Throw LZ4Exception for input shorter than the length prefix

[yawkat]

LZ4DecompressorWithLength read the 4-byte length prefix without checking that the input was long enough. Input with fewer than 4 bytes therefore failed with an ArrayIndexOutOfBoundsException or IndexOutOfBoundsException instead of the documented LZ4Exception. Examples:

new LZ4DecompressorWithLength(factory.safeDecompressor()).decompress(new byte[]{1, 0});
new LZ4DecompressorWithLength(factory.safeDecompressor())
    .decompress(ByteBuffer.wrap(new byte[]{1, 0}), 0, 2, dest, 0);

On the safe paths with an explicit srcLen < 4 inside a longer array, the prefix was read past srcLen, and the call then failed with an IllegalArgumentException for the negative remaining length.

All decompress overloads now check that at least 4 bytes are available before reading the prefix, and throw LZ4Exception if they aren't. This covers array and ByteBuffer, and fast and safe decompressors. The available length is srcLen for the safe paths, src.length - srcOff or src.limit() - srcOff for the fast paths, and src.remaining() for decompress(ByteBuffer, ByteBuffer). Invalid offsets still throw ArrayIndexOutOfBoundsException, as before. The public static getDecompressedLength helpers are unchanged.

Found by fuzzing with micronaut-fuzzing.

Tests: I added OutOfBoundsTest.inputShorterThanLengthPrefix for 0–3 byte inputs. It runs every overload with fast and safe decompressors, using heap and direct buffers. I also added safeInputShorterThanLengthPrefixWithTrailingBytes, which covers srcLen < 4 inside a longer array or buffer. Without the fix, all three test cases fail with AIOOBE or IAE. With the fix, OutOfBoundsTest and LZ4Test pass.

🤖 Generated with Claude Code