Reject short output in LZ4DecompressorWithLength safe paths

[yawkat]

Fixes #105.

The safe-decompressor overloads of LZ4DecompressorWithLength passed the declared length as maxDestLen but never checked that that many bytes were produced. As a result, a length prefix larger than the actual data had two effects:

• The allocating overload silently returned a truncated array.
• The non-allocating overloads returned a short count, which a caller relying on getDecompressedLength() could miss.

All safe paths now throw LZ4Exception when the decompressed size doesn't match the prefix. The fast paths already required an exact length.

• The allocating overload now allocates destLen itself and checks the count.
• decompress(ByteBuffer, ByteBuffer) checks before it updates any positions.

Javadoc is updated to match.

Behaviour change: only malformed input, where the prefix doesn't match the data, is affected. LZ4CompressorWithLength never produces such input.

Test: testDecompressorWithLengthRejectsShortOutput covers all seven safe overloads with heap and direct buffers. It also checks that buffer positions are unchanged after a failure. It fails without the fix. LZ4Test and OutOfBoundsTest pass.

🤖 Generated with Claude Code

[yawkat]

potentially breaking?

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.81%. Comparing base (f6e3304) to head (d19a787).
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Additional details and impacted files

@@             Coverage Diff              @@
##               main     #126      +/-   ##
============================================
+ Coverage     79.76%   79.81%   +0.05%     
- Complexity      562      564       +2     
============================================
  Files            42       42              
  Lines          1838     1843       +5     
  Branches        247      247              
============================================
+ Hits           1466     1471       +5     
+ Misses          239      238       -1     
- Partials        133      134       +1     

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