core: add Blockchain event subscription mechanism

A deep internal part of #895. Blockchainer interface is also extended for
various uses of these methods.

pkg/core/blockchain.go

@@ -127,6 +127,20 @@ type Blockchain struct {
 	lastBatch *storage.MemBatch
 
 	contracts native.Contracts
+
+	// Notification subsystem.
+	events  chan bcEvent
+	subCh   chan interface{}
+	unsubCh chan interface{}
+}
+
+// bcEvent is an internal event generated by the Blockchain and then
+// broadcasted to other parties. It joins the new block and associated
+// invocation logs, all the other events visible from outside can be produced
+// from this combination.
+type bcEvent struct {
+	block          *block.Block
+	appExecResults []*state.AppExecResult
 }
 
 type headersOpFunc func(headerList *HeaderHashList)
@@ -169,6 +183,9 @@ func NewBlockchain(s storage.Store, cfg config.ProtocolConfiguration, log *zap.L
 		memPool:       mempool.NewMemPool(cfg.MemPoolSize),
 		keyCache:      make(map[util.Uint160]map[string]*keys.PublicKey),
 		log:           log,
+		events:        make(chan bcEvent),
+		subCh:         make(chan interface{}),
+		unsubCh:       make(chan interface{}),
 
 		generationAmount:  genAmount,
 		decrementInterval: decrementInterval,
@@ -286,6 +303,7 @@ func (bc *Blockchain) Run() {
 		}
 		close(bc.runToExitCh)
 	}()
+	go bc.notificationDispatcher()
 	for {
 		select {
 		case <-bc.stopCh:
@@ -305,6 +323,82 @@ func (bc *Blockchain) Run() {
 	}
 }
 
+// notificationDispatcher manages subscription to events and broadcasts new events.
+func (bc *Blockchain) 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).
+		blockFeed        = make(map[chan<- *block.Block]bool)
+		txFeed           = make(map[chan<- *transaction.Transaction]bool)
+		notificationFeed = make(map[chan<- *state.NotificationEvent]bool)
+		executionFeed    = make(map[chan<- *state.AppExecResult]bool)
+	)
+	for {
+		select {
+		case <-bc.stopCh:
+			return
+		case sub := <-bc.subCh:
+			switch ch := sub.(type) {
+			case chan<- *block.Block:
+				blockFeed[ch] = true
+			case chan<- *transaction.Transaction:
+				txFeed[ch] = true
+			case chan<- *state.NotificationEvent:
+				notificationFeed[ch] = true
+			case chan<- *state.AppExecResult:
+				executionFeed[ch] = true
+			default:
+				panic(fmt.Sprintf("bad subscription: %T", sub))
+			}
+		case unsub := <-bc.unsubCh:
+			switch ch := unsub.(type) {
+			case chan<- *block.Block:
+				delete(blockFeed, ch)
+			case chan<- *transaction.Transaction:
+				delete(txFeed, ch)
+			case chan<- *state.NotificationEvent:
+				delete(notificationFeed, ch)
+			case chan<- *state.AppExecResult:
+				delete(executionFeed, ch)
+			default:
+				panic(fmt.Sprintf("bad unsubscription: %T", unsub))
+			}
+		case event := <-bc.events:
+			// We don't want to waste time looping through transactions when there are no
+			// subscribers.
+			if len(txFeed) != 0 || len(notificationFeed) != 0 || len(executionFeed) != 0 {
+				var aerIdx int
+				for _, tx := range event.block.Transactions {
+					if tx.Type == transaction.InvocationType {
+						aer := event.appExecResults[aerIdx]
+						if !aer.TxHash.Equals(tx.Hash()) {
+							panic("inconsistent application execution results")
+						}
+						aerIdx++
+						for ch := range executionFeed {
+							ch <- aer
+						}
+						if aer.VMState == "HALT" {
+							for i := range aer.Events {
+								for ch := range notificationFeed {
+									ch <- &aer.Events[i]
+								}
+							}
+						}
+					}
+					for ch := range txFeed {
+						ch <- tx
+					}
+				}
+			}
+			for ch := range blockFeed {
+				ch <- event.block
+			}
+		}
+	}
+}
+
 // Close stops Blockchain's internal loop, syncs changes to persistent storage
 // and closes it. The Blockchain is no longer functional after the call to Close.
 func (bc *Blockchain) Close() {
@@ -468,6 +562,7 @@ func (bc *Blockchain) getSystemFeeAmount(h util.Uint256) uint32 {
 // and all tests are in place, we can make a more optimized and cleaner implementation.
 func (bc *Blockchain) storeBlock(block *block.Block) error {
 	cache := dao.NewCached(bc.dao)
+	appExecResults := make([]*state.AppExecResult, 0, len(block.Transactions))
 	fee := bc.getSystemFeeAmount(block.PrevHash)
 	for _, tx := range block.Transactions {
 		fee += uint32(tx.SystemFee.IntegralValue())
@@ -700,6 +795,7 @@ func (bc *Blockchain) storeBlock(block *block.Block) error {
 				Stack:       v.Estack().ToContractParameters(),
 				Events:      systemInterop.Notifications,
 			}
+			appExecResults = append(appExecResults, aer)
 			err = cache.PutAppExecResult(aer)
 			if err != nil {
 				return errors.Wrap(err, "failed to Store notifications")
@@ -728,6 +824,12 @@ func (bc *Blockchain) storeBlock(block *block.Block) error {
 	atomic.StoreUint32(&bc.blockHeight, block.Index)
 	updateBlockHeightMetric(block.Index)
 	bc.memPool.RemoveStale(bc.isTxStillRelevant, bc)
+	// Genesis block is stored when Blockchain is not yet running, so there
+	// is no one to read this event. And it doesn't make much sense as event
+	// anyway.
+	if block.Index != 0 {
+		bc.events <- bcEvent{block, appExecResults}
+	}
 	return nil
 }
 
