consortium/v2: distribute finality reward for the voters in parent block

Because the finality votes are assembled after we FinalizeAndAssemble the block
and the finality reward distribution transaction is in FinalizeAndAssemble, we
cannot reward the finality voters in the current block right away. Instead, the
reward distribution is delayed until next block. So in the FinalizeAndAssemble,
we look at the finality voters in the parent header and distribute reward to
them.

Author: minh-bq

consensus/consortium/v2/consortium.go

@@ -725,17 +725,24 @@ func (c *Consortium) processSystemTransactions(chain consensus.ChainHeaderReader
 		return err
 	}
 
-	if c.chainConfig.IsShillin(header.Number) {
-		extraData, err := finality.DecodeExtra(header.Extra, c.chainConfig.IsShillin(header.Number))
+	// If the parent's block includes the finality votes, distribute reward for the voters
+	if c.chainConfig.IsShillin(new(big.Int).Sub(header.Number, common.Big1)) {
+		parentHeader := chain.GetHeaderByHash(header.ParentHash)
+		extraData, err := finality.DecodeExtra(parentHeader.Extra, true)
 		if err != nil {
 			return err
 		}
 		if extraData.HasFinalityVote == 1 {
+			parentSnap, err := c.snapshot(chain, parentHeader.Number.Uint64()-1, parentHeader.ParentHash, nil)
+			if err != nil {
+				return err
+			}
+
 			votedValidatorPositions := extraData.FinalityVotedValidators.Indices()
 			var votedValidators []common.Address
 			for _, position := range votedValidatorPositions {
 				// The header has been verified so there must be no out of bound here
-				votedValidators = append(votedValidators, snap.ValidatorsWithBlsPub[position].Address)
+				votedValidators = append(votedValidators, parentSnap.ValidatorsWithBlsPub[position].Address)
 			}
 
 			if err := c.contract.FinalityReward(transactOpts, votedValidators); err != nil {