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.

2 files changed, 46 insertions, 6 deletions

diff --git a/consensus/dexcon/dexcon.go b/consensus/dexcon/dexcon.go
index c837e3a43..3e520438b 100644
--- a/consensus/dexcon/dexcon.go
+++ b/consensus/dexcon/dexcon.go
@@ -17,6 +17,8 @@
 package dexcon
 
 import (
+	"encoding/hex"
+	"fmt"
 	"math/big"
 
 	"github.com/dexon-foundation/dexon/common"
@@ -24,11 +26,13 @@ import (
 	"github.com/dexon-foundation/dexon/core/state"
 	"github.com/dexon-foundation/dexon/core/types"
 	"github.com/dexon-foundation/dexon/core/vm"
+	"github.com/dexon-foundation/dexon/log"
 	"github.com/dexon-foundation/dexon/rpc"
 )
 
 type GovernanceStateFetcher interface {
 	GetStateForConfigAtRound(round uint64) *vm.GovernanceState
+	NotarySetNodeKeyAddresses(round uint64) (map[common.Address]struct{}, error)
 }
 
 // Dexcon is a delegated proof-of-stake consensus engine.
@@ -137,8 +141,39 @@ func (d *Dexcon) Finalize(chain consensus.ChainReader, header *types.Header, sta
 	gs := vm.GovernanceState{state}
 
 	height := gs.RoundHeight(new(big.Int).SetUint64(header.Round))
+
+	// The first block of a round is found.
 	if header.Round > 0 && height.Uint64() == 0 {
 		gs.PushRoundHeight(header.Number)
+
+		// Check for dead node and disqualify them.
+		// A dead node node is defined as: a notary set node that did not propose
+		// any block in the past round.
+		addrs, err := d.govStateFetcer.NotarySetNodeKeyAddresses(header.Round - 1)
+		if err != nil {
+			panic(err)
+		}
+
+		gcs := d.govStateFetcer.GetStateForConfigAtRound(header.Round - 1)
+
+		for addr := range addrs {
+			offset := gcs.NodesOffsetByNodeKeyAddress(addr)
+			if offset.Cmp(big.NewInt(0)) < 0 {
+				panic(fmt.Errorf("invalid notary set found, addr = %s", addr.String()))
+			}
+
+			node := gcs.Node(offset)
+			lastHeight := gs.LastProposedHeight(node.Owner)
+			prevRoundHeight := gs.RoundHeight(big.NewInt(int64(header.Round - 1)))
+
+			if lastHeight.Uint64() < prevRoundHeight.Uint64() {
+				log.Info("Disqualify node", "round", header.Round, "nodePubKey", hex.EncodeToString(node.PublicKey))
+				err = gs.Disqualify(node)
+				if err != nil {
+					log.Error("Failed to disqualify node", "err", err)
+				}
+			}
+		}
 	}
 
 	// Distribute block reward and halving condition.
@@ -147,16 +182,17 @@ func (d *Dexcon) Finalize(chain consensus.ChainReader, header *types.Header, sta
 	} else {
 		reward := d.calculateBlockReward(int64(header.Round), state)
 		state.AddBalance(header.Coinbase, reward)
-
+		header.Reward = reward
 		gs.IncTotalSupply(reward)
 
-		config := gs.Configuration()
+		// Record last proposed height.
+		gs.PutLastProposedHeight(header.Coinbase, header.Number)
 
 		// Check if halving checkpoint reached.
+		config := gs.Configuration()
 		if gs.TotalSupply().Cmp(config.NextHalvingSupply) >= 0 {
 			gs.MiningHalved()
 		}
-		header.Reward = reward
 	}
 
 	header.Root = state.IntermediateRoot(true)
diff --git a/consensus/dexcon/dexcon_test.go b/consensus/dexcon/dexcon_test.go
index f34823570..0181a80f3 100644
--- a/consensus/dexcon/dexcon_test.go
+++ b/consensus/dexcon/dexcon_test.go
@@ -31,14 +31,18 @@ import (
 	"github.com/dexon-foundation/dexon/params"
 )
 
-type GovStateFetcher struct {
+type govStateFetcher struct {
 	statedb *state.StateDB
 }
 
-func (g *GovStateFetcher) GetStateForConfigAtRound(_ uint64) *vm.GovernanceState {
+func (g *govStateFetcher) GetStateForConfigAtRound(_ uint64) *vm.GovernanceState {
 	return &vm.GovernanceState{g.statedb}
 }
 
+func (g *govStateFetcher) NotarySetNodeKeyAddresses(round uint64) (map[common.Address]struct{}, error) {
+	return make(map[common.Address]struct{}), nil
+}
+
 type DexconTestSuite struct {
 	suite.Suite
 
@@ -86,7 +90,7 @@ func (d *DexconTestSuite) SetupTest() {
 
 func (d *DexconTestSuite) TestBlockRewardCalculation() {
 	consensus := New()
-	consensus.SetGovStateFetcher(&GovStateFetcher{d.stateDB})
+	consensus.SetGovStateFetcher(&govStateFetcher{d.stateDB})
 
 	d.s.IncTotalStaked(big.NewInt(1e18))