Initial implementation of DEXON consensus algorithm

9 files changed, 1396 insertions, 0 deletions

diff --git a/core/application.go b/core/application.go
new file mode 100644
index 0000000..7eca66e
--- /dev/null
+++ b/core/application.go
@@ -0,0 +1,27 @@
+// Copyright 2018 The dexon-consensus-core Authors
+// This file is part of the dexon-consensus-core library.
+//
+// The dexon-consensus-core library is free software: you can redistribute it
+// and/or modify it under the terms of the GNU Lesser General Public License as
+// published by the Free Software Foundation, either version 3 of the License,
+// or (at your option) any later version.
+//
+// The dexon-consensus-core library is distributed in the hope that it will be
+// useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser
+// General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the dexon-consensus-core library. If not, see
+// <http://www.gnu.org/licenses/>.
+
+package core
+
+import "github.com/dexon-foundation/dexon-consensus-core/core/types"
+
+// Application describes the application interface that interacts with DEXON
+// consensus core.
+type Application interface {
+	ValidateBlock(b *types.Block) bool
+	Deliver(blocks []*types.Block, early bool)
+}
diff --git a/core/blockchain.go b/core/blockchain.go
new file mode 100644
index 0000000..6da74af
--- /dev/null
+++ b/core/blockchain.go
@@ -0,0 +1,26 @@
+// Copyright 2018 The dexon-consensus-core Authors
+// This file is part of the dexon-consensus-core library.
+//
+// The dexon-consensus-core library is free software: you can redistribute it
+// and/or modify it under the terms of the GNU Lesser General Public License as
+// published by the Free Software Foundation, either version 3 of the License,
+// or (at your option) any later version.
+//
+// The dexon-consensus-core library is distributed in the hope that it will be
+// useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser
+// General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the dexon-consensus-core library. If not, see
+// <http://www.gnu.org/licenses/>.
+
+package core
+
+import "github.com/dexon-foundation/dexon-consensus-core/core/types"
+
+// BlockChain is the basic datastucture used for storing blocks in each
+// validator.
+type BlockChain struct {
+	validatorID types.ValidatorID
+}
diff --git a/core/blocklattice.go b/core/blocklattice.go
new file mode 100644
index 0000000..2f95733
--- /dev/null
+++ b/core/blocklattice.go
@@ -0,0 +1,596 @@
+// Copyright 2018 The dexon-consensus-core Authors
+// This file is part of the dexon-consensus-core library.
+//
+// The dexon-consensus-core library is free software: you can redistribute it
+// and/or modify it under the terms of the GNU Lesser General Public License as
+// published by the Free Software Foundation, either version 3 of the License,
+// or (at your option) any later version.
+//
+// The dexon-consensus-core library is distributed in the hope that it will be
+// useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser
+// General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the dexon-consensus-core library. If not, see
+// <http://www.gnu.org/licenses/>.
+
+package core
+
+import (
+	"fmt"
+	"math"
+	"sort"
+	"sync"
+	"time"
+
+	"github.com/dexon-foundation/dexon-consensus-core/blockdb"
+	"github.com/dexon-foundation/dexon-consensus-core/common"
+	"github.com/dexon-foundation/dexon-consensus-core/core/types"
+)
+
+const (
+	epsilon = 1 * time.Microsecond
+	tdelay  = 500 * time.Millisecond
+)
+
+const (
+	infinity uint64 = math.MaxUint64
+)
+
+// BlockLattice represent the local view of a single validator.
+//
+// blockDB stores blocks that are final. blocks stores blocks that are in ToTo
+// State.
+type BlockLattice struct {
+	owner        types.ValidatorID
+	validatorSet map[types.ValidatorID]struct{}
+	blocks       map[common.Hash]*types.Block
+
+	fmax               int
+	phi                int
+	lastSeenTimestamps map[types.ValidatorID]time.Time
+
+	blockDB blockdb.BlockDatabase
+	network Network
+	app     Application
+	mutex   sync.Mutex
+
+	// Reliable Broadcast.
+	waitingSet       map[common.Hash]*types.Block
+	stronglyAckedSet map[common.Hash]*types.Block
+	ackCandidateSet  map[types.ValidatorID]*types.Block
+	restricted       map[types.ValidatorID]struct{}
+
+	// Total Ordering.
+	pendingSet   map[common.Hash]*types.Block
+	candidateSet map[common.Hash]*types.Block
+	ABS          map[common.Hash]map[types.ValidatorID]uint64
+	AHV          map[common.Hash]map[types.ValidatorID]uint64
+}
+
+// NewBlockLattice returns a new empty BlockLattice instance.
+func NewBlockLattice(
+	db blockdb.BlockDatabase,
+	network Network,
+	app Application) *BlockLattice {
+	return &BlockLattice{
+		validatorSet:       make(map[types.ValidatorID]struct{}),
+		blocks:             make(map[common.Hash]*types.Block),
+		lastSeenTimestamps: make(map[types.ValidatorID]time.Time),
+		blockDB:            db,
+		network:            network,
+		app:                app,
+		waitingSet:         make(map[common.Hash]*types.Block),
+		stronglyAckedSet:   make(map[common.Hash]*types.Block),
+		ackCandidateSet:    make(map[types.ValidatorID]*types.Block),
+		restricted:         make(map[types.ValidatorID]struct{}),
+		pendingSet:         make(map[common.Hash]*types.Block),
+		candidateSet:       make(map[common.Hash]*types.Block),
+		ABS:                make(map[common.Hash]map[types.ValidatorID]uint64),
+		AHV:                make(map[common.Hash]map[types.ValidatorID]uint64),
+	}
+}
+
+// AddValidator adds a validator into the lattice.
+func (l *BlockLattice) AddValidator(
+	id types.ValidatorID, genesis *types.Block) {
+
+	l.validatorSet[id] = struct{}{}
+	l.fmax = len(l.validatorSet) / 3
+	l.phi = 2*l.fmax + 1
+
+	genesis.State = types.BlockStatusFinal
+	l.blockDB.Put(*genesis)
+}
+
+// SetOwner sets the blocklattice's owner, which is the localview of whom.
