A middleware component is simply a Python class that conforms to a certain API. Before diving into the formal aspects of what that API is, let\u2019s look at a very simple example.<\/p>\n
High-traffic sites often need to deploy Django behind a load-balancing proxy. This can cause a few small complications, one of which is that every request\u2019s remote IP (request.META[“REMOTE_IP”]) will be that of the load balancer, not the actual IP making the request. Load balancers deal with this by setting a special header, X-Forwarded-For, to the actual requesting IP address. So here\u2019s a small bit of middleware that lets sites running behind a proxy still see the correct IP address in request.META[“REMOTE_ADDR”]:<\/p>\n
class SetRemoteAddrFromForwardedFor(object):
\ndef process_request(self, request):
\ntry:
\nreal_ip = request.META[‘HTTP_X_FORWARDED_FOR’]\nexcept KeyError:
\npass
\nelse:
\n# HTTP_X_FORWARDED_FOR can be a comma-separated list of IPs.
\n# Take just the first one.
\nreal_ip = real_ip.split(“,”)[0]\nrequest.META[‘REMOTE_ADDR’] = real_ip<\/p>\n
If this is installed, every request\u2019s X-Forwarded-For value will be automatically inserted into request.META[‘REMOTE_ADDR’]. This means your Django applications don\u2019t need to be concerned with whether they\u2019re behind a load-balancing proxy or not; they can simply access request.META[‘REMOTE_ADDR’], and that will work whether or not a proxy is being used. In fact, this is a common enough need that this piece of middleware is a built-in part of Django. It lives in django.middleware.http, and you can read a bit more about it in the next section.<\/p>\n
Middleware is a framework of hooks into Django\u2019s request\/response processing. It\u2019s a light, low-level plugin system for globally altering Django\u2019s input or output.<\/p>\n
Each middleware component is responsible for doing some specific function. For example, Django includes a middleware component, AuthenticationMiddleware, that associates users with requests using sessions.<\/p>\n
This document explains how middleware works, how you activate middleware, and how to write your own middleware. Django ships with some built-in middleware you can use right out of the box.<\/p>\n\n\n