[#401] control: Serve DropObjects RPC

Re-compile protobuf definition of Control service. Implement required
messages on DropObjects RPC request and response messages. Implement
`DropObjects` method on Control service server of the node. Use
`StorageEngine.Delete` method as a deleted object handler on server.

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

pkg/services/control/server/gc.go

@@ -0,0 +1,61 @@
+package control
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/nspcc-dev/neofs-api-go/pkg/object"
+	"github.com/nspcc-dev/neofs-node/pkg/services/control"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
+)
+
+// DeletedObjectHandler is a handler of objects to be removed.
+type DeletedObjectHandler func([]*object.Address) error
+
+// DropObjects marks objects to be removed from the local node.
+//
+// Objects are marked via garbage collector's callback.
+//
+// If some address is not a valid object address in a binary format, an error returns.
+// If request is unsigned or signed by disallowed key, permission error returns.
+func (s *Server) DropObjects(_ context.Context, req *control.DropObjectsRequest) (*control.DropObjectsResponse, error) {
+	// verify request
+	if err := s.isValidRequest(req); err != nil {
+		return nil, status.Error(codes.PermissionDenied, err.Error())
+	}
+
+	binAddrList := req.GetBody().GetAddressList()
+	addrList := make([]*object.Address, 0, len(binAddrList))
+
+	for i := range binAddrList {
+		a := object.NewAddress()
+
+		err := a.Unmarshal(binAddrList[i])
+		if err != nil {
+			return nil, status.Error(codes.InvalidArgument,
+				fmt.Sprintf("invalid binary object address: %v", err),
+			)
+		}
+
+		addrList = append(addrList, a)
+	}
+
+	err := s.delObjHandler(addrList)
+	if err != nil {
+		return nil, status.Error(codes.Internal, err.Error())
+	}
+
+	// create and fill response
+	resp := new(control.DropObjectsResponse)
+
+	body := new(control.DropObjectsResponse_Body)
+	resp.SetBody(body)
+
+	// sign the response
+	if err := SignMessage(s.key, resp); err != nil {
+		return nil, status.Error(codes.Internal, err.Error())
+	}
+
+	return resp, nil
+}

pkg/services/control/server/server.go

@@ -47,6 +47,8 @@ type cfg struct {
 	netMapSrc netmap.Source
 
 	nodeState NodeState
+
+	delObjHandler DeletedObjectHandler
 }
 
 func defaultCfg() *cfg {
@@ -103,3 +105,11 @@ func WithNodeState(state NodeState) Option {
 		c.nodeState = state
 	}
 }
+
+// WithDeletedObjectHandler returns option to function
+// which is called on the objects being deleted.
+func WithDeletedObjectHandler(h DeletedObjectHandler) Option {
+	return func(c *cfg) {
+		c.delObjHandler = h
+	}
+}