scrapy分布式Spiderソースコード分析と実現過程

分散フレームワークscrapy_redisは完全なコンポーネントを実現し、その中でもspiderを実現した.RedisSpiderは元のscrapyのSpiderを継承した上で少し変更され、初期URLはstart_urlsリストから読み出すのではなく、redis開始キューから読み出す.
scrapy_redisソースはscrapyにあります.redis.spiderではRedisSpider(分布爬虫類)だけでなくRedisCrawlSpider(分布深さ爬虫類)の論理も実現しているが,両者の多くの方法は一致している.
ソースコードは次のとおりです.

from scrapy import signals
from scrapy.exceptions import DontCloseSpider
from scrapy.spiders import Spider, CrawlSpider

from . import connection


# Default batch size matches default concurrent requests setting.

DEFAULT_START_URLS_BATCH_SIZE = 16

DEFAULT_START_URLS_KEY = '%(name)s:start_urls'


class RedisMixin(object):

    """Mixin class to implement reading urls from a redis queue."""

    # Per spider redis key, default to DEFAULT_START_URLS_KEY.

    redis_key = None

    # Fetch this amount of start urls when idle. Default to DEFAULT_START_URLS_BATCH_SIZE.

    redis_batch_size = None

    # Redis client instance.

    server = None


    def start_requests(self):

        """Returns a batch of start requests from redis."""

        return self.next_requests()


    def setup_redis(self, crawler=None):

        """Setup redis connection and idle signal.

        This should be called after the spider has set its crawler object.

        """

        if self.server is not None:

            return


        if crawler is None:

            # We allow optional crawler argument to keep backwards

            # compatibility.

            # XXX: Raise a deprecation warning.

            crawler = getattr(self, 'crawler', None)


        if crawler is None:

            raise ValueError("crawler is required")


        settings = crawler.settings


        if self.redis_key is None:

            self.redis_key = settings.get(

                'REDIS_START_URLS_KEY', DEFAULT_START_URLS_KEY,

            )


        self.redis_key = self.redis_key % {'name': self.name}


        if not self.redis_key.strip():

            raise ValueError("redis_key must not be empty")


        if self.redis_batch_size is None:

            self.redis_batch_size = settings.getint(

                'REDIS_START_URLS_BATCH_SIZE', DEFAULT_START_URLS_BATCH_SIZE,

            )


        try:

            self.redis_batch_size = int(self.redis_batch_size)

        except (TypeError, ValueError):

            raise ValueError("redis_batch_size must be an integer")


        self.logger.info("Reading start URLs from redis key '%(redis_key)s' "

                         "(batch size: %(redis_batch_size)s)", self.__dict__)


        self.server = connection.from_settings(crawler.settings)

        # The idle signal is called when the spider has no requests left,

        # that's when we will schedule new requests from redis queue

        crawler.signals.connect(self.spider_idle, signal=signals.spider_idle)


    def next_requests(self):

        """Returns a request to be scheduled or none."""

        use_set = self.settings.getbool('REDIS_START_URLS_AS_SET')

        fetch_one = self.server.spop if use_set else self.server.lpop

        # XXX: Do we need to use a timeout here?

        found = 0

        while found < self.redis_batch_size:

            data = fetch_one(self.redis_key)

            if not data:

                # Queue empty.

                break

            req = self.make_request_from_data(data)

            if req:

                yield req

                found += 1

            else:

                self.logger.debug("Request not made from data: %r", data)


        if found:

            self.logger.debug("Read %s requests from '%s'", found, self.redis_key)


    def make_request_from_data(self, data):

        # By default, data is an URL.

        if '://' in data:

            return self.make_requests_from_url(data)

        else:

            self.logger.error("Unexpected URL from '%s': %r", self.redis_key, data)


    def schedule_next_requests(self):

        """Schedules a request if available"""

        for req in self.next_requests():

            self.crawler.engine.crawl(req, spider=self)


    def spider_idle(self):

        """Schedules a request if available, otherwise waits."""

        # XXX: Handle a sentinel to close the spider.

        self.schedule_next_requests()

        raise DontCloseSpider


class RedisSpider(RedisMixin, Spider):

    """Spider that reads urls from redis queue when idle."""


