core: introduce mempool notifications

pkg/consensus/consensus.go

@@ -451,7 +451,7 @@ func (s *service) verifyBlock(b block.Block) bool {
 	}
 
 	var fee int64
-	var pool = mempool.New(len(coreb.Transactions), 0)
+	var pool = mempool.New(len(coreb.Transactions), 0, false)
 	var mainPool = s.Chain.GetMemPool()
 	for _, tx := range coreb.Transactions {
 		var err error

pkg/core/blockchain.go

@@ -122,8 +122,6 @@ type Blockchain struct {
 	// postBlock is a set of callback methods which should be run under the Blockchain lock after new block is persisted.
 	// Block's transactions are passed via mempool.
 	postBlock []func(blockchainer.Blockchainer, *mempool.Pool, *block.Block)
-	// poolTxWithDataCallbacks is a set of callback methods which should be run nuder the Blockchain lock after successful PoolTxWithData invocation.
-	poolTxWithDataCallbacks []func(t *transaction.Transaction, data interface{})
 
 	sbCommittee keys.PublicKeys
 
@@ -179,7 +177,7 @@ func NewBlockchain(s storage.Store, cfg config.ProtocolConfiguration, log *zap.L
 		dao:         dao.NewSimple(s, cfg.Magic, cfg.StateRootInHeader),
 		stopCh:      make(chan struct{}),
 		runToExitCh: make(chan struct{}),
-		memPool:     mempool.New(cfg.MemPoolSize, 0),
+		memPool:     mempool.New(cfg.MemPoolSize, 0, false),
 		sbCommittee: committee,
 		log:         log,
 		events:      make(chan bcEvent),
@@ -485,7 +483,7 @@ func (bc *Blockchain) AddBlock(block *block.Block) error {
 		if !block.MerkleRoot.Equals(merkle) {
 			return errors.New("invalid block: MerkleRoot mismatch")
 		}
-		mp = mempool.New(len(block.Transactions), 0)
+		mp = mempool.New(len(block.Transactions), 0, false)
 		for _, tx := range block.Transactions {
 			var err error
 			// Transactions are verified before adding them
@@ -1645,7 +1643,7 @@ func (bc *Blockchain) verifyStateRootWitness(r *state.MPTRoot) error {
 // current blockchain state. Note that this verification is completely isolated
 // from the main node's mempool.
 func (bc *Blockchain) VerifyTx(t *transaction.Transaction) error {
-	var mp = mempool.New(1, 0)
+	var mp = mempool.New(1, 0, false)
 	bc.lock.RLock()
 	defer bc.lock.RUnlock()
 	return bc.verifyAndPoolTx(t, mp, bc)
@@ -1679,19 +1677,7 @@ func (bc *Blockchain) PoolTxWithData(t *transaction.Transaction, data interface{
 			return err
 		}
 	}
-	if err := bc.verifyAndPoolTx(t, mp, feer, data); err != nil {
+	return bc.verifyAndPoolTx(t, mp, feer, data)
-		return err
-	}
-	for _, f := range bc.poolTxWithDataCallbacks {
-		f(t, data)
-	}
-	return nil
-}
-
-// RegisterPoolTxWithDataCallback registers new callback function which is called
-// under the Blockchain lock after successful PoolTxWithData invocation.
-func (bc *Blockchain) RegisterPoolTxWithDataCallback(f func(t *transaction.Transaction, data interface{})) {
-	bc.poolTxWithDataCallbacks = append(bc.poolTxWithDataCallbacks, f)
 }
 
 //GetStandByValidators returns validators from the configuration.
@@ -1912,11 +1898,6 @@ func (bc *Blockchain) newInteropContext(trigger trigger.Type, d dao.DAO, block *
 	return ic
 }
 
-// P2PNotaryModuleEnabled defines whether P2P notary module is enabled.
-func (bc *Blockchain) P2PNotaryModuleEnabled() bool {
-	return bc.config.P2PNotary.Enabled
-}
-
 // P2PSigExtensionsEnabled defines whether P2P signature extensions are enabled.
 func (bc *Blockchain) P2PSigExtensionsEnabled() bool {
 	return bc.config.P2PSigExtensions

pkg/core/blockchain_test.go

@@ -449,7 +449,7 @@ func TestVerifyTx(t *testing.T) {
 		require.True(t, errors.Is(err, ErrAlreadyExists))
 	})
 	t.Run("MemPoolOOM", func(t *testing.T) {
-		bc.memPool = mempool.New(1, 0)
+		bc.memPool = mempool.New(1, 0, false)
 		tx1 := bc.newTestTx(h, testScript)
 		tx1.NetworkFee += 10000 // Give it more priority.
 		require.NoError(t, accs[0].SignTx(tx1))
@@ -988,7 +988,7 @@ func TestVerifyTx(t *testing.T) {
 			return tx
 		}
 