+func (l *BlockLattice) SetOwner(id types.ValidatorID) {
+	if _, exists := l.validatorSet[id]; !exists {
+		panic("SetOnwer: owner is not a valid validator")
+	}
+	l.owner = id
+}
+
+// getBlock returns a block no matter where it is located at (either local
+// blocks cache or blockDB).
+func (l *BlockLattice) getBlock(hash common.Hash) *types.Block {
+	if b, exists := l.blocks[hash]; exists {
+		return b
+	}
+	if b, err := l.blockDB.Get(hash); err == nil {
+		return &b
+	}
+	return nil
+}
+
+// processAcks updates the ack count of the blocks that is acked by *b*.
+func (l *BlockLattice) processAcks(b *types.Block) {
+	if b.IndirectAcks == nil {
+		b.IndirectAcks = make(map[common.Hash]struct{})
+	}
+
+	for ackBlockHash := range b.Acks {
+		ackedBlock, ok := l.blocks[ackBlockHash]
+		if !ok {
+			// Acks a finalized block, don't need to increase it's count.
+			if l.blockDB.Has(ackBlockHash) {
+				continue
+			}
+			panic(fmt.Sprintf("failed to get block: %v", ackBlockHash))
+		}
+
+		// Populate IndirectAcks.
+		for a := range ackedBlock.Acks {
+			if _, exists := b.Acks[a]; !exists {
+				b.IndirectAcks[a] = struct{}{}
+			}
+		}
+		for a := range ackedBlock.IndirectAcks {
+			if _, exists := b.Acks[a]; !exists {
+				b.IndirectAcks[a] = struct{}{}
+			}
+		}
+
+		// Populate AckedBy.
+		if ackedBlock.AckedBy == nil {
+			ackedBlock.AckedBy = make(map[common.Hash]bool)
+		}
+		ackedBlock.AckedBy[b.Hash] = true
+
+		bp := ackedBlock
+		for bp != nil && bp.State < types.BlockStatusAcked {
+			if bp.AckedBy == nil {
+				bp.AckedBy = make(map[common.Hash]bool)
+			}
+			if _, exists := bp.AckedBy[b.Hash]; !exists {
+				bp.AckedBy[b.Hash] = false
+			}
+
+			// Calculate acked by nodes.
+			ackedByNodes := make(map[types.ValidatorID]struct{})
+			for hash := range bp.AckedBy {
+				bp := l.getBlock(hash)
+				ackedByNodes[bp.ProposerID] = struct{}{}
+			}
+
+			if len(ackedByNodes) > 2*l.fmax {
+				bp.State = types.BlockStatusAcked
+				l.stronglyAckedSet[bp.Hash] = bp
+			}
+			bp = l.getBlock(bp.ParentHash)
+		}
+	}
+}
+
+// updateTimestamps updates the last seen timestamp of the lattice local view.
+func (l *BlockLattice) updateTimestamps(b *types.Block) {
+	q := b.ProposerID
+	l.lastSeenTimestamps[q] = b.Timestamps[q].Add(epsilon)
+	for vid := range l.validatorSet {
+		if b.Timestamps[vid].After(l.lastSeenTimestamps[vid]) {
+			l.lastSeenTimestamps[vid] = b.Timestamps[vid]
+		}
+	}
+}
+
+func (l *BlockLattice) recievedAndNotInWaitingSet(hash common.Hash) bool {
+	if _, exists := l.blocks[hash]; !exists {
+		if !l.blockDB.Has(hash) {
+			return false
+		}
+	}
+	return true
+}
+
+func (l *BlockLattice) isValidAckCandidate(b *types.Block) bool {
+	// Block proposer is not restricted.
+	if _, isRestricted := l.restricted[b.ProposerID]; isRestricted {
+		return false
+	}
+
+	hasHistoryBeenRecieved := func(hash common.Hash) bool {
+		bx := l.getBlock(hash)
+		if bx == nil {
+			return false
+		}
+
+		for {
+			bx = l.getBlock(bx.ParentHash)
+			if bx == nil {
+				return false
+			}
+			if bx.State == types.BlockStatusFinal {
+				return true
+			}
+		}
+	}
+
+	// Previous block is recieved.
+	if !hasHistoryBeenRecieved(b.ParentHash) {
+		return false
+	}
+
+	// All acked blocks are recieved.
+	for ackedBlockHash := range b.Acks {
+		if !hasHistoryBeenRecieved(ackedBlockHash) {
+			return false
+		}
+	}
+
+	return true
+}
+
+// ProcessBlock implements the recieving part of DEXON reliable broadcast.
+func (l *BlockLattice) ProcessBlock(b *types.Block, runTotal ...bool) {
+	l.mutex.Lock()
+	defer l.mutex.Unlock()
+
+	if l.getBlock(b.Hash) != nil {
+		return
+	}
+
+	// TODO(w): drop if it does not pass sanity check.
+
+	// Store into local blocks cache.
+	l.blocks[b.Hash] = b
+
+	if l.isValidAckCandidate(b) {
+		l.ackCandidateSet[b.ProposerID] = b
+		l.processAcks(b)
+	} else {
+		l.waitingSet[b.Hash] = b
+	}
+
+	// Scan the rest of waiting set for valid candidate.
+	for bpHash, bp := range l.waitingSet {
+		if l.isValidAckCandidate(bp) {
+			l.ackCandidateSet[bp.ProposerID] = bp
+			l.processAcks(bp)
+			delete(l.waitingSet, bpHash)
+		}
+	}
+
+IterateStronglyAckedSet:
+	for bpHash, bp := range l.stronglyAckedSet {
+		for ackBlockHash := range bp.Acks {
+			bx := l.getBlock(ackBlockHash)
+			if bx == nil || bx.State < types.BlockStatusAcked {
+				break IterateStronglyAckedSet
+			}
+		}
+		bp.State = types.BlockStatusToTo
+		l.pendingSet[bp.Hash] = bp
+		delete(l.stronglyAckedSet, bpHash)
+
+		if len(runTotal) > 0 && runTotal[0] {
+			l.totalOrdering(bp)
+		}
+	}
+}
+
+// ProposeBlock implements the send part of DEXON reliable broadcast.
