isBase64 throws ArrayIndexOutOfBoundsException on some non-BASE64 bytes

• Key: CODEC-68
• Type: Bug
• Status: Closed
• Resolution: Duplicate
• Priority: Major
• Assignee: Unassigned
• Reporter: Robert Rodewald
• Affects Version/s: 1.3
• Fix Version/s: 1.4

Description

the following code throws an ArrayIndexOutOfBoundsException although it is perfectly valid (the byte 0x9c should be ignored according to the standard):

byte[x] = new byte[] { 'n', 'A', '=', '=', 0x9c };
Base64.decodeBase64(x);

The problem is the following method:

private static boolean isBase64(byte octect) {
        if (octect == PAD) {
            return true;
        } else if (base64Alphabet[octect] == -1) {
            return false;
        } else {
            return true;
        }
    }

in Java octect is a signed value, so it is not correct to use it as an offset for an array [0..254] which base64Alphabet is. 0x9c is -100!

FIX:
use base64Alphabet[ 0xff & octect ] in the "else if" block to convert the octet prior using it as an offset for the lookup table

Comments

[Henri Yandell]

I've added that as a unit test and it passes. I had to cast the 0x9c to a byte, but no other changes. I'll look later to see if the bugs already been caught and fixed.

[Henri Yandell]

The relevant line of code has already been changed to:

} else if (octect < 0 || base64Alphabet[octect] == -1) {

Thus it no longer gets an exception and is ignored.