unquote key name multiple times until stable value

moto/s3/utils.py

@@ -68,11 +68,22 @@ def metadata_from_headers(headers):
     return metadata
 
 
-def clean_key_name(key_name):
+def clean_key_name(key_name, attempts=4):
     if six.PY2:
-        return unquote(key_name.encode('utf-8')).decode('utf-8')
+        def uq(k):
+            return unquote(k.encode('utf-8')).decode('utf-8')
+    else:
+        uq = unquote
 
-    return unquote(key_name)
+    original = cleaned = key_name
+    last_attempt = attempts - 1
+    for attempt in range(attempts):
+        cleaned = uq(key_name)
+        if cleaned == key_name:
+            return cleaned
+        if attempt != last_attempt:
+            key_name = cleaned
+    raise Exception('unable to fully clean name: original %s, last clean %s prior clean %s' % (original, cleaned, key_name))
 
 
 class _VersionedKeyStore(dict):