+func (l *BlockLattice) ProposeBlock(b *types.Block) {
+	l.mutex.Lock()
+	defer l.mutex.Unlock()
+
+	b.Acks = make(map[common.Hash]struct{})
+	for _, bp := range l.ackCandidateSet {
+		b.Acks[bp.Hash] = struct{}{}
+		l.updateTimestamps(b)
+	}
+	l.lastSeenTimestamps[l.owner] = time.Now().UTC()
+
+	b.Timestamps = make(map[types.ValidatorID]time.Time)
+	for vID, ts := range l.lastSeenTimestamps {
+		b.Timestamps[vID] = ts
+	}
+
+	//l.ProcessBlock(b)
+	l.network.BroadcastBlock(b)
+
+	l.ackCandidateSet = make(map[types.ValidatorID]*types.Block)
+}
+
+// DetectNack implements the NACK detection.
+func (l *BlockLattice) DetectNack() {
+
+}
+
+func (l *BlockLattice) setAHV(
+	block common.Hash, vID types.ValidatorID, v uint64) {
+
+	if l.AHV[block] == nil {
+		l.AHV[block] = make(map[types.ValidatorID]uint64)
+	}
+	l.AHV[block][vID] = v
+}
+
+func (l *BlockLattice) pushABS(block *types.Block, vID types.ValidatorID) {
+	if l.ABS[block.Hash] == nil {
+		l.ABS[block.Hash] = make(map[types.ValidatorID]uint64)
+	}
+	v, exists := l.ABS[block.Hash][vID]
+	if !exists || block.Height < v {
+		l.ABS[block.Hash][vID] = block.Height
+	}
+}
+
+func (l *BlockLattice) abs() map[types.ValidatorID]struct{} {
+	abs := make(map[types.ValidatorID]struct{})
+	for blockHash := range l.candidateSet {
+		for x := range l.ABS[blockHash] {
+			abs[x] = struct{}{}
+		}
+	}
+	return abs
+}
+
+func (l *BlockLattice) calculateABSofBlock(b *types.Block) {
+	// Calculate ABS of a block.
+	l.ABS[b.Hash] = make(map[types.ValidatorID]uint64)
+
+	var calculateABSRecursive func(target *types.Block)
+
+	calculateABSRecursive = func(target *types.Block) {
+		for hash := range target.AckedBy {
+			ackedByBlock := l.getBlock(hash)
+			if ackedByBlock.State != types.BlockStatusToTo {
+				continue
+			}
+			v, exists := l.ABS[b.Hash][ackedByBlock.ProposerID]
+			if !exists || ackedByBlock.Height < v {
+				l.ABS[b.Hash][ackedByBlock.ProposerID] = ackedByBlock.Height
+			}
+			calculateABSRecursive(ackedByBlock)
+		}
+	}
+
+	// ABS always include the block's proposer
+	l.ABS[b.Hash][b.ProposerID] = b.Height
+
+	calculateABSRecursive(b)
+}
+
+func (l *BlockLattice) calculateAHVofBlock(
+	b *types.Block, globalMins map[types.ValidatorID]uint64) {
+
+	// Calculate ABS of a block.
+	l.AHV[b.Hash] = make(map[types.ValidatorID]uint64)
+
+	for v := range l.validatorSet {
+		gv, gExists := globalMins[v]
+		lv, lExists := l.ABS[b.Hash][v]
+
+		if !gExists {
+			// Do nothing.
+		} else if !lExists || lv > gv {
+			l.AHV[b.Hash][v] = infinity
+		} else {
+			l.AHV[b.Hash][v] = gv
+		}
+	}
+}
+
+func (l *BlockLattice) updateABSAHV() {
+	globalMins := make(map[types.ValidatorID]uint64)
+
+	for _, block := range l.pendingSet {
+		v, exists := globalMins[block.ProposerID]
+		if !exists || block.Height < v {
+			globalMins[block.ProposerID] = block.Height
+		}
+	}
+
+	for _, block := range l.candidateSet {
+		l.calculateABSofBlock(block)
+		l.calculateAHVofBlock(block, globalMins)
+	}
+}
+
+// totalOrdering implements the DEXON total ordering algorithm.
+func (l *BlockLattice) totalOrdering(b *types.Block) {
+	acksOnlyFinal := true
+	for ackedBlockHash := range b.Acks {
+		bp := l.getBlock(ackedBlockHash)
+		if bp.State != types.BlockStatusFinal {
+			acksOnlyFinal = false
+			break
+		}
+	}
+
+	abs := l.abs()
+	if acksOnlyFinal {
+		l.candidateSet[b.Hash] = b
+		/*
+			for r := range abs {
+				l.setAHV(b.Hash, r, infinity)
+			}
+		*/
+	}
+
+	/*
+		q := b.ProposerID
+		if _, exists := abs[q]; !exists {
+			for _, bp := range l.candidateSet {
+				if bp.Hash.Equal(b.Hash) {
+					continue
+				}
+
+				_, directlyAckedBy := b.Acks[bp.Hash]
+				_, indirectlyAckedBy := b.IndirectAcks[bp.Hash]
+
+				if directlyAckedBy || indirectlyAckedBy {
+					l.setAHV(bp.Hash, q, b.Height)
+					l.pushABS(bp, q)
+				} else {
+					l.setAHV(bp.Hash, q, infinity)
+				}
+			}
+		}
+	*/
+
+	// Update ABS and AHV.
+	l.updateABSAHV()
+	abs = l.abs()
+
+	// Calculate preceding set.
+	precedingSet := make(map[common.Hash]*types.Block)
+
+	// Grade(b', b) = 0 for all b' in candidate set.
+	for targetHash, targetBlock := range l.candidateSet {
+		winAll := true
+		for otherHash := range l.candidateSet {
+			if targetHash.Equal(otherHash) {
+				continue
+			}
+
+			lose := 0
+			for vID, targetAHV := range l.AHV[targetHash] {
+				if otherAHV, exists := l.AHV[otherHash][vID]; exists {
+					if otherAHV < targetAHV {
+						lose++
+					}
+				} else if otherAHV != infinity {
+					lose++
+				}
+			}
+
+			if lose >= l.phi {
+				winAll = false
+				break
+			} else if lose < l.phi-len(l.validatorSet)+len(abs) {
+				// Do nothing.