-		mp := mempool.New(10, 1)
+		mp := mempool.New(10, 1, false)
 		verificationF := func(bc blockchainer.Blockchainer, tx *transaction.Transaction, data interface{}) error {
 			if data.(int) > 5 {
 				return errors.New("bad data")

pkg/core/blockchainer/blockchainer.go

@@ -64,7 +64,6 @@ type Blockchainer interface {
 	ManagementContractHash() util.Uint160
 	PoolTx(t *transaction.Transaction, pools ...*mempool.Pool) error
 	PoolTxWithData(t *transaction.Transaction, data interface{}, mp *mempool.Pool, feer mempool.Feer, verificationFunction func(bc Blockchainer, t *transaction.Transaction, data interface{}) error) error
-	RegisterPoolTxWithDataCallback(f func(t *transaction.Transaction, data interface{}))
 	RegisterPostBlock(f func(Blockchainer, *mempool.Pool, *block.Block))
 	SetNotary(mod services.Notary)
 	SubscribeForBlocks(ch chan<- *block.Block)

pkg/core/mempool/feer.go

@@ -12,5 +12,4 @@ type Feer interface {
 	GetUtilityTokenBalance(util.Uint160) *big.Int
 	BlockHeight() uint32
 	P2PSigExtensionsEnabled() bool
-	P2PNotaryModuleEnabled() bool
 }

pkg/core/mempool/mem_pool.go

@@ -10,6 +10,7 @@ import (
 
 	"github.com/nspcc-dev/neo-go/pkg/core/transaction"
 	"github.com/nspcc-dev/neo-go/pkg/util"
+	"go.uber.org/atomic"
 )
 
 var (
@@ -69,8 +70,14 @@ type Pool struct {
 
 	resendThreshold uint32
 	resendFunc      func(*transaction.Transaction, interface{})
-	// removeStaleCallback is a callback method which is called after item is removed from the mempool.
+
-	removeStaleCallback func(*transaction.Transaction, interface{})
+	// subscriptions for mempool events
+	subscriptionsEnabled bool
+	subscriptionsOn      atomic.Bool
+	stopCh               chan struct{}
+	events               chan Event
+	subCh                chan chan<- Event // there are no other events in mempool except Event, so no need in generic subscribers type
+	unsubCh              chan chan<- Event
 }
 
 func (p items) Len() int           { return len(p) }
@@ -251,6 +258,13 @@ func (mp *Pool) Add(t *transaction.Transaction, fee Feer, data ...interface{}) e
 			delete(mp.oracleResp, attrs[0].Value.(*transaction.OracleResponse).ID)
 		}
 		mp.verifiedTxes[len(mp.verifiedTxes)-1] = pItem
+		if mp.subscriptionsOn.Load() {
+			mp.events <- Event{
+				Type: TransactionRemoved,
+				Tx:   unlucky.txn,
+				Data: unlucky.data,
+			}
+		}
 	} else {
 		mp.verifiedTxes = append(mp.verifiedTxes, pItem)
 	}
@@ -271,6 +285,14 @@ func (mp *Pool) Add(t *transaction.Transaction, fee Feer, data ...interface{}) e
 
 	updateMempoolMetrics(len(mp.verifiedTxes))
 	mp.lock.Unlock()
+
+	if mp.subscriptionsOn.Load() {
+		mp.events <- Event{
+			Type: TransactionAdded,
+			Tx:   pItem.txn,
+			Data: pItem.data,
+		}
+	}
 	return nil
 }
 
