slash_middleware.py

from django import http
from django.utils.http import urlquote
from django.core import urlresolvers


class AppendOrRemoveSlashMiddleware(object):
    """
    Like django's built in APPEND_SLASH functionality, but also works in reverse. Eg
    will remove the slash if a slash-appended url won't resolve, but its non-slashed
    counterpart will.

    See http://gregbrown.co.nz/code/append-or-remove-slash/ for more information.
    """

    def process_request(self, request):
        """
        Returns a redirect if adding/removing a slash is appropriate. 
        """
        
        # check if the url is valid
        urlconf = getattr(request, 'urlconf', None)
        if not _is_valid_path(request.path_info, urlconf):
            # if not, check if adding/removing the trailing slash helps
            if request.path_info.endswith('/'):
                new_path = request.path_info[:-1]
            else:
                new_path = request.path_info + '/'
            
            if _is_valid_path(new_path, urlconf):
                # if the new url is valid, redirect to it
                if request.get_host():
                    new_url = "%s://%s%s" % (request.is_secure() and 'https' or 'http', request.get_host(), urlquote(new_path))
                else:
                    new_url = urlquote(new_path)
                if request.GET:
                    new_url += '?' + request.META['QUERY_STRING']
                return http.HttpResponsePermanentRedirect(new_url)

            
        
def _is_valid_path(path, urlconf=None):
    """
    Returns True if the given path resolves against the default URL resolver,
    False otherwise.
    """
    try:
        urlresolvers.resolve(path, urlconf)
        return True
    except urlresolvers.Resolver404:
        return False