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/ downloadermiddlewares / ajaxcrawl.py
# -*- coding: utf-8 -*-
from __future__ import absolute_import
import re
import logging
import six
from w3lib import html
from scrapy.exceptions import NotConfigured
from scrapy.http import HtmlResponse
logger = logging.getLogger(__name__)
class AjaxCrawlMiddleware(object):
"""
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):
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 = settings.getint('AJAXCRAWL_MAXSIZE', 32768)
@classmethod
def from_crawler(cls, crawler):
return cls(crawler.settings)
def process_response(self, request, response, spider):
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):
"""
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.compile(six.u(r'<meta\s+name=["\']fragment["\']\s+content=["\']!["\']/?>'))
def _has_ajaxcrawlable_meta(text):
"""
>>> _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