tendermint/consensus/state.go

/*

* Terms:

  NewHeight, NewRound, Propose, Prevote, Precommit represent state machine steps. (aka RoundStep).

  To "prevote/precommit" something means to broadcast a prevote/precommit vote for something.

  (H,R) means a particular height H and round R.  A vote "at (H,R)" is a vote signed with (H,R).

* Proposals:

  A proposal is signed and published by the designated proposer at each round.
  A proposal at (H,R) is composed of a proposed block of height H, and optionally a POL round number.
  The POL round number R' (where R' < R) is set to the latest POL round known to the proposer.
  If the proposer is locked on a block, it must include a POL round for the proposal.

* POL and Justification of votes:

  A set of +2/3 of prevotes for a particular block or <nil> at (H,R) is called a POL (proof-of-lock).
  A POL for <nil> might instead be called a proof-of-unlock, but it's better to have a single terminology for both.

  Each precommit which changes the lock at round R must be justified by a POL
  where +2/3 prevoted for some block or <nil> at some round, equal to or less than R,
  but greater than the last round at which the lock was changed.

    POL = Proof-of-Lock = +2/3 prevotes for block B (or +2/3 prevotes for <nil>) at (H,R)

    lastLockChangeRound < POLRound <= newLockChangeRound

  Without the POLRound <= newLockChangeRound condition, an unlock would be possible from a
  future condition that hasn't happened yet, so it destroys deterministic accountability.

  The point of the above inequality is to ensure that changes in the lock (locking/unlocking/lock-changing)
  are always justified by something that happened "in the past" by round numbers, so if there is a problem,
  we can deterministically figure out "when it was caused" and by who.

  If there is a blockchain halt or fork, the blame will fall on +1/3 of Byzantine voting power =
	who cannot push the blame into earlier rounds. (See lemma 4).

* Block commits:

  The set of +2/3 of precommits at the same round for the same block is called a commit.

  A block contains the last block's commit which is comprised of +2/3 precommit votes at (H-1,R).
  While all the precommits in the commit are from the same height & round (ordered by validator index),
  some precommits may be absent (e.g. if the validator's precommit vote didn't reach the proposer in time),
  or some precommits may be for different blockhashes for the last block hash (which is fine).

* Consensus State Machine Overview:

  During NewHeight/NewRound/Propose/Prevote/Precommit:
  * Nodes gossip the proposal block proposed by the designated proposer at round.
  * Nodes gossip prevotes/precommits at rounds [0...currentRound+1] (currentRound+1 to allow round-skipping)
  * Nodes gossip prevotes for the proposal's POL (proof-of-lock) round if proposed.
  * Nodes gossip to late nodes (lagging in height) with precommits of the commit round (aka catchup)

  Upon each state transition, the height/round/step is broadcast to neighboring peers.

* NewRound(height:H,round:R):
  * Set up new round.                                                --> goto Propose(H,R)
  * NOTE: Not much happens in this step. It exists for clarity.

* Propose(height:H,round:R):
  * Upon entering Propose:
    * The designated proposer proposes a block at (H,R).
  * The Propose step ends:
    * After `timeoutPropose` after entering Propose.                 --> goto Prevote(H,R)
    * After receiving proposal block and all POL prevotes.           --> goto Prevote(H,R)
    * After any +2/3 prevotes received at (H,R+1).                   --> goto Prevote(H,R+1)
    * After any +2/3 precommits received at (H,R+1).                 --> goto Precommit(H,R+1)
    * After +2/3 precommits received for a particular block.         --> goto Commit(H)

* Prevote(height:H,round:R):
  * Upon entering Prevote, each validator broadcasts its prevote vote.
    * If the validator is locked on a block, it prevotes that.
    * Else, if the proposed block from Propose(H,R) is good, it prevotes that.
    * Else, if the proposal is invalid or wasn't received on time, it prevotes <nil>.
  * The Prevote step ends:
    * After +2/3 prevotes for a particular block or <nil>.           --> goto Precommit(H,R)
    * After `timeoutPrevote` after receiving any +2/3 prevotes.      --> goto Precommit(H,R)
    * After any +2/3 prevotes received at (H,R+1).                   --> goto Prevote(H,R+1)
    * After any +2/3 precommits received at (H,R+1).                 --> goto Precommit(H,R+1)
    * After +2/3 precommits received for a particular block.         --> goto Commit(H)

* Precommit(height:H,round:R):
  * Upon entering Precommit, each validator broadcasts its precommit vote.
    * If the validator had seen +2/3 of prevotes for a particular block from Prevote(H,R),
      it locks (changes lock to) that block and precommits that block.
    * Else, if the validator had seen +2/3 of prevotes for <nil>, it unlocks and precommits <nil>.
    * Else, if +2/3 of prevotes for a particular block or <nil> is not received on time,
      it precommits what it's locked on, or <nil>.
  * The Precommit step ends:
    * After +2/3 precommits for a particular block.                  --> goto Commit(H)
    * After +2/3 precommits for <nil>.                               --> goto NewRound(H,R+1)
    * After `timeoutPrecommit` after receiving any +2/3 precommits.  --> goto NewRound(H,R+1)
    * After any +2/3 prevotes received at (H,R+1).                   --> goto Prevote(H,R+1)
    * After any +2/3 precommits received at (H,R+1).                 --> goto Precommit(H,R+1)

* Commit(height:H):
  * Set CommitTime = now
  * Wait until block is received.                                    --> goto NewHeight(H+1)

* NewHeight(height:H):
  * Move Precommits to LastCommit and increment height.
  * Set StartTime = CommitTime+timeoutCommit
  * Wait until `StartTime` to receive straggler commits.             --> goto NewRound(H,0)

* Proof of Safety:
  If a good validator commits at round R, it's because it saw +2/3 of precommits at round R.
  This implies that (assuming tolerance bounds) +1/3 of honest nodes are still locked at round R+1.
  These locked validators will remain locked until they see +2/3 prevote for something
  else, but this won't happen because +1/3 are locked and honest.

