Ryu REST API 実装

Ryu REST API 実装方法

対象

• Ryu
• OVS
• Python2.17
• REST API

上記を理解している人を対象としています。
ですが、投稿主はあまり理解していですが、実装できているので意外となんとかなるかも

動作確認

• python2.7
• Ryu 4.13
• OVS 2.5.2

実装

ofctl_rest.py（GitHub）
RyuのREST APIの実装は公式が提供してくれていますので、上記のリンクから実装することは可能です。
ですが、Pythonはインデントに気をつけなければならない言語ですので、いざ自分のソースコードに実装するとなるとなかなか面倒になります。

なので、今回私が説明する実装方法は必要なメソッドやクラスをなるべく外のファイルに追いやり、必要最低限の実装をする方法を説明します。
※また、各ファイルにおいて不必要なimportがある可能はあります。

必要になるファイルは全部で３つになります。
- test.py (ryu-manager test.py)
- restClass.py
- restExtends.py

restClass.py

restClass.py

from ryu.exception import RyuException
from ryu.app.wsgi import  ControllerBase, Response
import string,json
import logging,ast
from ryu.lib import ofctl_v1_3, ofctl_v1_2, ofctl_v1_0
from ryu.ofproto import ofproto_v1_3, ofproto_v1_2, ofproto_v1_0

LOG = logging.getLogger('SimpleRouter')
#LOG.setLevel(logging.DEBUG)
logging.basicConfig()

supported_ofctl = { 
    ofproto_v1_0.OFP_VERSION: ofctl_v1_0,
    ofproto_v1_2.OFP_VERSION: ofctl_v1_2 ,
    ofproto_v1_3.OFP_VERSION: ofctl_v1_3 
}

################################################################
### from restClass import *
################################################################
def stats_method(method):
    def wrapper(self, req, dpid, *args, **kwargs):
        # Get datapath instance from DPSet
        try:
            dp = self.dpset.get(int(str(dpid), 0))
        except ValueError:
            LOG.exception('Invalid dpid: %s', dpid)
            return Response(status=400)
        if dp is None:
            LOG.error('No such Datapath: %s', dpid)
            return Response(status=404)
        # Get lib/ofctl_* module
        try:
            ofctl = supported_ofctl.get(dp.ofproto.OFP_VERSION)
        except KeyError:
            LOG.exception('Unsupported OF version: %s', dp.ofproto.OFP_VERSION)
            return Response(status=501)
        # Invoke RouterController method
        try:
            ret = method(self, req, dp, ofctl, *args, **kwargs)
            return Response(content_type='application/json', body=json.dumps(ret))
        except ValueError:
            LOG.exception('Invalid syntax: %s', req.body)
            return Response(status=400)
        except AttributeError:
            LOG.exception('Unsupported OF request in this version: %s', dp.ofproto.OFP_VERSION)
            return Response(status=501)
    return wrapper

def command_method(method):
    def wrapper(self, req, *args, **kwargs):
        try:
            if req.body:
                body = ast.literal_eval(req.body.decode('utf-8'))
            else:
                body = {}
        except SyntaxError:
            LOG.exception('Invalid syntax: %s', req.body)
            return Response(status=400)
        dpid = body.get('dpid', None)
        if not dpid:
            try:
                dpid = kwargs.pop('dpid')
            except KeyError:
                LOG.exception('Cannot get dpid from request parameters')
                return Response(status=400)
        try:
            dp = self.dpset.get(int(str(dpid), 0))
        except ValueError:
            LOG.exception('Invalid dpid: %s', dpid)
            return Response(status=400)
        if dp is None:
            LOG.error('No such Datapath: %s', dpid)
            return Response(status=404)
        try:
            ofctl = supported_ofctl.get(dp.ofproto.OFP_VERSION)
        except KeyError:
            LOG.exception('Unsupported OF version: version=%s', dp.ofproto.OFP_VERSION)
            return Response(status=501)
        try:
            method(self, req, dp, ofctl, body, *args, **kwargs)
            return Response(status=200)
        except ValueError:
            LOG.exception('Invalid syntax: %s', req.body)
            return Response(status=400)
        except AttributeError:
            LOG.exception('Unsupported OF request in this version: %s',
                            dp.ofproto.OFP_VERSION)
            return Response(status=501)
        except CommandNotFoundError as e:
            LOG.exception(e.message)
            return Response(status=404)
        except PortNotFoundError as e:
            LOG.exception(e.message)
            return Response(status=404)
    return wrapper

