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"""This module implements the Scraper component which parses responses and
extracts information from them"""
from collections import deque
from twisted.python.failure import Failure
from twisted.internet import defer
from scrapy.utils.defer import defer_result, defer_succeed, parallel, iter_errback
from scrapy.utils.spider import iterate_spider_output
from scrapy.utils.misc import load_object
from scrapy.exceptions import CloseSpider, DropItem, IgnoreRequest
from scrapy import signals
from scrapy.http import Request, Response
from scrapy.item import BaseItem
from scrapy.core.spidermw import SpiderMiddlewareManager
from scrapy import log
class Slot(object):
"""Scraper slot (one per running spider)"""
MIN_RESPONSE_SIZE = 1024
def __init__(self, max_active_size=5000000):
self.max_active_size = max_active_size
self.queue = deque()
self.active = set()
self.active_size = 0
self.itemproc_size = 0
self.closing = None
def add_response_request(self, response, request):
deferred = defer.Deferred()
self.queue.append((response, request, deferred))
if isinstance(response, Response):
self.active_size += max(len(response.body), self.MIN_RESPONSE_SIZE)
else:
self.active_size += self.MIN_RESPONSE_SIZE
return deferred
def next_response_request_deferred(self):
response, request, deferred = self.queue.popleft()
self.active.add(request)
return response, request, deferred
def finish_response(self, response, request):
self.active.remove(request)
if isinstance(response, Response):
self.active_size -= max(len(response.body), self.MIN_RESPONSE_SIZE)
else:
self.active_size -= self.MIN_RESPONSE_SIZE
def is_idle(self):
return not (self.queue or self.active)
def needs_backout(self):
return self.active_size > self.max_active_size
class Scraper(object):
def __init__(self, crawler):
self.slot = None
self.spidermw = SpiderMiddlewareManager.from_crawler(crawler)
itemproc_cls = load_object(crawler.settings['ITEM_PROCESSOR'])
self.itemproc = itemproc_cls.from_crawler(crawler)
self.concurrent_items = crawler.settings.getint('CONCURRENT_ITEMS')
self.crawler = crawler
self.signals = crawler.signals
self.logformatter = crawler.logformatter
@defer.inlineCallbacks
def open_spider(self, spider):
"""Open the given spider for scraping and allocate resources for it"""
self.slot = Slot()
yield self.itemproc.open_spider(spider)
def close_spider(self, spider):
"""Close a spider being scraped and release its resources"""
slot = self.slot
slot.closing = defer.Deferred()
slot.closing.addCallback(self.itemproc.close_spider)
self._check_if_closing(spider, slot)
return slot.closing
def is_idle(self):
"""Return True if there isn't any more spiders to process"""
return not self.slot
def _check_if_closing(self, spider, slot):
if slot.closing and slot.is_idle():
slot.closing.callback(spider)
def enqueue_scrape(self, response, request, spider):
slot = self.slot
dfd = slot.add_response_request(response, request)
def finish_scraping(_):
slot.finish_response(response, request)
self._check_if_closing(spider, slot)
self._scrape_next(spider, slot)
return _
dfd.addBoth(finish_scraping)
dfd.addErrback(log.err, 'Scraper bug processing %s' % request, \
spider=spider)
self._scrape_next(spider, slot)
return dfd
def _scrape_next(self, spider, slot):
while slot.queue:
response, request, deferred = slot.next_response_request_deferred()
self._scrape(response, request, spider).chainDeferred(deferred)
def _scrape(self, response, request, spider):
"""Handle the downloaded response or failure trough the spider
callback/errback"""
assert isinstance(response, (Response, Failure))
dfd = self._scrape2(response, request, spider) # returns spiders processed output
dfd.addErrback(self.handle_spider_error, request, response, spider)
dfd.addCallback(self.handle_spider_output, request, response, spider)
return dfd
def _scrape2(self, request_result, request, spider):
"""Handle the different cases of request's result been a Response or a
Failure"""
if not isinstance(request_result, Failure):
return self.spidermw.scrape_response(self.call_spider, \
request_result, request, spider)
else:
# FIXME: don't ignore errors in spider middleware
dfd = self.call_spider(request_result, request, spider)
return dfd.addErrback(self._log_download_errors, \
request_result, request, spider)
def call_spider(self, result, request, spider):
result.request = request
dfd = defer_result(result)
dfd.addCallbacks(request.callback or spider.parse, request.errback)
return dfd.addCallback(iterate_spider_output)
def handle_spider_error(self, _failure, request, response, spider):
exc = _failure.value
if isinstance(exc, CloseSpider):
self.crawler.engine.close_spider(spider, exc.reason or 'cancelled')
return
log.err(_failure, "Spider error processing %s" % request, spider=spider)
self.signals.send_catch_log(signal=signals.spider_error, failure=_failure, response=response, \
spider=spider)
self.crawler.stats.inc_value("spider_exceptions/%s" % _failure.value.__class__.__name__, \
spider=spider)
def handle_spider_output(self, result, request, response, spider):
if not result:
return defer_succeed(None)
it = iter_errback(result, self.handle_spider_error, request, response, spider)
dfd = parallel(it, self.concurrent_items,
self._process_spidermw_output, request, response, spider)
return dfd
def _process_spidermw_output(self, output, request, response, spider):
"""Process each Request/Item (given in the output parameter) returned
from the given spider
"""
if isinstance(output, Request):
self.crawler.engine.crawl(request=output, spider=spider)
elif isinstance(output, BaseItem):
self.slot.itemproc_size += 1
dfd = self.itemproc.process_item(output, spider)
dfd.addBoth(self._itemproc_finished, output, response, spider)
return dfd
elif output is None:
pass
else:
typename = type(output).__name__
log.msg(format='Spider must return Request, BaseItem or None, '
'got %(typename)r in %(request)s',
level=log.ERROR, spider=spider, request=request, typename=typename)
def _log_download_errors(self, spider_failure, download_failure, request, spider):
"""Log and silence errors that come from the engine (typically download
errors that got propagated thru here)
"""
if isinstance(download_failure, Failure) \
and not download_failure.check(IgnoreRequest):
if download_failure.frames:
log.err(download_failure, 'Error downloading %s' % request,
spider=spider)
else:
errmsg = download_failure.getErrorMessage()
if errmsg:
log.msg(format='Error downloading %(request)s: %(errmsg)s',
level=log.ERROR, spider=spider, request=request,
errmsg=errmsg)
if spider_failure is not download_failure:
return spider_failure
def _itemproc_finished(self, output, item, response, spider):
"""ItemProcessor finished for the given ``item`` and returned ``output``
"""
self.slot.itemproc_size -= 1
if isinstance(output, Failure):
ex = output.value
if isinstance(ex, DropItem):
logkws = self.logformatter.dropped(item, ex, response, spider)
log.msg(spider=spider, **logkws)
return self.signals.send_catch_log_deferred(signal=signals.item_dropped, \
item=item, response=response, spider=spider, exception=output.value)
else:
log.err(output, 'Error processing %s' % item, spider=spider)
else:
logkws = self.logformatter.scraped(output, response, spider)
log.msg(spider=spider, **logkws)
return self.signals.send_catch_log_deferred(signal=signals.item_scraped, \
item=output, response=response, spider=spider)
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