@@ -309,6 +331,13 @@ func (mp *Pool) removeInternal(hash util.Uint256, feer Feer) {
 		if attrs := tx.GetAttributes(transaction.OracleResponseT); len(attrs) != 0 {
 			delete(mp.oracleResp, attrs[0].Value.(*transaction.OracleResponse).ID)
 		}
+		if mp.subscriptionsOn.Load() {
+			mp.events <- Event{
+				Type: TransactionRemoved,
+				Tx:   itm.txn,
+				Data: itm.data,
+			}
+		}
 	}
 	updateMempoolMetrics(len(mp.verifiedTxes))
 }
@@ -328,8 +357,7 @@ func (mp *Pool) RemoveStale(isOK func(*transaction.Transaction) bool, feer Feer)
 	}
 	height := feer.BlockHeight()
 	var (
-		staleItems   []item
+		staleItems []item
-		removedItems []item
 	)
 	for _, itm := range mp.verifiedTxes {
 		if isOK(itm.txn) && mp.checkPolicy(itm.txn, policyChanged) && mp.tryAddSendersFee(itm.txn, feer, true) {
@@ -353,17 +381,18 @@ func (mp *Pool) RemoveStale(isOK func(*transaction.Transaction) bool, feer Feer)
 			if attrs := itm.txn.GetAttributes(transaction.OracleResponseT); len(attrs) != 0 {
 				delete(mp.oracleResp, attrs[0].Value.(*transaction.OracleResponse).ID)
 			}
-			if feer.P2PSigExtensionsEnabled() && feer.P2PNotaryModuleEnabled() && mp.removeStaleCallback != nil {
+			if mp.subscriptionsOn.Load() {
-				removedItems = append(removedItems, itm)
+				mp.events <- Event{
+					Type: TransactionRemoved,
+					Tx:   itm.txn,
+					Data: itm.data,
+				}
 			}
 		}
 	}
 	if len(staleItems) != 0 {
 		go mp.resendStaleItems(staleItems)
 	}
-	if len(removedItems) != 0 {
-		go mp.postRemoveStale(removedItems)
-	}
 	mp.verifiedTxes = newVerifiedTxes
 	mp.lock.Unlock()
 }
@@ -388,16 +417,23 @@ func (mp *Pool) checkPolicy(tx *transaction.Transaction, policyChanged bool) boo
 }
 
 // New returns a new Pool struct.
-func New(capacity int, payerIndex int) *Pool {
+func New(capacity int, payerIndex int, enableSubscriptions bool) *Pool {
-	return &Pool{
+	mp := &Pool{
-		verifiedMap:  make(map[util.Uint256]*transaction.Transaction),
+		verifiedMap:          make(map[util.Uint256]*transaction.Transaction),
-		verifiedTxes: make([]item, 0, capacity),
+		verifiedTxes:         make([]item, 0, capacity),
-		capacity:     capacity,
+		capacity:             capacity,
-		payerIndex:   payerIndex,
+		payerIndex:           payerIndex,
-		fees:         make(map[util.Uint160]utilityBalanceAndFees),
+		fees:                 make(map[util.Uint160]utilityBalanceAndFees),
-		conflicts:    make(map[util.Uint256][]util.Uint256),
+		conflicts:            make(map[util.Uint256][]util.Uint256),
-		oracleResp:   make(map[uint64]util.Uint256),
+		oracleResp:           make(map[uint64]util.Uint256),
+		subscriptionsEnabled: enableSubscriptions,
+		stopCh:               make(chan struct{}),
+		events:               make(chan Event),
+		subCh:                make(chan chan<- Event),
+		unsubCh:              make(chan chan<- Event),
 	}
+	mp.subscriptionsOn.Store(false)
+	return mp
 }
 
 // SetResendThreshold sets threshold after which transaction will be considered stale
@@ -409,25 +445,12 @@ func (mp *Pool) SetResendThreshold(h uint32, f func(*transaction.Transaction, in
 	mp.resendFunc = f
 }
 
-// SetRemoveStaleCallback registers new callback method which should be called after mempool item is kicked off.
-func (mp *Pool) SetRemoveStaleCallback(f func(t *transaction.Transaction, data interface{})) {
-	mp.lock.Lock()
-	defer mp.lock.Unlock()
-	mp.removeStaleCallback = f
-}
-
 func (mp *Pool) resendStaleItems(items []item) {
 	for i := range items {
 		mp.resendFunc(items[i].txn, items[i].data)
 	}
 }
 
