*: support extra dBFT stage

block.go

@@ -20,6 +20,11 @@ type Block[H Hash] interface {
 
 	// Transactions returns block's transaction list.
 	Transactions() []Transaction[H]
-	// SetTransactions sets block's transaction list.
+	// SetTransactions sets block's transaction list. For anti-MEV extension
+	// transactions provided via this call are taken directly from PreBlock level
+	// and thus, may be out-of-date. Thus, with anti-MEV extension enabled it's
+	// suggested to use this method as a Block finalizer since it will be called
+	// right before the block approval. Do not rely on this with anti-MEV extension
+	// disabled.
 	SetTransactions([]Transaction[H])
 }

check.go

@@ -30,9 +30,57 @@
 		zap.Int("M", d.M()))
 
 	if hasRequest && count >= d.M() {
+		if d.isAntiMEVExtensionEnabled() {
+			d.sendPreCommit()
+			d.changeTimer(d.SecondsPerBlock)
+			d.checkPreCommit()
+		} else {
+			d.sendCommit()
+			d.changeTimer(d.SecondsPerBlock)
+			d.checkCommit()
+		}
+	}
+}
+
+func (d *DBFT[H]) checkPreCommit() {
+	if !d.hasAllTransactions() {
+		d.Logger.Debug("check preCommit: some transactions are missing", zap.Any("hashes", d.MissingTransactions))
+		return
+	}
+
+	count := 0
+	for _, msg := range d.PreCommitPayloads {
+		if msg != nil && msg.ViewNumber() == d.ViewNumber {
+			count++
+		}
+	}
+
+	if count < d.M() {
+		d.Logger.Debug("not enough PreCommits to create PreBlock", zap.Int("count", count))
+		return
+	}
+
+	d.preBlock = d.CreatePreBlock()
+
+	d.Logger.Info("processing PreBlock",
+		zap.Uint32("height", d.BlockIndex),
+		zap.Uint("view", uint(d.ViewNumber)),
+		zap.Int("tx_count", len(d.preBlock.Transactions())))
+
+	if !d.preBlockProcessed {
+		d.preBlockProcessed = true
+		d.ProcessPreBlock(d.preBlock)
+	}
+
+	// Require PreCommit sent by self for reliability. This condition may be removed
+	// in the future.
+	if d.PreCommitSent() {
+		d.verifyCommitPayloadsAgainstHeader()
 		d.sendCommit()
 		d.changeTimer(d.SecondsPerBlock)
 		d.checkCommit()
+	} else {
+		d.Logger.Debug("can't send commit since self preCommit not yet sent")
 	}
 }
 

commit.go

@@ -3,6 +3,7 @@ package dbft
 // Commit is an interface for dBFT Commit message.
 type Commit interface {
 	// Signature returns commit's signature field
-	// which is a block signature for the current epoch.
+	// which is a final block signature for the current epoch for both dBFT 2.0 and
+	// for anti-MEV extension.
 	Signature() []byte
 }