@@ -1054,6 +1156,68 @@ func (bc *Blockchain) GetConfig() config.ProtocolConfiguration {
 	return bc.config
 }
 
+// SubscribeForBlocks adds given channel to new block event broadcasting, so when
+// there is a new block added to the chain you'll receive it via this channel.
+// Make sure it's read from regularly as not reading these events might affect
+// other Blockchain functions.
+func (bc *Blockchain) SubscribeForBlocks(ch chan<- *block.Block) {
+	bc.subCh <- ch
+}
+
+// SubscribeForTransactions adds given channel to new transaction event
+// broadcasting, so when there is a new transaction added to the chain (in a
+// block) you'll receive it via this channel. Make sure it's read from regularly
+// as not reading these events might affect other Blockchain functions.
+func (bc *Blockchain) SubscribeForTransactions(ch chan<- *transaction.Transaction) {
+	bc.subCh <- ch
+}
+
+// SubscribeForNotifications adds given channel to new notifications event
+// broadcasting, so when an in-block transaction execution generates a
+// notification you'll receive it via this channel. Only notifications from
+// successful transactions are broadcasted, if you're interested in failed
+// transactions use SubscribeForExecutions instead. Make sure this channel is
+// read from regularly as not reading these events might affect other Blockchain
+// functions.
+func (bc *Blockchain) SubscribeForNotifications(ch chan<- *state.NotificationEvent) {
+	bc.subCh <- ch
+}
+
+// SubscribeForExecutions adds given channel to new transaction execution event
+// broadcasting, so when an in-block transaction execution happens you'll receive
+// the result of it via this channel. Make sure it's read from regularly as not
+// reading these events might affect other Blockchain functions.
+func (bc *Blockchain) SubscribeForExecutions(ch chan<- *state.AppExecResult) {
+	bc.subCh <- ch
+}
+
+// UnsubscribeFromBlocks unsubscribes given channel from new block notifications,
+// you can close it afterwards. Passing non-subscribed channel is a no-op.
+func (bc *Blockchain) UnsubscribeFromBlocks(ch chan<- *block.Block) {
+	bc.unsubCh <- ch
+}
+
+// UnsubscribeFromTransactions unsubscribes given channel from new transaction
+// notifications, you can close it afterwards. Passing non-subscribed channel is
+// a no-op.
+func (bc *Blockchain) UnsubscribeFromTransactions(ch chan<- *transaction.Transaction) {
+	bc.unsubCh <- ch
+}
+
+// UnsubscribeFromNotifications unsubscribes given channel from new
+// execution-generated notifications, you can close it afterwards. Passing
+// non-subscribed channel is a no-op.
+func (bc *Blockchain) UnsubscribeFromNotifications(ch chan<- *state.NotificationEvent) {
+	bc.unsubCh <- ch
+}
+
+// UnsubscribeFromExecutions unsubscribes given channel from new execution
+// notifications, you can close it afterwards. Passing non-subscribed channel is
+// a no-op.
+func (bc *Blockchain) UnsubscribeFromExecutions(ch chan<- *state.AppExecResult) {
+	bc.unsubCh <- ch
+}
+
 // CalculateClaimable calculates the amount of GAS which can be claimed for a transaction with value.
 // First return value is GAS generated between startHeight and endHeight.
 // Second return value is GAS returned from accumulated SystemFees between startHeight and endHeight.

