web: do not send 500 on invalid If-Modified-Since header

#3408
tornadoweb · Jul 8, 2024 · 0577219 · 0577219
1 parent e978117
commit 0577219
Showing 1 changed file with 4 additions and 1 deletion.
diff --git a/tornado/web.py b/tornado/web.py
@@ -2861,7 +2861,10 @@ def should_return_304(self) -> bool:
         # content has not been modified
         ims_value = self.request.headers.get("If-Modified-Since")
         if ims_value is not None:
-            if_since = email.utils.parsedate_to_datetime(ims_value)
+            try:
+                if_since = email.utils.parsedate_to_datetime(ims_value)
+            except ValueError:
+                return False
             if if_since.tzinfo is None:
                 if_since = if_since.replace(tzinfo=datetime.timezone.utc)
             assert self.modified is not None