分析一个请求的生命周期以及在该周期中 Django 框架的各个中间件的 process_request 、 process_view 、process_response 是怎么参与的
首先浏览器发起请求：当请求到 Django 框架的时候，
根据中间件的注册顺序依次执行：
-
根据注册顺序执行所有中间件的 process_request:
[process_request, process_request, process_request, process_request, process_request] -
根据注册顺序执行所有中间件的 process_view:
[process_view, process_view, process_view, process_view, process_view] -
执行根据 URL 找到的视图函数
-
根据注册顺序执行所有中间件的 process_response:
[process_response, process_response, process_response, process_response, process_response]
源码分析：
D:\WorkSpace\HelloNG\src\testcode\djangoTest\robappdj\robappdj\wsgi.py：
application = get_wsgi_application() ----------------------------------------------step 1
C:\Python27\Lib\site-packages\django\core\wsgi.py
def get_wsgi_application():
"""
The public interface to Django's WSGI support. Should return a WSGI
callable.
Allows us to avoid making django.core.handlers.WSGIHandler public API, in
case the internal WSGI implementation changes or moves in the future.
"""
django.setup()
return WSGIHandler() -----------------------------------------------------------step 2
C:\Python27\Lib\site-packages\django\core\handlers\wsgi.py：
class WSGIHandler(base.BaseHandler):
initLock = Lock()
request_class = WSGIRequest
def __call__(self, environ, start_response):
# Set up middleware if needed. We couldn't do this earlier, because
# settings weren't available.
if self._request_middleware is None:
with self.initLock:
try:
# Check that middleware is still uninitialized.
if self._request_middleware is None:
self.load_middleware()
except:
# Unload whatever middleware we got
self._request_middleware = None
raise
set_script_prefix(get_script_name(environ))
signals.request_started.send(sender=self.__class__, environ=environ)
try:
request = self.request_class(environ)
except UnicodeDecodeError:
logger.warning('Bad Request (UnicodeDecodeError)',
exc_info=sys.exc_info(),
extra={
'status_code': 400,
}
)
response = http.HttpResponseBadRequest()
else:
response = self.get_response(request) -------------------------------step 3
class BaseHandler(object):
# Changes that are always applied to a response (in this order).
response_fixes = [
http.fix_location_header,
http.conditional_content_removal,
]
def __init__(self):
self._request_middleware = None
self._view_middleware = None
self._template_response_middleware = None
self._response_middleware = None
self._exception_middleware = None
def get_response(self, request):
"Returns an HttpResponse object for the given HttpRequest"
# Setup default url resolver for this thread, this code is outside
# the try/except so we don't get a spurious "unbound local
# variable" exception in the event an exception is raised before
# resolver is set
urlconf = settings.ROOT_URLCONF
urlresolvers.set_urlconf(urlconf)
resolver = urlresolvers.RegexURLResolver(r'^/', urlconf)
try:
response = None
# Apply request middleware
for middleware_method in self._request_middleware: ------------------------step4_1: process_request
response = middleware_method(request)
if response:
break
if response is None:
if hasattr(request, 'urlconf'):
# Reset url resolver with a custom urlconf.
urlconf = request.urlconf
urlresolvers.set_urlconf(urlconf)
resolver = urlresolvers.RegexURLResolver(r'^/', urlconf)
resolver_match = resolver.resolve(request.path_info)
callback, callback_args, callback_kwargs = resolver_match
request.resolver_match = resolver_match
# Apply view middleware
for middleware_method in self._view_middleware: ------------------------step4_2: process_view
response = middleware_method(request, callback, callback_args, callback_kwargs)
if response:
break
if response is None:
wrapped_callback = self.make_view_atomic(callback) -----------------------step4_3: 根据 URL 找到的视图函数
try:
response = wrapped_callback(request, *callback_args, **callback_kwargs)
except Exception as e:
# If the view raised an exception, run it through exception
# middleware, and if the exception middleware returns a
# response, use that. Otherwise, reraise the exception.
for middleware_method in self._exception_middleware:
response = middleware_method(request, e)
if response:
break
if response is None:
raise
# Complain if the view returned None (a common error).
if response is None:
if isinstance(callback, types.FunctionType): # FBV
view_name = callback.__name__
else: # CBV
view_name = callback.__class__.__name__ + '.__call__'
raise ValueError("The view %s.%s didn't return an HttpResponse object. It returned None instead."
% (callback.__module__, view_name))
# If the response supports deferred rendering, apply template
# response middleware and then render the response
if hasattr(response, 'render') and callable(response.render):
for middleware_method in self._template_response_middleware:
response = middleware_method(request, response)
# Complain if the template response middleware returned None (a common error).
if response is None:
raise ValueError(
"%s.process_template_response didn't return an "
"HttpResponse object. It returned None instead."
% (middleware_method.__self__.__class__.__name__))
response = response.render()
except http.Http404 as e:
logger.warning('Not Found: %s', request.path,
extra={
'status_code': 404,
'request': request
})
if settings.DEBUG:
response = debug.technical_404_response(request, e)
else:
response = self.get_exception_response(request, resolver, 404)
except PermissionDenied:
logger.warning(
'Forbidden (Permission denied): %s', request.path,
extra={
'status_code': 403,
'request': request
})
response = self.get_exception_response(request, resolver, 403)
except MultiPartParserError:
logger.warning(
'Bad request (Unable to parse request body): %s', request.path,
extra={
'status_code': 400,
'request': request
})
response = self.get_exception_response(request, resolver, 400)
except SuspiciousOperation as e:
# The request logger receives events for any problematic request
# The security logger receives events for all SuspiciousOperations
security_logger = logging.getLogger('django.security.%s' %
e.__class__.__name__)
security_logger.error(
force_text(e),
extra={
'status_code': 400,
'request': request
})
if settings.DEBUG:
return debug.technical_500_response(request, *sys.exc_info(), status_code=400)
response = self.get_exception_response(request, resolver, 400)
except SystemExit:
# Allow sys.exit() to actually exit. See tickets #1023 and #4701
raise
except: # Handle everything else.
# Get the exception info now, in case another exception is thrown later.
signals.got_request_exception.send(sender=self.__class__, request=request)
response = self.handle_uncaught_exception(request, resolver, sys.exc_info())
try:
# Apply response middleware, regardless of the response
for middleware_method in self._response_middleware: ------------------------step4_4: process_response
response = middleware_method(request, response)
# Complain if the response middleware returned None (a common error).
if response is None:
raise ValueError(
"%s.process_response didn't return an "
"HttpResponse object. It returned None instead."
% (middleware_method.__self__.__class__.__name__))
response = self.apply_response_fixes(request, response)
except: # Any exception should be gathered and handled
signals.got_request_exception.send(sender=self.__class__, request=request)
response = self.handle_uncaught_exception(request, resolver, sys.exc_info())
response._closable_objects.append(request)
return response
