A Scenic Drive through the Django Request-Response Cycle

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THE DJANGO REQUEST-RESPONSE CYCLE A Scenic Drive Though Daniel Langer [email protected] @dlanger

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DANIEL LANGER Je m’appelle Handmade in Toronto

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THE DJANGO REQUEST-RESPONSE CYCLE A Scenic Drive Though

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LOTS OF THESE Django has http://www.safetysign.com/images/catlog/product/large/J6014.png

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CLIENT

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THE REQUEST

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THE REQUEST $ curl -v http://www.daniellanger.com/hello/mtl/

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THE REQUEST $ curl -v http://www.daniellanger.com/hello/mtl/ > GET /hello/mtl/ HTTP/1.1 > Host: www.daniellanger.com > Accept: */*

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http://www.google.com/about/datacenters/gallery/#/all/5 THE INTERNET http://www.google.com/about/datacenters/gallery/#/all/5

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THE WEB SERVER http://bit.ly/1jPAhEC

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INTERFACE? mod_python FastCGI CGI

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WEB SERVER GATEWAY INTERFACE PEP 333 December 2007 Phillip Eby

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WEB SERVER GATEWAY INTERFACE def simple_app(environ, start_response): response_headers = [('Content-type', 'text/plain')] start_response(‘200 OK’, response_headers) return ['Hello world!\n']

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DJANGO SPEAKS WSGI class WSGIHandler(base.BaseHandler): def __call__(self, environ, start_response): [...] response = self.get_response(request) [...] start_response(status, response_headers) return response

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DJANGO.CORE.HANDLERS.BASEHANDLER 1. Request middleware 2. Resolve request.path_info 3. View middleware 4. View 5. Response middleware * Exception middleware (maybe)

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MIDDLEWARE? A small digression

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MIDDLEWARE A small digression “[A] light, low-level ‘plugin’ system for globally altering Django’s input or output.” - https://docs.djangoproject.com/en/dev/topics/http/middleware/

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MIDDLEWARE A small digression MIDDLEWARE_CLASSES = ( 'django.middleware.common.CommonMiddleware', 'django.middleware.csrf.CsrfViewMiddleware', [...] )

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DJANGO.CORE.HANDLERS.BASEHANDLER 1. Request middleware 2. Resolve request.path_info 3. View middleware 4. View 5. Response middleware * Exception middleware (maybe)

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REQUEST MIDDLEWARE class PyConRequestMiddleware(object): def process_request(self, request): return None # or HttpResponse

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BREAK TIME http://bit.ly/1mNlxWE

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CLIENT WEB SERVER WSGI REQUEST Middleware

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DJANGO.CORE.HANDLERS.BASEHANDLER 1. Request middleware 2. Resolve request.path_info 3. View middleware 4. View 5. Response middleware * Exception middleware (maybe)

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DJANGO.CORE.URLRESOLVERS http://www.daniellanger.com/hello/mtl/

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DJANGO.CORE.URLRESOLVERS http://www.daniellanger.com/hello/mtl/ urlpatterns = patterns('' url(r'^hello/mtl/$', HiMtlView, name=‘hi__mtl’), url(r'^hello/(?P\w+)/$', HiCityView, name=‘hi_city’), )

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DJANGO.CORE.URLRESOLVERS http://www.daniellanger.com/hello/mtl/ urlpatterns = patterns('' url(r'^hello/(?P\w+)/$', HiCityView, name=‘hi_city’), url(r'^hello/mtl/$', HiMtlView, name=‘hi__mtl’), ]

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DJANGO.CORE.URLRESOLVERS urlpatterns = patterns('' url(r'^hello/(?P\w+)/$', HiCityView, name=‘hi_city’), ) {% url ‘hi_city’ city=ottawa %} reverse(‘hi_city’, kwargs={‘city’: ‘ottawa’}) # Both return http://www.daniellanger.com/hello/ottawa/

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DJANGO.CORE.URLRESOLVERS urlpatterns = patterns('' url(r'^cdn_hi/(?P\w+)/$', HiCityView, name=‘hi_city’), ) {% url ‘hi_city’ city=ottawa %} reverse(‘hi_city’, kwargs={‘city’: ‘ottawa’}) # Both return http://www.daniellanger.com/cdn_hi/ottawa/

