# Test Case: LZMA Compressed File Read

**Test ID**: TC004-lzma-compressed-read  

**G5 fixture contract**: Use [G5-MANUAL-SETUP.md](G5-MANUAL-SETUP.md).
Its generated paths, source comparisons, structured corruption offsets, and
cleanup rules supersede placeholder examples in this file.
**Category**: Compression  
**Priority**: High  
**Regression**: None

## Objective
Verify correct decompression and reading of LZMA/MicroLZMA-compressed files (newly implemented in repo18 iteration 1).

## Preconditions
- EROFS image with LZMA-compressed files: `test-lzma.erofs`
- Known reference file: `original-large.txt` (uncompressed source)
- Compressed file in image: `/compressed/large.txt`
- Mount point: `/mnt/test`

## Test Steps
1. Mount the LZMA test image:
   ```sh
   unit=$(mdconfig -a -t vnode -f test-lzma.erofs)
   mount -t erofs -o ro /dev/${unit} /mnt/test
   ```

2. Verify file exists and check size:
   ```
   ls -lh /mnt/test/compressed/large.txt
   stat -f "Size: %z bytes" /mnt/test/compressed/large.txt
   ```

3. Read entire compressed file:
   ```
   cat /mnt/test/compressed/large.txt > /tmp/lzma-decompressed.txt
   ```

4. Verify decompression correctness:
   ```
   sha256 /tmp/lzma-decompressed.txt
   sha256 original-large.txt
   ```

5. Compare byte-for-byte:
   ```
   cmp /tmp/lzma-decompressed.txt original-large.txt
   echo $?
   ```

6. Test random access read:
   ```
   dd if=/mnt/test/compressed/large.txt of=/tmp/lzma-middle.txt bs=1k skip=100 count=10
   dd if=original-large.txt of=/tmp/orig-middle.txt bs=1k skip=100 count=10
   cmp /tmp/lzma-middle.txt /tmp/orig-middle.txt
   ```

7. Test end-of-file read:
   ```
   tail -c 1000 /mnt/test/compressed/large.txt > /tmp/lzma-tail.txt
   tail -c 1000 original-large.txt > /tmp/orig-tail.txt
   cmp /tmp/lzma-tail.txt /tmp/orig-tail.txt
   ```

## Expected Results
- Step 1: Mount succeeds
- Step 2: File size matches original uncompressed size exactly
- Step 4: SHA256 checksums are identical
- Step 5: Exit code 0 (files identical)
- Step 6: Middle section matches (random access works)
- Step 7: Tail matches (EOF handling correct)

## Verification Method
- Complete data integrity check via SHA256
- Partial read correctness (random access)
- No memory corruption or crashes during decompression
- Verify LZMA decoder internal state:
  - 1846 probability models initialized
  - Range decoder normalization correct
  - Dictionary buffer within bounds

## Cleanup
```
umount /mnt/test
mdconfig -d -u "${unit}"
rm /tmp/lzma-*.txt /tmp/orig-*.txt
```

## Notes
- **NEW in repo18**: This is the first iteration with LZMA support
- LZMA provides maximum compression ratio (~30-50% smaller than LZ4)
- MicroLZMA is a variant without header, commonly used in EROFS
- Self-contained implementation in `src/decompressor_lzma.c`
- Reference implementation: XZ Embedded minimal decoder
- Critical test for repo18 iteration 1 validation
- Regression marker: First LZMA implementation, high priority for validation
