[#324] morph/listener: Register handlers of new chain blocks

Extend Listener with RegisterBlockHandler method. All block handlers are
called on each block read from Subscriber.BlockNotifications channel.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/morph/event/handler.go

@@ -1,8 +1,15 @@
 package event
 
+import (
+	"github.com/nspcc-dev/neo-go/pkg/core/block"
+)
+
 // Handler is an Event processing function.
 type Handler func(Event)
 
+// BlockHandler is a chain block processing function.
+type BlockHandler func(*block.Block)
+
 // HandlerInfo is a structure that groups
 // the parameters of the handler of particular
 // contract event.

pkg/morph/event/listener.go

@@ -43,6 +43,13 @@ type Listener interface {
 
 	// Must stop the event listener.
 	Stop()
+
+	// Must register chain block handler.
+	//
+	// The specified handler must be called after each capture and parsing of the new block from chain.
+	//
+	// Must ignore nil handlers.
+	RegisterBlockHandler(BlockHandler)
 }
 
 // ListenerParams is a group of parameters
@@ -67,6 +74,8 @@ type listener struct {
 	log *zap.Logger
 
 	subscriber subscriber.Subscriber
+
+	blockHandlers []BlockHandler
 }
 
 const newListenerFailMsg = "could not instantiate Listener"
@@ -144,6 +153,13 @@ func (s listener) listen(ctx context.Context, intError chan<- error) error {
 }
 
 func (s listener) listenLoop(ctx context.Context, chEvent <-chan *state.NotificationEvent, intErr chan<- error) {
+	blockChan, err := s.subscriber.BlockNotifications()
+	if err != nil {
+		intErr <- errors.Wrap(err, "could not open block notifications channel")
+
+		return
+	}
+
 loop:
 	for {
 		select {
@@ -166,6 +182,23 @@ loop:
 			}
 
 			s.parseAndHandle(notifyEvent)
+		case b, ok := <-blockChan:
+			if !ok {
+				s.log.Warn("stop event listener by block channel")
+				if intErr != nil {
+					intErr <- errors.New("new block notification channel is closed")
+				}
+
+				break loop
+			} else if b == nil {
+				s.log.Warn("nil block was caught")
+				continue loop
+			}
+
+			// TODO: consider asynchronous execution
+			for i := range s.blockHandlers {
+				s.blockHandlers[i](b)
+			}
 		}
 	}
 }
@@ -313,6 +346,15 @@ func (s listener) Stop() {
 	s.subscriber.Close()
 }
 
+func (s *listener) RegisterBlockHandler(handler BlockHandler) {
+	if handler == nil {
+		s.log.Warn("ignore nil block handler")
+		return
+	}
+
+	s.blockHandlers = append(s.blockHandlers, handler)
+}
+
 // NewListener create the notification event listener instance and returns Listener interface.
 func NewListener(p ListenerParams) (Listener, error) {
 	switch {

pkg/morph/subscriber/subscriber.go

@@ -2,7 +2,6 @@ package subscriber
 
 import (
 	"context"
-	"errors"
 	"sync"
 	"time"
 
@@ -11,6 +10,7 @@ import (
 	"github.com/nspcc-dev/neo-go/pkg/rpc/client"
 	"github.com/nspcc-dev/neo-go/pkg/rpc/response"
 	"github.com/nspcc-dev/neo-go/pkg/util"
+	"github.com/pkg/errors"
 	"go.uber.org/zap"
 )
 
@@ -20,7 +20,7 @@ type (
 		SubscribeForNotification(...util.Uint160) (<-chan *state.NotificationEvent, error)
 		UnsubscribeForNotification()
 		Close()
-		BlockNotifications() <-chan *block.Block
+		BlockNotifications() (<-chan *block.Block, error)
 	}
 
 	subscriber struct {
@@ -103,8 +103,18 @@ func (s *subscriber) Close() {
 	s.client.Close()
 }
 
-func (s *subscriber) BlockNotifications() <-chan *block.Block {
+func (s *subscriber) BlockNotifications() (<-chan *block.Block, error) {
-	return s.blockChan
+	if err := s.client.Init(); err != nil {
+		return nil, errors.Wrap(err, "could not init ws client")
+	}
+
+	if _, err := s.client.SubscribeForNewBlocks(nil); err != nil {
+		return nil, errors.Wrap(err, "could not subscribe for new block events")
+	}
+
+	s.blockChan = make(chan *block.Block)
+
+	return s.blockChan, nil
 }
 
 func (s *subscriber) routeNotifications(ctx context.Context) {
@@ -163,17 +173,12 @@ func New(ctx context.Context, p *Params) (Subscriber, error) {
 		return nil, err
 	}
 
-	if _, err := wsClient.SubscribeForNewBlocks(nil); err != nil {
-		return nil, err
-	}
-
 	sub := &subscriber{
 		RWMutex:   new(sync.RWMutex),
 		log:       p.Log,
 		client:    wsClient,
 		notify:    make(chan *state.NotificationEvent),
 		notifyIDs: make(map[util.Uint160]string),
-		blockChan: make(chan *block.Block),
 	}
 
 	// Worker listens all events from neo-go websocket and puts them