add a 'missing slash' regular expression for Location patterns in order to…

add a 'missing slash' regular expression for Location patterns in order to account for dropped slash with the i4x:// pattern. Certain redirect cases will cause this 2nd slash to be dropped (I think via Nginx)

common/lib/xmodule/xmodule/modulestore/__init__.py

@@ -23,6 +23,15 @@ URL_RE = re.compile("""
     (@(?P<revision>[^/]+))?
     """, re.VERBOSE)
 
+MISSING_SLASH_URL_RE = re.compile("""
+    (?P<tag>[^:]+):/
+    (?P<org>[^/]+)/
+    (?P<course>[^/]+)/
+    (?P<category>[^/]+)/
+    (?P<name>[^@]+)
+    (@(?P<revision>[^/]+))?
+    """, re.VERBOSE)
+
 # TODO (cpennington): We should decide whether we want to expand the
 # list of valid characters in a location
 INVALID_CHARS = re.compile(r"[^\w.-]")
@@ -164,9 +173,13 @@ class Location(_LocationBase):
         if isinstance(location, basestring):
             match = URL_RE.match(location)
             if match is None:
+                # cdodge:
+                # check for a dropped slash near the i4x:// element of the location string. This can happen with some
+                # redirects (e.g. edx.org -> www.edx.org which I think happens in Nginx)
+                match = MISSING_SLASH_URL_RE.match(location)
+                if match is None:
                     log.debug('location is instance of %s but no URL match' % basestring)
                     raise InvalidLocationError(location)    
-            else:
             groups = match.groupdict()
             check_dict(groups)
             return _LocationBase.__new__(_cls, **groups)