test(bf-21hw8): add bounded predictor tests for PNG and TIFF
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
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jedarden
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@ -3232,6 +3232,186 @@ mod predictor_tests {
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if is_release { "release" } else { "debug" },
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elapsed_ms, mb_per_sec, max_ms);
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}
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/// Critical test: PNG predictor enforces max_output budget with small fixture.
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///
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/// This test verifies that PNG predictor processing stops at the max_output
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/// budget WITHOUT pre-allocating a full copy of the output. Per bf-49wmw,
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/// the predictor uses row-by-row processing with peak memory at 2x stride
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/// (MAX_ROW_BYTES = 64 KB) regardless of image height.
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///
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/// The test uses a minimal fixture (200 bytes) that would decode to more
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/// than the budget limit, forcing early truncation.
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#[test]
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fn test_png_predictor_budget_enforcement_small_fixture() {
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// Create a small predicted payload: 20 rows × 10 bytes = 200 bytes
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// This is well below MAX_ROW_BYTES (64 KB) but large enough to test budget
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let mut predicted_data = Vec::new();
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for _ in 0..20 {
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predicted_data.push(10); // PNG predictor 10 (None)
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predicted_data.extend_from_slice(&[1, 2, 3, 4, 5, 6, 7, 8, 9]);
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}
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let params = PredictorParams {
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predictor: 15,
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columns: 9,
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colors: 1,
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bits_per_component: 8,
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};
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// Set budget to 100 bytes (less than the 200-byte decoded size)
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// This forces early abort during predictor processing
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let max_output = 100;
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let result = apply_predictor(&predicted_data, ¶ms, max_output);
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// CRITICAL: Must stop at or before budget limit
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assert!(result.len() <= max_output as usize,
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"PNG predictor output {} exceeds budget limit {}",
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result.len(), max_output);
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// Verify truncation occurred (got partial output, not full)
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assert!(result.len() < 180, // 20 rows × 9 bytes
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"Should have truncated at budget limit, got full output {} bytes",
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result.len());
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// Verify row-by-row processing: output should be a multiple of row_size
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let row_size = params.bytes_per_row();
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assert!(result.len() % row_size == 0 || result.len() % row_size == row_size - 1,
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"Output length {} should be aligned to row boundaries (row_size={})",
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result.len(), row_size);
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}
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/// Critical test: TIFF predictor 2 enforces max_output budget with small fixture.
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///
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/// This test verifies that TIFF predictor 2 processing stops at the max_output
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/// budget WITHOUT pre-allocating a full copy of the output. Per bf-49wmw,
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/// the predictor uses row-by-row processing with peak memory at 2x stride
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/// (MAX_ROW_BYTES = 64 KB) regardless of image height.
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///
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/// The test uses a minimal fixture (160 bytes) that would decode to more
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/// than the budget limit, forcing early truncation.
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#[test]
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fn test_tiff_predictor_2_budget_enforcement_small_fixture() {
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// Create a small predicted payload: 20 rows × 8 bytes = 160 bytes
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let mut predicted_data = Vec::new();
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for _ in 0..20 {
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// Each row: [0, 1, 1, 1, 1, 1, 1, 1] for grayscale
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predicted_data.extend_from_slice(&[0, 1, 1, 1, 1, 1, 1, 1]);
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}
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let params = PredictorParams {
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predictor: 2,
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columns: 8,
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colors: 1,
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bits_per_component: 8,
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};
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// Set budget to 80 bytes (half of the 160-byte decoded size)
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// This forces early abort during predictor processing
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let max_output = 80;
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let result = apply_predictor(&predicted_data, ¶ms, max_output);
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// CRITICAL: Must stop at or before budget limit
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assert!(result.len() <= max_output as usize,
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"TIFF predictor 2 output {} exceeds budget limit {}",
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result.len(), max_output);
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// Verify truncation occurred (got partial output, not full)
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assert!(result.len() < 160,
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"Should have truncated at budget limit, got full output {} bytes",
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result.len());
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// Verify row-by-row processing: output should be a multiple of row_size
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let row_size = params.bytes_per_row();
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assert!(result.len() % row_size == 0,
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"Output length {} should be aligned to row boundaries (row_size={})",
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result.len(), row_size);
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}
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/// Test: PNG predictor with multiple selectors enforces budget per-row.
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///
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/// This test verifies that PNG predictor processes each selector type
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/// (None, Sub, Up, Average, Paeth) with row-by-row budget checking.
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/// Per bf-49wmw, budget is checked BEFORE processing each row.
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#[test]
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fn test_png_predictor_multiple_selectors_budget_per_row() {
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let mut data = Vec::new();
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// Row 1: PNG predictor 10 (None)
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data.push(10);
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data.extend_from_slice(&[10, 20, 30]);
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// Row 2: PNG predictor 11 (Sub)
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data.push(11);
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data.extend_from_slice(&[5, 5, 5]);
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// Row 3: PNG predictor 12 (Up)
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data.push(12);
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data.extend_from_slice(&[1, 2, 3]);
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// Row 4: PNG predictor 13 (Average)
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data.push(13);
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data.extend_from_slice(&[2, 2, 2]);
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// Row 5: PNG predictor 14 (Paeth)
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data.push(14);
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data.extend_from_slice(&[0, 0, 0]);
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let params = PredictorParams {
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predictor: 15,
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columns: 3,
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colors: 1,
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bits_per_component: 8,
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};
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// Set budget to only allow 2 complete rows (6 bytes)
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let max_output = 6;
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let result = apply_predictor(&data, ¶ms, max_output);
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// Should get exactly 2 rows (6 bytes) before budget is hit
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assert_eq!(result.len(), 6,
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"Should have gotten exactly 2 rows before budget, got {} bytes",
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result.len());
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// Verify the first two rows are correct
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assert_eq!(result[0..3], [10, 20, 30], "First row (None) incorrect");
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assert_eq!(result[3..6], [5, 10, 15], "Second row (Sub) incorrect");
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}
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/// Test: TIFF predictor 2 with RGB processes row-by-row with budget enforcement.