#
class CommandNotFoundError(RyuException):
    message = 'No such command : %(cmd)s'

#
class PortNotFoundError(RyuException):
    message = 'No such port info: %(port_no)s'

#
class RouterController(ControllerBase):
    def __init__(self, req, link, data, **config):
        super(RouterController, self).__init__(req, link, data, **config)
        self.dpset = data['dpset']
        self.waiters = data['waiters']

    def get_dpids(self, req, **_kwargs):
        dps = list(self.dpset.dps.keys())
        body = json.dumps(dps)
        return Response(content_type='application/json', body=body)

    @stats_method
    def get_desc_stats(self, req, dp, ofctl, **kwargs):
        return ofctl.get_desc_stats(dp, self.waiters)

    @stats_method
    def get_flow_desc(self, req, dp, ofctl, **kwargs):
        flow = req.json if req.body else {}
        return ofctl.get_flow_desc(dp, self.waiters, flow)

    @stats_method
    def get_flow_stats(self, req, dp, ofctl, **kwargs):
        flow = req.json if req.body else {}
        return ofctl.get_flow_stats(dp, self.waiters, flow)

    @stats_method
    def get_aggregate_flow_stats(self, req, dp, ofctl, **kwargs):
        flow = req.json if req.body else {}
        return ofctl.get_aggregate_flow_stats(dp, self.waiters, flow)

    @stats_method
    def get_table_stats(self, req, dp, ofctl, **kwargs):
        return ofctl.get_table_stats(dp, self.waiters)

    @stats_method
    def get_table_features(self, req, dp, ofctl, **kwargs):
        return ofctl.get_table_features(dp, self.waiters)

    @stats_method
    def get_port_stats(self, req, dp, ofctl, port=None, **kwargs):
        if port == "ALL":
            port = None
        return ofctl.get_port_stats(dp, self.waiters, port)

    @stats_method
    def get_queue_stats(self, req, dp, ofctl, port=None, queue_id=None, **kwargs):
        if port == "ALL":
            port = None
        if queue_id == "ALL":
            queue_id = None
        return ofctl.get_queue_stats(dp, self.waiters, port, queue_id)

    @stats_method
    def get_queue_config(self, req, dp, ofctl, port=None, **kwargs):
        if port == "ALL":
            port = None
        return ofctl.get_queue_config(dp, self.waiters, port)

    @stats_method
    def get_queue_desc(self, req, dp, ofctl, port=None, queue=None, **_kwargs):
        if port == "ALL":
            port = None
        if queue == "ALL":
            queue = None
        return ofctl.get_queue_desc(dp, self.waiters, port, queue)

    @stats_method
    def get_meter_features(self, req, dp, ofctl, **kwargs):
        return ofctl.get_meter_features(dp, self.waiters)

    @stats_method
    def get_meter_config(self, req, dp, ofctl, meter_id=None, **kwargs):
        if meter_id == "ALL":
            meter_id = None
        return ofctl.get_meter_config(dp, self.waiters, meter_id)

    @stats_method
    def get_meter_desc(self, req, dp, ofctl, meter_id=None, **kwargs):
        if meter_id == "ALL":
            meter_id = None
        return ofctl.get_meter_desc(dp, self.waiters, meter_id)

