cross shard state reading error fix

internal/chain/engine.go

@@ -127,7 +127,7 @@ func (e *engineImpl) VerifySeal(chain engine.ChainReader, header *block.Header)
 	}
 	parentHash := header.ParentHash()
 	parentHeader := chain.GetHeader(parentHash, header.Number().Uint64()-1)
-	parentQuorum, err := QuorumForBlock(chain, parentHeader)
+	parentQuorum, err := QuorumForBlock(chain, parentHeader, false)
 	if err != nil {
 		return errors.Wrapf(err,
 			"cannot calculate quorum for block %s", header.Number())
@@ -160,12 +160,18 @@ func (e *engineImpl) Finalize(chain engine.ChainReader, header *block.Header, st
 }
 
 // QuorumForBlock returns the quorum for the given block header.
-func QuorumForBlock(chain engine.ChainReader, h *block.Header) (quorum int, err error) {
-	ss, err := chain.ReadShardState(h.Epoch())
-	if err != nil {
-		return 0, ctxerror.New("failed to read shard state of epoch",
-			"epoch", h.Epoch().Uint64())
+func QuorumForBlock(chain engine.ChainReader, h *block.Header, reCalculate bool) (quorum int, err error) {
+	var ss shard.State
+	if reCalculate {
+		ss = core.CalculateShardState(h.Epoch())
+	} else {
+		ss, err = chain.ReadShardState(h.Epoch())
+		if err != nil {
+			return 0, ctxerror.New("failed to read shard state of epoch",
+				"epoch", h.Epoch().Uint64()).WithCause(err)
+		}
 	}
+
 	c := ss.FindCommitteeByID(h.ShardID())
 	if c == nil {
 		return 0, errors.Errorf(
@@ -191,7 +197,7 @@ func (e *engineImpl) VerifyHeaderWithSignature(chain engine.ChainReader, header
 	}
 
 	hash := header.Hash()
-	quorum, err := QuorumForBlock(chain, header)
+	quorum, err := QuorumForBlock(chain, header, reCalculate)
 	if err != nil {
 		return errors.Wrapf(err,
 			"cannot calculate quorum for block %s", header.Number())