-func (mp *Pool) postRemoveStale(items []item) {
-	for i := range items {
-		mp.removeStaleCallback(items[i].txn, items[i].data)
-	}
-}
-
 // TryGetValue returns a transaction and its fee if it exists in the memory pool.
 func (mp *Pool) TryGetValue(hash util.Uint256) (*transaction.Transaction, bool) {
 	mp.lock.RLock()

pkg/core/mempool/mem_pool_test.go

@@ -44,12 +44,8 @@ func (fs *FeerStub) P2PSigExtensionsEnabled() bool {
 	return fs.p2pSigExt
 }
 
-func (fs *FeerStub) P2PNotaryModuleEnabled() bool {
-	return false
-}
-
 func testMemPoolAddRemoveWithFeer(t *testing.T, fs Feer) {
-	mp := New(10, 0)
+	mp := New(10, 0, false)
 	tx := transaction.New(netmode.UnitTestNet, []byte{byte(opcode.PUSH1)}, 0)
 	tx.Nonce = 0
 	tx.Signers = []transaction.Signer{{Account: util.Uint160{1, 2, 3}}}
@@ -70,7 +66,7 @@ func testMemPoolAddRemoveWithFeer(t *testing.T, fs Feer) {
 }
 
 func TestMemPoolRemoveStale(t *testing.T) {
-	mp := New(5, 0)
+	mp := New(5, 0, false)
 	txs := make([]*transaction.Transaction, 5)
 	for i := range txs {
 		txs[i] = transaction.New(netmode.UnitTestNet, []byte{byte(opcode.PUSH1)}, 0)
@@ -121,7 +117,7 @@ func TestMemPoolAddRemove(t *testing.T) {
 func TestOverCapacity(t *testing.T) {
 	var fs = &FeerStub{balance: 10000000}
 	const mempoolSize = 10
-	mp := New(mempoolSize, 0)
+	mp := New(mempoolSize, 0, false)
 
 	for i := 0; i < mempoolSize; i++ {
 		tx := transaction.New(netmode.UnitTestNet, []byte{byte(opcode.PUSH1)}, 0)
@@ -197,7 +193,7 @@ func TestOverCapacity(t *testing.T) {
 func TestGetVerified(t *testing.T) {
 	var fs = &FeerStub{}
 	const mempoolSize = 10
-	mp := New(mempoolSize, 0)
+	mp := New(mempoolSize, 0, false)
 
 	txes := make([]*transaction.Transaction, 0, mempoolSize)
 	for i := 0; i < mempoolSize; i++ {
@@ -221,7 +217,7 @@ func TestGetVerified(t *testing.T) {
 func TestRemoveStale(t *testing.T) {
 	var fs = &FeerStub{}
 	const mempoolSize = 10
-	mp := New(mempoolSize, 0)
+	mp := New(mempoolSize, 0, false)
 
 	txes1 := make([]*transaction.Transaction, 0, mempoolSize/2)
 	txes2 := make([]*transaction.Transaction, 0, mempoolSize/2)
@@ -254,7 +250,7 @@ func TestRemoveStale(t *testing.T) {
 }
 
 func TestMemPoolFees(t *testing.T) {
-	mp := New(10, 0)
+	mp := New(10, 0, false)
 	fs := &FeerStub{balance: 10000000}
 	sender0 := util.Uint160{1, 2, 3}
 	tx0 := transaction.New(netmode.UnitTestNet, []byte{byte(opcode.PUSH1)}, 0)
@@ -365,7 +361,7 @@ func TestMempoolItemsOrder(t *testing.T) {
 }
 
 func TestMempoolAddRemoveOracleResponse(t *testing.T) {
-	mp := New(3, 0)
+	mp := New(3, 0, false)
 	nonce := uint32(0)
 	fs := &FeerStub{balance: 10000}
 	newTx := func(netFee int64, id uint64) *transaction.Transaction {
@@ -435,7 +431,7 @@ func TestMempoolAddRemoveOracleResponse(t *testing.T) {
 
 func TestMempoolAddRemoveConflicts(t *testing.T) {
 	capacity := 6
-	mp := New(capacity, 0)
+	mp := New(capacity, 0, false)
 	var (
 		fs           = &FeerStub{p2pSigExt: true, balance: 100000}
 		nonce uint32 = 1
@@ -565,7 +561,7 @@ func TestMempoolAddWithDataGetData(t *testing.T) {
 		blockHeight: 5,
 		balance:     100,
 	}
-	mp := New(10, 1)
+	mp := New(10, 1, false)
 	newTx := func(t *testing.T, netFee int64) *transaction.Transaction {
 		tx := transaction.New(netmode.UnitTestNet, []byte{byte(opcode.RET)}, 0)
 		tx.Signers = []transaction.Signer{{}, {}}

