Scrapy源码剖析之自定义Scrapy框架

Posted 2022-09-19 jintian

from twisted.internet import reactor   # 事件循环（终止条件，所有的socket都已经移除）
from twisted.web.client import getPage # socket对象（如果下载完成，自动从时间循环中移除...）
from twisted.internet import defer     # defer.Deferred 特殊的socket对象 （不会发请求，手动移除）
from queue import Queue

class Request(object):
    """
    用于封装用户请求相关信息
    """
    def __init__(self,url,callback):
        self.url = url
        self.callback = callback

class HttpResponse(object):

    def __init__(self,content,request):
        self.content = content
        self.request = request

class Scheduler(object):
    """
    任务调度器
    """
    def __init__(self):
        self.q = Queue()

    def open(self):
        pass

    def next_request(self):
        try:
            req = self.q.get(block=False)
        except Exception as e:
            req = None
        return req

    def enqueue_request(self,req):
        self.q.put(req)

    def size(self):
        return self.q.qsize()

class ExecutionEngine(object):
    """
    引擎：所有调度
    """
    def __init__(self):
        self._close = None
        self.scheduler = None
        self.max = 5
        self.crawlling = []
    def get_response_callback(self,content,request):
        self.crawlling.remove(request)
        response = HttpResponse(content,request)
        result = request.callback(response)
        import types
        if isinstance(result,types.GeneratorType):
            for req in result:
                self.scheduler.enqueue_request(req)

    def _next_request(self):
        if self.scheduler.size() == 0 and len(self.crawlling) == 0:
            self._close.callback(None)
            return

        while len(self.crawlling) < self.max:
            req = self.scheduler.next_request()
            if not req:
                return
            self.crawlling.append(req)
            d = getPage(req.url.encode(‘utf-8‘))
            d.addCallback(self.get_response_callback,req)
            d.addCallback(lambda _:reactor.callLater(0,self._next_request))

    @defer.inlineCallbacks
    def open_spider(self,start_requests):
        self.scheduler = Scheduler()
        yield self.scheduler.open()
        while True:
            try:
                req = next(start_requests)
            except StopIteration as e:
                break
            self.scheduler.enqueue_request(req)
        reactor.callLater(0,self._next_request)

    @defer.inlineCallbacks
    def start(self):
        self._close = defer.Deferred()
        yield self._close

class Crawler(object):
    """
    用户封装调度器以及引擎的...
    """
    def _create_engine(self):
        return ExecutionEngine()

    def _create_spider(self,spider_cls_path):
        """

        :param spider_cls_path:  spider.chouti.ChoutiSpider
        :return:
        """
        module_path,cls_name = spider_cls_path.rsplit(‘.‘,maxsplit=1)
        import importlib
        m = importlib.import_module(module_path)
        cls = getattr(m,cls_name)
        return cls()

    @defer.inlineCallbacks
    def crawl(self,spider_cls_path):
        engine = self._create_engine()
        spider = self._create_spider(spider_cls_path)
        start_requests = iter(spider.start_requests())
        yield engine.open_spider(start_requests)
        yield engine.start()

class CrawlerProcess(object):
    """
    开启事件循环
    """
    def __init__(self):
        self._active = set()

    def crawl(self,spider_cls_path):
        """
        :param spider_cls_path:
        :return:
        """
        crawler = Crawler()
        d = crawler.crawl(spider_cls_path)
        self._active.add(d)

    def start(self):
        dd = defer.DeferredList(self._active)
        dd.addBoth(lambda _:reactor.stop())

        reactor.run()

class Commond(object):

    def run(self):
        crawl_process = CrawlerProcess()
        spider_cls_path_list = [‘spider.chouti.ChoutiSpider‘,‘spider.cnblogs.CnblogsSpider‘,]
        for spider_cls_path in spider_cls_path_list:
            crawl_process.crawl(spider_cls_path)
        crawl_process.start()


if __name__ == ‘__main__‘:
    cmd = Commond()
    cmd.run()

engine.py