* Proof of Liveness:
  Lemma 1: If +1/3 good nodes are locked on two different blocks, the proposers' POLRound will
    eventually cause nodes locked from the earlier round to unlock.
    -> `timeoutProposalR` increments with round R, while the block.size && POL prevote size
       are fixed, so eventually we'll be able to "fully gossip" the block & POL.
    TODO: cap the block.size at something reasonable.
  Lemma 2: If a good node is at round R, neighboring good nodes will soon catch up to round R.
  Lemma 3: If a node at (H,R) receives +2/3 prevotes for a block (or +2/3 for <nil>) at (H,R+1),
    it will enter NewRound(H,R+1).
  Lemma 4: Terminal conditions imply the existence of deterministic accountability, for
    a synchronous (fixed-duration) protocol extension (judgement).
    TODO: define terminal conditions (fork and non-decision).
    TODO: define new assumptions for the synchronous judgement period.


                            +-------------------------------------+
                            v                                     |(Wait til `CommmitTime+timeoutCommit`)
                      +-----------+                         +-----+-----+
         +----------> |  Propose  +--------------+          | NewHeight |
         |            +-----------+              |          +-----------+
         |                                       |                ^
         |(Else, after timeoutPrecommit)         v                |
   +-----+-----+                           +-----------+          |
   | Precommit |  <------------------------+  Prevote  |          |
   +-----+-----+                           +-----------+          |
         |(When +2/3 Precommits for block found)                  |
         v                                                        |
   +--------------------------------------------------------------------+
   |  Commit                                                            |
   |                                                                    |
   |  * Set CommitTime = now;                                           |
   |  * Wait for block, then stage/save/commit block;                   |
   +--------------------------------------------------------------------+

*/

package consensus

import (
	"bytes"
	"errors"
	"fmt"
	"sync"
	"sync/atomic"
	"time"

	"github.com/tendermint/tendermint/account"
	"github.com/tendermint/tendermint/binary"
	bc "github.com/tendermint/tendermint/blockchain"
	. "github.com/tendermint/tendermint/common"
	. "github.com/tendermint/tendermint/consensus/types"
	"github.com/tendermint/tendermint/events"
	mempl "github.com/tendermint/tendermint/mempool"
	sm "github.com/tendermint/tendermint/state"
	"github.com/tendermint/tendermint/types"
)

var (
	timeoutPropose        = 3000 * time.Millisecond // Maximum duration of RoundStepPropose
	timeoutPrevote0       = 1000 * time.Millisecond // After any +2/3 prevotes received, wait this long for stragglers.
	timeoutPrevoteDelta   = 0500 * time.Millisecond // timeoutPrevoteN is timeoutPrevote0 + timeoutPrevoteDelta*N
	timeoutPrecommit0     = 1000 * time.Millisecond // After any +2/3 precommits received, wait this long for stragglers.
	timeoutPrecommitDelta = 0500 * time.Millisecond // timeoutPrecommitN is timeoutPrecommit0 + timeoutPrecommitDelta*N
	timeoutCommit         = 2000 * time.Millisecond // After +2/3 commits received for committed block, wait this long for stragglers in the next height's RoundStepNewHeight.
)

var (
	ErrInvalidProposalSignature = errors.New("Error invalid proposal signature")
	ErrInvalidProposalPOLRound  = errors.New("Error invalid proposal POL round")
)

//-----------------------------------------------------------------------------
// RoundStepType enum type

type RoundStepType uint8 // These must be numeric, ordered.

const (
	RoundStepNewHeight     = RoundStepType(0x01) // Wait til CommitTime + timeoutCommit
	RoundStepNewRound      = RoundStepType(0x02) // Setup new round and go to RoundStepPropose
	RoundStepPropose       = RoundStepType(0x03) // Did propose, gossip proposal
	RoundStepPrevote       = RoundStepType(0x04) // Did prevote, gossip prevotes
	RoundStepPrevoteWait   = RoundStepType(0x05) // Did receive any +2/3 prevotes, start timeout
	RoundStepPrecommit     = RoundStepType(0x06) // Did precommit, gossip precommits
	RoundStepPrecommitWait = RoundStepType(0x07) // Did receive any +2/3 precommits, start timeout
	RoundStepCommit        = RoundStepType(0x08) // Entered commit state machine
	// NOTE: RoundStepNewHeight acts as RoundStepCommitWait.
)

func (rs RoundStepType) String() string {
	switch rs {
	case RoundStepNewHeight:
		return "RoundStepNewHeight"
	case RoundStepNewRound:
		return "RoundStepNewRound"
	case RoundStepPropose:
		return "RoundStepPropose"
	case RoundStepPrevote:
		return "RoundStepPrevote"
	case RoundStepPrevoteWait:
		return "RoundStepPrevoteWait"
	case RoundStepPrecommit:
		return "RoundStepPrecommit"
	case RoundStepPrecommitWait:
		return "RoundStepPrecommitWait"
	case RoundStepCommit:
		return "RoundStepCommit"
	default:
		panic(Fmt("Unknown RoundStep %X", rs))
	}
}

//-----------------------------------------------------------------------------

// Immutable when returned from ConsensusState.GetRoundState()
type RoundState struct {
	Height             int // Height we are working on
	Round              int
	Step               RoundStepType
	StartTime          time.Time
	CommitTime         time.Time // Subjective time when +2/3 precommits for Block at Round were found
	Validators         *sm.ValidatorSet
	Proposal           *Proposal
	ProposalBlock      *types.Block
	ProposalBlockParts *types.PartSet
	LockedRound        int
	LockedBlock        *types.Block
	LockedBlockParts   *types.PartSet
	Votes              *HeightVoteSet
	LastCommit         *VoteSet // Last precommits at Height-1
	LastValidators     *sm.ValidatorSet
}

