in memory
)
// fecPacket is a decoded FEC packet
type fecPacket []byte
func (bts fecPacket) seqid() uint32 { return binary.LittleEndian.Uint32(bts) }
func (bts fecPacket) flag() uint16 { return binary.LittleEndian.Uint16(bts[4:]) }
func (bts fecPacket) data() []byte { return bts[6:] }
// fecElement has auxcilliary time field
type fecElement struct {
fecPacket
ts uint32
}
// fecDecoder for decoding incoming packets
type fecDecoder struct {
rxlimit int // queue size limit
dataShards int
parityShards int
shardSize int
rx []fecElement // ordered receive queue
// caches
decodeCache [][]byte
flagCache []bool
// zeros
zeros []byte
// RS decoder
codec reedsolomon.Encoder
// auto tune fec parameter
autoTune autoTune
}
func newFECDecoder(dataShards, parityShards int) *fecDecoder {
if dataShards <= 0 || parityShards <= 0 {
return nil
}
dec := new(fecDecoder)
dec.dataShards = dataShards
dec.parityShards = parityShards
dec.shardSize = dataShards + parityShards
dec.rxlimit = rxFECMulti * dec.shardSize
codec, err := reedsolomon.New(dataShards, parityShards)
if err != nil {
return nil
}
dec.codec = codec
dec.decodeCache = make([][]byte, dec.shardSize)
dec.flagCache = make([]bool, dec.shardSize)
dec.zeros = make([]byte, mtuLimit)
return dec
}
// decode a fec packet
func (dec *fecDecoder) decode(in fecPacket) (recovered [][]byte) {
// sample to auto FEC tuner
if in.flag() == typeData {
dec.autoTune.Sample(true, in.seqid())
} else {
dec.autoTune.Sample(false, in.seqid())
}
// check if FEC parameters is out of sync
var shouldTune bool
if int(in.seqid())%dec.shardSize < dec.dataShards {
if in.flag() != typeData { // expect typeData
shouldTune = true
}
} else {
if in.flag() != typeParity {
shouldTune = true
}
}
if shouldTune {
autoDS := dec.autoTune.FindPeriod(true)
autoPS := dec.autoTune.FindPeriod(false)
// edges found, we can tune parameters now
if autoDS > 0 && autoPS > 0 && autoDS < 256 && autoPS < 256 {
// and make sure it's different
if autoDS != dec.dataShards || autoPS != dec.parityShards {
dec.dataShards = autoDS
dec.parityShards = autoPS
dec.shardSize = autoDS + autoPS
dec.rxlimit = rxFECMulti * dec.shardSize
codec, err := reedsolomon.New(autoDS, autoPS)
if err != nil {
return nil
}
dec.codec = codec
dec.decodeCache = make([][]byte, dec.shardSize)
dec.flagCache = make([]bool, dec.shardSize)
//log.Println("autotune to :", dec.dataShards, dec.parityShards)
}
}
}
// insertion
n := len(dec.rx) - 1
insertIdx := 0
for i := n; i >= 0; i-- {
if in.seqid() == dec.rx[i].seqid() { // de-duplicate
return nil
} else if _itimediff(in.seqid(), dec.rx[i].seqid()) > 0 { // insertion
insertIdx = i + 1
break
}
}
// make a copy
pkt := fecPacket(xmitBuf.Get().([]byte)[:len(in)])
copy(pkt, in)
elem := fecElement{pkt, currentMs()}
// insert into ordered rx queue
if insertIdx == n+1 {
dec.rx = append(dec.rx, elem)
} else {
dec.rx = append(dec.rx, fecElement{})
copy(dec.rx[insertIdx+1:], dec.rx[insertIdx:]) // shift right
dec.rx[insertIdx] = elem
}
// shard range for current packet
shardBegin := pkt.seqid() - pkt.seqid()%uint32(dec.shardSize)
shardEnd := shardBegin + uint32(dec.shardSize) - 1
// max search range in ordered queue for current shard
searchBegin := insertIdx - int(pkt.seqid()%uint32(dec.shardSize))
if searchBegin < 0 {
searchBegin = 0
}
searchEnd := searchBegin + dec.shardSize - 1
if searchEnd >= len(dec.rx) {
searchEnd = len(dec.rx) - 1
}
// re-construct datashards
if searchEnd-searchBegin+1 >= dec.dataShards {
var numshard, numDataShard, first, maxlen int
// zero caches
shards := dec.decodeCache
shardsflag := dec.flagCache
for k := range dec.decodeCache {
shards[k] = nil
shardsflag[k] = false
}
// shard assembly
for i := searchBegin; i <= searchEnd; i++ {
seqid := dec.rx[i].seqid()
if _itimediff(seqid, shardEnd) > 0 {
break
} else if _itimediff(seqid, shardBegin) >= 0 {
shards[seqid%uint32(dec.shardSize)] = dec.rx[i].data()
shardsflag[seqid%uint32(dec.shardSize)] = true
numshard++
if dec.rx[i].flag() == typeData {
numDataShard++
}
if numshard == 1 {
first = i
}
if len(dec.rx[i].data()) > maxlen {
maxlen = len(dec.rx[i].data())
}
}
}
if numDataShard == dec.dataShards {
// case 1: no loss on data shards
dec.rx = dec.freeRange(first, numshard, dec.rx)
} else if numshard >= dec.dataShards {
// case 2: loss on data shards, but it's recoverable from parity shards
for k := range shards {
if shards[k] != nil {