    @stats_method
    def get_meter_stats(self, req, dp, ofctl, meter_id=None, **kwargs):
        if meter_id == "ALL":
            meter_id = None
        return ofctl.get_meter_stats(dp, self.waiters, meter_id)

    @stats_method
    def get_group_features(self, req, dp, ofctl, **kwargs):
        return ofctl.get_group_features(dp, self.waiters)

    @stats_method
    def get_group_desc(self, req, dp, ofctl, group_id=None, **kwargs):
        if dp.ofproto.OFP_VERSION < ofproto_v1_5.OFP_VERSION:
            return ofctl.get_group_desc(dp, self.waiters)
        else:
            return ofctl.get_group_desc(dp, self.waiters, group_id)

    @stats_method
    def get_group_stats(self, req, dp, ofctl, group_id=None, **kwargs):
        if group_id == "ALL":
            group_id = None
        return ofctl.get_group_stats(dp, self.waiters, group_id)

    @stats_method
    def get_port_desc(self, req, dp, ofctl, port_no=None, **kwargs):
        if dp.ofproto.OFP_VERSION < ofproto_v1_5.OFP_VERSION:
            return ofctl.get_port_desc(dp, self.waiters)
        else:
            return ofctl.get_port_desc(dp, self.waiters, port_no)

    @stats_method
    def get_role(self, req, dp, ofctl, **kwargs):
        return ofctl.get_role(dp, self.waiters)

    @command_method
    def mod_flow_entry(self, req, dp, ofctl, flow, cmd, **kwargs):
        cmd_convert = {
            'add': dp.ofproto.OFPFC_ADD,
            'modify': dp.ofproto.OFPFC_MODIFY,
            'modify_strict': dp.ofproto.OFPFC_MODIFY_STRICT,
            'delete': dp.ofproto.OFPFC_DELETE,
            'delete_strict': dp.ofproto.OFPFC_DELETE_STRICT,
        }
        mod_cmd = cmd_convert.get(cmd, None)
        if mod_cmd is None:
            raise CommandNotFoundError(cmd=cmd)
        ofctl.mod_flow_entry(dp, flow, mod_cmd)

    @command_method
    def delete_flow_entry(self, req, dp, ofctl, flow, **kwargs):
        if ofproto_v1_0.OFP_VERSION == dp.ofproto.OFP_VERSION:
            flow = {}
        else:
            flow = {'table_id': dp.ofproto.OFPTT_ALL}
        ofctl.mod_flow_entry(dp, flow, dp.ofproto.OFPFC_DELETE)

    @command_method
    def mod_meter_entry(self, req, dp, ofctl, meter, cmd, **kwargs):
        cmd_convert = {
            'add': dp.ofproto.OFPMC_ADD,
            'modify': dp.ofproto.OFPMC_MODIFY,
            'delete': dp.ofproto.OFPMC_DELETE
        }
        mod_cmd = cmd_convert.get(cmd, None)
        if mod_cmd is None:
            raise CommandNotFoundError(cmd=cmd)
        ofctl.mod_meter_entry(dp, meter, mod_cmd)


    @command_method
    def mod_group_entry(self, req, dp, ofctl, group, cmd, **kwargs):
        cmd_convert = {
            'add': dp.ofproto.OFPGC_ADD,
            'modify': dp.ofproto.OFPGC_MODIFY,
            'delete': dp.ofproto.OFPGC_DELETE,
        }
        mod_cmd = cmd_convert.get(cmd, None)
        if mod_cmd is None:
            raise CommandNotFoundError(cmd=cmd)
        ofctl.mod_group_entry(dp, group, mod_cmd)