func (rs *RoundState) String() string {
	return rs.StringIndented("")
}

func (rs *RoundState) StringIndented(indent string) string {
	return fmt.Sprintf(`RoundState{
%s  H:%v R:%v S:%v
%s  StartTime:     %v
%s  CommitTime:    %v
%s  Validators:    %v
%s  Proposal:      %v
%s  ProposalBlock: %v %v
%s  LockedRound:   %v
%s  LockedBlock:   %v %v
%s  Votes:         %v
%s  LastCommit: %v
%s  LastValidators:    %v
%s}`,
		indent, rs.Height, rs.Round, rs.Step,
		indent, rs.StartTime,
		indent, rs.CommitTime,
		indent, rs.Validators.StringIndented(indent+"    "),
		indent, rs.Proposal,
		indent, rs.ProposalBlockParts.StringShort(), rs.ProposalBlock.StringShort(),
		indent, rs.LockedRound,
		indent, rs.LockedBlockParts.StringShort(), rs.LockedBlock.StringShort(),
		indent, rs.Votes.StringIndented(indent+"    "),
		indent, rs.LastCommit.StringShort(),
		indent, rs.LastValidators.StringIndented(indent+"    "),
		indent)
}

func (rs *RoundState) StringShort() string {
	return fmt.Sprintf(`RoundState{H:%v R:%v S:%v ST:%v}`,
		rs.Height, rs.Round, rs.Step, rs.StartTime)
}

//-----------------------------------------------------------------------------

// Tracks consensus state across block heights and rounds.
type ConsensusState struct {
	started uint32
	stopped uint32
	quit    chan struct{}

	blockStore     *bc.BlockStore
	mempoolReactor *mempl.MempoolReactor
	privValidator  *sm.PrivValidator
	newStepCh      chan *RoundState

	mtx sync.Mutex
	RoundState
	state       *sm.State    // State until height-1.
	stagedBlock *types.Block // Cache last staged block.
	stagedState *sm.State    // Cache result of staged block.

	evsw events.Fireable
	evc  *events.EventCache // set in stageBlock and passed into state
}

func NewConsensusState(state *sm.State, blockStore *bc.BlockStore, mempoolReactor *mempl.MempoolReactor) *ConsensusState {
	cs := &ConsensusState{
		quit:           make(chan struct{}),
		blockStore:     blockStore,
		mempoolReactor: mempoolReactor,
		newStepCh:      make(chan *RoundState, 10),
	}
	cs.updateToState(state, true)
	// Don't call scheduleRound0 yet.
	// We do that upon Start().
	cs.maybeRebond()
	cs.reconstructLastCommit(state)
	return cs
}

// Reconstruct LastCommit from SeenValidation, which we saved along with the block,
// (which happens even before saving the state)
func (cs *ConsensusState) reconstructLastCommit(state *sm.State) {
	if state.LastBlockHeight == 0 {
		return
	}
	lastPrecommits := NewVoteSet(state.LastBlockHeight, 0, types.VoteTypePrecommit, state.LastBondedValidators)
	seenValidation := cs.blockStore.LoadSeenValidation(state.LastBlockHeight)
	for idx, precommit := range seenValidation.Precommits {
		added, _, err := lastPrecommits.AddByIndex(idx, precommit)
		if !added || err != nil {
			panic(Fmt("Failed to reconstruct LastCommit: %v", err))
		}
	}
	if !lastPrecommits.HasTwoThirdsMajority() {
		panic("Failed to reconstruct LastCommit: Does not have +2/3 maj")
	}
	cs.LastCommit = lastPrecommits
}

func (cs *ConsensusState) GetState() *sm.State {
	cs.mtx.Lock()
	defer cs.mtx.Unlock()
	return cs.state.Copy()
}

func (cs *ConsensusState) GetRoundState() *RoundState {
	cs.mtx.Lock()
	defer cs.mtx.Unlock()
	return cs.getRoundState()
}

func (cs *ConsensusState) getRoundState() *RoundState {
	rs := cs.RoundState // copy
	return &rs
}

func (cs *ConsensusState) NewStepCh() chan *RoundState {
	return cs.newStepCh
}

func (cs *ConsensusState) Start() {
	if atomic.CompareAndSwapUint32(&cs.started, 0, 1) {
		log.Info("Starting ConsensusState")
		cs.scheduleRound0(cs.Height)
	}
}

// EnterNewRound(height, 0) at cs.StartTime.
func (cs *ConsensusState) scheduleRound0(height int) {
	//log.Debug("scheduleRound0", "now", time.Now(), "startTime", cs.StartTime)
	sleepDuration := cs.StartTime.Sub(time.Now())
	go func() {
		if 0 < sleepDuration {
			time.Sleep(sleepDuration)
		}
		cs.EnterNewRound(height, 0)
	}()
}

func (cs *ConsensusState) Stop() {
	if atomic.CompareAndSwapUint32(&cs.stopped, 0, 1) {
		log.Info("Stopping ConsensusState")
		close(cs.quit)
	}
}

func (cs *ConsensusState) IsStopped() bool {
	return atomic.LoadUint32(&cs.stopped) == 1
}

// Updates ConsensusState and increments height to match that of state.
// The round becomes 0 and cs.Step becomes RoundStepNewHeight.
func (cs *ConsensusState) updateToState(state *sm.State, contiguous bool) {
	// SANITY CHECK
	if contiguous && 0 < cs.Height && cs.Height != state.LastBlockHeight {
		panic(Fmt("updateToState() expected state height of %v but found %v",
			cs.Height, state.LastBlockHeight))
	}
	// END SANITY CHECK

	// Reset fields based on state.
	validators := state.BondedValidators
	height := state.LastBlockHeight + 1 // next desired block height
	lastPrecommits := (*VoteSet)(nil)
	if contiguous && cs.Votes != nil {
		if !cs.Votes.Precommits(cs.Round).HasTwoThirdsMajority() {
			panic("updateToState(state, true) called but last Precommit round didn't have +2/3")
		}
		lastPrecommits = cs.Votes.Precommits(cs.Round)
	}