dlen := len(shards[k])
shards[k] = shards[k][:maxlen]
copy(shards[k][dlen:], dec.zeros)
} else if k < dec.dataShards {
shards[k] = xmitBuf.Get().([]byte)[:0]
}
}
if err := dec.codec.ReconstructData(shards); err == nil {
for k := range shards[:dec.dataShards] {
if !shardsflag[k] {
// recovered data should be recycled
recovered = append(recovered, shards[k])
}
}
}
dec.rx = dec.freeRange(first, numshard, dec.rx)
}
}
// keep rxlimit
if len(dec.rx) > dec.rxlimit {
if dec.rx[0].flag() == typeData { // track the unrecoverable data
atomic.AddUint64(&DefaultSnmp.FECShortShards, 1)
}
dec.rx = dec.freeRange(0, 1, dec.rx)
}
// timeout policy
current := currentMs()
numExpired := 0
for k := range dec.rx {
if _itimediff(current, dec.rx[k].ts) > fecExpire {
numExpired++
continue
}
break
}
if numExpired > 0 {
dec.rx = dec.freeRange(0, numExpired, dec.rx)
}
return
}
// free a range of fecPacket
func (dec *fecDecoder) freeRange(first, n int, q []fecElement) []fecElement {
for i := first; i < first+n; i++ { // recycle buffer
xmitBuf.Put([]byte(q[i].fecPacket))
}
if first == 0 && n < cap(q)/2 {
return q[n:]
}
copy(q[first:], q[first+n:])
return q[:len(q)-n]
}
// release all segments back to xmitBuf
func (dec *fecDecoder) release() {
if n := len(dec.rx); n > 0 {
dec.rx = dec.freeRange(0, n, dec.rx)
}
}
type (
// fecEncoder for encoding outgoing packets
fecEncoder struct {
dataShards int
parityShards int
shardSize int
paws uint32 // Protect Against Wrapped Sequence numbers
next uint32 // next seqid
shardCount int // count the number of datashards collected
maxSize int // track maximum data length in datashard
headerOffset int // FEC header offset
payloadOffset int // FEC payload offset
// caches
shardCache [][]byte
encodeCache [][]byte
// zeros
zeros []byte
// RS encoder
codec reedsolomon.Encoder
}
)
func newFECEncoder(dataShards, parityShards, offset int) *fecEncoder {
if dataShards <= 0 || parityShards <= 0 {
return nil
}
enc := new(fecEncoder)
enc.dataShards = dataShards
enc.parityShards = parityShards
enc.shardSize = dataShards + parityShards
enc.paws = 0xffffffff / uint32(enc.shardSize) * uint32(enc.shardSize)
enc.headerOffset = offset
enc.payloadOffset = enc.headerOffset + fecHeaderSize
codec, err := reedsolomon.New(dataShards, parityShards)
if err != nil {
return nil
}
enc.codec = codec
// caches
enc.encodeCache = make([][]byte, enc.shardSize)
enc.shardCache = make([][]byte, enc.shardSize)
for k := range enc.shardCache {
enc.shardCache[k] = make([]byte, mtuLimit)
}
enc.zeros = make([]byte, mtuLimit)
return enc
}
// encodes the packet, outputs parity shards if we have collected quorum datashards
// notice: the contents of 'ps' will be re-written in successive calling
func (enc *fecEncoder) encode(b []byte) (ps [][]byte) {
// The header format:
// | FEC SEQID(4B) | FEC TYPE(2B) | SIZE (2B) | PAYLOAD(SIZE-2) |
// |<-headerOffset |<-payloadOffset
enc.markData(b[enc.headerOffset:])
binary.LittleEndian.PutUint16(b[enc.payloadOffset:], uint16(len(b[enc.payloadOffset:])))
// copy data from payloadOffset to fec shard cache
sz := len(b)
enc.shardCache[enc.shardCount] = enc.shardCache[enc.shardCount][:sz]
copy(enc.shardCache[enc.shardCount][enc.payloadOffset:], b[enc.payloadOffset:])
enc.shardCount++
// track max datashard length
if sz > enc.maxSize {
enc.maxSize = sz
}
// Generation of Reed-Solomon Erasure Code
if enc.shardCount == enc.dataShards {
// fill '0' into the tail of each datashard
for i := 0; i < enc.dataShards; i++ {
shard := enc.shardCache[i]
slen := len(shard)
copy(shard[slen:enc.maxSize], enc.zeros)
}
// construct equal-sized slice with stripped header
cache := enc.encodeCache
for k := range cache {
cache[k] = enc.shardCache[k][enc.payloadOffset:enc.maxSize]
}
// encoding
if err := enc.codec.Encode(cache); err == nil {
ps = enc.shardCache[enc.dataShards:]
for k := range ps {
enc.markParity(ps[k][enc.headerOffset:])
ps[k] = ps[k][:enc.maxSize]
}
}
// counters resetting
enc.shardCount = 0
enc.maxSize = 0
}
return
}
func (enc *fecEncoder) markData(data []byte) {
binary.LittleEndian.PutUint32(data, enc.next)
binary.LittleEndian.PutUint16(data[4:], typeData)
enc.next++
}
func (enc *fecEncoder) markParity(data []byte) {
binary.LittleEndian.PutUint32(data, enc.next)
binary.LittleEndian.PutUint16(data[4:], typeParity)
// sequence wrap will only happen at parity shard
enc.next = (enc.next + 1) % enc.paws
}