    @command_method
    def mod_port_behavior(self, req, dp, ofctl, port_config, cmd, **kwargs):
        port_no = port_config.get('port_no', None)
        port_no = int(str(port_no), 0)
        port_info = self.dpset.port_state[int(dp.id)].get(port_no)
        if port_info:
            port_config.setdefault('hw_addr', port_info.hw_addr)
            if dp.ofproto.OFP_VERSION < ofproto_v1_4.OFP_VERSION:
                port_config.setdefault('advertise', port_info.advertised)
            else:
                port_config.setdefault('properties', port_info.properties)
        else:
            raise PortNotFoundError(port_no=port_no)
        if cmd != 'modify':
            raise CommandNotFoundError(cmd=cmd)
        ofctl.mod_port_behavior(dp, port_config)

    @command_method
    def send_experimenter(self, req, dp, ofctl, exp, **kwargs):
        ofctl.send_experimenter(dp, exp)

    @command_method
    def set_role(self, req, dp, ofctl, role, **kwargs):
        ofctl.set_role(dp, role)

restExtends.py

restExtends.py

from ryu.controller.handler import set_ev_cls
from ryu.controller import ofp_event
from ryu.controller.handler import MAIN_DISPATCHER
from ryu.app.wsgi import WSGIApplication
from ryu.controller import dpset
import socket
import types
import string,json
import commands,logging,ast
from ryu.lib import ofctl_v1_3, ofctl_v1_2, ofctl_v1_0
from ryu.ofproto import ofproto_v1_3, ofproto_v1_2, ofproto_v1_0
from restClass import RouterController

supported_ofctl = { 
    ofproto_v1_0.OFP_VERSION: ofctl_v1_0,
    ofproto_v1_2.OFP_VERSION: ofctl_v1_2,
    ofproto_v1_3.OFP_VERSION: ofctl_v1_3 
}

class RestExtends():
    def mapping(self, *args, **kwargs):
        self.dpset = kwargs['dpset']
        wsgi = kwargs['wsgi']
        self.waiters = {}
        self.data = {}
        self.data['dpset'] = self.dpset
        self.data['waiters'] = self.waiters
        mapper = wsgi.mapper
        print 'REST API  join in'
        wsgi.registory['RouterController'] = self.data

        path = '/stats'
        uri = path + '/switches'
        mapper.connect('stats', uri,
                        controller=RouterController, action='get_dpids',
                        conditions=dict(method=['GET']))

        uri = path + '/desc/{dpid}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='get_desc_stats',
                        conditions=dict(method=['GET']))

        uri = path + '/flowdesc/{dpid}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='get_flow_stats',
                        conditions=dict(method=['GET', 'POST']))

        uri = path + '/flow/{dpid}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='get_flow_stats',
                        conditions=dict(method=['GET', 'POST']))

        uri = path + '/aggregateflow/{dpid}'
        mapper.connect('stats', uri,
                        controller=RouterController,
                        action='get_aggregate_flow_stats',
                        conditions=dict(method=['GET', 'POST']))

        uri = path + '/table/{dpid}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='get_table_stats',
                        conditions=dict(method=['GET']))

        uri = path + '/tablefeatures/{dpid}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='get_table_features',
                        conditions=dict(method=['GET']))

        uri = path + '/port/{dpid}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='get_port_stats',
                        conditions=dict(method=['GET']))

        uri = path + '/port/{dpid}/{port}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='get_port_stats',
                        conditions=dict(method=['GET']))

        uri = path + '/queue/{dpid}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='get_queue_stats',
                        conditions=dict(method=['GET']))

        uri = path + '/queue/{dpid}/{port}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='get_queue_stats',
                        conditions=dict(method=['GET']))

        uri = path + '/queue/{dpid}/{port}/{queue_id}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='get_queue_stats',
                        conditions=dict(method=['GET']))

        uri = path + '/queueconfig/{dpid}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='get_queue_config',
                        conditions=dict(method=['GET']))

        uri = path + '/queueconfig/{dpid}/{port}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='get_queue_config',
                        conditions=dict(method=['GET']))

        uri = path + '/queuedesc/{dpid}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='get_queue_desc',
                        conditions=dict(method=['GET']))

        uri = path + '/queuedesc/{dpid}/{port}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='get_queue_desc',
                        conditions=dict(method=['GET']))

