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"""
This module implements the Downloader Middleware manager. For more information
see the Downloader Middleware doc in:
docs/topics/downloader-middleware.rst
"""
from scrapy.core import signals
from scrapy.utils.signal import send_catch_log
from scrapy import log
from scrapy.http import Request, Response
from scrapy.core.exceptions import NotConfigured
from scrapy.utils.misc import load_object
from scrapy.utils.defer import mustbe_deferred
from scrapy.utils.conf import build_component_list
from scrapy.conf import settings
class DownloaderMiddlewareManager(object):
def __init__(self):
self.loaded = False
self.enabled = {}
self.disabled = {}
self.request_middleware = []
self.response_middleware = []
self.exception_middleware = []
self.load()
def _add_middleware(self, mw):
if hasattr(mw, 'process_request'):
self.request_middleware.append(mw.process_request)
if hasattr(mw, 'process_response'):
self.response_middleware.insert(0, mw.process_response)
if hasattr(mw, 'process_exception'):
self.exception_middleware.insert(0, mw.process_exception)
def load(self):
"""Load middleware defined in settings module"""
mwlist = build_component_list(settings['DOWNLOADER_MIDDLEWARES_BASE'], \
settings['DOWNLOADER_MIDDLEWARES'])
self.enabled.clear()
self.disabled.clear()
for mwpath in mwlist:
try:
cls = load_object(mwpath)
mw = cls()
self.enabled[cls.__name__] = mw
self._add_middleware(mw)
except NotConfigured, e:
self.disabled[cls.__name__] = mwpath
if e.args:
log.msg(e)
log.msg("Enabled downloader middlewares: %s" % ", ".join(self.enabled.keys()), \
level=log.DEBUG)
self.loaded = True
def download(self, download_func, request, spider):
def process_request(request):
for method in self.request_middleware:
response = method(request=request, spider=spider)
assert response is None or isinstance(response, (Response, Request)), \
'Middleware %s.process_request must return None, Response or Request, got %s' % \
(method.im_self.__class__.__name__, response.__class__.__name__)
if response:
return response
return download_func(request=request, spider=spider)
def process_response(response):
assert response is not None, 'Received None in process_response'
if isinstance(response, Request):
return response
for method in self.response_middleware:
response = method(request=request, response=response, spider=spider)
assert isinstance(response, (Response, Request)), \
'Middleware %s.process_response must return Response or Request, got %s' % \
(method.im_self.__class__.__name__, type(response))
if isinstance(response, Request):
send_catch_log(signal=signals.response_received, \
sender=self.__class__, response=response, spider=spider)
return response
send_catch_log(signal=signals.response_received, sender=self.__class__, \
response=response, spider=spider)
return response
def process_exception(_failure):
exception = _failure.value
for method in self.exception_middleware:
response = method(request=request, exception=exception, spider=spider)
assert response is None or isinstance(response, (Response, Request)), \
'Middleware %s.process_exception must return None, Response or Request, got %s' % \
(method.im_self.__class__.__name__, type(response))
if response:
return response
return _failure
deferred = mustbe_deferred(process_request, request)
deferred.addErrback(process_exception)
deferred.addCallback(process_response)
return deferred
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