troggle/core/middleware.py

from django.conf import settings
from django import http
from django.urls import reverse, resolve,Resolver404
"""Non-standard django middleware is loaded from this file.
"""

class SmartAppendSlashMiddleware(object):
    """
    "SmartAppendSlash" middleware for taking care of URL rewriting.

    This middleware appends a missing slash, if:
    * the SMART_APPEND_SLASH setting is True
    * the URL without the slash does not exist
    * the URL with an appended slash does exist.
    Otherwise it won't touch the URL.
    """

    def process_request(self, request):
        '''Called for every url so return as quickly as possible
        Append a slash if SMART_APPEND_SLASH is set, the resulting URL resolves and it doesn't without the /
        '''
        if not settings.SMART_APPEND_SLASH:
            return None
 
        if request.path.endswith('/'):
            return None
            
        if request.path.endswith('_edit'):
            return None

        host = http.HttpRequest.get_host(request)
        old_url = [host, request.path]
        if _resolves(old_url[1]):
            return None
         
        # So: it does not resolve according to our criteria, i.e. _edit doesn't count
        new_url = old_url[:]       
        new_url[1] = new_url[1] + '/'
        if not _resolves(new_url[1]):
            return None
        else:          
            if settings.DEBUG and request.method == 'POST':
                # replace this exception with a redirect to an error page
                raise RuntimeError("You called this URL via POST, but the URL doesn't end in a slash and you have SMART_APPEND_SLASH set. Django can't redirect to the slash URL while maintaining POST data. Change your form to point to %s%s (note the trailing slash), or set SMART_APPEND_SLASH=False in your Django settings." % (new_url[0], new_url[1]))
        if new_url != old_url:
            # Redirect
            if new_url[0]:
                newurl = "%s://%s%s" % (request.is_secure() and 'https' or 'http', new_url[0], new_url[1])
            else:
                newurl = new_url[1]
            if request.GET:
                newurl += '?' + request.GET.urlencode()
            return http.HttpResponsePermanentRedirect(newurl)

        return None

def _resolves(url):
    try:
        # If the URL does not resolve, the function raises a Resolver404 exception (a subclass of Http404) 
        match = resolve(url)
        # this will ALWAYS be resolved by expopages because it will produce pagenotfound if not the thing asked for
        # so handle this in expopages, not in middleware 
        return True
    except Resolver404:
        return False
    except:
        print(url)
        raise