Django middleware to aid in implementing support for "Do Not Track" HTTP headers.

donottrack_middleware.py

"""
A Django middleware, to aid in implementing the HTTP header-based
"Do Not Track" mechanism described in [1] and a few of the myriad variations.
Known browsers utilizing this option include Firefox 4+, Internet Explorer 9+,
and Safari under Mac OS X 10.7.

This does nothing by itself. It remains the application's responsibility to
ensure that the `tracking_opt_out` attribute is used to toggle first party
tracking and disable or notify third parties of the user's preference.

[1] http://tools.ietf.org/html/draft-mayer-do-not-track-00
"""
__author__ = "Mike Tigas <mike@tig.as>"
__license__ = "Public domain; http://creativecommons.org/publicdomain/zero/1.0/"

class TrackingCheck(object):
    """
    Sets `request.tracking_opt_out=True` if the request has one of the known
    "do not track" explicit opt-out HTTP headers.

    Sets a `DNT` response header back to the client, confirming that we
    understand "do not track" headers, at the very least.
    """
    def process_request(self, request):
        # DNT: 1
        optout = request.META.get("HTTP_DNT", False) \
                 or request.META.get("HTTP_X_DNT", "0")
        if optout.strip() == "1":
            setattr(request, "tracking_opt_out", True)
            return None

        # X-Do-Not-Track: 1
        optout = request.META.get("HTTP_X_DO_NOT_TRACK", "0")
        if optout.strip() == "1":
            setattr(request, "tracking_opt_out", True)
            return None

        # X-Tracking-Choice: do-not-track
        optout = request.META.get("HTTP_X_TRACKING_CHOICE", False) \
                 or request.META.get("HTTP_TRACKING_PREFERENCE", "")
        if optout.strip() == "do-not-track":
            setattr(request, "tracking_opt_out", True)
            return None

        setattr(request, "tracking_opt_out", False)

    def process_response(self, request, response):
        # We're actually not doing anything with `request.tracking_opt_out`
        # at the moment.
        response['DNT'] = "0 (sorry)"

        # TODO
        #response['DNT'] = "1"
        return response