    @classmethod

    def from_crawler(self, crawler, *args, **kwargs):

        obj = super(RedisSpider, self).from_crawler(crawler, *args, **kwargs)

        obj.setup_redis(crawler)

        return obj


class RedisCrawlSpider(RedisMixin, CrawlSpider):

    """Spider that reads urls from redis queue when idle."""


    @classmethod

    def from_crawler(self, crawler, *args, **kwargs):

        obj = super(RedisCrawlSpider, self).from_crawler(crawler, *args, **kwargs)

        obj.setup_redis(crawler)

        return obj

スタートスタートスタート_requestsメソッドは、Redisからすべての接続を取得し、URLのデリバリーリストと比較してデリバリーし、デリバリーされないmake_を介してrequests_from_url(url)はエンジンに渡され、スケジューラに渡されます.ここでは一般的な爬虫類の考え方と一致しています.
エンジンがタスクキューが空のメッセージを受信するとSpider_が呼び出されます.idleメソッド、schedule_を呼び出すnext_requestsは、取得した開始URLを反復してエンジンに渡し、タスクが完了するまでサブコール開始キュー内のURLを開始します.

   def schedule_next_requests(self):

        """Schedules a request if available"""

        for req in self.next_requests():

            self.crawler.engine.crawl(req, spider=self)


    def spider_idle(self):

        """Schedules a request if available, otherwise waits."""

        # XXX: Handle a sentinel to close the spider.

        self.schedule_next_requests()

        raise DontCloseSpider

RedisSpiderとRedisCrawlSpiderは簡単で、SpiderとRedisMiXineを継承し、setup_を実現しました異なるcrawlerに基づいてsetting、redis_を初期化するredisメソッドkey、およびconnectインタフェースを介してspiderにspiderをバインドidle信号バインド.

class RedisSpider(RedisMixin, Spider):

    """Spider that reads urls from redis queue when idle."""


    @classmethod

    def from_crawler(self, crawler, *args, **kwargs):

        obj = super(RedisSpider, self).from_crawler(crawler, *args, **kwargs)

        obj.setup_redis(crawler)

        return obj


class RedisCrawlSpider(RedisMixin, CrawlSpider):

    """Spider that reads urls from redis queue when idle."""


    @classmethod

    def from_crawler(self, crawler, *args, **kwargs):

        obj = super(RedisCrawlSpider, self).from_crawler(crawler, *args, **kwargs)

        obj.setup_redis(crawler)

        return obj


 def setup_redis(self, crawler=None):

        """Setup redis connection and idle signal.

        This should be called after the spider has set its crawler object.

        """

        if self.server is not None:

            return


        if crawler is None:

            # We allow optional crawler argument to keep backwards

            # compatibility.

            # XXX: Raise a deprecation warning.

            crawler = getattr(self, 'crawler', None)


        if crawler is None:

            raise ValueError("crawler is required")


        settings = crawler.settings


        if self.redis_key is None:

            self.redis_key = settings.get(

                'REDIS_START_URLS_KEY', DEFAULT_START_URLS_KEY,

            )


        self.redis_key = self.redis_key % {'name': self.name}


        if not self.redis_key.strip():

            raise ValueError("redis_key must not be empty")


        if self.redis_batch_size is None:

            self.redis_batch_size = settings.getint(

                'REDIS_START_URLS_BATCH_SIZE', DEFAULT_START_URLS_BATCH_SIZE,

            )


        try:

            self.redis_batch_size = int(self.redis_batch_size)

        except (TypeError, ValueError):

            raise ValueError("redis_batch_size must be an integer")


        self.logger.info("Reading start URLs from redis key '%(redis_key)s' "

                         "(batch size: %(redis_batch_size)s)", self.__dict__)


        self.server = connection.from_settings(crawler.settings)

        # The idle signal is called when the spider has no requests left,

        # that's when we will schedule new requests from redis queue

        crawler.signals.connect(self.spider_idle, signal=signals.spider_idle)

まとめ:RedisSpider初期Redisキューからstart_を取得urlはRequestを生成し、scrapyエンジンに渡して対応するRedis schedulerスケジューリングに渡し、デマンドとエンキューを完了します.スケジューリング条件がキュー内のRequestがエンジンからダウンロードに渡されることを満たすと、ResponseオブジェクトがSpider解析に渡され、新しいRequestが生成され、引き続きキャプチャされる.新しいRequestが生成されないまで、Spiderは開始キューからURLを取得し、前回のループを継続し、もちろんキューにないと爬虫類は終了します.