	// RoundState fields
	cs.Height = height
	cs.Round = 0
	cs.Step = RoundStepNewHeight
	if cs.CommitTime.IsZero() {
		// "Now" makes it easier to sync up dev nodes.
		// We add timeoutCommit to allow transactions
		// to be gathered for the first block.
		// And alternative solution that relies on clocks:
		//  cs.StartTime = state.LastBlockTime.Add(timeoutCommit)
		cs.StartTime = time.Now().Add(timeoutCommit)
	} else {
		cs.StartTime = cs.CommitTime.Add(timeoutCommit)
	}
	cs.CommitTime = time.Time{}
	cs.Validators = validators
	cs.Proposal = nil
	cs.ProposalBlock = nil
	cs.ProposalBlockParts = nil
	cs.LockedRound = 0
	cs.LockedBlock = nil
	cs.LockedBlockParts = nil
	cs.Votes = NewHeightVoteSet(height, validators)
	cs.LastCommit = lastPrecommits
	cs.LastValidators = state.LastBondedValidators

	cs.state = state
	cs.stagedBlock = nil
	cs.stagedState = nil

	// Finally, broadcast RoundState
	cs.newStepCh <- cs.getRoundState()
}

// If we're unbonded, broadcast RebondTx.
func (cs *ConsensusState) maybeRebond() {
	if cs.privValidator == nil || !cs.state.UnbondingValidators.HasAddress(cs.privValidator.Address) {
		return
	}
	rebondTx := &types.RebondTx{
		Address: cs.privValidator.Address,
		Height:  cs.Height,
	}
	err := cs.privValidator.SignRebondTx(cs.state.ChainID, rebondTx)
	if err == nil {
		err := cs.mempoolReactor.BroadcastTx(rebondTx)
		if err != nil {
			log.Error("Failed to broadcast RebondTx",
				"height", cs.Height, "round", cs.Round, "tx", rebondTx, "error", err)
		} else {
			log.Info("Signed and broadcast RebondTx",
				"height", cs.Height, "round", cs.Round, "tx", rebondTx)
		}
	} else {
		log.Warn("Error signing RebondTx", "height", cs.Height, "round", cs.Round, "tx", rebondTx, "error", err)
	}
}

func (cs *ConsensusState) SetPrivValidator(priv *sm.PrivValidator) {
	cs.mtx.Lock()
	defer cs.mtx.Unlock()
	cs.privValidator = priv
}

//-----------------------------------------------------------------------------

// Enter: +2/3 precommits for nil at (height,round-1)
// Enter: `timeoutPrecommits` after any +2/3 precommits from (height,round-1)
// Enter: `startTime = commitTime+timeoutCommit` from NewHeight(height)
// NOTE: cs.StartTime was already set for height.
func (cs *ConsensusState) EnterNewRound(height int, round int) {
	cs.mtx.Lock()
	defer cs.mtx.Unlock()
	if cs.Height != height || round < cs.Round || (cs.Round == round && cs.Step != RoundStepNewHeight) {
		log.Debug(Fmt("EnterNewRound(%v/%v): Invalid args. Current step: %v/%v/%v", height, round, cs.Height, cs.Round, cs.Step))
		return
	}
	if now := time.Now(); cs.StartTime.After(now) {
		log.Warn("Need to set a buffer and log.Warn() here for sanity.", "startTime", cs.StartTime, "now", now)
	}

	// Increment validators if necessary
	validators := cs.Validators
	if cs.Round < round {
		validators = validators.Copy()
		validators.IncrementAccum(round - cs.Round)
	}

	// Setup new round
	cs.Round = round
	cs.Step = RoundStepNewRound
	cs.Validators = validators
	cs.Proposal = nil
	cs.ProposalBlock = nil
	cs.ProposalBlockParts = nil
	cs.Votes.SetRound(round + 1) // also track next round (round+1) to allow round-skipping

	// Immediately go to EnterPropose.
	go cs.EnterPropose(height, round)
}

// Enter: from NewRound(height,round).
func (cs *ConsensusState) EnterPropose(height int, round int) {
	cs.mtx.Lock()
	defer cs.mtx.Unlock()
	if cs.Height != height || round < cs.Round || (cs.Round == round && RoundStepPropose <= cs.Step) {
		log.Debug(Fmt("EnterPropose(%v/%v): Invalid args. Current step: %v/%v/%v", height, round, cs.Height, cs.Round, cs.Step))
		return
	}

	defer func() {
		// Done EnterPropose:
		cs.Round = round
		cs.Step = RoundStepPropose
		cs.newStepCh <- cs.getRoundState()

		// If we already have the proposal + POL, then goto Prevote
		if cs.isProposalComplete() {
			go cs.EnterPrevote(height, cs.Round)
		}
	}()

	// This step times out after `timeoutPropose`
	go func() {
		time.Sleep(timeoutPropose)
		cs.EnterPrevote(height, round)
	}()

	// Nothing more to do if we're not a validator
	if cs.privValidator == nil {
		return
	}

	if !bytes.Equal(cs.Validators.Proposer().Address, cs.privValidator.Address) {
		log.Debug("EnterPropose: Not our turn to propose", "proposer", cs.Validators.Proposer().Address, "privValidator", cs.privValidator)
	} else {
		log.Debug("EnterPropose: Our turn to propose", "proposer", cs.Validators.Proposer().Address, "privValidator", cs.privValidator)
		cs.decideProposal(height, round)
	}
}

// Decides on the next proposal and sets them onto cs.Proposal*
func (cs *ConsensusState) decideProposal(height int, round int) {
	var block *types.Block
	var blockParts *types.PartSet

	// Decide on block
	if cs.LockedBlock != nil {
		// If we're locked onto a block, just choose that.
		block, blockParts = cs.LockedBlock, cs.LockedBlockParts
	} else {
		// Create a new proposal block from state/txs from the mempool.
		block, blockParts = cs.createProposalBlock()
	}

	// Make proposal
	proposal := NewProposal(height, round, blockParts.Header(), cs.Votes.POLRound())
	err := cs.privValidator.SignProposal(cs.state.ChainID, proposal)
	if err == nil {
		log.Info("Signed and set proposal", "height", height, "round", round, "proposal", proposal)
		log.Debug(Fmt("Signed and set proposal block: %v", block))
		// Set fields
		cs.Proposal = proposal
		cs.ProposalBlock = block
		cs.ProposalBlockParts = blockParts
	} else {
		log.Warn("EnterPropose: Error signing proposal", "height", height, "round", round, "error", err)
	}

