Fixed #25302 (again) -- Ignored scheme when checking for bad referers.

The check introduced in 4ce433e was too strict in real life. The poorly
implemented bots this patch attempted to ignore are sloppy when it comes
to http vs. https.

django/middleware/common.py

@@ -8,6 +8,7 @@ from django.core.exceptions import PermissionDenied
 from django.core.mail import mail_managers
 from django.utils.cache import get_conditional_response, set_response_etag
 from django.utils.encoding import force_text
+from django.utils.six.moves.urllib.parse import urlparse
 
 logger = logging.getLogger('django.request')
 
@@ -163,13 +164,17 @@ class BrokenLinkEmailsMiddleware(object):
         according to project settings or in three specific situations:
          - If the referer is empty.
          - If a '?' in referer is identified as a search engine source.
-         - If the referer is equal to the current URL (assumed to be a
-           malicious bot).
+         - If the referer is equal to the current URL, ignoring the scheme
+           (assumed to be a poorly implemented bot).
         """
-        full_url = "%s://%s/%s" % (request.scheme, domain, uri.lstrip('/'))
-        if (not referer or
-                (not self.is_internal_request(domain, referer) and '?' in referer) or
-                (referer == uri or referer == full_url)):
+        if not referer:
+            return True
+
+        if not self.is_internal_request(domain, referer) and '?' in referer:
+            return True
+
+        parsed_referer = urlparse(referer)
+        if parsed_referer.netloc in ['', domain] and parsed_referer.path == uri:
             return True
 
         return any(pattern.search(uri) for pattern in settings.IGNORABLE_404_URLS)