[#973] ir: Listen and process Put/Delete events of Subnet contract

Define notification events, implement parsers. Add morph client of
Subnet contract. Listen, verify and approve events in Inner Ring app.

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

pkg/innerring/processors/subnet/put.go

@@ -0,0 +1,82 @@
+package subnetevents
+
+import (
+	"errors"
+	"fmt"
+
+	"github.com/nspcc-dev/neofs-sdk-go/owner"
+	"github.com/nspcc-dev/neofs-sdk-go/subnet"
+	subnetid "github.com/nspcc-dev/neofs-sdk-go/subnet/id"
+)
+
+// Put represents notification about NeoFS subnet creation.
+// Generated by a contract when intending to create a subnet.
+type Put interface {
+	// Contains ID of the subnet to be created.
+	eventWithID
+
+	// ReadCreator reads user ID of the subnet creator.
+	// Returns an error if ID is missing.
+	ReadCreator(id *owner.ID) error
+
+	// ReadInfo reads information about subnet to be created.
+	ReadInfo(info *subnet.Info) error
+}
+
+// PutValidator asserts intent to create a subnet.
+type PutValidator struct{}
+
+// errDiffOwner is returned when subnet owners differ.
+var errDiffOwner = errors.New("diff subnet owners")
+
+// errDiffID is returned when subnet IDs differ.
+var errDiffID = errors.New("diff subnet IDs")
+
+// Assert processes the attempt to create a subnet. Approves the creation through nil return.
+//
+// All read errors of Put are forwarded.
+//
+// Returns an error on:
+//   * zero subnet creation;
+//   * empty ID or different from the one wired into info;
+//   * empty owner ID or different from the one wired into info.
+func (x PutValidator) Assert(event Put) error {
+	var err error
+
+	// read ID
+	var id subnetid.ID
+	if err = event.ReadID(&id); err != nil {
+		return fmt.Errorf("read ID: %w", err)
+	}
+
+	// prevent zero subnet creation
+	if subnetid.IsZero(id) {
+		return zeroSubnetOp{
+			op: "creation",
+		}
+	}
+
+	// read creator's user ID in NeoFS system
+	var creator owner.ID
+	if err = event.ReadCreator(&creator); err != nil {
+		return fmt.Errorf("read creator: %w", err)
+	}
+
+	// read information about the subnet
+	var info subnet.Info
+	if err = event.ReadInfo(&info); err != nil {
+		return fmt.Errorf("read info: %w", err)
+	}
+
+	// check if explicit ID equals to the one from info
+	if !subnet.IDEquals(info, id) {
+		return errDiffID
+	}
+
+	// check if explicit creator equals to the one from info
+	if !subnet.IsOwner(info, creator) {
+		return errDiffOwner
+	}
+
+	return nil
+}