from django.core.exceptions import MiddlewareNotUsed

from django.utils.http import http_date

class ConditionalGetMiddleware(object):

    """

    Handles conditional GET operations. If the response has a ETag or

    Last-Modified header, and the request has If-None-Match or

    If-Modified-Since, the response is replaced by an HttpNotModified.

    Also sets the Date and Content-Length response-headers.

    """

    def process_response(self, request, response):

        response['Date'] = http_date()

        if not response.has_header('Content-Length'):

            response['Content-Length'] = str(len(response.content))

        if response.has_header('ETag'):

            if_none_match = request.META.get('HTTP_IF_NONE_MATCH', None)

            if if_none_match == response['ETag']:

                # Setting the status is enough here. The response handling path

                # automatically removes content for this status code (in

                # http.conditional_content_removal()).

                response.status_code = 304

        if response.has_header('Last-Modified'):

            if_modified_since = request.META.get('HTTP_IF_MODIFIED_SINCE', None)

            if if_modified_since == response['Last-Modified']:

                # Setting the status code is enough here (same reasons as

                # above).

                response.status_code = 304

        return response

class SetRemoteAddrFromForwardedFor(object):

    """

    This middleware has been removed; see the Django 1.1 release notes for

    details.

    It previously set REMOTE_ADDR based on HTTP_X_FORWARDED_FOR. However, after

    investiagtion, it turns out this is impossible to do in a general manner:

    different proxies treat the X-Forwarded-For header differently. Thus, a

    built-in middleware can lead to application-level security problems, and so

    this was removed in Django 1.1

    """

    def __init__(self):

        import warnings

        warnings.warn("SetRemoteAddrFromForwardedFor has been removed. "

                      "See the Django 1.1 release notes for details.",

                      category=DeprecationWarning)

        raise MiddlewareNotUsed()