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"""
Downloader Middleware manager
See documentation in docs/topics/downloader-middleware.rst
"""
from scrapy.http import Request, Response
from scrapy.middleware import MiddlewareManager
from scrapy.utils.defer import mustbe_deferred
from scrapy.utils.conf import build_component_list
class DownloaderMiddlewareManager(MiddlewareManager):
component_name = 'downloader middleware'
@classmethod
def _get_mwlist_from_settings(cls, settings):
return build_component_list(settings['DOWNLOADER_MIDDLEWARES_BASE'], \
settings['DOWNLOADER_MIDDLEWARES'])
def _add_middleware(self, mw):
if hasattr(mw, 'process_request'):
self.methods['process_request'].append(mw.process_request)
if hasattr(mw, 'process_response'):
self.methods['process_response'].insert(0, mw.process_response)
if hasattr(mw, 'process_exception'):
self.methods['process_exception'].insert(0, mw.process_exception)
def download(self, download_func, request, spider):
def process_request(request):
for method in self.methods['process_request']:
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.methods['process_response']:
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):
return response
return response
def process_exception(_failure):
exception = _failure.value
for method in self.methods['process_exception']:
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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