pkg/core/mempool/subscriptions.go

@@ -0,0 +1,86 @@
+package mempool
+
+import (
+	"github.com/nspcc-dev/neo-go/pkg/core/transaction"
+)
+
+// EventType represents mempool event type.
+type EventType byte
+
+const (
+	// TransactionAdded marks transaction addition mempool event.
+	TransactionAdded EventType = 0x01
+	// TransactionRemoved marks transaction removal mempool event.
+	TransactionRemoved EventType = 0x02
+)
+
+// Event represents one of mempool events: transaction was added or removed from mempool.
+type Event struct {
+	Type EventType
+	Tx   *transaction.Transaction
+	Data interface{}
+}
+
+// RunSubscriptions runs subscriptions goroutine if mempool subscriptions are enabled.
+// You should manually free the resources by calling StopSubscriptions on mempool shutdown.
+func (mp *Pool) RunSubscriptions() {
+	if !mp.subscriptionsEnabled {
+		panic("subscriptions are disabled")
+	}
+	if !mp.subscriptionsOn.Load() {
+		mp.subscriptionsOn.Store(true)
+		go mp.notificationDispatcher()
+	}
+}
+
+// StopSubscriptions stops mempool events loop.
+func (mp *Pool) StopSubscriptions() {
+	if !mp.subscriptionsEnabled {
+		panic("subscriptions are disabled")
+	}
+	if mp.subscriptionsOn.Load() {
+		mp.subscriptionsOn.Store(false)
+		close(mp.stopCh)
+	}
+}
+
+// SubscribeForTransactions adds given channel to new mempool event broadcasting, so when
+// there is a new transactions added to mempool or an existing transaction removed from
+// mempool you'll receive it via this channel.
+func (mp *Pool) SubscribeForTransactions(ch chan<- Event) {
+	if mp.subscriptionsOn.Load() {
+		mp.subCh <- ch
+	}
+}
+
+// UnsubscribeFromTransactions unsubscribes given channel from new mempool notifications,
+// you can close it afterwards. Passing non-subscribed channel is a no-op.
+func (mp *Pool) UnsubscribeFromTransactions(ch chan<- Event) {
+	if mp.subscriptionsOn.Load() {
+		mp.unsubCh <- ch
+	}
+}
+
+// notificationDispatcher manages subscription to events and broadcasts new events.
+func (mp *Pool) notificationDispatcher() {
+	var (
+		// These are just sets of subscribers, though modelled as maps
+		// for ease of management (not a lot of subscriptions is really
+		// expected, but maps are convenient for adding/deleting elements).
+		txFeed = make(map[chan<- Event]bool)
+	)
+	for {
+		select {
+		case <-mp.stopCh:
+			return
+		case sub := <-mp.subCh:
+			txFeed[sub] = true
+		case unsub := <-mp.unsubCh:
+			delete(txFeed, unsub)
+		case event := <-mp.events:
+			for ch := range txFeed {
+				ch <- event
+			}
+		}
+	}
+}

pkg/core/mempool/subscriptions_test.go

@@ -0,0 +1,98 @@
+package mempool
+
+import (
+	"testing"
+	"time"
+
+	"github.com/nspcc-dev/neo-go/pkg/config/netmode"
+	"github.com/nspcc-dev/neo-go/pkg/core/transaction"
+	"github.com/nspcc-dev/neo-go/pkg/util"
+	"github.com/nspcc-dev/neo-go/pkg/vm/opcode"
+	"github.com/stretchr/testify/require"
+)
+
+func TestSubscriptions(t *testing.T) {
+	t.Run("disabled subscriptions", func(t *testing.T) {
+		mp := New(5, 0, false)
+		require.Panics(t, func() {
+			mp.RunSubscriptions()
+		})
+		require.Panics(t, func() {
+			mp.StopSubscriptions()
+		})
+	})
+
+	t.Run("enabled subscriptions", func(t *testing.T) {
+		fs := &FeerStub{balance: 100}
+		mp := New(2, 0, true)
+		mp.RunSubscriptions()
+		subChan1 := make(chan Event, 3)
+		subChan2 := make(chan Event, 3)
+		mp.SubscribeForTransactions(subChan1)
+		defer mp.StopSubscriptions()
+
+		txs := make([]*transaction.Transaction, 4)
+		for i := range txs {
+			txs[i] = transaction.New(netmode.UnitTestNet, []byte{byte(opcode.PUSH1)}, 0)
+			txs[i].Nonce = uint32(i)
+			txs[i].Signers = []transaction.Signer{{Account: util.Uint160{1, 2, 3}}}
+			txs[i].NetworkFee = int64(i)
+		}
+
+		// add tx
+		require.NoError(t, mp.Add(txs[0], fs))
+		require.Eventually(t, func() bool { return len(subChan1) == 1 }, time.Second, time.Millisecond*100)
+		event := <-subChan1
+		require.Equal(t, Event{Type: TransactionAdded, Tx: txs[0]}, event)
+
+		// severak subscribers
+		mp.SubscribeForTransactions(subChan2)
+		require.NoError(t, mp.Add(txs[1], fs))
+		require.Eventually(t, func() bool { return len(subChan1) == 1 && len(subChan2) == 1 }, time.Second, time.Millisecond*100)
+		event1 := <-subChan1
+		event2 := <-subChan2
+		require.Equal(t, Event{Type: TransactionAdded, Tx: txs[1]}, event1)
+		require.Equal(t, Event{Type: TransactionAdded, Tx: txs[1]}, event2)
+
+		// reach capacity
+		require.NoError(t, mp.Add(txs[2], &FeerStub{}))
+		require.Eventually(t, func() bool { return len(subChan1) == 2 && len(subChan2) == 2 }, time.Second, time.Millisecond*100)
+		event1 = <-subChan1
+		event2 = <-subChan2
+		require.Equal(t, Event{Type: TransactionRemoved, Tx: txs[0]}, event1)
+		require.Equal(t, Event{Type: TransactionRemoved, Tx: txs[0]}, event2)
+		event1 = <-subChan1
+		event2 = <-subChan2
+		require.Equal(t, Event{Type: TransactionAdded, Tx: txs[2]}, event1)
+		require.Equal(t, Event{Type: TransactionAdded, Tx: txs[2]}, event2)
+
+		// remove tx
+		mp.Remove(txs[1].Hash(), fs)
+		require.Eventually(t, func() bool { return len(subChan1) == 1 && len(subChan2) == 1 }, time.Second, time.Millisecond*100)
+		event1 = <-subChan1
+		event2 = <-subChan2
+		require.Equal(t, Event{Type: TransactionRemoved, Tx: txs[1]}, event1)
+		require.Equal(t, Event{Type: TransactionRemoved, Tx: txs[1]}, event2)
+
+		// remove stale
+		mp.RemoveStale(func(tx *transaction.Transaction) bool {
+			if tx.Hash().Equals(txs[2].Hash()) {
+				return false
+			}
+			return true
+		}, fs)
+		require.Eventually(t, func() bool { return len(subChan1) == 1 && len(subChan2) == 1 }, time.Second, time.Millisecond*100)
+		event1 = <-subChan1
+		event2 = <-subChan2
+		require.Equal(t, Event{Type: TransactionRemoved, Tx: txs[2]}, event1)
+		require.Equal(t, Event{Type: TransactionRemoved, Tx: txs[2]}, event2)
+
+		// unsubscribe
+		mp.UnsubscribeFromTransactions(subChan1)
+		require.NoError(t, mp.Add(txs[3], fs))
+		require.Eventually(t, func() bool { return len(subChan2) == 1 }, time.Second, time.Millisecond*100)
+		event2 = <-subChan2
+		require.Equal(t, 0, len(subChan1))
+		require.Equal(t, Event{Type: TransactionAdded, Tx: txs[3]}, event2)
+	})
+}

pkg/network/helper_test.go

@@ -52,7 +52,7 @@ type testChain struct {
 
 func newTestChain() *testChain {
 	return &testChain{
-		Pool:                  mempool.New(10, 0),
+		Pool:                  mempool.New(10, 0, false),
 		poolTx:                func(*transaction.Transaction) error { return nil },
 		poolTxWithData:        func(*transaction.Transaction, interface{}, *mempool.Pool) error { return nil },
 		blocks:                make(map[util.Uint256]*block.Block),
@@ -143,10 +143,6 @@ func (chain *testChain) P2PSigExtensionsEnabled() bool {
 	return true
 }
 
