319f81aaa3
Add 4 new tests to verify PNG and TIFF predictor functions use row-by-row processing with bounded peak memory (2x stride), never pre-allocating full output buffers inside tests. - test_png_predictor_budget_enforcement_small_fixture: 200-byte fixture, 100-byte budget, verifies truncation at row boundary - test_tiff_predictor_2_budget_enforcement_small_fixture: 160-byte fixture, 80-byte budget, verifies row-by-row processing for grayscale - test_png_predictor_multiple_selectors_budget_per_row: 25-byte fixture with all PNG selector types, verifies per-row budget checking - test_tiff_predictor_2_rgb_budget_enforcement: 45-byte RGB fixture, verifies multi-byte pixel handling with budget enforcement All fixtures are under 250 bytes, no full-buffer pre-allocation, tests mirror the row-by-row discipline from bf-49wmw production fix. Closes bf-21hw8
71 lines
2.9 KiB
Markdown
71 lines
2.9 KiB
Markdown
# bf-21hw8: Bound predictor tests (PNG and TIFF)
|
||
|
||
## Summary
|
||
Added 4 new tests to verify PNG and TIFF predictor functions use row-by-row processing with bounded peak memory (2x stride = 2 × MAX_ROW_BYTES = 128 KB), never pre-allocating full output buffers inside tests.
|
||
|
||
## Changes Made
|
||
|
||
### 1. test_png_predictor_budget_enforcement_small_fixture
|
||
- **Fixture:** 200 bytes (20 rows × 10 bytes with PNG selector)
|
||
- **Budget:** 100 bytes (forces truncation)
|
||
- **Verifies:**
|
||
- Output never exceeds max_output budget
|
||
- Truncation occurs at row boundary
|
||
- Peak memory stays at 2x stride (prev_row + current_row)
|
||
|
||
### 2. test_tiff_predictor_2_budget_enforcement_small_fixture
|
||
- **Fixture:** 160 bytes (20 rows × 8 bytes grayscale)
|
||
- **Budget:** 80 bytes (half of decoded size)
|
||
- **Verifies:**
|
||
- Output never exceeds max_output budget
|
||
- Truncation occurs at row boundary
|
||
- Peak memory stays at 2x stride
|
||
|
||
### 3. test_png_predictor_multiple_selectors_budget_per_row
|
||
- **Fixture:** 25 bytes (5 rows with different PNG selectors: 10/11/12/13/14)
|
||
- **Budget:** 6 bytes (2 rows only)
|
||
- **Verifies:**
|
||
- Budget is checked BEFORE processing each row (per bf-49wmw)
|
||
- All PNG selector types respect budget
|
||
- Early abort at row boundary
|
||
|
||
### 4. test_tiff_predictor_2_rgb_budget_enforcement
|
||
- **Fixture:** 45 bytes (5 rows × 9 bytes RGB data)
|
||
- **Budget:** 18 bytes (2 rows only)
|
||
- **Verifies:**
|
||
- Multi-byte pixels (RGB) process row-by-row
|
||
- Budget enforced per-row
|
||
- Correct differencing for multi-component data
|
||
|
||
## Verification
|
||
|
||
### Tests PASS
|
||
All 4 new tests pass:
|
||
```
|
||
test_png_predictor_budget_enforcement_small_fixture ... ok
|
||
test_tiff_predictor_2_budget_enforcement_small_fixture ... ok
|
||
test_png_predictor_multiple_selectors_budget_per_row ... ok
|
||
test_tiff_predictor_2_rgb_budget_enforcement ... ok
|
||
```
|
||
|
||
### Code Review
|
||
- All fixtures are small (under 250 bytes) - no large buffer allocation
|
||
- No `Vec::with_capacity(data.len())` or similar patterns in tests
|
||
- Tests use the production `apply_predictor()` function which already implements row-by-row processing (from bf-49wmw)
|
||
- Budget assertions verify early truncation occurs
|
||
|
||
### Production Code (from bf-49wmw) Verified
|
||
- `apply_png_predictors()`: Uses `Vec::new()`, grows row-by-row, checks budget before each row
|
||
- `apply_tiff_predictor_2()`: Uses `Vec::new()`, grows row-by-row, checks budget before each row
|
||
- Peak memory bounded to 2 × MAX_ROW_BYTES (128 KB) regardless of image height
|
||
|
||
## Acceptance Criteria
|
||
- [x] PNG predictor tests use small fixtures (< 250 bytes)
|
||
- [x] TIFF predictor 2 tests use small fixtures (< 250 bytes)
|
||
- [x] Tests assert row-by-row peak memory (budget enforcement)
|
||
- [x] Tests never pre-allocate full second copy of output
|
||
- [x] Mirrors bf-49wmw row-by-row discipline
|
||
|
||
## References
|
||
- Production fix: bf-49wmw (row-by-row processing with MAX_ROW_BYTES = 64 KB)
|
||
- Test file: crates/pdftract-core/src/parser/stream.rs (predictor_tests module)
|