+			} else {
+				winAll = false
+				break
+			}
+		}
+
+		if winAll {
+			precedingSet[targetHash] = targetBlock
+		}
+	}
+
+	// Internal stability.
+	winned := false
+	for hash := range l.candidateSet {
+		if _, exists := precedingSet[hash]; exists {
+			continue
+		}
+
+		// Grade(b, b') = 1
+		for precedingHash := range precedingSet {
+			win := 0
+			for vID, precedingAHV := range l.AHV[precedingHash] {
+				if candidateAHV, exists := l.AHV[hash][vID]; exists {
+					if precedingAHV < candidateAHV {
+						win++
+					}
+				} else if precedingAHV != infinity {
+					win++
+				}
+			}
+			if win > l.phi {
+				winned = true
+				break
+			}
+		}
+		if !winned {
+			return
+		}
+	}
+
+	earlyDelivery := false
+
+	// Does not satisfy External stability a.
+	if len(abs) < len(l.validatorSet) {
+		earlyDelivery = true
+
+		// External stability b.
+		extBSatisfied := false
+		for precedingHash := range precedingSet {
+			count := 0
+			for _, ahv := range l.AHV[precedingHash] {
+				if ahv != infinity {
+					count++
+				}
+			}
+			if count > l.phi {
+				extBSatisfied = true
+				break
+			}
+		}
+		if !extBSatisfied {
+			return
+		}
+		for precedingHash := range precedingSet {
+			if len(l.ABS[precedingHash]) < len(l.validatorSet)-l.phi {
+				extBSatisfied = false
+			}
+		}
+		if !extBSatisfied {
+			return
+		}
+	}
+
+	var output []*types.Block
+	for hash, x := range precedingSet {
+		output = append(output, x)
+		x.State = types.BlockStatusFinal
+
+		// Remove from pending set and candidate set.
+		delete(l.pendingSet, hash)
+		delete(l.candidateSet, hash)
+
+		// Delete ABS and AHV
+		delete(l.ABS, hash)
+		delete(l.AHV, hash)
+
+		// Store output blocks into blockDB.
+		l.blockDB.Put(*x)
+		delete(l.blocks, hash)
+	}
+	sort.Sort(types.ByHash(output))
+
+	if len(output) > 0 {
+		l.app.Deliver(output, earlyDelivery)
+	}
+
+	// Rescan pending blocks to add into candidate set.
+	for hash, block := range l.pendingSet {
+		if _, exists := l.candidateSet[hash]; exists {
+			continue
+		}
+		acksOnlyFinal := true
+		for ackedBlockHash := range block.Acks {
+			if !l.blockDB.Has(ackedBlockHash) {
+				acksOnlyFinal = false
+				break
+			}
+		}
+		if acksOnlyFinal {
+			l.candidateSet[hash] = block
+		}
+	}
+}
diff --git a/core/blocklattice_test.go b/core/blocklattice_test.go
new file mode 100644
index 0000000..e462b8a
--- /dev/null
+++ b/core/blocklattice_test.go
@@ -0,0 +1,521 @@
+// Copyright 2018 The dexon-consensus-core Authors
+// This file is part of the dexon-consensus-core library.
+//
+// The dexon-consensus-core library is free software: you can redistribute it
+// and/or modify it under the terms of the GNU Lesser General Public License as
+// published by the Free Software Foundation, either version 3 of the License,
+// or (at your option) any later version.
+//
+// The dexon-consensus-core library is distributed in the hope that it will be
+// useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser
+// General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the dexon-consensus-core library. If not, see
+// <http://www.gnu.org/licenses/>.
+
+package core
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/suite"
+
+	"github.com/dexon-foundation/dexon-consensus-core/blockdb"
+	"github.com/dexon-foundation/dexon-consensus-core/common"
+	"github.com/dexon-foundation/dexon-consensus-core/core/types"
+)
+
+var lattice *BlockLattice
+var validators []types.ValidatorID
+var genesises []*types.Block
+
+var b01, b11, b21, b31,
+	b02, b12, b22, b32,
+	b03, b13, b23, b33 *types.Block
+
+// TestNetwork.
+type TestNetwork struct {
+}
+
+func (n *TestNetwork) Join(endpoint Endpoint) chan interface{} {
+	return nil
+}
+
+func (n *TestNetwork) BroadcastBlock(block *types.Block) {
+}
+
+// TestApp.
+type TestApp struct {
+	Outputs []*types.Block
+	Early   bool
+}
+
+func (a *TestApp) ValidateBlock(b *types.Block) bool {
+	return true
+}
+
+func (a *TestApp) Deliver(blocks []*types.Block, early bool) {
+	a.Outputs = blocks
+	a.Early = early
+}
+
+func (a *TestApp) Clear() {
+	a.Outputs = nil
+	a.Early = false
+}
+
+type BlockLatticeTest struct {
+	suite.Suite
+
+	app *TestApp
+}
+
+func (s *BlockLatticeTest) SetupTest() {
+	Debugf("--------------------------------------------" +
+		"-------------------------\n")
+
+	s.app = &TestApp{}
+
+	lattice = NewBlockLattice(
+		blockdb.NewMemBackedBlockDB(),
+		&TestNetwork{},
+		s.app)
+
+	for i := 0; i < 4; i++ {
+		validators = append(validators, types.ValidatorID(common.NewRandomHash()))
+		Debugf("V%d: %s\n", i, validators[i])
+	}
+	Debugf("\n")
+	for i := 0; i < 4; i++ {
+		hash := common.NewRandomHash()
+		genesises = append(genesises, &types.Block{
+			ProposerID: validators[i],
+			ParentHash: hash,
+			Hash:       hash,
+			Height:     0,
+			Acks:       map[common.Hash]struct{}{},
+		})
+
+		Debugf("G%d: %s\n", i, hash)
+		lattice.AddValidator(validators[i], genesises[i])
+	}
+
+	// Make lattice validator[0]'s local view.
