[bug 849480] Simplify get_next_url.

- Improve test coverage of sumo.utils.get_next_url.
- Simplify implementation, since we no longer need to implement
  is_safe_url ourselves.
- Drop untested semantics/checks, like LOGIN_URL.
- Early returns are nice and clean.

apps/sumo/tests/test__utils.py

@@ -43,18 +43,43 @@ def tearDown(self):
         self.patcher.stop()
         super(GetNextUrlTests, self).tearDown()
 
-    def test_https(self):
-        """Verify that protocol and domain get removed for https."""
-        r = self.r.post('/users/login',
-                        {'next': 'https://su.mo.com/kb/new?f=b'})
-        eq_('/kb/new?f=b', get_next_url(r))
+    def test_query_string(self):
+        """Query-strings remain intact."""
+        r = self.r.get('/', {'next': '/new?f=b'})
+        eq_('/new?f=b', get_next_url(r))
 
-    def test_http(self):
-        """Verify that protocol and domain get removed for http."""
+    def test_good_host_https(self):
+        """Full URLs work with valid hosts."""
         r = self.r.post('/users/login',
-                        {'next': 'http://su.mo.com/kb/new'})
+                        {'next': 'https://su.mo.com/kb/new'})
+        eq_('https://su.mo.com/kb/new', get_next_url(r))
+
+    def test_post(self):
+        """'next' in POST overrides GET."""
+        r = self.r.post('/?next=/foo', {'next': '/bar'})
+        eq_('/bar', get_next_url(r))
+
+    def test_get(self):
+        """'next' can be a query-string parameter."""
+        r = self.r.get('/users/login', {'next': '/kb/new'})
         eq_('/kb/new', get_next_url(r))
 
+    def test_referer(self):
+        """Use HTTP referer if nothing else."""
+        r = self.r.get('/')
+        r.META['HTTP_REFERER'] = 'http://su.mo.com/new'
+        eq_('http://su.mo.com/new', get_next_url(r))
+
+    def test_bad_host_https(self):
+        r = self.r.get('/', {'next': 'https://example.com'})
+        eq_(None, get_next_url(r))
+
+    def test_bad_host_protocol_relative(self):
+        """Protocol-relative URLs do not let bad hosts through."""
+        r = self.r.get('/', {'next': '//example.com'})
+        eq_(None, get_next_url(r))
+
+
 class JSONTests(TestCase):
     def test_truncated_noop(self):
         """Make sure short enough things are unmodified."""

apps/sumo/utils.py

@@ -5,7 +5,7 @@
 from django.contrib.sites.models import Site
 from django.db import models
 from django.db.models.signals import pre_delete
-from django.utils.http import urlencode
+from django.utils.http import urlencode, is_safe_url
 
 from sumo import paginator
 
@@ -117,22 +117,8 @@ def get_next_url(request):
     else:
         url = request.META.get('HTTP_REFERER')
 
-    if url:
-        parsed_url = urlparse.urlparse(url)
-        # Don't redirect outside of SUMO.
-        # Don't include protocol+domain, so if we are https we stay that way.
-        if parsed_url.scheme:
-            site_domain = Site.objects.get_current().domain
-            url_domain = parsed_url.netloc
-            if site_domain != url_domain:
-                url = None
-            else:
-                url = u'?'.join([getattr(parsed_url, x) for x in
-                                ('path', 'query') if getattr(parsed_url, x)])
-
-        # Don't redirect right back to login or logout page
-        if parsed_url.path in [settings.LOGIN_URL, settings.LOGOUT_URL]:
-            url = None
+    if not is_safe_url(url, Site.objects.get_current().domain):
+        return None
 
     return url