import datetime

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.

    Removes the content from any response to a HEAD request.

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

    """

    def process_response(self, request, response):

        now = datetime.datetime.utcnow()

        response['Date'] = now.strftime('%a, %d %b %Y %H:%M:%S GMT')

        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']:

                response.status_code = 304

                response.content = ''

                response['Content-Length'] = '0'

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

            last_mod = response['Last-Modified']

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

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

                response.status_code = 304

                response.content = ''

                response['Content-Length'] = '0'

        if request.method == 'HEAD':

            response.content = ''

        return response

class SetRemoteAddrFromForwardedFor(object):

    """

    Middleware that sets REMOTE_ADDR based on HTTP_X_FORWARDED_FOR, if the

    latter is set. This is useful if you're sitting behind a reverse proxy that

    causes each request's REMOTE_ADDR to be set to 127.0.0.1.

    Note that this does NOT validate HTTP_X_FORWARDED_FOR. If you're not behind

    a reverse proxy that sets HTTP_X_FORWARDED_FOR automatically, do not use

    this middleware. Anybody can spoof the value of HTTP_X_FORWARDED_FOR, and

    because this sets REMOTE_ADDR based on HTTP_X_FORWARDED_FOR, that means

    anybody can "fake" their IP address. Only use this when you can absolutely

    trust the value of HTTP_X_FORWARDED_FOR.

    """

    def process_request(self, request):

        try:

            real_ip = request.META['HTTP_X_FORWARDED_FOR']

        except KeyError:

            return None

        else:

            # HTTP_X_FORWARDED_FOR can be a comma-separated list of IPs.

            # Take just the first one.

            real_ip = real_ip.split(",")[0]

            request.META['REMOTE_ADDR'] = real_ip