}

// Returns true if the proposal block is complete &&
// (if POLRound was proposed, we have +2/3 prevotes from there).
func (cs *ConsensusState) isProposalComplete() bool {
	if cs.Proposal == nil || cs.ProposalBlock == nil {
		return false
	}
	if cs.Proposal.POLRound < 0 {
		return true
	} else {
		return cs.Votes.Prevotes(cs.Proposal.POLRound).HasTwoThirdsMajority()
	}
}

// Create the next block to propose and return it.
// NOTE: make it side-effect free for clarity.
func (cs *ConsensusState) createProposalBlock() (block *types.Block, blockParts *types.PartSet) {
	var validation *types.Validation
	if cs.Height == 1 {
		// We're creating a proposal for the first block.
		// The validation is empty, but not nil.
		validation = &types.Validation{}
	} else if cs.LastCommit.HasTwoThirdsMajority() {
		// Make the validation from LastCommit
		validation = cs.LastCommit.MakeValidation()
	} else {
		// This shouldn't happen.
		log.Error("EnterPropose: Cannot propose anything: No validation for the previous block.")
		return
	}
	txs := cs.mempoolReactor.Mempool.GetProposalTxs()
	block = &types.Block{
		Header: &types.Header{
			ChainID:        cs.state.ChainID,
			Height:         cs.Height,
			Time:           time.Now(),
			Fees:           0, // TODO fees
			NumTxs:         len(txs),
			LastBlockHash:  cs.state.LastBlockHash,
			LastBlockParts: cs.state.LastBlockParts,
			StateHash:      nil, // Will set afterwards.
		},
		LastValidation: validation,
		Data: &types.Data{
			Txs: txs,
		},
	}

	// Set the block.Header.StateHash.
	err := cs.state.ComputeBlockStateHash(block)
	if err != nil {
		log.Error("EnterPropose: Error setting state hash", "error", err)
		return
	}

	blockParts = block.MakePartSet()
	return block, blockParts
}

// Enter: `timeoutPropose` after entering Propose.
// Enter: proposal block and POL is ready.
// Enter: any +2/3 prevotes for future round.
// Prevote for LockedBlock if we're locked, or ProposalBlock if valid.
// Otherwise vote nil.
func (cs *ConsensusState) EnterPrevote(height int, round int) {
	cs.mtx.Lock()
	defer cs.mtx.Unlock()
	if cs.Height != height || round < cs.Round || (cs.Round == round && RoundStepPrevote <= cs.Step) {
		log.Debug(Fmt("EnterPrevote(%v/%v): Invalid args. Current step: %v/%v/%v", height, round, cs.Height, cs.Round, cs.Step))
		return
	}

	// Sign and broadcast vote as necessary
	cs.doPrevote(height, round)

	// Done EnterPrevote:
	cs.Round = round
	cs.Step = RoundStepPrevote
	cs.newStepCh <- cs.getRoundState()
	/* This isn't necessary because addVote() does it for us.
	if cs.Votes.Prevotes(round).HasTwoThirdsAny() {
		go cs.EnterPrevoteWait(height, round)
	}*/
}

func (cs *ConsensusState) doPrevote(height int, round int) {
	// If a block is locked, prevote that.
	if cs.LockedBlock != nil {
		log.Debug("EnterPrevote: Block was locked")
		cs.signAddVote(types.VoteTypePrevote, cs.LockedBlock.Hash(), cs.LockedBlockParts.Header())
		return
	}

	// If ProposalBlock is nil, prevote nil.
	if cs.ProposalBlock == nil {
		log.Warn("EnterPrevote: ProposalBlock is nil")
		cs.signAddVote(types.VoteTypePrevote, nil, types.PartSetHeader{})
		return
	}

	// Try staging cs.ProposalBlock
	err := cs.stageBlock(cs.ProposalBlock, cs.ProposalBlockParts)
	if err != nil {
		// ProposalBlock is invalid, prevote nil.
		log.Warn("EnterPrevote: ProposalBlock is invalid", "error", err)
		cs.signAddVote(types.VoteTypePrevote, nil, types.PartSetHeader{})
		return
	}

	// Prevote cs.ProposalBlock
	cs.signAddVote(types.VoteTypePrevote, cs.ProposalBlock.Hash(), cs.ProposalBlockParts.Header())
	return
}

// Enter: any +2/3 prevotes at next round.
func (cs *ConsensusState) EnterPrevoteWait(height int, round int) {
	cs.mtx.Lock()
	defer cs.mtx.Unlock()
	if cs.Height != height || round < cs.Round || (cs.Round == round && RoundStepPrevoteWait <= cs.Step) {
		log.Debug(Fmt("EnterPrevoteWait(%v/%v): Invalid args. Current step: %v/%v/%v", height, round, cs.Height, cs.Round, cs.Step))
		return
	}
	if !cs.Votes.Prevotes(round).HasTwoThirdsAny() {
		panic(Fmt("EnterPrevoteWait(%v/%v), but Prevotes does not have any +2/3 votes", height, round))
	}

	// Done EnterPrevoteWait:
	cs.Round = round
	cs.Step = RoundStepPrevoteWait
	cs.newStepCh <- cs.getRoundState()

	// After `timeoutPrevote0+timeoutPrevoteDelta*round`, EnterPrecommit()
	go func() {
		time.Sleep(timeoutPrevote0 + timeoutPrevote0*time.Duration(round))
		cs.EnterPrecommit(height, round)
	}()
}

// Enter: +2/3 precomits for block or nil.
// Enter: `timeoutPrevote` after any +2/3 prevotes.
// Enter: any +2/3 precommits for next round.
// Lock & precommit the ProposalBlock if we have enough prevotes for it,
// else, unlock an existing lock and precommit nil if +2/3 of prevotes were nil,
// else, precommit locked block or nil otherwise.
func (cs *ConsensusState) EnterPrecommit(height int, round int) {
	cs.mtx.Lock()
	defer cs.mtx.Unlock()
	if cs.Height != height || round < cs.Round || (cs.Round == round && RoundStepPrecommit <= cs.Step) {
		log.Debug(Fmt("EnterPrecommit(%v/%v): Invalid args. Current step: %v/%v/%v", height, round, cs.Height, cs.Round, cs.Step))
		return
	}

	defer func() {
		// Done EnterPrecommit:
		cs.Round = round
		cs.Step = RoundStepPrecommit
		cs.newStepCh <- cs.getRoundState()
		/* This isn't necessary because addVote() does it for us.
		if cs.Votes.Precommits(round).HasTwoThirdsAny() {
			go cs.EnterPrecommitWait(height, round)
		}*/
	}()

	hash, partsHeader, ok := cs.Votes.Prevotes(round).TwoThirdsMajority()