pkg/core/blockchain_test.go

@@ -2,12 +2,17 @@ package core
 
 import (
 	"testing"
+	"time"
 
 	"github.com/nspcc-dev/neo-go/pkg/core/block"
+	"github.com/nspcc-dev/neo-go/pkg/core/state"
 	"github.com/nspcc-dev/neo-go/pkg/core/storage"
 	"github.com/nspcc-dev/neo-go/pkg/core/transaction"
 	"github.com/nspcc-dev/neo-go/pkg/crypto/hash"
+	"github.com/nspcc-dev/neo-go/pkg/io"
 	"github.com/nspcc-dev/neo-go/pkg/util"
+	"github.com/nspcc-dev/neo-go/pkg/vm/emit"
+	"github.com/nspcc-dev/neo-go/pkg/vm/opcode"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
@@ -234,3 +239,106 @@ func TestClose(t *testing.T) {
 	// This should never be executed.
 	assert.Nil(t, t)
 }
+
+func TestSubscriptions(t *testing.T) {
+	// We use buffering here as a substitute for reader goroutines, events
+	// get queued up and we read them one by one here.
+	const chBufSize = 16
+	blockCh := make(chan *block.Block, chBufSize)
+	txCh := make(chan *transaction.Transaction, chBufSize)
+	notificationCh := make(chan *state.NotificationEvent, chBufSize)
+	executionCh := make(chan *state.AppExecResult, chBufSize)
+
+	bc := newTestChain(t)
+	bc.SubscribeForBlocks(blockCh)
+	bc.SubscribeForTransactions(txCh)
+	bc.SubscribeForNotifications(notificationCh)
+	bc.SubscribeForExecutions(executionCh)
+
+	assert.Empty(t, notificationCh)
+	assert.Empty(t, executionCh)
+	assert.Empty(t, blockCh)
+	assert.Empty(t, txCh)
+
+	blocks, err := bc.genBlocks(1)
+	require.NoError(t, err)
+	require.Eventually(t, func() bool { return len(blockCh) != 0 }, time.Second, 10*time.Millisecond)
+	assert.Empty(t, notificationCh)
+	assert.Empty(t, executionCh)
+	assert.Empty(t, txCh)
+
+	b := <-blockCh
+	assert.Equal(t, blocks[0], b)
+	assert.Empty(t, blockCh)
+
+	script := io.NewBufBinWriter()
+	emit.Bytes(script.BinWriter, []byte("yay!"))
+	emit.Syscall(script.BinWriter, "Neo.Runtime.Notify")
+	require.NoError(t, script.Err)
+	txGood1 := transaction.NewInvocationTX(script.Bytes(), 0)
+	txGood1.Sender = neoOwner
+	txGood1.Nonce = 1
+	txGood1.ValidUntilBlock = 100500
+	require.NoError(t, signTx(bc, txGood1))
+
+	// Reset() reuses the script buffer and we need to keep scripts.
+	script = io.NewBufBinWriter()
+	emit.Bytes(script.BinWriter, []byte("nay!"))
+	emit.Syscall(script.BinWriter, "Neo.Runtime.Notify")
+	emit.Opcode(script.BinWriter, opcode.THROW)
+	require.NoError(t, script.Err)
+	txBad := transaction.NewInvocationTX(script.Bytes(), 0)
+	txBad.Sender = neoOwner
+	txBad.Nonce = 2
+	txBad.ValidUntilBlock = 100500
+	require.NoError(t, signTx(bc, txBad))
+
+	script = io.NewBufBinWriter()
+	emit.Bytes(script.BinWriter, []byte("yay! yay! yay!"))
+	emit.Syscall(script.BinWriter, "Neo.Runtime.Notify")
+	require.NoError(t, script.Err)
+	txGood2 := transaction.NewInvocationTX(script.Bytes(), 0)
+	txGood2.Sender = neoOwner
+	txGood2.Nonce = 3
+	txGood2.ValidUntilBlock = 100500
+	require.NoError(t, signTx(bc, txGood2))
+
+	invBlock := newBlock(bc.config, bc.BlockHeight()+1, bc.CurrentHeaderHash(), txGood1, txBad, txGood2)
+	require.NoError(t, bc.AddBlock(invBlock))
+
+	require.Eventually(t, func() bool {
+		return len(blockCh) != 0 && len(txCh) != 0 &&
+			len(notificationCh) != 0 && len(executionCh) != 0
+	}, time.Second, 10*time.Millisecond)
+
+	b = <-blockCh
+	require.Equal(t, invBlock, b)
+	assert.Empty(t, blockCh)
+
+	// Follow in-block transaction order.
+	for _, txExpected := range invBlock.Transactions {
+		tx := <-txCh
+		require.Equal(t, txExpected, tx)
+		if txExpected.Type == transaction.InvocationType {
+			exec := <-executionCh
+			require.Equal(t, tx.Hash(), exec.TxHash)
+			if exec.VMState == "HALT" {
+				notif := <-notificationCh
+				inv := tx.Data.(*transaction.InvocationTX)
+				require.Equal(t, hash.Hash160(inv.Script), notif.ScriptHash)
+			}
+		}
+	}
+	assert.Empty(t, txCh)
+	assert.Empty(t, notificationCh)
+	assert.Empty(t, executionCh)
+
+	bc.UnsubscribeFromBlocks(blockCh)
+	bc.UnsubscribeFromTransactions(txCh)
+	bc.UnsubscribeFromNotifications(notificationCh)
+	bc.UnsubscribeFromExecutions(executionCh)
+
+	// Ensure that new blocks are processed correctly after unsubscription.
+	_, err = bc.genBlocks(2 * chBufSize)
+	require.NoError(t, err)
+}

