RFR: 8328874: Class::forName0 should validate the class name length early [v13]

[Chen Liang]

On Thu, 4 Sep 2025 15:54:38 GMT, Guanqiang Han <ghan at openjdk.org> wrote:

>> src/java.base/share/classes/jdk/internal/util/ModifiedUtf.java line 80:
>> 
>>> 78:      */
>>> 79:     @ForceInline
>>> 80:     public static boolean classNameLengthIsValid(String name) {
>> 
>> This can be reused by `DataOutput` too, so maybe just `isEncodable`
>
> @liach This only checks the encoded length rather than full encodability — would a name like isValidLen be more accurate?

Sure, we can go with that name!

>> src/java.base/share/classes/jdk/internal/util/ModifiedUtf.java line 87:
>> 
>>> 85:             return true;
>>> 86:         }
>>> 87:         // Check exact Modified UTF-8 length.
>> 
>> Before doing that, I recommend another fast path `if (nameLen > MAX_LEN) return false`.
>
> @liach I was thinking whether it might be better to place **if (nameLen > MAX_LEN) return false** after the **if (nameLen <= MAX_LEN / 3) return true** check, since in most cases nameLen will be smaller than MAX_LEN / 3 and this order would optimize for the common case.

Yep, this is after the true check.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/26802#discussion_r2322832084
PR Review Comment: https://git.openjdk.org/jdk/pull/26802#discussion_r2322832768