	// If we don't have two thirds of prevotes, just precommit locked block or nil
	if !ok {
		if cs.LockedBlock != nil {
			log.Info("EnterPrecommit: No +2/3 prevotes during EnterPrecommit. Precommitting lock.")
			cs.signAddVote(types.VoteTypePrecommit, cs.LockedBlock.Hash(), cs.LockedBlockParts.Header())
		} else {
			log.Info("EnterPrecommit: No +2/3 prevotes during EnterPrecommit. Precommitting nil.")
			cs.signAddVote(types.VoteTypePrecommit, nil, types.PartSetHeader{})
		}
		return
	}

	// +2/3 prevoted nil. Unlock and precommit nil.
	if len(hash) == 0 {
		if cs.LockedBlock == nil {
			log.Info("EnterPrecommit: +2/3 prevoted for nil.")
		} else {
			log.Info("EnterPrecommit: +2/3 prevoted for nil. Unlocking")
			cs.LockedRound = 0
			cs.LockedBlock = nil
			cs.LockedBlockParts = nil
		}
		cs.signAddVote(types.VoteTypePrecommit, nil, types.PartSetHeader{})
		return
	}

	// At this point, +2/3 prevoted for a particular block.

	// If +2/3 prevoted for already locked block, precommit it.
	if cs.LockedBlock.HashesTo(hash) {
		log.Info("EnterPrecommit: +2/3 prevoted locked block.")
		cs.signAddVote(types.VoteTypePrecommit, hash, partsHeader)
		return
	}

	// If +2/3 prevoted for proposal block, stage and precommit it
	if cs.ProposalBlock.HashesTo(hash) {
		log.Info("EnterPrecommit: +2/3 prevoted proposal block.")
		// Validate the block.
		if err := cs.stageBlock(cs.ProposalBlock, cs.ProposalBlockParts); err != nil {
			panic(Fmt("EnterPrecommit: +2/3 prevoted for an invalid block: %v", err))
		}
		cs.LockedRound = round
		cs.LockedBlock = cs.ProposalBlock
		cs.LockedBlockParts = cs.ProposalBlockParts
		cs.signAddVote(types.VoteTypePrecommit, hash, partsHeader)
		return
	}

	// Otherwise, we need to fetch the +2/3 prevoted block.
	// Unlock and precommit nil.
	// The +2/3 prevotes for this round is the POL for our unlock.
	if cs.Votes.POLRound() < round {
		panic(Fmt("This POLRound shold be %v but got %", round, cs.Votes.POLRound()))
	}
	cs.LockedRound = 0
	cs.LockedBlock = nil
	cs.LockedBlockParts = nil
	if !cs.ProposalBlockParts.HasHeader(partsHeader) {
		cs.ProposalBlock = nil
		cs.ProposalBlockParts = types.NewPartSetFromHeader(partsHeader)
	}
	cs.signAddVote(types.VoteTypePrecommit, nil, types.PartSetHeader{})
	return
}

// Enter: any +2/3 precommits for next round.
func (cs *ConsensusState) EnterPrecommitWait(height int, round int) {
	cs.mtx.Lock()
	defer cs.mtx.Unlock()
	if cs.Height != height || round < cs.Round || (cs.Round == round && RoundStepPrecommitWait <= cs.Step) {
		log.Debug(Fmt("EnterPrecommitWait(%v/%v): Invalid args. Current step: %v/%v/%v", height, round, cs.Height, cs.Round, cs.Step))
		return
	}
	if !cs.Votes.Precommits(round).HasTwoThirdsAny() {
		panic(Fmt("EnterPrecommitWait(%v/%v), but Precommits does not have any +2/3 votes", height, round))
	}

	// Done EnterPrecommitWait:
	cs.Round = round
	cs.Step = RoundStepPrecommitWait
	cs.newStepCh <- cs.getRoundState()

	// After `timeoutPrecommit0+timeoutPrecommitDelta*round`, EnterNewRound()
	go func() {
		time.Sleep(timeoutPrecommit0 + timeoutPrecommitDelta*time.Duration(round))
		// If we have +2/3 of precommits for a particular block (or nil),
		// we already entered commit (or the next round).
		// So just try to transition to the next round,
		// which is what we'd do otherwise.
		cs.EnterNewRound(height, round+1)
	}()
}

// Enter: +2/3 precommits for block
func (cs *ConsensusState) EnterCommit(height int) {
	cs.mtx.Lock()
	defer cs.mtx.Unlock()
	if cs.Height != height || RoundStepCommit <= cs.Step {
		log.Debug(Fmt("EnterCommit(%v): Invalid args. Current step: %v/%v/%v", height, cs.Height, cs.Round, cs.Step))
		return
	}

	defer func() {
		// Done Entercommit:
		// keep ca.Round the same, it points to the right Precommits set.
		cs.Step = RoundStepCommit
		cs.newStepCh <- cs.getRoundState()

		// Maybe finalize immediately.
		cs.tryFinalizeCommit(height)
	}()

	// SANITY CHECK
	hash, partsHeader, ok := cs.Votes.Precommits(cs.Round).TwoThirdsMajority()
	if !ok {
		panic("RunActionCommit() expects +2/3 precommits")
	}
	// END SANITY CHECK

	// The Locked* fields no longer matter.
	// Move them over to ProposalBlock if they match the commit hash,
	// otherwise they can now be cleared.
	if cs.LockedBlock.HashesTo(hash) {
		cs.ProposalBlock = cs.LockedBlock
		cs.ProposalBlockParts = cs.LockedBlockParts
		cs.LockedRound = 0
		cs.LockedBlock = nil
		cs.LockedBlockParts = nil
	} else {
		cs.LockedRound = 0
		cs.LockedBlock = nil
		cs.LockedBlockParts = nil
	}

