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https://issues.apache.org/jira/browse/RNG-170?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Alex Herbert resolved RNG-170.
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Resolution: Fixed
Fixed in commit:
c3c802117da90523ecc0dd1507d895ac9c3f5f54
Range checks now applied as per JDK 9 Objects.checkFromIndexSize.
> nextBytes(byte[], int, int) to be consistent with JDK range checks for index
> out of bounds empty bytes
> ------------------------------------------------------------------------------------------------------
>
> Key: RNG-170
> URL: https://issues.apache.org/jira/browse/RNG-170
> Project: Commons RNG
> Issue Type: Bug
> Components: core
> Affects Versions: 1.4
> Reporter: Alex Herbert
> Priority: Trivial
> Fix For: 1.5
>
>
> The implementation of nextBytes is inconsistent:
> {code:java}
> UniformRandomProvider rng = RandomSource.KISS.create();
> byte[] empty = {};
> // OK
> rng.nextBytes(empty);
> // Throws IndexOutOfBoundsException
> rng.nextBytes(empty, 0, empty.length);
> {code}
> This also throws:
> {code:java}
> byte[] bytes = new byte[10];
> // Throws IndexOutOfBoundsException
> rng.nextBytes(bytes, 0, -1);
> {code}
> The second exception is index out of bounds. This could be:
> - illegal argument exception (negative length)
> - index out of bounds
> - ignore
> The case for ignoring negative length is this loop:
>
> {code:java}
> for (int j = 0; j < len; j++) {
> bytes[start + j]++;
> } {code}
> Will not throw for a negative length irrespective of the start index.
>
> The nextBytes(byte[], int, int) method is not in the JDK generators so there
> is no precedent for what to do for a negative length here. However
> System.arraycopy uses the start+length arguments. This test:
> {code:java}
> @ParameterizedTest
> @CsvSource({
> // OK
> "10, 0, 10",
> "10, 5, 5",
> "10, 9, 1",
> "0, 0, 0",
> // Bad
> "10, 0, 11",
> "10, 10, 1",
> "10, 10, 2147483647",
> "10, 0, -1",
> "10, 5, -1",
> })
> void testNextBytesIndices(int size, int start, int len) {
> final SplitMix64 rng = new SplitMix64(123);
> final byte[] bytes = new byte[size];
> // Be consistent with System.arraycopy
> try {
> System.arraycopy(bytes, start, bytes, start, len);
> } catch (Exception ex) {
> // nextBytes should throw the same exception
> Assertions.assertThrows(ex.getClass(), () ->
> rng.nextBytes(bytes, start, len));
> return;
> }
> // OK
> rng.nextBytes(bytes, start, len);
> }
> {code}
> Shows the exception raised should be ArrayIndexOutOfBoundsException
> (currently it is IndexOutOfBoundsException). It also shows that
> System.arraycopy will allows zero length for an empty array with start=0.
> I suggest updating the method nextBytes(byte[], start, len) to throw
> consistent exceptions matching System.arraycopy. This is a minimal change to
> switch to ArrayIndexOutOfBoundException and to ignore zero length byte[] when
> start=len=0.
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