django-cache-headers 0.2

Configurable middleware to add HTTP caching headers for URL's.

Django Cache Headers
====================

.. figure:: https://travis-ci.org/praekelt/django-cache-headers.svg?branch=develop
:align: center
:alt: Travis

Overview
--------

Django Cache Headers allows you to set HTTP caching headers for URL patterns
according to certain policies. It does not perform any caching itself - it
merely sets the headers on the response which are then interpreted by eg. Nginx.

Installation
------------

1. Install or add ``django-cache-headers`` to your Python path.
2. Add ``cache_headers`` to your ``INSTALLED_APPS`` setting.
3. Add ``cache_headers.middleware.CacheHeadersMiddleware`` before
SessionMiddleware and AuthenticationMiddleware to your ``MIDDLEWARE_CLASSES`` setting.

Policies
--------
Django Cache Headers provides four caching policies. You may define your own policies.:

1. all-users - response is marked as cached once for all users.
2. anonymous-only - response is marked as cached once only for anonymous users.
3. anonymous-and-authenticated - response is marked as cached once for anonymous users and once for authenticated users.
4. per-user - response is marked as cached once for anonymous users and for each authenticated user individually.

Sample Varnish config file
--------------------------

# Use 4.0 format
vcl 4.0;

# Default upstream
backend default {
.host = "127.0.0.1";
.port = "8080";
}

# Access control
acl purge {
"localhost";
"127.0.0.1";
}

# vcl_recv adapted from the Varnish default
sub vcl_recv {
if (req.method == "PURGE") {
if (!client.ip ~ purge) {
return(synth(405, "Not allowed."));
}
return(purge);
}

if (req.method == "PRI") {
# We do not support SPDY or HTTP/2.0
return(synth(405));
}

if (req.method != "GET" &&
req.method != "HEAD" &&
req.method != "PUT" &&
req.method != "POST" &&
req.method != "TRACE" &&
req.method != "OPTIONS" &&
req.method != "DELETE") {
# Non-RFC2616 or CONNECT which is weird
return(pipe);
}

if (req.method != "GET" && req.method != "HEAD") {
# We only deal with GET and HEAD by default
return(pass);
}
if (req.http.Authorization) {
# Not cacheable by default
return(pass);
}
return(hash);
}

# Useful headers
sub vcl_deliver {
if (obj.hits > 0) {
set resp.http.X-Cache = "HIT";
} else {
set resp.http.X-Cache = "MISS";
}
}

sub vcl_hash {
# Cache even with cookies present. Note we don't delete the cookies.
# Also, we only consider cookies in X-Cookie-Hash as part of the hash.
# This value is set by the relevant Django Cache Headers policy.
set req.http.X-Cookie-Hash = "";
if (req.http.X-Hash-Cookies) {
set req.http.X-Cookie-Pattern = ";(" + req.http.X-Hash-Cookies + ")=";
set req.http.X-Cookie-Hash = ";" + req.http.Cookie;
# VCL does not currently support variables in regsuball, so hardcode
#set req.http.X-Cookie-Hash = regsuball(req.http.X-Cookie-Hash, req.http.X-Cookie-Pattern, "; \1=");
if (req.http.X-Cookie-Hash == "messages") {
set req.http.X-Cookie-Hash = regsuball(req.http.X-Cookie-Hash, ";(messages)=", "; \1=");
}
if (req.http.X-Cookie-Hash == "messages|isauthenticated") {
set req.http.X-Cookie-Hash = regsuball(req.http.X-Cookie-Hash, ";(messages|isauthenticated)=", "; \1=");
}
if (req.http.X-Cookie-Hash == "messages|sessionid") {
set req.http.X-Cookie-Hash = regsuball(req.http.X-Cookie-Hash, ";(messages|sessionid)=", "; \1=");
}
set req.http.X-Cookie-Hash = regsuball(req.http.X-Cookie-Hash, ";[^ ][^;]*", "");
set req.http.X-Cookie-Hash = regsuball(req.http.X-Cookie-Hash, "^[; ]+|[; ]+$", "");
}
hash_data(req.http.X-Cookie-Hash);
}

Settings
--------

The ``timeouts`` key combines the policy, timeout in seconds and URL regexes in a nested dictionary::

CACHE_HEADERS = {
"timeouts": {
"all-users": {
60: (
"^/all-users/",
)
},
"anonymous-only": {
60: (
"^/anonymous-only/",
)
},
"anonymous-and-authenticated": {
60: (
"^/anonymous-and-authenticated/",
)
},
"per-user": {
60: (
"^/per-user/",
)
},
"custom-policy": {
60: (
"^/custom-policy/",
)
}
}
}

Authors
=======

Praekelt Consulting
-------------------

* Hedley Roos

Changelog
=========

0.2
---
#. Ignoring cookies completely when setting headers turned out to be a mistake due to too many security concerns. Restore them.

0.1.3
-----
#. Handle case where user may also be logged in and a cookie not being set.

0.1.2
-----
#. Use the s-maxage header for compatability with Varnish.

0.1.1
-----
#. Leave response untouched if status code is not 200.

0.1
---
#. Initial release.