	// If we don't have the block being committed, set up to get it.
	if !cs.ProposalBlock.HashesTo(hash) {
		if !cs.ProposalBlockParts.HasHeader(partsHeader) {
			// We're getting the wrong block.
			// Set up ProposalBlockParts and keep waiting.
			cs.ProposalBlock = nil
			cs.ProposalBlockParts = types.NewPartSetFromHeader(partsHeader)
		} else {
			// We just need to keep waiting.
		}
	}
}

// If we have the block AND +2/3 commits for it, finalize.
func (cs *ConsensusState) tryFinalizeCommit(height int) {
	// SANITY CHECK
	if cs.Height != height {
		panic(Fmt("tryFinalizeCommit() cs.Height: %v vs height: %v", cs.Height, height))
	}
	// END SANITY CHECK

	hash, _, ok := cs.Votes.Precommits(cs.Round).TwoThirdsMajority()
	if !ok || len(hash) == 0 {
		return // There was no +2/3 majority, or +2/3 was for <nil>.
	}
	if !cs.ProposalBlock.HashesTo(hash) {
		return // We don't have the commit block.
	}
	go cs.FinalizeCommit(height)
}

// Increment height and goto RoundStepNewHeight
func (cs *ConsensusState) FinalizeCommit(height int) {
	cs.mtx.Lock()
	defer cs.mtx.Unlock()

	if cs.Height != height || cs.Step != RoundStepCommit {
		log.Debug(Fmt("FinalizeCommit(%v): Invalid args. Current step: %v/%v/%v", height, cs.Height, cs.Round, cs.Step))
		return
	}

	hash, header, ok := cs.Votes.Precommits(cs.Round).TwoThirdsMajority()

	// SANITY CHECK
	if !ok {
		panic(Fmt("Cannot FinalizeCommit, commit does not have two thirds majority"))
	}
	if !cs.ProposalBlockParts.HasHeader(header) {
		panic(Fmt("Expected ProposalBlockParts header to be commit header"))
	}
	if !cs.ProposalBlock.HashesTo(hash) {
		panic(Fmt("Cannot FinalizeCommit, ProposalBlock does not hash to commit hash"))
	}
	if err := cs.stageBlock(cs.ProposalBlock, cs.ProposalBlockParts); err != nil {
		panic(Fmt("+2/3 committed an invalid block: %v", err))
	}
	// END SANITY CHECK

	log.Debug(Fmt("Finalizing commit of block: %v", cs.ProposalBlock))
	// We have the block, so stage/save/commit-vote.
	cs.saveBlock(cs.ProposalBlock, cs.ProposalBlockParts, cs.Votes.Precommits(cs.Round))
	// Increment height.
	cs.updateToState(cs.stagedState, true)
	// cs.StartTime is already set.
	// Schedule Round0 to start soon.
	go cs.scheduleRound0(height + 1)
	// If we're unbonded, broadcast RebondTx.
	cs.maybeRebond()

	// By here,
	// * cs.Height has been increment to height+1
	// * cs.Step is now RoundStepNewHeight
	// * cs.StartTime is set to when we will start round0.
	return
}

//-----------------------------------------------------------------------------

func (cs *ConsensusState) SetProposal(proposal *Proposal) error {
	cs.mtx.Lock()
	defer cs.mtx.Unlock()

	// Already have one
	if cs.Proposal != nil {
		return nil
	}

	// Does not apply
	if proposal.Height != cs.Height || proposal.Round != cs.Round {
		return nil
	}

	// We don't care about the proposal if we're already in RoundStepCommit.
	if RoundStepCommit <= cs.Step {
		return nil
	}

	// Verify POLRound, which must be -1 or between 0 and proposal.Round exclusive.
	if proposal.POLRound != -1 &&
		(proposal.POLRound < 0 || proposal.Round <= proposal.POLRound) {
		return ErrInvalidProposalPOLRound
	}

	// Verify signature
	if !cs.Validators.Proposer().PubKey.VerifyBytes(account.SignBytes(cs.state.ChainID, proposal), proposal.Signature) {
		return ErrInvalidProposalSignature
	}

	cs.Proposal = proposal
	cs.ProposalBlockParts = types.NewPartSetFromHeader(proposal.BlockPartsHeader)
	return nil
}

// NOTE: block is not necessarily valid.
func (cs *ConsensusState) AddProposalBlockPart(height int, part *types.Part) (added bool, err error) {
	cs.mtx.Lock()
	defer cs.mtx.Unlock()

	// Blocks might be reused, so round mismatch is OK
	if cs.Height != height {
		return false, nil
	}

	// We're not expecting a block part.
	if cs.ProposalBlockParts == nil {
		return false, nil // TODO: bad peer? Return error?
	}

	added, err = cs.ProposalBlockParts.AddPart(part)
	if err != nil {
		return added, err
	}
	if added && cs.ProposalBlockParts.IsComplete() {
		// Added and completed!
		var n int64
		var err error
		cs.ProposalBlock = binary.ReadBinary(&types.Block{}, cs.ProposalBlockParts.GetReader(), &n, &err).(*types.Block)
		log.Debug("Received complete proposal", "hash", cs.ProposalBlock.Hash())
		if cs.Step == RoundStepPropose && cs.isProposalComplete() {
			// Move onto the next step
			go cs.EnterPrevote(height, cs.Round)
		} else if cs.Step == RoundStepCommit {
			// If we're waiting on the proposal block...
			cs.tryFinalizeCommit(height)
		}
		return true, err
	}
	return added, nil
}

func (cs *ConsensusState) AddVote(address []byte, vote *types.Vote, peerKey string) (added bool, index int, err error) {
	cs.mtx.Lock()
	defer cs.mtx.Unlock()

	return cs.addVote(address, vote, peerKey)
}

//-----------------------------------------------------------------------------

func (cs *ConsensusState) addVote(address []byte, vote *types.Vote, peerKey string) (added bool, index int, err error) {
	// A precommit for the previous height?
	if vote.Height+1 == cs.Height && vote.Type == types.VoteTypePrecommit {
		added, index, err = cs.LastCommit.AddByAddress(address, vote)
		if added {
			log.Debug(Fmt("Added to lastPrecommits: %v", cs.LastCommit.StringShort()))
		}
		return
	}

