Source code for scrapy.downloadermiddlewares.ajaxcrawl

from __future__ import annotations

import logging
import re
from typing import TYPE_CHECKING, Union

from w3lib import html

from scrapy import Request, Spider
from scrapy.crawler import Crawler
from scrapy.exceptions import NotConfigured
from scrapy.http import HtmlResponse, Response
from scrapy.settings import BaseSettings

    # typing.Self requires Python 3.11
    from typing_extensions import Self

logger = logging.getLogger(__name__)

[docs]class AjaxCrawlMiddleware: """ Handle 'AJAX crawlable' pages marked as crawlable via meta tag. For more info see """ def __init__(self, settings: BaseSettings): if not settings.getbool("AJAXCRAWL_ENABLED"): raise NotConfigured # XXX: Google parses at least first 100k bytes; scrapy's redirect # middleware parses first 4k. 4k turns out to be insufficient # for this middleware, and parsing 100k could be slow. # We use something in between (32K) by default. self.lookup_bytes: int = settings.getint("AJAXCRAWL_MAXSIZE", 32768) @classmethod def from_crawler(cls, crawler: Crawler) -> Self: return cls(crawler.settings) def process_response( self, request: Request, response: Response, spider: Spider ) -> Union[Request, Response]: if not isinstance(response, HtmlResponse) or response.status != 200: return response if request.method != "GET": # other HTTP methods are either not safe or don't have a body return response if "ajax_crawlable" in request.meta: # prevent loops return response if not self._has_ajax_crawlable_variant(response): return response # scrapy already handles #! links properly ajax_crawl_request = request.replace(url=request.url + "#!") logger.debug( "Downloading AJAX crawlable %(ajax_crawl_request)s instead of %(request)s", {"ajax_crawl_request": ajax_crawl_request, "request": request}, extra={"spider": spider}, ) ajax_crawl_request.meta["ajax_crawlable"] = True return ajax_crawl_request def _has_ajax_crawlable_variant(self, response: Response) -> bool: """ Return True if a page without hash fragment could be "AJAX crawlable" according to """ body = response.text[: self.lookup_bytes] return _has_ajaxcrawlable_meta(body)
# XXX: move it to w3lib? _ajax_crawlable_re: re.Pattern[str] = re.compile( r'<meta\s+name=["\']fragment["\']\s+content=["\']!["\']/?>' ) def _has_ajaxcrawlable_meta(text: str) -> bool: """ >>> _has_ajaxcrawlable_meta('<html><head><meta name="fragment" content="!"/></head><body></body></html>') True >>> _has_ajaxcrawlable_meta("<html><head><meta name='fragment' content='!'></head></html>") True >>> _has_ajaxcrawlable_meta('<html><head><!--<meta name="fragment" content="!"/>--></head><body></body></html>') False >>> _has_ajaxcrawlable_meta('<html></html>') False """ # Stripping scripts and comments is slow (about 20x slower than # just checking if a string is in text); this is a quick fail-fast # path that should work for most pages. if "fragment" not in text: return False if "content" not in text: return False text = html.remove_tags_with_content(text, ("script", "noscript")) text = html.replace_entities(text) text = html.remove_comments(text) return is not None