Bug #5447: Failure in bin:pack-integer with little-endian negative integer - Saxon - Saxonica Developer Community

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Bug #5447

closed

Failure in bin:pack-integer with little-endian negative integer

Added by Michael Kay over 2 years ago. Updated almost 2 years ago.

Status:

Closed

Priority:

Normal

Assignee:

Michael Kay

Category:

EXSLT extensions

Sprint/Milestone:

Start date:

2022-04-04

Due date:

% Done:

100%

Estimated time:

Legacy ID:

Applies to branch:

10, 11, trunk

Fix Committed on Branch:

10, 11, trunk

Fixed in Maintenance Release:

11.4, 12.0, 10.9

Platforms:

Description

At line 1100, in method packBytes (called by pack-integer), is the loop

               while (length > 0)
                    result[i++] = (byte) (255);

which is clearly wrong because the condition doesn't change within the loop.

It's possible that this code is unreachable; more likely, it's not reached by any of our test cases. We have relatively few tests for bin:pack-integer on negative numbers, but it's a complicated path.

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Updated by Michael Kay over 2 years ago

The bug can be very easily demonstrated with the test

Q{http://expath.org/ns/binary}pack-integer(-23, 4, 'LE')

(Essentially, any attempt to call pack-integer with a negative value in littleEndian format.

It doesn't cause an infinite loop, it loops until it hits an array-bounds failure:

java.lang.ArrayIndexOutOfBoundsException: Index 4 out of bounds for length 4
	at com.saxonica.functions.extfn.EXPathBinaryFunctionSet.packBytes(EXPathBinaryFunctionSet.java:1096)
	at com.saxonica.functions.extfn.EXPathBinaryFunctionSet.access$800(EXPathBinaryFunctionSet.java:24)
	at com.saxonica.functions.extfn.EXPathBinaryFunctionSet$BinaryPackInteger.call(EXPathBinaryFunctionSet.java:589)

It's rather surprising that there are no test cases that catch this. The "binary" test set from John Lumley appears to have no tests that exercise negative numbers in pack-integer. The "binary2" test set from Christian Grün does have tests for negative numbers, but none of them are little-endian.

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Updated by Michael Kay over 2 years ago

Subject changed from Code smell in EXPathBinaryFunctionSet to Failure in bin:pack-integer with little-endian negative integer
Status changed from New to In Progress

Fix tested on main development branch.

Leaving open until tests are updated and the fix is ported to other branches.

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