	// A prevote/precommit for this height?
	if vote.Height == cs.Height {
		height := cs.Height
		added, index, err = cs.Votes.AddByAddress(address, vote, peerKey)
		if added {
			switch vote.Type {
			case types.VoteTypePrevote:
				prevotes := cs.Votes.Prevotes(vote.Round)
				log.Debug(Fmt("Added to prevotes: %v", prevotes.StringShort()))
				// First, unlock if prevotes is a valid POL.
				// >> lockRound < POLRound <= unlockOrChangeLockRound (see spec)
				// NOTE: If (lockRound < POLRound) but !(POLRound <= unlockOrChangeLockRound),
				// we'll still EnterNewRound(H,vote.R) and EnterPrecommit(H,vote.R) to process it
				// there.
				if (cs.LockedBlock != nil) && (cs.LockedRound < vote.Round) && (vote.Round <= cs.Round) {
					hash, _, ok := prevotes.TwoThirdsMajority()
					if ok && !cs.LockedBlock.HashesTo(hash) {
						log.Info("Unlocking because of POL.", "lockedRound", cs.LockedRound, "POLRound", vote.Round)
						cs.LockedRound = 0
						cs.LockedBlock = nil
						cs.LockedBlockParts = nil
					}
				}
				if cs.Round <= vote.Round && prevotes.HasTwoThirdsAny() {
					// Round-skip over to PrevoteWait or goto Precommit.
					go func() {
						if cs.Round < vote.Round {
							cs.EnterNewRound(height, vote.Round)
						}
						if prevotes.HasTwoThirdsMajority() {
							cs.EnterPrecommit(height, vote.Round)
						} else {
							cs.EnterPrevote(height, vote.Round)
							cs.EnterPrevoteWait(height, vote.Round)
						}
					}()
				} else if cs.Proposal != nil && 0 <= cs.Proposal.POLRound && cs.Proposal.POLRound == vote.Round {
					// If the proposal is now complete, enter prevote of cs.Round.
					if cs.isProposalComplete() {
						go cs.EnterPrevote(height, cs.Round)
					}
				}
			case types.VoteTypePrecommit:
				precommits := cs.Votes.Precommits(vote.Round)
				log.Debug(Fmt("Added to precommit: %v", precommits.StringShort()))
				if cs.Round <= vote.Round && precommits.HasTwoThirdsAny() {
					go func() {
						hash, _, ok := precommits.TwoThirdsMajority()
						if ok && len(hash) == 0 {
							cs.EnterNewRound(height, vote.Round+1)
							return
						} else if cs.Round < vote.Round {
							cs.EnterNewRound(height, vote.Round)
						}
						if ok {
							cs.EnterCommit(height)
						} else {
							cs.EnterPrecommit(height, vote.Round)
							cs.EnterPrecommitWait(height, vote.Round)
						}
					}()
				}
			default:
				panic(Fmt("Unexpected vote type %X", vote.Type)) // Should not happen.
			}
		}
		return
	}

	// Height mismatch, bad peer? TODO
	return
}

func (cs *ConsensusState) stageBlock(block *types.Block, blockParts *types.PartSet) error {
	if block == nil {
		panic("Cannot stage nil block")
	}

	// Already staged?
	blockHash := block.Hash()
	if cs.stagedBlock != nil && len(blockHash) != 0 && bytes.Equal(cs.stagedBlock.Hash(), blockHash) {
		return nil
	}

	// Create a copy of the state for staging
	stateCopy := cs.state.Copy()
	// reset the event cache and pass it into the state
	cs.evc = events.NewEventCache(cs.evsw)
	stateCopy.SetFireable(cs.evc)

	// Commit block onto the copied state.
	// NOTE: Basic validation is done in state.AppendBlock().
	err := sm.ExecBlock(stateCopy, block, blockParts.Header())
	if err != nil {
		return err
	} else {
		cs.stagedBlock = block
		cs.stagedState = stateCopy
		return nil
	}
}

func (cs *ConsensusState) signAddVote(type_ byte, hash []byte, header types.PartSetHeader) *types.Vote {
	if cs.privValidator == nil || !cs.Validators.HasAddress(cs.privValidator.Address) {
		return nil
	}
	vote := &types.Vote{
		Height:     cs.Height,
		Round:      cs.Round,
		Type:       type_,
		BlockHash:  hash,
		BlockParts: header,
	}
	err := cs.privValidator.SignVote(cs.state.ChainID, vote)
	if err == nil {
		_, _, err := cs.addVote(cs.privValidator.Address, vote, "")
		log.Info("Signed and added vote", "height", cs.Height, "round", cs.Round, "vote", vote, "error", err)
		return vote
	} else {
		log.Warn("Error signing vote", "height", cs.Height, "round", cs.Round, "vote", vote, "error", err)
		return nil
	}
}

// Save Block, save the +2/3 Commits we've seen
func (cs *ConsensusState) saveBlock(block *types.Block, blockParts *types.PartSet, commits *VoteSet) {

	// The proposal must be valid.
	if err := cs.stageBlock(block, blockParts); err != nil {
		panic(Fmt("saveBlock() an invalid block: %v", err))
	}

	// Save to blockStore.
	if cs.blockStore.Height() < block.Height {
		seenValidation := commits.MakeValidation()
		cs.blockStore.SaveBlock(block, blockParts, seenValidation)
	}

	// Save the state.
	cs.stagedState.Save()

	// Update mempool.
	cs.mempoolReactor.Mempool.ResetForBlockAndState(block, cs.stagedState)

	// Fire off event
	go func(block *types.Block) {
		cs.evsw.FireEvent(types.EventStringNewBlock(), block)
		cs.evc.Flush()
	}(block)

}

// implements events.Eventable
func (cs *ConsensusState) SetFireable(evsw events.Fireable) {
	cs.evsw = evsw
}