config.go

@@ -20,9 +20,14 @@
 	// if current time is less than that of previous context.
 	// By default use millisecond precision.
 	TimestampIncrement uint64
+	// AntiMEVExtensionEnablingHeight denotes the height starting from which dBFT
+	// Anti-MEV extensions should be enabled. -1 means no extension is enabled.
+	AntiMEVExtensionEnablingHeight int64
 	// GetKeyPair returns an index of the node in the list of validators
 	// together with it's key pair.
 	GetKeyPair func([]PublicKey) (int, PrivateKey, PublicKey)
+	// NewPreBlockFromContext should allocate, fill from Context and return new block.PreBlock.
+	NewPreBlockFromContext func(ctx *Context[H]) PreBlock[H]
 	// NewBlockFromContext should allocate, fill from Context and return new block.Block.
 	NewBlockFromContext func(ctx *Context[H]) Block[H]
 	// RequestTx is a callback which is called when transaction contained
@@ -36,10 +41,14 @@
 	// GetVerified returns a slice of verified transactions
 	// to be proposed in a new block.
 	GetVerified func() []Transaction[H]
+	// VerifyPreBlock verifies if preBlock is valid.
+	VerifyPreBlock func(b PreBlock[H]) bool
 	// VerifyBlock verifies if block is valid.
 	VerifyBlock func(b Block[H]) bool
 	// Broadcast should broadcast payload m to the consensus nodes.
 	Broadcast func(m ConsensusPayload[H])
+	// ProcessBlock is called every time new preBlock is accepted.
+	ProcessPreBlock func(b PreBlock[H])
 	// ProcessBlock is called every time new block is accepted.
 	ProcessBlock func(b Block[H])
 	// GetBlock should return block with hash.
@@ -63,6 +72,8 @@
 	NewPrepareResponse func(preparationHash H) PrepareResponse[H]
 	// NewChangeView is a constructor for payload.ChangeView.
 	NewChangeView func(newViewNumber byte, reason ChangeViewReason, timestamp uint64) ChangeView
+	// NewPreCommit is a constructor for payload.PreCommit.
+	NewPreCommit func(data []byte) PreCommit
 	// NewCommit is a constructor for payload.Commit.
 	NewCommit func(signature []byte) Commit
 	// NewRecoveryRequest is a constructor for payload.RecoveryRequest.
@@ -73,6 +84,10 @@
 	VerifyPrepareRequest func(p ConsensusPayload[H]) error
 	// VerifyPrepareResponse performs external PrepareResponse verification and returns nil if it's successful.
 	VerifyPrepareResponse func(p ConsensusPayload[H]) error
+	// VerifyPreCommit performs external PreCommit verification and returns nil if it's successful.
+	// Note that PreBlock-dependent PreCommit verification should be performed inside PreBlock.Verify
+	// callback.
+	VerifyPreCommit func(p ConsensusPayload[H]) error
 }
 
 const defaultSecondsPerBlock = time.Second * 15
@@ -101,6 +116,10 @@
 
 		VerifyPrepareRequest:  func(ConsensusPayload[H]) error { return nil },
 		VerifyPrepareResponse: func(ConsensusPayload[H]) error { return nil },
+
+		AntiMEVExtensionEnablingHeight: -1,
+		VerifyPreBlock:                 func(PreBlock[H]) bool { return true },
+		VerifyPreCommit:                func(ConsensusPayload[H]) error { return nil },
 	}
 }
 
@@ -131,6 +150,20 @@
 		return errors.New("NewRecoveryRequest is nil")
 	} else if cfg.NewRecoveryMessage == nil {
 		return errors.New("NewRecoveryMessage is nil")
+	} else if cfg.AntiMEVExtensionEnablingHeight >= 0 {
+		if cfg.NewPreBlockFromContext == nil {
+			return errors.New("NewPreBlockFromContext is nil")
+		} else if cfg.ProcessPreBlock == nil {
+			return errors.New("ProcessPreBlock is nil")
+		} else if cfg.NewPreCommit == nil {
+			return errors.New("NewPreCommit is nil")
+		}
+	} else if cfg.NewPreBlockFromContext != nil {
+		return errors.New("NewPreBlockFromContext is set, but AntiMEVExtensionEnablingHeight is not specified")
+	} else if cfg.ProcessPreBlock != nil {
+		return errors.New("ProcessPreBlock is set, but AntiMEVExtensionEnablingHeight is not specified")
+	} else if cfg.NewPreCommit != nil {
+		return errors.New("NewPreCommit is set, but AntiMEVExtensionEnablingHeight is not specified")
 	}
 
 	return nil
@@ -164,13 +197,27 @@
 	}
 }
 
+// WithAntiMEVExtensionEnablingHeight sets AntiMEVExtensionEnablingHeight.
+func WithAntiMEVExtensionEnablingHeight[H Hash](h int64) func(config *Config[H]) {
+	return func(cfg *Config[H]) {
+		cfg.AntiMEVExtensionEnablingHeight = h
+	}
+}
+
 // WithTimestampIncrement sets TimestampIncrement.
 func WithTimestampIncrement[H Hash](u uint64) func(config *Config[H]) {
 	return func(cfg *Config[H]) {
 		cfg.TimestampIncrement = u
 	}
 }
 