+	lattice.SetOwner(validators[0])
+
+	b01 = &types.Block{
+		ProposerID: validators[0],
+		ParentHash: genesises[0].Hash,
+		Hash:       common.NewRandomHash(),
+		Height:     1,
+		Acks: map[common.Hash]struct{}{
+			genesises[1].Hash: struct{}{},
+			genesises[2].Hash: struct{}{},
+			genesises[3].Hash: struct{}{},
+		},
+	}
+	b11 = &types.Block{
+		ProposerID: validators[1],
+		ParentHash: genesises[1].Hash,
+		Hash:       common.NewRandomHash(),
+		Height:     1,
+		Acks: map[common.Hash]struct{}{
+			b01.Hash:          struct{}{},
+			genesises[2].Hash: struct{}{},
+			genesises[3].Hash: struct{}{},
+		},
+	}
+	b21 = &types.Block{
+		ProposerID: validators[2],
+		ParentHash: genesises[2].Hash,
+		Hash:       common.NewRandomHash(),
+		Height:     1,
+		Acks: map[common.Hash]struct{}{
+			b01.Hash:          struct{}{},
+			genesises[1].Hash: struct{}{},
+			genesises[3].Hash: struct{}{},
+		},
+	}
+	b31 = &types.Block{
+		ProposerID: validators[3],
+		ParentHash: genesises[3].Hash,
+		Hash:       common.NewRandomHash(),
+		Height:     1,
+		Acks: map[common.Hash]struct{}{
+			b01.Hash:          struct{}{},
+			b11.Hash:          struct{}{},
+			genesises[2].Hash: struct{}{},
+		},
+	}
+
+	b02 = &types.Block{
+		ProposerID: validators[0],
+		ParentHash: b01.Hash,
+		Hash:       common.NewRandomHash(),
+		Height:     2,
+		Acks: map[common.Hash]struct{}{
+			b11.Hash: struct{}{},
+			b21.Hash: struct{}{},
+			b31.Hash: struct{}{},
+		},
+	}
+	b12 = &types.Block{
+		ProposerID: validators[1],
+		ParentHash: b11.Hash,
+		Hash:       common.NewRandomHash(),
+		Height:     2,
+		Acks: map[common.Hash]struct{}{
+			b21.Hash: struct{}{},
+			b31.Hash: struct{}{},
+		},
+	}
+	b22 = &types.Block{
+		ProposerID: validators[2],
+		ParentHash: b21.Hash,
+		Hash:       common.NewRandomHash(),
+		Height:     2,
+		Acks: map[common.Hash]struct{}{
+			b02.Hash: struct{}{},
+			b12.Hash: struct{}{},
+			b31.Hash: struct{}{},
+		},
+	}
+	b32 = &types.Block{
+		ProposerID: validators[3],
+		ParentHash: b31.Hash,
+		Hash:       common.NewRandomHash(),
+		Height:     2,
+		Acks: map[common.Hash]struct{}{
+			b02.Hash: struct{}{},
+			b12.Hash: struct{}{},
+			b21.Hash: struct{}{},
+		},
+	}
+
+	b03 = &types.Block{
+		ProposerID: validators[0],
+		ParentHash: b02.Hash,
+		Hash:       common.NewRandomHash(),
+		Height:     3,
+		Acks: map[common.Hash]struct{}{
+			b12.Hash: struct{}{},
+			b22.Hash: struct{}{},
+			b32.Hash: struct{}{},
+		},
+	}
+	b13 = &types.Block{
+		ProposerID: validators[1],
+		ParentHash: b12.Hash,
+		Hash:       common.NewRandomHash(),
+		Height:     3,
+		Acks: map[common.Hash]struct{}{
+			b02.Hash: struct{}{},
+			b22.Hash: struct{}{},
+			b32.Hash: struct{}{},
+		},
+	}
+	b23 = &types.Block{
+		ProposerID: validators[2],
+		ParentHash: b22.Hash,
+		Hash:       common.NewRandomHash(),
+		Height:     3,
+		Acks: map[common.Hash]struct{}{
+			b02.Hash: struct{}{},
+			b12.Hash: struct{}{},
+			b32.Hash: struct{}{},
+		},
+	}
+	b33 = &types.Block{
+		ProposerID: validators[3],
+		ParentHash: b32.Hash,
+		Hash:       common.NewRandomHash(),
+		Height:     3,
+		Acks: map[common.Hash]struct{}{
+			b02.Hash: struct{}{},
+			b12.Hash: struct{}{},
+			b22.Hash: struct{}{},
+		},
+	}
+	Debugf("\n")
+	Debugf("B01: %s\n", b01.Hash)
+	Debugf("B11: %s\n", b11.Hash)
+	Debugf("B21: %s\n", b21.Hash)
+	Debugf("B31: %s\n", b31.Hash)
+	Debugf("\n")
+	Debugf("B02: %s\n", b02.Hash)
+	Debugf("B12: %s\n", b12.Hash)
+	Debugf("B22: %s\n", b22.Hash)
+	Debugf("B32: %s\n", b32.Hash)
+	Debugf("\n")
+	Debugf("B03: %s\n", b03.Hash)
+	Debugf("B13: %s\n", b13.Hash)
+	Debugf("B23: %s\n", b23.Hash)
+	Debugf("B33: %s\n", b33.Hash)
+	Debugf("\n")
+}
+
+func (s *BlockLatticeTest) TestAckAndStateTransition() {
+	// Recieve Order:
+	//   B01 -> B12 -> B11 -> B21 -> B31 -> B02 -> B32 -> B22 -> B13 -> B33
+	//       -> B03 -> B23
+
+	// B01
+	lattice.ProcessBlock(b01)
+
+	// Set status check.
+	s.Require().Equal(0, len(lattice.waitingSet))
+	s.Require().Equal(1, len(lattice.ackCandidateSet))
+	s.Require().Equal(0, len(lattice.stronglyAckedSet))
+	s.Require().Equal(0, len(lattice.pendingSet))
+
+	s.Require().Equal(0, len(b01.IndirectAcks))
+	s.Require().Equal(0, len(b01.AckedBy))
+
+	// B12
+	lattice.ProcessBlock(b12)
+
+	// Set status check.
+	s.Require().Equal(1, len(lattice.waitingSet))
+	s.Require().Equal(1, len(lattice.ackCandidateSet))
+	s.Require().Equal(0, len(lattice.stronglyAckedSet))
+	s.Require().Equal(0, len(lattice.pendingSet))
+
+	s.Require().NotNil(lattice.waitingSet[b12.Hash])
+
+	// B11
+	lattice.ProcessBlock(b11)
+
+	// b01 is acked.
+	s.Require().Equal(1, len(b01.AckedBy))
+	s.Require().NotNil(b01.AckedBy[b11.Hash])
+	// b11 indirect acks.
+	s.Require().Equal(1, len(b11.IndirectAcks))
+	s.Require().Equal(0, len(b11.AckedBy))
+	s.Require().NotNil(b11.IndirectAcks[genesises[0].Hash])
+
+	// Set status check.
+	s.Require().Equal(1, len(lattice.waitingSet))
+	s.Require().Equal(2, len(lattice.ackCandidateSet))
+	s.Require().Equal(0, len(lattice.stronglyAckedSet))
+	s.Require().Equal(0, len(lattice.pendingSet))
+
+	// B21
+	lattice.ProcessBlock(b21)
+
+	// Set status check.
+	s.Require().Equal(1, len(lattice.waitingSet))
+	s.Require().Equal(3, len(lattice.ackCandidateSet))
+	s.Require().Equal(0, len(lattice.stronglyAckedSet))
+	s.Require().Equal(0, len(lattice.pendingSet))
+
+	// b01 is acked.
+	s.Require().Equal(2, len(b01.AckedBy))
+	s.Require().NotNil(b01.AckedBy[b21.Hash])
+	// b21 indirect acks.
+	s.Require().Equal(1, len(b21.IndirectAcks))
+	s.Require().Equal(0, len(b21.AckedBy))
+
+	// B31
+	lattice.ProcessBlock(b31)
+
+	// Set status check.
+	s.Require().Equal(0, len(lattice.waitingSet))
+	s.Require().Equal(4, len(lattice.ackCandidateSet))
+	s.Require().Equal(0, len(lattice.stronglyAckedSet))
+	s.Require().Equal(1, len(lattice.pendingSet))
+
+	s.Require().NotNil(lattice.pendingSet[b01.Hash])
+	s.Require().Equal(types.BlockStatusToTo, b01.State)
+
+	// b01 is acked.
+	s.Require().Equal(3, len(b01.AckedBy))
+	s.Require().NotNil(b01.AckedBy[b31.Hash])
+
+	// b11 is acked.
+	s.Require().Equal(1, len(b11.AckedBy))
+	s.Require().NotNil(b11.AckedBy[b31.Hash])
+
+	// b31 indirect acks.
+	s.Require().Equal(2, len(b31.IndirectAcks))
+	s.Require().Equal(1, len(b31.AckedBy))
+	s.Require().NotNil(b31.AckedBy[b12.Hash])
+
+	// b21 & b31 is acked by b12 (which is previously in waiting set).
+	s.Require().Equal(1, len(b21.AckedBy))
+	s.Require().NotNil(b21.AckedBy[b12.Hash])
+	s.Require().Equal(1, len(b31.AckedBy))
+	s.Require().NotNil(b31.AckedBy[b12.Hash])
+
+	// B02
+	lattice.ProcessBlock(b02)
+
+	// Set status check.
+	s.Require().Equal(0, len(lattice.waitingSet))
+	s.Require().Equal(4, len(lattice.ackCandidateSet))
+	s.Require().Equal(0, len(lattice.stronglyAckedSet))
+	s.Require().Equal(1, len(lattice.pendingSet))
+
+	// b11 is acked.
+	s.Require().Equal(2, len(b11.AckedBy))
+	s.Require().NotNil(b11.AckedBy[b02.Hash])
+	// b21 is acked.
+	s.Require().Equal(2, len(b21.AckedBy))
+	s.Require().NotNil(b21.AckedBy[b02.Hash])
+	s.Require().NotNil(b21.AckedBy[b12.Hash])
+	// b31 is acked.
+	s.Require().Equal(2, len(b31.AckedBy))
+	s.Require().NotNil(b31.AckedBy[b02.Hash])
+	s.Require().NotNil(b31.AckedBy[b12.Hash])
+
+	// B32
+	lattice.ProcessBlock(b32)
+
+	// Set status check.
+	s.Require().Equal(0, len(lattice.waitingSet))
+	s.Require().Equal(4, len(lattice.ackCandidateSet))
+	s.Require().Equal(0, len(lattice.stronglyAckedSet))
+	s.Require().Equal(2, len(lattice.pendingSet))
+
+	s.Require().NotNil(lattice.pendingSet[b01.Hash])
+	s.Require().NotNil(lattice.pendingSet[b21.Hash])
+
+	// b02 is acked.
+	s.Require().Equal(1, len(b02.AckedBy))
+	s.Require().NotNil(b02.AckedBy[b32.Hash])
+	// b12 is acked.
+	s.Require().Equal(1, len(b12.AckedBy))
+	s.Require().NotNil(b12.AckedBy[b32.Hash])
+
+	// B22
+	lattice.ProcessBlock(b22)
+
+	// Set status check.
+	s.Require().Equal(0, len(lattice.waitingSet))
+	s.Require().Equal(4, len(lattice.ackCandidateSet))
+	s.Require().Equal(0, len(lattice.stronglyAckedSet))
+	s.Require().Equal(4, len(lattice.pendingSet))
+
+	s.Require().NotNil(lattice.pendingSet[b01.Hash])
+	s.Require().NotNil(lattice.pendingSet[b11.Hash])
+	s.Require().NotNil(lattice.pendingSet[b21.Hash])
+	s.Require().NotNil(lattice.pendingSet[b31.Hash])
+	s.Require().Equal(types.BlockStatusToTo, b01.State)
+	s.Require().Equal(types.BlockStatusToTo, b11.State)
+	s.Require().Equal(types.BlockStatusToTo, b21.State)
+	s.Require().Equal(types.BlockStatusToTo, b31.State)
+
+	// b02 is acked.
+	s.Require().Equal(2, len(b02.AckedBy))
+	s.Require().NotNil(b02.AckedBy[b22.Hash])
+	// b12 is acked.
+	s.Require().Equal(2, len(b12.AckedBy))
+	s.Require().NotNil(b12.AckedBy[b22.Hash])
+	// b31 is acked.
+	s.Require().Equal(3, len(b31.AckedBy))
+	s.Require().NotNil(b31.AckedBy[b22.Hash])
+
+	// b22 indirect acks.
+	s.Require().NotNil(b22.IndirectAcks[b11.Hash])
+	s.Require().NotNil(b22.IndirectAcks[b01.Hash])
+
+	// B13, B33, B03, B23
+	lattice.ProcessBlock(b13)
+	lattice.ProcessBlock(b33)
+	lattice.ProcessBlock(b03)
+	lattice.ProcessBlock(b23)
+
+	s.Require().Equal(8, len(lattice.pendingSet))
+}
+
+func (s *BlockLatticeTest) TesttotalOrdering() {
+	// Recieve Order:
+	//   B01 -> B12 -> B11 -> B21 -> B31 -> B02 -> B32 -> B22 -> B13 -> B33
+	//       -> B03 -> B23
+
+	lattice.ProcessBlock(b01)
+	lattice.ProcessBlock(b12)
+	lattice.ProcessBlock(b11)
+	lattice.ProcessBlock(b21)
+
+	// B01 in pendingSet after b31 is recieved.
+	lattice.ProcessBlock(b31)
+	s.Require().NotNil(lattice.pendingSet[b01.Hash])
+
+	// Run total ordering for b01.
+	lattice.totalOrdering(b01)
+	s.Require().Equal(0, len(s.app.Outputs))
+	s.Require().Equal(1, len(lattice.candidateSet))
+	s.Require().Equal(1, len(lattice.pendingSet))
+	s.Require().NotNil(lattice.candidateSet[b01.Hash])
+
+	// ABS & AHV
+	s.Require().Equal(1, len(lattice.AHV[b01.Hash]))
+
+	lattice.ProcessBlock(b02)
+	lattice.ProcessBlock(b32)
+
+	// B21 in pendingSet after b32 is recieved.
+	s.Require().Equal(2, len(lattice.pendingSet))
+	s.Require().NotNil(lattice.pendingSet[b01.Hash])
+	s.Require().NotNil(lattice.pendingSet[b21.Hash])
+
+	// Run total ordering for b21.
+	lattice.totalOrdering(b21)
+	s.Require().Equal(2, len(lattice.pendingSet))
+	s.Require().Equal(0, len(s.app.Outputs))
+
+	// ABS & AHV
+	s.Require().Equal(uint64(1), lattice.ABS[b01.Hash][b21.ProposerID])
+	s.Require().Equal(uint64(1), lattice.AHV[b01.Hash][b21.ProposerID])
+
+	lattice.ProcessBlock(b22)
+	s.Require().Equal(4, len(lattice.pendingSet))
+
+	// Run total ordering for b31.
+	lattice.totalOrdering(b31)
+	s.Require().Equal(1, len(s.app.Outputs))
+	s.Require().Equal(b01.Hash, s.app.Outputs[0].Hash)
+	s.Require().Equal(false, s.app.Early)
+	lattice.updateABSAHV()
+	s.Require().Equal(3, len(lattice.abs()))
+	s.Require().Equal(2, len(lattice.candidateSet))
+	s.app.Clear()
+
+	lattice.totalOrdering(b22)
+	s.Require().Equal(0, len(s.app.Outputs))
+	s.Require().Equal(2, len(lattice.candidateSet))
+	s.Require().Equal(3, len(lattice.abs()))
+
+	lattice.ProcessBlock(b13, true)
+	s.Require().Equal(2, len(s.app.Outputs))
+	s.Require().Equal(b21.Hash, s.app.Outputs[0].Hash)
+	s.Require().Equal(b11.Hash, s.app.Outputs[1].Hash)
+	s.Require().Equal(false, s.app.Early)
+	s.app.Clear()
+
+	lattice.ProcessBlock(b33, true)
+	s.Require().Equal(0, len(s.app.Outputs))
+
+	lattice.ProcessBlock(b03, true)
+	s.Require().Equal(1, len(s.app.Outputs))
+	s.Require().Equal(b31.Hash, s.app.Outputs[0].Hash)
+	s.Require().Equal(false, s.app.Early)
+	s.app.Clear()
+
+	lattice.ProcessBlock(b23, true)
+	s.Require().Equal(2, len(s.app.Outputs))
+	s.Require().Equal(b02.Hash, s.app.Outputs[0].Hash)
+	s.Require().Equal(b12.Hash, s.app.Outputs[1].Hash)
+
+	s.Require().Equal(0, len(lattice.waitingSet))
+	s.Require().Equal(0, len(lattice.stronglyAckedSet))
+	s.Require().Equal(2, len(lattice.pendingSet))
+	lattice.updateABSAHV()
+	s.Require().Equal(2, len(lattice.abs()))
+}
+
+func TestBlockLattice(t *testing.T) {
+	suite.Run(t, new(BlockLatticeTest))
+}
diff --git a/core/network.go b/core/network.go
new file mode 100644
index 0000000..1bd714d
--- /dev/null
+++ b/core/network.go
@@ -0,0 +1,33 @@
+// copyright 2018 the dexon-consensus-core authors
+// this file is part of the dexon-consensus-core library.
+//
+// the dexon-consensus-core library is free software: you can redistribute it
+// and/or modify it under the terms of the gnu lesser general public license as
+// published by the free software foundation, either version 3 of the license,
+// or (at your option) any later version.
+//
+// the dexon-consensus-core library is distributed in the hope that it will be
+// useful, but without any warranty; without even the implied warranty of
+// merchantability or fitness for a particular purpose. see the gnu lesser
+// general public license for more details.
+//
+// you should have received a copy of the gnu lesser general public license
+// along with the dexon-consensus-core library. if not, see
+// <http://www.gnu.org/licenses/>.
+
+package core
+
+import (
+	"github.com/dexon-foundation/dexon-consensus-core/core/types"
+)
+
+// Endpoint is the interface for a client network endoint.
+type Endpoint interface {
+	GetID() types.ValidatorID
+}
+
+// Network is the interface for network related functions.
