Fix safe_join to allow joining a base path with an empty string

CHANGELOG.rst

@@ -1,6 +1,12 @@
 django-storages change log
 ==========================
 
+1.6.1 (UNRELEASED)
+******************
+
+* Fix regression in ``safe_join()`` to allow joining a base path with an empty
+  string.
+
 1.6 (2017-06-21)
 ******************
 
@@ -363,4 +369,3 @@ since March 2013.
 
 .. _#89: https://bitbucket.org/david/django-storages/issue/89/112-broke-the-mosso-backend
 .. _pull request #5: https://bitbucket.org/david/django-storages/pull-request/5/fixed-path-bug-and-added-testcase-for
-

storages/utils.py

@@ -60,15 +60,15 @@ def safe_join(base, *paths):
     """
     base_path = force_text(base)
     base_path = base_path.rstrip('/')
-    paths = [force_text(p) for p in paths]
+    paths = [base_path + '/'] + [force_text(p) for p in paths if p]
 
-    final_path = posixpath.normpath(posixpath.join(base_path + '/', *paths))
+    final_path = posixpath.normpath(posixpath.join(*paths))
     # posixpath.normpath() strips the trailing /. Add it back.
     if paths[-1].endswith('/'):
         final_path += '/'
 
     # Ensure final_path starts with base_path and that the next character after
-    # the final path is /.
+    # the base path is /.
     base_path_len = len(base_path)
     if (not final_path.startswith(base_path) or final_path[base_path_len] != '/'):
         raise ValueError('the joined path is located outside of the base path'

tests/test_utils.py

@@ -90,3 +90,7 @@ def test_datetime_isoformat(self):
         dt = datetime.datetime(2017, 5, 19, 14, 45, 37, 123456)
         path = utils.safe_join('base_url', dt.isoformat())
         self.assertEqual(path, 'base_url/2017-05-19T14:45:37.123456')
+
+    def test_join_empty_string(self):
+        path = utils.safe_join('base_url', '')
+        self.assertEqual(path, 'base_url/')