consensus: dexcon: disqualify dead node (#280)

Since a qualified node might fail stopped, we need to remove them from
qualified nodes to maintain network integrity. We do this by inspect the
previous round to see if there are dead nodes. A dead node is a notary
set node that does not propose any block in the previous round. We
disqualify them by fining them so their staked value is 1 wei below
minStake. This make them unqualified for being notary set in the follow
on rounds.

1 files changed, 48 insertions, 1 deletions

diff --git a/core/vm/oracle_contracts.go b/core/vm/oracle_contracts.go
index c138a6b4a..ac6d7315c 100644
--- a/core/vm/oracle_contracts.go
+++ b/core/vm/oracle_contracts.go
@@ -62,6 +62,7 @@ const (
 	nodesLoc
 	nodesOffsetByAddressLoc
 	nodesOffsetByNodeKeyAddressLoc
+	lastProposedHeightLoc
 	crsRoundLoc
 	crsLoc
 	dkgRoundLoc
@@ -332,7 +333,8 @@ func (s *GovernanceState) DecTotalStaked(amount *big.Int) {
 //     string location;
 //     string url;
 //     uint256 unstaked;
-//     uint256 unstaked_at;
+//     uint256 unstakedAt;
+//     uint256 lastProposedHeight;
 // }
 //
 // Node[] nodes;
@@ -543,6 +545,16 @@ func (s *GovernanceState) GetNodeByID(id coreTypes.NodeID) (*nodeInfo, error) {
 	return node, nil
 }
 
+// mapping(address => uint256) public lastProposedHeight;
+func (s *GovernanceState) LastProposedHeight(addr common.Address) *big.Int {
+	loc := s.getMapLoc(big.NewInt(lastProposedHeightLoc), addr.Bytes())
+	return s.getStateBigInt(loc)
+}
+func (s *GovernanceState) PutLastProposedHeight(addr common.Address, height *big.Int) {
+	loc := s.getMapLoc(big.NewInt(lastProposedHeightLoc), addr.Bytes())
+	s.setStateBigInt(loc, height)
+}
+
 // uint256 public crsRound;
 func (s *GovernanceState) CRSRound() *big.Int {
 	return s.getStateBigInt(big.NewInt(crsRoundLoc))
@@ -960,6 +972,31 @@ func (s *GovernanceState) Register(
 	s.IncTotalStaked(staked)
 }
 
+func (s *GovernanceState) Disqualify(n *nodeInfo) error {
+	nodeAddr, err := publicKeyToNodeKeyAddress(n.PublicKey)
+	if err != nil {
+		return err
+	}
+
+	// Node might already been unstaked in the latest state.
+	offset := s.NodesOffsetByNodeKeyAddress(nodeAddr)
+	if offset.Cmp(big.NewInt(0)) < 0 {
+		return errors.New("node does not exist")
+	}
+
+	// Fine the node so it's staked value is 1 wei under minStake.
+	node := s.Node(offset)
+	extra := new(big.Int).Sub(new(big.Int).Sub(node.Staked, node.Fined), s.MinStake())
+	amount := new(big.Int).Add(extra, big.NewInt(1))
+
+	if amount.Cmp(big.NewInt(0)) > 0 {
+		node.Fined = new(big.Int).Add(node.Fined, amount)
+		s.UpdateNode(offset, node)
+	}
+
+	return nil
+}
+
 const decimalMultiplier = 100000000.0
 
 // Configuration returns the current configuration.
@@ -2248,6 +2285,16 @@ func (g *GovernanceContract) Run(evm *EVM, input []byte, contract *Contract) (re
 			return nil, errExecutionReverted
 		}
 		return res, nil
+	case "lastProposedHeight":
+		address := common.Address{}
+		if err := method.Inputs.Unpack(&address, arguments); err != nil {
+			return nil, errExecutionReverted
+		}
+		res, err := method.Outputs.Pack(g.state.LastProposedHeight(address))
+		if err != nil {
+			return nil, errExecutionReverted
+		}
+		return res, nil
 	case "lockupPeriod":
 		res, err := method.Outputs.Pack(g.state.LockupPeriod())
 		if err != nil {