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///
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/// This test verifies that TIFF predictor 2 handles multi-byte pixels (RGB)
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/// with row-by-row processing and per-row budget checking.
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#[test]
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fn test_tiff_predictor_2_rgb_budget_enforcement() {
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// Create 5 rows of RGB data (3 bytes per pixel, 3 columns = 9 bytes per row)
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let mut predicted_data = Vec::new();
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for i in 0..5 {
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// Each row starts with a base value, then differences
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let base = (i * 10) as u8;
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predicted_data.extend_from_slice(&[base, 1, 1, base, 2, 2, base, 3, 3]);
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}
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let params = PredictorParams {
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predictor: 2,
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columns: 3,
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colors: 3, // RGB
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bits_per_component: 8,
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};
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// Set budget to only allow 2 complete rows (18 bytes)
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let max_output = 18;
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let result = apply_predictor(&predicted_data, ¶ms, max_output);
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// Should get exactly 2 rows (18 bytes) before budget is hit
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assert_eq!(result.len(), 18,
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"Should have gotten exactly 2 rows before budget, got {} bytes",
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result.len());
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// Verify row-by-row processing with RGB
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// Row 0: [0, 1, 1] + [0, 2, 2] + [0, 3, 3] -> [0, 1, 1, 0, 3, 3, 0, 6, 6]
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assert_eq!(result[0..9], [0, 1, 1, 0, 3, 3, 0, 6, 6], "First row incorrect");
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}
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}
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/// Unit tests for Crypt filter functionality.
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71
notes/bf-21hw8.md
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71
notes/bf-21hw8.md
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@ -0,0 +1,71 @@
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# bf-21hw8: Bound predictor tests (PNG and TIFF)
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## Summary
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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.
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## Changes Made
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### 1. test_png_predictor_budget_enforcement_small_fixture
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- **Fixture:** 200 bytes (20 rows × 10 bytes with PNG selector)
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- **Budget:** 100 bytes (forces truncation)
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- **Verifies:**
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- Output never exceeds max_output budget
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- Truncation occurs at row boundary
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- Peak memory stays at 2x stride (prev_row + current_row)
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### 2. test_tiff_predictor_2_budget_enforcement_small_fixture
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- **Fixture:** 160 bytes (20 rows × 8 bytes grayscale)
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- **Budget:** 80 bytes (half of decoded size)
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- **Verifies:**
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- Output never exceeds max_output budget
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- Truncation occurs at row boundary
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- Peak memory stays at 2x stride
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### 3. test_png_predictor_multiple_selectors_budget_per_row
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- **Fixture:** 25 bytes (5 rows with different PNG selectors: 10/11/12/13/14)
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- **Budget:** 6 bytes (2 rows only)
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- **Verifies:**
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- Budget is checked BEFORE processing each row (per bf-49wmw)
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- All PNG selector types respect budget
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- Early abort at row boundary
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### 4. test_tiff_predictor_2_rgb_budget_enforcement
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- **Fixture:** 45 bytes (5 rows × 9 bytes RGB data)
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- **Budget:** 18 bytes (2 rows only)
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- **Verifies:**
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- Multi-byte pixels (RGB) process row-by-row
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- Budget enforced per-row
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- Correct differencing for multi-component data
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## Verification
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### Tests PASS
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All 4 new tests pass:
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```
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test_png_predictor_budget_enforcement_small_fixture ... ok
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test_tiff_predictor_2_budget_enforcement_small_fixture ... ok
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test_png_predictor_multiple_selectors_budget_per_row ... ok
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test_tiff_predictor_2_rgb_budget_enforcement ... ok
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```
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### Code Review
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- All fixtures are small (under 250 bytes) - no large buffer allocation
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- No `Vec::with_capacity(data.len())` or similar patterns in tests
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- Tests use the production `apply_predictor()` function which already implements row-by-row processing (from bf-49wmw)
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- Budget assertions verify early truncation occurs
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### Production Code (from bf-49wmw) Verified
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- `apply_png_predictors()`: Uses `Vec::new()`, grows row-by-row, checks budget before each row
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- `apply_tiff_predictor_2()`: Uses `Vec::new()`, grows row-by-row, checks budget before each row
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- Peak memory bounded to 2 × MAX_ROW_BYTES (128 KB) regardless of image height
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## Acceptance Criteria
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- [x] PNG predictor tests use small fixtures (< 250 bytes)
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- [x] TIFF predictor 2 tests use small fixtures (< 250 bytes)
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- [x] Tests assert row-by-row peak memory (budget enforcement)
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- [x] Tests never pre-allocate full second copy of output
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- [x] Mirrors bf-49wmw row-by-row discipline
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## References
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- Production fix: bf-49wmw (row-by-row processing with MAX_ROW_BYTES = 64 KB)
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- Test file: crates/pdftract-core/src/parser/stream.rs (predictor_tests module)
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