        uri = path + '/queuedesc/{dpid}/{port}/{queue}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='get_queue_desc',
                        conditions=dict(method=['GET']))

        uri = path + '/meterfeatures/{dpid}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='get_meter_features',
                        conditions=dict(method=['GET']))

        uri = path + '/meterconfig/{dpid}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='get_meter_config',
                        conditions=dict(method=['GET']))

        uri = path + '/meterconfig/{dpid}/{meter_id}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='get_meter_config',
                        conditions=dict(method=['GET']))

        uri = path + '/meterdesc/{dpid}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='get_meter_desc',
                        conditions=dict(method=['GET']))

        uri = path + '/meterdesc/{dpid}/{meter_id}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='get_meter_desc',
                        conditions=dict(method=['GET']))

        uri = path + '/meter/{dpid}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='get_meter_stats',
                        conditions=dict(method=['GET']))

        uri = path + '/meter/{dpid}/{meter_id}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='get_meter_stats',
                        conditions=dict(method=['GET']))

        uri = path + '/groupfeatures/{dpid}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='get_group_features',
                        conditions=dict(method=['GET']))

        uri = path + '/groupdesc/{dpid}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='get_group_desc',
                        conditions=dict(method=['GET']))

        uri = path + '/groupdesc/{dpid}/{group_id}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='get_group_desc',
                        conditions=dict(method=['GET']))

        uri = path + '/group/{dpid}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='get_group_stats',
                        conditions=dict(method=['GET']))

        uri = path + '/group/{dpid}/{group_id}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='get_group_stats',
                        conditions=dict(method=['GET']))

        uri = path + '/portdesc/{dpid}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='get_port_desc',
                        conditions=dict(method=['GET']))

        uri = path + '/portdesc/{dpid}/{port_no}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='get_port_desc',
                        conditions=dict(method=['GET']))

        uri = path + '/role/{dpid}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='get_role',
                        conditions=dict(method=['GET']))

        uri = path + '/flowentry/{cmd}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='mod_flow_entry',
                        conditions=dict(method=['POST']))

        uri = path + '/flowentry/clear/{dpid}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='delete_flow_entry',
                        conditions=dict(method=['DELETE']))

        uri = path + '/meterentry/{cmd}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='mod_meter_entry',
                        conditions=dict(method=['POST']))

        uri = path + '/groupentry/{cmd}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='mod_group_entry',
                        conditions=dict(method=['POST']))

        uri = path + '/portdesc/{cmd}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='mod_port_behavior',
                        conditions=dict(method=['POST']))

        uri = path + '/experimenter/{dpid}'
        mapper.connect('stats', uri,
                        controller=RouterController, action='send_experimenter',
                        conditions=dict(method=['POST']))

        uri = path + '/role'
        mapper.connect('stats', uri,
                        controller=RouterController, action='set_role',
                        conditions=dict(method=['POST']))

