consensus/parlia: support recovery when snapshot of parlia gone in di…

…sk (#2587)

consensus/parlia/parlia.go

@@ -54,7 +54,7 @@ const (
  inMemoryHeaders = 86400 // Number of recent headers to keep in memory for double sign detection,
 
  checkpointInterval = 1024 // Number of blocks after which to save the snapshot to the database
- defaultEpochLength = uint64(100) // Default number of blocks of checkpoint to update validatorSet from contract
+ defaultEpochLength = uint64(200) // Default number of blocks of checkpoint to update validatorSet from contract
  defaultTurnLength = uint8(1) // Default consecutive number of blocks a validator receives priority for block production
 
  extraVanity = 32 // Fixed number of extra-data prefix bytes reserved for signer vanity
@@ -739,25 +739,56 @@ func (p *Parlia) snapshot(chain consensus.ChainHeaderReader, number uint64, hash
  }
  }
 
- // If we're at the genesis, snapshot the initial state.
- if number == 0 {
- checkpoint := chain.GetHeaderByNumber(number)
- if checkpoint != nil {
- // get checkpoint data
- hash := checkpoint.Hash()
-
+ // If we're at the genesis, snapshot the initial state. Alternatively if we have
+ // piled up more headers than allowed to be reorged (chain reinit from a freezer),
+ // consider the checkpoint trusted and snapshot it.
+ // An offset `p.config.Epoch - 1` can ensure getting the right validators.
+ if number == 0 || ((number+1)%p.config.Epoch == 0 && (len(headers) > int(params.FullImmutabilityThreshold))) {
+ var (
+ checkpoint *types.Header
+ blockHash common.Hash
+ )
+ if number == 0 {
+ checkpoint = chain.GetHeaderByNumber(0)
+ if checkpoint != nil {
+ blockHash = checkpoint.Hash()
+ }
+ } else {
+ checkpoint = chain.GetHeaderByNumber(number + 1 - p.config.Epoch)
+ blockHeader := chain.GetHeaderByNumber(number)
+ if blockHeader != nil {
+ blockHash = blockHeader.Hash()
+ }
+ }
+ if checkpoint != nil && blockHash != (common.Hash{}) {
  // get validators from headers
  validators, voteAddrs, err := parseValidators(checkpoint, p.chainConfig, p.config)
  if err != nil {
  return nil, err
  }
 
  // new snapshot
- snap = newSnapshot(p.config, p.signatures, number, hash, validators, voteAddrs, p.ethAPI)
+ snap = newSnapshot(p.config, p.signatures, number, blockHash, validators, voteAddrs, p.ethAPI)
+
+ // get turnLength from headers and use that for new turnLength
+ turnLength, err := parseTurnLength(checkpoint, p.chainConfig, p.config)
+ if err != nil {
+ return nil, err
+ }
+ if turnLength != nil {
+ snap.TurnLength = *turnLength
+ }
+
+ // snap.Recents is currently empty, which affects the following:
+ // a. The function SignRecently - This is acceptable since an empty snap.Recents results in a more lenient check.
+ // b. The function blockTimeVerifyForRamanujanFork - This is also acceptable as it won't be invoked during `snap.apply`.
+ // c. This may cause a mismatch in the slash systemtx, but the transaction list is not verified during `snap.apply`.
+
+ // snap.Attestation is nil, but Snapshot.updateAttestation will handle it correctly.
  if err := snap.store(p.db); err != nil {
  return nil, err
  }
- log.Info("Stored checkpoint snapshot to disk", "number", number, "hash", hash)
+ log.Info("Stored checkpoint snapshot to disk", "number", number, "hash", blockHash)
  break
  }
  }