fix autotune fec mis-align when parameters are different

fec.go

@@ -45,7 +45,8 @@ type fecDecoder struct {
  codec reedsolomon.Encoder
 
  // auto tune fec parameter
- autoTune autoTune
+ autoTune autoTune
+ shouldTune bool
 }
 
 func newFECDecoder(dataShards, parityShards int) *fecDecoder {
@@ -78,18 +79,17 @@ func (dec *fecDecoder) decode(in fecPacket) (recovered [][]byte) {
  }
 
  // 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
+ dec.shouldTune = true
  }
  } else {
  if in.flag() != typeParity {
- shouldTune = true
+ dec.shouldTune = true
  }
  }
 
- if shouldTune {
+ if dec.shouldTune {
  autoDS := dec.autoTune.FindPeriod(true)
  autoPS := dec.autoTune.FindPeriod(false)
 
@@ -108,11 +108,17 @@ func (dec *fecDecoder) decode(in fecPacket) (recovered [][]byte) {
  dec.codec = codec
  dec.decodeCache = make([][]byte, dec.shardSize)
  dec.flagCache = make([]bool, dec.shardSize)
+ dec.shouldTune = false
  //log.Println("autotune to :", dec.dataShards, dec.parityShards)
  }
  }
  }
 
+ // parameters in tuning
+ if dec.shouldTune {
+ return nil
+ }
+
  // insertion
  n := len(dec.rx) - 1
  insertIdx := 0