django-cache-headers 0.2.2

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

Django Cache Headers

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

Save this snippet as /etc/varnish/default.vcl:

# 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

0.2.2

1. Iterate over regexes in order of most specific (longest) to least specific (shortest).

2. Revert OrderedDict change since it is not required anymore due to the above change.

0.2.1

1. Use an OrderedDict for guaranteed policy iteration order.

0.2

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

0.1.3

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

0.1.2

1. Use the s-maxage header for compatability with Varnish.

0.1.1

1. Leave response untouched if status code is not 200.

0.1

1. Initial release.