+// WithNewPreBlockFromContext sets NewPreBlockFromContext.
+func WithNewPreBlockFromContext[H Hash](f func(ctx *Context[H]) PreBlock[H]) func(config *Config[H]) {
+	return func(cfg *Config[H]) {
+		cfg.NewPreBlockFromContext = f
+	}
+}
+
 // WithNewBlockFromContext sets NewBlockFromContext.
 func WithNewBlockFromContext[H Hash](f func(ctx *Context[H]) Block[H]) func(config *Config[H]) {
 	return func(cfg *Config[H]) {
@@ -206,6 +253,13 @@
 	}
 }
 
+// WithVerifyPreBlock sets VerifyPreBlock.
+func WithVerifyPreBlock[H Hash](f func(b PreBlock[H]) bool) func(config *Config[H]) {
+	return func(cfg *Config[H]) {
+		cfg.VerifyPreBlock = f
+	}
+}
+
 // WithVerifyBlock sets VerifyBlock.
 func WithVerifyBlock[H Hash](f func(b Block[H]) bool) func(config *Config[H]) {
 	return func(cfg *Config[H]) {
@@ -227,6 +281,13 @@
 	}
 }
 
+// WithProcessPreBlock sets ProcessPreBlock.
+func WithProcessPreBlock[H Hash](f func(b PreBlock[H])) func(config *Config[H]) {
+	return func(cfg *Config[H]) {
+		cfg.ProcessPreBlock = f
+	}
+}
+
 // WithGetBlock sets GetBlock.
 func WithGetBlock[H Hash](f func(h H) Block[H]) func(config *Config[H]) {
 	return func(cfg *Config[H]) {
@@ -297,6 +358,13 @@
 	}
 }
 
+// WithNewPreCommit sets NewPreCommit.
+func WithNewPreCommit[H Hash](f func(signature []byte) PreCommit) func(config *Config[H]) {
+	return func(cfg *Config[H]) {
+		cfg.NewPreCommit = f
+	}
+}
+
 // WithNewRecoveryRequest sets NewRecoveryRequest.
 func WithNewRecoveryRequest[H Hash](f func(ts uint64) RecoveryRequest) func(config *Config[H]) {
 	return func(cfg *Config[H]) {
@@ -324,3 +392,10 @@
 		cfg.VerifyPrepareResponse = f
 	}
 }
+
+// WithVerifyPreCommit sets VerifyPreCommit.
+func WithVerifyPreCommit[H Hash](f func(preCommit ConsensusPayload[H]) error) func(config *Config[H]) {
+	return func(cfg *Config[H]) {
+		cfg.VerifyPreCommit = f
+	}
+}

consensus_message.go

@@ -15,6 +15,8 @@ type ConsensusMessage[H Hash] interface {
 	GetPrepareRequest() PrepareRequest[H]
 	// GetPrepareResponse returns payload as if it was PrepareResponse.
 	GetPrepareResponse() PrepareResponse[H]
+	// GetPreCommit returns payload as if it was PreCommit.
+	GetPreCommit() PreCommit
 	// GetCommit returns payload as if it was Commit.
 	GetCommit() Commit
 	// GetRecoveryRequest returns payload as if it was RecoveryRequest.

consensus_message_type.go

@@ -5,11 +5,12 @@
 // MessageType is a type for dBFT consensus messages.
 type MessageType byte
 
-// 6 following constants enumerate all possible type of consensus message.
+// 7 following constants enumerate all possible type of consensus message.
 const (
 	ChangeViewType      MessageType = 0x00
 	PrepareRequestType  MessageType = 0x20
 	PrepareResponseType MessageType = 0x21
+	PreCommitType       MessageType = 0x31
 	CommitType          MessageType = 0x30
 	RecoveryRequestType MessageType = 0x40
 	RecoveryMessageType MessageType = 0x41
@@ -26,6 +27,8 @@
 		return "PrepareResponse"
 	case CommitType:
 		return "Commit"
+	case PreCommitType:
+		return "PreCommit"
 	case RecoveryRequestType:
 		return "RecoveryRequest"
 	case RecoveryMessageType: