[#1243] node: Add "hot" notifications

Wrap engine with notifications writer (if configured so) to allow sending
notifications right after the object is saved in the local storage.
"Hot" notifications are sent for objects with the following tick epoch
values:
1. 0;
2. *current epoch*.

Signed-off-by: Pavel Karpy <carpawell@nspcc.ru>

cmd/neofs-node/object.go

@@ -40,6 +40,7 @@ import (
 	apistatus "github.com/nspcc-dev/neofs-sdk-go/client/status"
 	cid "github.com/nspcc-dev/neofs-sdk-go/container/id"
 	eaclSDK "github.com/nspcc-dev/neofs-sdk-go/eacl"
+	objectSDK "github.com/nspcc-dev/neofs-sdk-go/object"
 	addressSDK "github.com/nspcc-dev/neofs-sdk-go/object/address"
 	"github.com/nspcc-dev/neofs-sdk-go/owner"
 	"github.com/nspcc-dev/neofs-sdk-go/util/signature"
@@ -250,11 +251,25 @@ func initObjectService(c *cfg) {
 
 	c.workers = append(c.workers, pol)
 
+	var os putsvc.ObjectStorage
+	if c.cfgNotifications.enabled {
+		os = engineWithNotifications{
+			e:            ls,
+			nw:           c.cfgNotifications.nw,
+			ns:           c.cfgNetmap.state,
+			defaultTopic: c.cfgNotifications.defaultTopic,
+		}
+	} else {
+		os = engineWithoutNotifications{
+			e: ls,
+		}
+	}
+
 	sPut := putsvc.NewService(
 		putsvc.WithKeyStorage(keyStorage),
 		putsvc.WithClientConstructor(coreConstructor),
 		putsvc.WithMaxSizeSource(c),
-		putsvc.WithLocalStorage(ls),
+		putsvc.WithObjectStorage(os),
 		putsvc.WithContainerSource(c.cfgObject.cnrSource),
 		putsvc.WithNetworkMapSource(c.cfgObject.netMapSource),
 		putsvc.WithNetmapKeys(c),
@@ -531,3 +546,40 @@ func (c *reputationClientConstructor) Get(info coreclient.NodeInfo) (coreclient.
 
 	return cl, nil
 }
+
+type engineWithNotifications struct {
+	e  *engine.StorageEngine
+	nw notificationWriter
+	ns netmap.State
+
+	defaultTopic string
+}
+
+func (e engineWithNotifications) Put(o *objectSDK.Object) error {
+	if err := engine.Put(e.e, o); err != nil {
+		return err
+	}
+
+	ni, err := o.NotificationInfo()
+	if err == nil {
+		if epoch := ni.Epoch(); epoch == 0 || epoch == e.ns.CurrentEpoch() {
+			topic := ni.Topic()
+
+			if topic == "" {
+				topic = e.defaultTopic
+			}
+
+			e.nw.Notify(topic, objectCore.AddressOf(o))
+		}
+	}
+
+	return nil
+}
+
+type engineWithoutNotifications struct {
+	e *engine.StorageEngine
+}
+
+func (e engineWithoutNotifications) Put(o *objectSDK.Object) error {
+	return engine.Put(e.e, o)
+}