    @set_ev_cls([ofp_event.EventOFPStatsReply,
                 ofp_event.EventOFPDescStatsReply,
                 ofp_event.EventOFPFlowStatsReply,
                 ofp_event.EventOFPAggregateStatsReply,
                 ofp_event.EventOFPTableStatsReply,
                 ofp_event.EventOFPTableFeaturesStatsReply,
                 ofp_event.EventOFPPortStatsReply,
                 ofp_event.EventOFPQueueStatsReply,
                 ofp_event.EventOFPQueueDescStatsReply,
                 ofp_event.EventOFPMeterStatsReply,
                 ofp_event.EventOFPMeterFeaturesStatsReply,
                 ofp_event.EventOFPMeterConfigStatsReply,
                 ofp_event.EventOFPGroupStatsReply,
                 ofp_event.EventOFPGroupFeaturesStatsReply,
                 ofp_event.EventOFPGroupDescStatsReply,
                 ofp_event.EventOFPPortDescStatsReply
                 ], MAIN_DISPATCHER)
    def stats_reply_handler(self, ev):
        msg = ev.msg
        dp = msg.datapath
        print 'stats_reply_handler'
        print msg
        print dp        
        if dp.id not in self.waiters:
            return
        if msg.xid not in self.waiters[dp.id]:
            return
        lock, msgs = self.waiters[dp.id][msg.xid]
        msgs.append(msg)
        flags = 0
        if dp.ofproto.OFP_VERSION == ofproto_v1_0.OFP_VERSION:
            flags = dp.ofproto.OFPSF_REPLY_MORE
        elif dp.ofproto.OFP_VERSION == ofproto_v1_2.OFP_VERSION:
            flags = dp.ofproto.OFPSF_REPLY_MORE
        elif dp.ofproto.OFP_VERSION >= ofproto_v1_3.OFP_VERSION:
            flags = dp.ofproto.OFPMPF_REPLY_MORE
        if msg.flags & flags:
            return
        del self.waiters[dp.id][msg.xid]
        lock.set()

    @set_ev_cls([ofp_event.EventOFPSwitchFeatures,
                 ofp_event.EventOFPQueueGetConfigReply,
                 ofp_event.EventOFPRoleReply,
                 ], MAIN_DISPATCHER)
    def features_reply_handler(self, ev):
        msg = ev.msg
        dp = msg.datapath
        print 'features_reply_handler'
        print msg
        print dp
        if dp.id not in self.waiters:
            return
        if msg.xid not in self.waiters[dp.id]:
            return
        lock, msgs = self.waiters[dp.id][msg.xid]
        msgs.append(msg)
        del self.waiters[dp.id][msg.xid]
        lock.set()

次はこれら２つのファイルを本体から読み込んでいきましょう。
今回test.pyに記述する内容はREST APIを実装するのに必要なものだけにしてありますので、自分の環境に合わせて実装してください。

test.py

test.py

from restExtends import RestExtends
from restClass import *
from ryu.lib import ofctl_v1_0, ofctl_v1_2, ofctl_v1_3, ofctl_v1_4, ofctl_v1_5
from ryu.ofproto import ofproto_v1_0, ofproto_v1_2, ofproto_v1_3, ofproto_v1_4, ofproto_v1_5
from webob.response import Response
from ryu.app.wsgi import WSGIApplication, Response
from ryu.controller import dpset


supported_ofctl = { 
    ofproto_v1_0.OFP_VERSION: ofctl_v1_0,
    ofproto_v1_2.OFP_VERSION: ofctl_v1_2,
    ofproto_v1_3.OFP_VERSION: ofctl_v1_3,
    ofproto_v1_4.OFP_VERSION: ofctl_v1_4,
    ofproto_v1_5.OFP_VERSION: ofctl_v1_5 
}

class Test(app_manager.RyuApp, RestExtends):
    _CONTEXTS = {'dpset': dpset.DPSet,'wsgi': WSGIApplication}

    def __init__(self, *args, **kwargs):
        super(SimpleRouter, self).__init__(*args, **kwargs)
        self.mapping(*args, **kwargs)

ここで気をつけなければならないのは、Testは"app_manager.RyuApp"だけではなく”RestExtends”も継承していることです。

pythonは多重継承ができる言語なので、REST APIを実装するにあたりTestクラスに実装しなければならないメソッドなどを”RestExtends”にまとめて継承することで簡略化しています。
イニシャライズで呼び出しています。

self.mapping(*args, **kwargs)
上記のコードで'RestExtends.py'で実装されている’mapping’メソッドを呼び出し、URLのマッピングを行なっています。
なので、URLを変えたいとか機能を増やしたいのであれば'RestExtends.py'で実装されている’mapping’メソッドを編集してください。また、URL対応する関数は'restClass.py'の’RouterController’クラスを編集してください。

これまでで、自分のRyu環境にお手軽にREST APIを実装することが可能になります。