[IBFT] Change quorum size calculation (#513)

* recalculate quorum size for IBFT - ceil(2/3 * N), N - number of validators

consensus/ibft/ibft.go

@@ -916,12 +916,12 @@ func (i *Ibft) runValidateState() {
 			panic(fmt.Sprintf("BUG: %s", reflect.TypeOf(msg.Type)))
 		}
 
-		if i.state.numPrepared() > i.state.NumValid() {
+		if i.state.numPrepared() >= i.state.validators.QuorumSize() {
 			// we have received enough pre-prepare messages
 			sendCommit()
 		}
 
-		if i.state.numCommitted() > i.state.NumValid() {
+		if i.state.numCommitted() >= i.state.validators.QuorumSize() {
 			// we have received enough commit messages
 			sendCommit()
 
@@ -1102,17 +1102,15 @@ func (i *Ibft) runRoundChangeState() {
 		// we only expect RoundChange messages right now
 		num := i.state.AddRoundMessage(msg)
 
-		if num == i.state.NumValid() {
+		if num == i.state.validators.MaxFaultyNodes()+1 && i.state.view.Round < msg.View.Round {
+			// weak certificate, try to catch up if our round number is smaller
+			// update timer
+			timeout = exponentialTimeout(i.state.view.Round)
+			sendRoundChange(msg.View.Round)
+		} else if num == i.state.validators.QuorumSize() {
 			// start a new round immediately
 			i.state.view.Round = msg.View.Round
 			i.setState(AcceptState)
-		} else if num == i.state.validators.MaxFaultyNodes()+1 {
-			// weak certificate, try to catch up if our round number is smaller
-			if i.state.view.Round < msg.View.Round {
-				// update timer
-				timeout = exponentialTimeout(i.state.view.Round)
-				sendRoundChange(msg.View.Round)
-			}
 		}
 	}
 }

consensus/ibft/ibft_test.go

@@ -342,7 +342,7 @@ func TestTransition_RoundChangeState_CatchupRound(t *testing.T) {
 	m.expect(expectResult{
 		sequence: 1,
 		round:    2,
-		outgoing: 1, // our new round change
+		outgoing: 2, // our new round change
 		state:    AcceptState,
 	})
 }

consensus/ibft/sign.go

@@ -207,7 +207,7 @@ func verifyCommitedFields(snap *Snapshot, header *types.Header) error {
 	// Valid committed seals must be at least 2F+1
 	// 	2F 	is the required number of honest validators who provided the committed seals
 	// 	+1	is the proposer
-	if validSeals := len(visited); validSeals <= 2*snap.Set.MaxFaultyNodes() {
+	if validSeals := len(visited); validSeals < snap.Set.QuorumSize() {
 		return fmt.Errorf("not enough seals to seal block")
 	}
 

consensus/ibft/sign_test.go

@@ -63,7 +63,7 @@ func TestSign_CommittedSeals(t *testing.T) {
 	}
 
 	// Correct
-	assert.NoError(t, buildCommittedSeal([]string{"A", "B", "C"}))
+	assert.NoError(t, buildCommittedSeal([]string{"A", "B", "C", "D"}))
 
 	// Failed - Repeated signature
 	assert.Error(t, buildCommittedSeal([]string{"A", "A"}))

consensus/ibft/state.go

@@ -2,6 +2,7 @@ package ibft
 
 import (
 	"fmt"
+	"math"
 	"sync/atomic"
 
 	"github.com/0xPolygon/polygon-edge/consensus/ibft/proto"
@@ -96,15 +97,6 @@ func (c *currentState) setState(s IbftState) {
 	atomic.StoreUint64(stateAddr, uint64(s))
 }
 
-// NumValid returns the number of required messages
-func (c *currentState) NumValid() int {
-	// According to the IBFT spec, the number of valid messages
-	// needs to be 2F + 1
-	// The 1 missing from this equation is accounted for elsewhere
-	// (the current node tallying the messages will include its own message)
-	return 2 * c.validators.MaxFaultyNodes()
-}
-
 // getErr returns the current error, if any, and consumes it
 func (c *currentState) getErr() error {
 	err := c.err
@@ -153,7 +145,12 @@ func (c *currentState) unlock() {
 
 // cleanRound deletes the specific round messages
 func (c *currentState) cleanRound(round uint64) {
-	delete(c.roundMessages, round)
+	//	clear messages from previous round
+	for r := range c.roundMessages {
+		if r < round {
+			delete(c.roundMessages, r)
+		}
+	}
 }
 
 // AddRoundMessage adds a message to the round, and returns the round message size
@@ -306,3 +303,20 @@ func (v *ValidatorSet) MaxFaultyNodes() int {
 	// It should always take the floor of the result
 	return (len(*v) - 1) / 3
 }
+
+// QuorumSize returns the number of required messages for consensus
+func (v ValidatorSet) QuorumSize() int {
+	//	if the number of validators is less than 4,
+	//	then the entire set is required
+	if v.MaxFaultyNodes() == 0 {
+		/*
+			N: 1 -> Q: 1
+			N: 2 -> Q: 2
+			N: 3 -> Q: 3
+		*/
+		return v.Len()
+	}
+
+	// (quorum optimal)	Q = ceil(2/3 * N)
+	return int(math.Ceil(2 * float64(v.Len()) / 3))
+}

consensus/ibft/state_test.go

@@ -1,6 +1,7 @@
 package ibft
 
 import (
+	"strconv"
 	"testing"
 
 	"github.com/0xPolygon/polygon-edge/consensus/ibft/proto"
@@ -28,6 +29,44 @@ func TestState_FaultyNodes(t *testing.T) {
 	}
 }
 
+//	TestNumValid checks if the quorum size is calculated
+//	correctly based on number of validators (network size).
+func TestNumValid(t *testing.T) {
+	cases := []struct {
+		Network, Quorum uint64
+	}{
+		{1, 1},
+		{2, 2},
+		{3, 3},
+		{4, 3},
+		{5, 4},
+		{6, 4},
+		{7, 5},
+		{8, 6},
+		{9, 6},
+	}
+
+	addAccounts := func(
+		pool *testerAccountPool,
+		numAccounts int,
+	) {
+		// add accounts
+		for i := 0; i < numAccounts; i++ {
+			pool.add(strconv.Itoa(i))
+		}
+	}
+
+	for _, c := range cases {
+		pool := newTesterAccountPool(int(c.Network))
+		addAccounts(pool, int(c.Network))
+
+		assert.Equal(t,
+			int(c.Quorum),
+			pool.ValidatorSet().QuorumSize(),
+		)
+	}
+}
+
 func TestState_AddMessages(t *testing.T) {
 	pool := newTesterAccountPool()
 	pool.add("A", "B", "C", "D")