Fix lower bound checking in scan_once / raw_decode API #98v3.5.3

1 files changed, 5 insertions, 0 deletions

diff --git a/simplejson/scanner.py b/simplejson/scanner.py
index b7918b3..5abed35 100644
--- a/simplejson/scanner.py
+++ b/simplejson/scanner.py
@@ -118,6 +118,11 @@ def py_make_scanner(context):
             raise JSONDecodeError(errmsg, string, idx)
 
     def scan_once(string, idx):
+        if idx < 0:
+            # Ensure the same behavior as the C speedup, otherwise
+            # this would work for *some* negative string indices due
+            # to the behavior of __getitem__ for strings. #98
+            raise JSONDecodeError('Expecting value', string, idx)
         try:
             return _scan_once(string, idx)
         finally: