DDMReader.readLengthAndCodePoint() decodes long integer incorrectly

• Key: DERBY-2935
• Type: Bug
• Status: Closed
• Resolution: Fixed
• Priority: Minor
• Assignee: Knut Anders Hatlen
• Reporter: Knut Anders Hatlen
• Component/s: Network Server
• Affects Version/s: 10.1.3.1, 10.2.2.0, 10.3.1.4, 10.4.1.3
• Fix Version/s: 10.3.3.0, 10.4.1.3

Description

DDMReader.readLengthAndCodePoint() contains code to decode a long integer from a byte array. This code is broken since it uses int operations and not long operations in the decoding. The long might be encoded using four, six or eight bytes, and since Derby currently always uses the four bytes encoding, the bug is not exposed in the current code.

Comments

[Knut Anders Hatlen]

The attached patch fixes the decoding by forcing promotion of the operands to long. The regression tests ran cleanly.

[Bryan Pendleton]

Is it possible to write a new regression test, with some Long values which
require 6 and/or 8 bytes to encode, which demonstrates the bug and the fix?

I don't think it's possible to test the fix with a JDBC test, at least, since Derby doesn't support data types with length >= 2^31, but it might be possible to force 6 and 8 byte values in derbynet/testProtocol.java. I'll see if I can come up with something.

[Knut Anders Hatlen]

Adding a test which used 8 bytes for the length wasn't that difficult, but since there is no way of sending data that needs the high four bytes of the length field, the test passes regardless of the fix. So I guess the best way to demonstrate the bug and the fix is by running this program:

public class ll {
    public static void main(String[] args) {
        long l1 = ((byte) 1 & 0xFF) << 56;
        long l2 = ((byte) 1 & 0xFFL) << 56;
        System.out.println("l1 = " + l1);
        System.out.println("l2 = " + l2);
    }
}

Which prints:

l1 = 16777216
l2 = 72057594037927936

[Knut Anders Hatlen]

Attaching a test which uses 8 bytes for the length. The test passes both with and without the fix. I'm only attaching it in case someone wants to experiment with it to find ways to expose the bug.

[Knut Anders Hatlen]

Committed revision 557513.