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DJANGO.CORE.HANDLERS.BASEHANDLER 1. Request middleware 2. Resolve request.path_info 3. View middleware 4. View 5. Response middleware * Exception middleware (maybe)

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DJANGO.CORE.HANDLERS.BASEHANDLER 1. Request middleware 2. Resolve request.path_info 3. View middleware 4. View 5. Response middleware * Exception middleware (maybe)

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VIEWS def HiMtlView(request): html = “Bonjour Mtl!” return HttpResponse(html)

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RESPONSES? HttpResponse HttpResponseRedirect JsonResponse StreamingHttpResponse

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VIEWS def HiMtlView(request): html = “Bonjour Mtl!” return HttpResponse(html)

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CLASS-BASED VIEWS from django.views.generic import View class HiMtlView(View): def get(self, request): html = “Bonjour Mtl!” return HttpResponse(html)

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TEMPLATES IN VIEWS from django.shortcuts import render def HiMtlView(request): context = {‘city’: ‘Montreal’} return render(request, ‘hello.html’, context) # hello.html Bonjour {{ city }}!

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TEMPLATES IN VIEWS def HiMtlView(request): context = {‘city’: ‘Montreal’} return render(request, ‘hello.html’, context) # hello.html Bonjour {{ city }} (from {{ request_city }}!)

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TEMPLATES IN VIEWS def HiMtlView(request): context = { ‘city’: ‘Montreal’, ‘request_city’: GeoIP.get_city(request)} return render(request, ‘hello.html’, context) # hello.html Bonjour {{ city }} (from {{ request_city }}!)

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CONTEXT PROCESSORS def HiMtlView(request): context = { ‘city’: ‘Montreal’, ‘request_city’: GeoIP.get_city(request)} return render(request, ‘hello.html’, context) # hello.html Bonjour {{ city }} (from {{ request_city }}!)

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CONTEXT PROCESSORS def request_city(request) return { ‘request_city’: GeoIP.get_city(request), }

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CONTEXT PROCESSORS def HiMtlView(request): context = {‘city’: ‘Montreal’} return render(request, ‘hello.html’, context) # hello.html Bonjour {{ city }} (from {{ request_city }}!)

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The Doe Corporation presents PAUSE PAUSE- CAFE http://www.roadfood.com/photos/20865.jpg

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CLIENT WEB SERVER WSGI URL RESOLUTION VIEW REQUEST Middleware VIEW Middleware

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DJANGO.CORE.HANDLERS.BASEHANDLER 1. Request middleware 2. Resolve request.path_info 3. View middleware 4. View 5. Response middleware * Exception middleware (maybe)

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RESPONSE MIDDLEWARE class PyConResponseMiddleware(object): def process_response(self, request, response): return None # or HttpResponse

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MIDDLEWARE class PyConMiddleware(object): def process_request(self, request): return None # or HttpResponse def process_response(self, request, response): return response # or new HttpResponse

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MIDDLEWARE MIDDLEWARE_CLASSES = ( 'django.middleware.common.CommonMiddleware', 'django.middleware.csrf.CsrfViewMiddleware', 'PyConMiddleware', [...] )

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DJANGO.CORE.HANDLERS.BASEHANDLER 1. Request middleware 2. Resolve request.path_info 3. View middleware 4. View 5. Response middleware * Exception middleware (maybe)

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EXCEPTION MIDDLEWARE class PyConMiddleware(object): def process_exception(self, request, exception): return None # or HttpResponse

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WEB SERVER GATEWAY INTERFACE class WSGIHandler(base.BaseHandler): def __call__(self, environ, start_response): [...] response = self.get_response(request) [...] start_response(status, response_headers) return response

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THE RESPONSE $ curl -v http://www.daniellanger.com/hello/mtl/ > GET /hello/mtl/ HTTP/1.1 > Host: www.daniellanger.com > Accept: */* < HTTP/1.1 200 OK < Server: nginx < Content-Type: text/html;charset=UTF-8 < Content-Length: 33 Bonjour Montreal! (from Toronto)

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CLIENT WEB SERVER WSGI URL RESOLUTION VIEW WSGI WEB SERVER CLIENT REQUEST Middleware RESPONSE Middleware VIEW Middleware EXCEPTION Middleware

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@dlanger