-func (chain *testChain) P2PNotaryModuleEnabled() bool {
-	return false
-}
-
 func (chain *testChain) GetMaxBlockSystemFee() int64 {
 	panic("TODO")
 }
@@ -289,9 +285,6 @@ func (chain *testChain) PoolTx(tx *transaction.Transaction, _ ...*mempool.Pool)
 func (chain testChain) SetOracle(services.Oracle) {
 	panic("TODO")
 }
-func (chain *testChain) RegisterPoolTxWithDataCallback(f func(t *transaction.Transaction, data interface{})) {
-	panic("TODO")
-}
 func (chain *testChain) SetNotary(notary services.Notary) {
 	panic("TODO")
 }

pkg/network/notary_feer.go

@@ -32,11 +32,6 @@ func (f NotaryFeer) P2PSigExtensionsEnabled() bool {
 	return f.bc.P2PSigExtensionsEnabled()
 }
 
-// P2PNotaryModuleEnabled implements mempool.Feer interface.
-func (f NotaryFeer) P2PNotaryModuleEnabled() bool {
-	return f.bc.P2PNotaryModuleEnabled()
-}
-
 // NewNotaryFeer returns new NotaryFeer instance.
 func NewNotaryFeer(bc blockchainer.Blockchainer) NotaryFeer {
 	return NotaryFeer{

pkg/network/server.go

@@ -137,14 +137,14 @@ func newServerFromConstructors(config ServerConfig, chain blockchainer.Blockchai
 	}
 	if chain.P2PSigExtensionsEnabled() {
 		s.notaryFeer = NewNotaryFeer(chain)
-		s.notaryRequestPool = mempool.New(chain.GetConfig().P2PNotaryRequestPayloadPoolSize, 1)
+		s.notaryRequestPool = mempool.New(chain.GetConfig().P2PNotaryRequestPayloadPoolSize, 1, chain.GetConfig().P2PNotary.Enabled)
 		chain.RegisterPostBlock(func(bc blockchainer.Blockchainer, txpool *mempool.Pool, _ *block.Block) {
 			s.notaryRequestPool.RemoveStale(func(t *transaction.Transaction) bool {
 				return bc.IsTxStillRelevant(t, txpool, true)
 			}, s.notaryFeer)
 		})
 		if chain.GetConfig().P2PNotary.Enabled {
-			n, err := notary.NewNotary(chain, s.log, func(tx *transaction.Transaction) error {
+			n, err := notary.NewNotary(chain, s.notaryRequestPool, s.log, func(tx *transaction.Transaction) error {
 				r := s.RelayTxn(tx)
 				if r != RelaySucceed {
 					return fmt.Errorf("can't pool notary tx: hash %s, reason: %d", tx.Hash().StringLE(), byte(r))
@@ -156,11 +156,6 @@ func newServerFromConstructors(config ServerConfig, chain blockchainer.Blockchai
 			}
 			s.notaryModule = n
 			chain.SetNotary(n)
-			chain.RegisterPoolTxWithDataCallback(func(_ *transaction.Transaction, data interface{}) {
-				if notaryRequest, ok := data.(*payload.P2PNotaryRequest); ok {
-					s.notaryModule.OnNewRequest(notaryRequest)
-				}
-			})
 			chain.RegisterPostBlock(func(bc blockchainer.Blockchainer, pool *mempool.Pool, b *block.Block) {
 				s.notaryModule.PostPersist(bc, pool, b)
 			})
@@ -261,6 +256,10 @@ func (s *Server) Start(errChan chan error) {
 	if s.oracle != nil {
 		go s.oracle.Run()
 	}
+	if s.notaryModule != nil {
+		s.notaryRequestPool.RunSubscriptions()
+		go s.notaryModule.Run()
+	}
 	go s.relayBlocksLoop()
 	go s.bQueue.run()
 	go s.transport.Accept()
@@ -283,6 +282,10 @@ func (s *Server) Shutdown() {
 	if s.oracle != nil {
 		s.oracle.Shutdown()
 	}
+	if s.notaryModule != nil {
+		s.notaryModule.Stop()
+		s.notaryRequestPool.StopSubscriptions()
+	}
 	close(s.quit)
 }
 
