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
if TYPE_CHECKING:
# 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 https://developers.google.com/webmasters/ajax-crawling/docs/getting-started.
"""
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 https://developers.google.com/webmasters/ajax-crawling/docs/getting-started.
"""
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 _ajax_crawlable_re.search(text) is not None