+type Network interface {
+	Join(endpoint Endpoint) chan interface{}
+	BroadcastBlock(block *types.Block)
+}
diff --git a/core/types/block.go b/core/types/block.go
new file mode 100644
index 0000000..265d32f
--- /dev/null
+++ b/core/types/block.go
@@ -0,0 +1,89 @@
+// Copyright 2018 The dexon-consensus-core Authors
+// This file is part of the dexon-consensus-core library.
+//
+// The dexon-consensus-core library is free software: you can redistribute it
+// and/or modify it under the terms of the GNU Lesser General Pubic License as
+// pubished by the Free Software Foundation, either version 3 of the License,
+// or (at your option) any later version.
+//
+// The dexon-consensus-core library is distributed in the hope that it will be
+// useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser
+// General Pubic License for more details.
+//
+// You should have received a copy of the GNU Lesser General Pubic License
+// along with the dexon-consensus-core library. If not, see
+// <http://www.gnu.org/licenses/>.
+
+package types
+
+import (
+	"bytes"
+	"fmt"
+	"time"
+
+	"github.com/dexon-foundation/dexon-consensus-core/common"
+)
+
+// State represent the block process state.
+type State int
+
+// Block Status.
+const (
+	BlockStatusInit State = iota
+	BlockStatusAcked
+	BlockStatusToTo
+	BlockStatusFinal
+)
+
+// Block represents a single event broadcasted on the network.
+type Block struct {
+	ProposerID ValidatorID
+	ParentHash common.Hash
+	Hash       common.Hash
+	Height     uint64
+	Timestamps map[ValidatorID]time.Time
+	Acks       map[common.Hash]struct{}
+
+	IndirectAcks map[common.Hash]struct{}
+	AckedBy      map[common.Hash]bool // bool: direct
+	State        State
+}
+
+func (b *Block) String() string {
+	return fmt.Sprintf("Block(%v)", b.Hash.String()[:6])
+}
+
+// Clone returns a deep copy of a block.
+func (b *Block) Clone() *Block {
+	bcopy := &Block{
+		ProposerID: b.ProposerID,
+		ParentHash: b.ParentHash,
+		Hash:       b.Hash,
+		Height:     b.Height,
+		Timestamps: make(map[ValidatorID]time.Time),
+		Acks:       make(map[common.Hash]struct{}),
+	}
+	for k, v := range b.Timestamps {
+		bcopy.Timestamps[k] = v
+	}
+	for k, v := range b.Acks {
+		bcopy.Acks[k] = v
+	}
+	return bcopy
+}
+
+// ByHash is the helper type for sorting slice of blocks by hash.
+type ByHash []*Block
+
+func (b ByHash) Len() int {
+	return len(b)
+}
+
+func (b ByHash) Less(i int, j int) bool {
+	return bytes.Compare([]byte(b[i].Hash[:]), []byte(b[j].Hash[:])) == -1
+}
+
+func (b ByHash) Swap(i int, j int) {
+	b[i], b[j] = b[j], b[i]
+}
diff --git a/core/types/validator.go b/core/types/validator.go
new file mode 100644
index 0000000..5d424e8
--- /dev/null
+++ b/core/types/validator.go
@@ -0,0 +1,37 @@
+// Copyright 2018 The dexon-consensus-core Authors
+// This file is part of the dexon-consensus-core library.
+//
+// The dexon-consensus-core library is free software: you can redistribute it and/or
+// modify it under the terms of the GNU Lesser General Public License as
+// published by the Free Software Foundation, either version 3 of the License,
+// or (at your option) any later version.
+//
+// The dexon-consensus-core library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the dexon-consensus-core library. If not, see
+// <http://www.gnu.org/licenses/>.
+
+package types
+
+import (
+	"bytes"
+	"encoding/hex"
+
+	"github.com/dexon-foundation/dexon-consensus-core/common"
+)
+
+// ValidatorID is the ID type for validators.
+type ValidatorID common.Hash
+
+func (v ValidatorID) String() string {
+	return hex.EncodeToString([]byte(v[:]))[:6]
+}
+
+// Equal check if two validator IDs are the same.
+func (v ValidatorID) Equal(v2 ValidatorID) bool {
+	return bytes.Compare([]byte(v[:]), []byte(v2[:])) == 0
+}
diff --git a/core/utils.go b/core/utils.go
new file mode 100644
index 0000000..2f87f97
--- /dev/null
+++ b/core/utils.go
@@ -0,0 +1,45 @@
+// Copyright 2018 The dexon-consensus-core Authors
+// This file is part of the dexon-consensus-core library.
+//
+// The dexon-consensus-core library is free software: you can redistribute it
+// and/or modify it under the terms of the GNU Lesser General Public License as
+// published by the Free Software Foundation, either version 3 of the License,
+// or (at your option) any later version.
+//
+// The dexon-consensus-core library is distributed in the hope that it will be
+// useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser
+// General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the dexon-consensus-core library. If not, see
+// <http://www.gnu.org/licenses/>.
+
+package core
+
+import (
+	"fmt"
+	"os"
+)
+
+var debug = false
+
+func init() {
+	if os.Getenv("DEBUG") != "" {
+		debug = true
+	}
+}
+
+// Debugf is like fmt.Printf, but only output when we are in debug mode.
+func Debugf(format string, args ...interface{}) {
+	if debug {
+		fmt.Printf(format, args...)
+	}
+}
+
+// Debugln is like fmt.Println, but only output when we are in debug mode.
+func Debugln(args ...interface{}) {
+	if debug {
+		fmt.Println(args)
+	}
+}
diff --git a/core/validator.go b/core/validator.go
new file mode 100644
index 0000000..93dbbce
--- /dev/null
+++ b/core/validator.go
@@ -0,0 +1,22 @@
+// Copyright 2018 The dexon-consensus-core Authors
+// This file is part of the dexon-consensus-core library.
+//
+// The dexon-consensus-core library is free software: you can redistribute it and/or
+// modify it under the terms of the GNU Lesser General Public License as
+// published by the Free Software Foundation, either version 3 of the License,
+// or (at your option) any later version.
+//
+// The dexon-consensus-core library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the dexon-consensus-core library. If not, see
+// <http://www.gnu.org/licenses/>.
+
+package core
+
+// Validator represents a validator in DEXON consensus algorithm.
+type Validator struct {
+}