@@ -1195,13 +1198,6 @@ func (s *Server) initStaleMemPools() {
 	mp.SetResendThreshold(uint32(threshold), s.broadcastTX)
 	if s.chain.P2PSigExtensionsEnabled() {
 		s.notaryRequestPool.SetResendThreshold(uint32(threshold), s.broadcastP2PNotaryRequestPayload)
-		if s.chain.GetConfig().P2PNotary.Enabled {
-			s.notaryRequestPool.SetRemoveStaleCallback(func(_ *transaction.Transaction, data interface{}) {
-				if notaryRequest, ok := data.(*payload.P2PNotaryRequest); ok {
-					s.notaryModule.OnRequestRemoval(notaryRequest)
-				}
-			})
-		}
 	}
 }
 

pkg/network/server_test.go

@@ -850,7 +850,6 @@ func (f feerStub) FeePerByte() int64                            { return 1 }
 func (f feerStub) GetUtilityTokenBalance(util.Uint160) *big.Int { return big.NewInt(100000000) }
 func (f feerStub) BlockHeight() uint32                          { return f.blockHeight }
 func (f feerStub) P2PSigExtensionsEnabled() bool                { return false }
-func (f feerStub) P2PNotaryModuleEnabled() bool                 { return false }
 func (f feerStub) GetBaseExecFee() int64                        { return interop.DefaultBaseExecFee }
 
 func TestMemPool(t *testing.T) {

pkg/rpc/server/server_helper_test.go

@@ -126,10 +126,6 @@ func (fs FeerStub) P2PSigExtensionsEnabled() bool {
 	return false
 }
 
-func (fs FeerStub) P2PNotaryModuleEnabled() bool {
-	return false
-}
-
 func (fs FeerStub) GetBaseExecFee() int64 {
 	return interop.DefaultBaseExecFee
 }

pkg/services/notary/notary.go

@@ -41,6 +41,11 @@ type (
 		accMtx      sync.RWMutex
 		currAccount *wallet.Account
 		wallet      *wallet.Wallet
+
+		mp *mempool.Pool
+		// requests channel
+		reqCh  chan mempool.Event
+		stopCh chan struct{}
 	}
 
 	// Config represents external configuration for Notary module.
@@ -74,7 +79,7 @@ type request struct {
 }
 
 // NewNotary returns new Notary module.
-func NewNotary(bc blockchainer.Blockchainer, log *zap.Logger, onTransaction func(tx *transaction.Transaction) error) (*Notary, error) {
+func NewNotary(bc blockchainer.Blockchainer, mp *mempool.Pool, log *zap.Logger, onTransaction func(tx *transaction.Transaction) error) (*Notary, error) {
 	cfg := bc.GetConfig().P2PNotary
 	w := cfg.UnlockWallet
 	wallet, err := wallet.NewWalletFromFile(w.Path)
@@ -102,9 +107,38 @@ func NewNotary(bc blockchainer.Blockchainer, log *zap.Logger, onTransaction func
 		},
 		wallet:        wallet,
 		onTransaction: onTransaction,
+		mp:            mp,
+		reqCh:         make(chan mempool.Event),
+		stopCh:        make(chan struct{}),
 	}, nil
 }
 
+// Run runs Notary module and should be called in a separate goroutine.
+func (n *Notary) Run() {
+	n.mp.SubscribeForTransactions(n.reqCh)
+	for {
+		select {
+		case <-n.stopCh:
+			n.mp.UnsubscribeFromTransactions(n.reqCh)
+			return
+		case event := <-n.reqCh:
+			if req, ok := event.Data.(*payload.P2PNotaryRequest); ok {
+				switch event.Type {
+				case mempool.TransactionAdded:
+					n.OnNewRequest(req)
+				case mempool.TransactionRemoved:
+					n.OnRequestRemoval(req)
+				}
+			}
+		}
+	}
+}
+
+// Stop shutdowns Notary module.
+func (n *Notary) Stop() {
+	close(n.stopCh)
+}
+
 // OnNewRequest is a callback method which is called after new notary request is added to the notary request pool.
 func (n *Notary) OnNewRequest(payload *payload.P2PNotaryRequest) {
 	if n.getAccount() == nil {