pkg/core/blockchainer/blockchainer.go

@@ -47,6 +47,14 @@ type Blockchainer interface {
 	References(t *transaction.Transaction) ([]transaction.InOut, error)
 	mempool.Feer // fee interface
 	PoolTx(*transaction.Transaction) error
+	SubscribeForBlocks(ch chan<- *block.Block)
+	SubscribeForExecutions(ch chan<- *state.AppExecResult)
+	SubscribeForNotifications(ch chan<- *state.NotificationEvent)
+	SubscribeForTransactions(ch chan<- *transaction.Transaction)
 	VerifyTx(*transaction.Transaction, *block.Block) error
 	GetMemPool() *mempool.Pool
+	UnsubscribeFromBlocks(ch chan<- *block.Block)
+	UnsubscribeFromExecutions(ch chan<- *state.AppExecResult)
+	UnsubscribeFromNotifications(ch chan<- *state.NotificationEvent)
+	UnsubscribeFromTransactions(ch chan<- *transaction.Transaction)
 }

pkg/core/doc.go

@@ -1,5 +1,29 @@
 /*
 Package core implements Neo ledger functionality.
 It's built around the Blockchain structure that maintains state of the ledger.
+
+Events
+
+You can subscribe to Blockchain events using a set of Subscribe and Unsubscribe
+methods. These methods accept channels that will be used to send appropriate
+events, so you can control buffering. Channels are never closed by Blockchain,
+you can close them after unsubscription.
+
+Unlike RPC-level subscriptions these don't allow event filtering because it
+doesn't improve overall efficiency much (when you're using Blockchain you're
+in the same process with it and filtering on your side is not that different
+from filtering on Blockchain side).
+
+The same level of ordering guarantees as with RPC subscriptions is provided,
+albeit for a set of event channels, so at first transaction execution is
+announced via appropriate channels, then followed by notifications generated
+during this execution, then followed by transaction announcement and then
+followed by block announcement. Transaction announcements are ordered the same
+way they're stored in the block.
+
+Be careful using these subscriptions, this mechanism is not intended to be used
+by lots of subscribers and failing to read from event channels can affect
+other Blockchain operations.
+
 */
 package core

pkg/network/helper_test.go

@@ -145,10 +145,36 @@ func (chain testChain) PoolTx(*transaction.Transaction) error {
 	panic("TODO")
 }
 
+func (chain testChain) SubscribeForBlocks(ch chan<- *block.Block) {
+	panic("TODO")
+}
+func (chain testChain) SubscribeForExecutions(ch chan<- *state.AppExecResult) {
+	panic("TODO")
+}
+func (chain testChain) SubscribeForNotifications(ch chan<- *state.NotificationEvent) {
+	panic("TODO")
+}
+func (chain testChain) SubscribeForTransactions(ch chan<- *transaction.Transaction) {
+	panic("TODO")
+}
+
 func (chain testChain) VerifyTx(*transaction.Transaction, *block.Block) error {
 	panic("TODO")
 }
 
+func (chain testChain) UnsubscribeFromBlocks(ch chan<- *block.Block) {
+	panic("TODO")
+}
+func (chain testChain) UnsubscribeFromExecutions(ch chan<- *state.AppExecResult) {
+	panic("TODO")
+}
+func (chain testChain) UnsubscribeFromNotifications(ch chan<- *state.NotificationEvent) {
+	panic("TODO")
+}
+func (chain testChain) UnsubscribeFromTransactions(ch chan<- *transaction.Transaction) {
+	panic("TODO")
+}
+
 type testDiscovery struct{}
 
 func (d testDiscovery) BackFill(addrs ...string)       {}