From 6d59706cc403ac13ea6a5180ca4acbbd45af2402 Mon Sep 17 00:00:00 2001 From: jedarden Date: Fri, 22 May 2026 15:00:32 -0400 Subject: [PATCH] docs(pdftract-6bxw): add ObjStm parser verification note Add comprehensive verification note documenting that the ObjStm parser implementation is complete and all acceptance criteria are met. All 16 unit tests pass, covering: - N=10 object parsing (critical test) - /Extends chain handling - Circular reference detection - Truncated ObjStm recovery - Decompression bomb protection - Cache hit verification (Arc::ptr_eq) - Missing key errors - Embedded stream rejection - Depth limit enforcement Refs: pdftract-6bxw --- notes/pdftract-6bxw.md | 138 +++++++++++++++++------------------------ 1 file changed, 58 insertions(+), 80 deletions(-) diff --git a/notes/pdftract-6bxw.md b/notes/pdftract-6bxw.md index f31497d..da6978e 100644 --- a/notes/pdftract-6bxw.md +++ b/notes/pdftract-6bxw.md @@ -5,19 +5,20 @@ Implement object stream (ObjStm) parser with decompress, cache, and /Extends cha ## Implementation Summary -### Files Modified -- `crates/pdftract-core/src/parser/objstm.rs` - Complete ObjStm parser implementation +### Files +- `crates/pdftract-core/src/parser/objstm.rs` - Complete ObjStm parser implementation (1280 lines) +- `crates/pdftract-core/src/parser/mod.rs` - Re-exports ObjStm types ### Implementation Details The ObjectStmParser provides: 1. **Decompression**: Uses Phase 1.5's `decode_stream()` function to decompress ObjStm stream data -2. **Caching**: `Arc>>` for thread-safe caching -3. **Extends chain**: Recursive loading with cycle detection and depth limit (MAX_EXTENDS_DEPTH = 16) +2. **Caching**: `Arc>>` for thread-safe cached access +3. **Extends chain**: Recursive loading with cycle detection (HashSet in_progress) and depth limit (MAX_EXTENDS_DEPTH = 16) 4. **API**: - `get_object(host_objstm_ref, embedded_index, source, resolve_fn)` - Main API for xref type-2 entry resolution - - `load_object_stream(obj_stm_ref, stream_dict, source, resolve_fn)` - Bulk loading API - - `get_cached(obj_ref)` - Check cache + - `load_object_stream(obj_stm_ref, stream, source, resolve_fn)` - Bulk loading API + - `get_cached(obj_ref)` - Check cache without loading - `is_cached(obj_ref)` - Check if cached - `take_diagnostics()` - Get accumulated diagnostics @@ -25,93 +26,70 @@ The ObjectStmParser provides: 1. **Object Stream Format**: - Header: N pairs of (object_number, offset) in first `/First` bytes - - Body: N embedded objects (no `obj`/`endobj` wrapper) + - Body: N embedded objects (no `obj`/`endobj` wrapper per spec) - Optional `/Extends N G R` for chain to parent ObjStm -2. **Error Handling**: - - `MissingKey`: Required `/N` or `/First` missing - - `InvalidFormat`: Malformed header or data - - `CircularRef`: Cycle detected in `/Extends` chain - - `DepthExceeded`: `/Extends` chain exceeds 16 levels - - `DecompressionFailed`: Stream decompression failed +2. **Error Handling** (ObjStmError enum): + - `MissingKey`: Required `/N` or `/First` missing → DiagCode::StructMissingKey + - `InvalidFormat`: Malformed header or data → DiagCode::StructInvalidObjstm + - `CircularRef`: Cycle detected in `/Extends` chain → DiagCode::StructCircularRef + - `DepthExceeded`: `/Extends` chain exceeds 16 levels → DiagCode::StructDepthExceeded + - `DecompressionFailed`: Stream decompression failed → DiagCode::StreamDecodeError 3. **Safety**: - - Decompression bomb limit enforced (max_decompress_bytes) - - Embedded streams rejected (spec violation) - - Generation number must be 0 for embedded objects - - Thread-safe caching with Arc and RwLock - -### Unit Tests - -The following tests verify all acceptance criteria: - -1. **test_parse_simple_objstm** - Basic ObjStm with N=2 objects - - Creates flate-compressed stream with header "1 0 2 3" and objects "42", "true" - - Verifies both objects parse correctly - -2. **test_parse_objstm_10_objects** - **CRITICAL TEST** (Acceptance Criterion 1) - - Creates ObjStm with N=10 objects of all types - - Verifies all 10 objects dereference correctly by 0-based index - -3. **test_objstm_extends_chain** - **Extends chain** (Acceptance Criterion 2) - - Parent ObjStm with 3 objects, child ObjStm with 2 objects extending parent - - Verifies both ObjStms' objects are accessible - -4. **test_circular_ref_detection** - **Cyclic /Extends** (Acceptance Criterion 3) - - ObjStm with `/Extends` pointing to itself - - Verifies `CircularRef` error is emitted - -5. **test_truncated_objstm_body** - **Truncated ObjStm** (Acceptance Criterion 4) - - ObjStm where last object is truncated ("fal" instead of "false") - - Verifies partial objects returned and diagnostics emitted - -6. **test_decompression_bomb_objstm** - **Decompression bomb** (Acceptance Criterion 5) - - ObjStm with very small max_decompress_bytes limit - - Verifies STREAM_BOMB diagnostic emitted - -7. **test_cache_hit** - **Cache verification** (Acceptance Criterion 6) - - Loads same ObjStm twice - - Verifies second call returns cached Arc via `Arc::ptr_eq` - -8. **test_get_object_api** - Xref type-2 entry resolution API - - Tests the `get_object()` method with 0-based index - - Verifies caching on second call - -9. **test_embedded_stream_rejected** - Embedded stream detection - - Verifies embedded objects that are Streams are rejected with diagnostic - -10. **test_extends_depth_exceeded** - Depth limit enforcement - - Creates chain of 17 ObjStms (exceeds MAX_EXTENDS_DEPTH of 16) - - Verifies `DepthExceeded` error - -11. **test_missing_key_n** - Missing /N key - - Verifies `MissingKey` error when /N is absent - -12. **test_missing_key_first** - Missing /First key - - Verifies `MissingKey` error when /First is absent + - Decompression bomb limit enforced via doc_decompress_counter + - Embedded streams rejected (spec violation) → STRUCT_INVALID_OBJSTM diagnostic + - Thread-safe caching with Arc> for concurrent reads + - Cycle detection prevents infinite loops in /Extends chains ## Acceptance Criteria Status | Criterion | Status | Test | |-----------|--------|------| -| Critical test: N=10 objects all dereference | ✅ PASS | test_parse_objstm_10_objects | -| /Extends chain: both ObjStms' objects dereference | ✅ PASS | test_objstm_extends_chain | -| Cyclic /Extends: emits STRUCT_CIRCULAR_REF | ✅ PASS | test_circular_ref_detection | -| Truncated ObjStm: partial objects + diagnostic | ✅ PASS | test_truncated_objstm_body | +| Critical test: N=10 objects all dereference correctly | ✅ PASS | test_parse_objstm_10_objects | +| /Extends chain: both ObjStms' objects dereference correctly | ✅ PASS | test_objstm_extends_chain | +| Cyclic /Extends: emits STRUCT_CIRCULAR_REF, no infinite loop | ✅ PASS | test_circular_ref_detection | +| Truncated ObjStm: partial objects + STRUCT_INVALID_OBJSTM | ✅ PASS | test_truncated_objstm_body | | Decompression bomb: emits STREAM_BOMB | ✅ PASS | test_decompression_bomb_objstm | -| Cache hit: returns cached Arc | ✅ PASS | test_cache_hit | +| Cache hit: returns cached Arc (Arc::ptr_eq verified) | ✅ PASS | test_cache_hit | +| Missing /N or /First: emits STRUCT_MISSING_KEY | ✅ PASS | test_missing_key_n, test_missing_key_first | +| /Extends depth exceeded: emits STRUCT_DEPTH_EXCEEDED | ✅ PASS | test_extends_depth_exceeded | +| Embedded stream rejected: emits STRUCT_INVALID_OBJSTM | ✅ PASS | test_embedded_stream_rejected | +| get_object API for type-2 entries | ✅ PASS | test_get_object_api | + +## Test Results (2026-05-22) + +``` +running 16 tests +test parser::objstm::tests::test_max_extends_depth ... ok +test parser::objstm::tests::test_missing_key_first ... ok +test parser::objstm::tests::test_circular_ref_detection ... ok +test parser::objstm::tests::test_obj_stm_parser_default ... ok +test parser::objstm::tests::test_missing_key_n ... ok +test parser::objstm::tests::test_obj_stm_error_display ... ok +test parser::objstm::tests::test_obj_stm_parser_new ... ok +test parser::objstm::tests::test_decompression_bomb_objstm ... ok +test parser::objstm::tests::test_cache_hit ... ok +test parser::objstm::tests::test_get_object_api ... ok +test parser::objstm::tests::test_embedded_stream_rejected ... ok +test parser::objstm::tests::test_parse_simple_objstm ... ok +test parser::objstm::tests::test_truncated_objstm_body ... ok +test parser::objstm::tests::test_objstm_extends_chain ... ok +test parser::objstm::tests::test_parse_objstm_10_objects ... ok +test parser::objstm::tests::test_extends_depth_exceeded ... ok + +test result: ok. 16 passed; 0 failed; 0 ignored; 0 measured; 442 filtered out +``` ## Integration Points -1. **Phase 1.3 (xref)**: The `get_object()` method is designed to be called by the xref resolver when it encounters a type-2 (compressed) xref entry. The API signature matches the xref resolver's needs. +1. **Phase 1.3 (xref)**: The `get_object()` method is designed to be called by the xref resolver when it encounters a type-2 (compressed) xref entry (`XrefEntry::Compressed { obj_stm_nr, index }`). The API signature accepts `(host_objstm_ref, embedded_index)` and returns `PdfObject`. -2. **Phase 1.5 (stream decoder)**: Uses `decode_stream()` function to decompress the ObjStm stream data with full filter pipeline support. +2. **Phase 1.5 (stream decoder)**: Uses `decode_stream()` function to decompress the ObjStm stream data with full filter pipeline support (FlateDecode, ASCII85Decode, etc.). -3. **Diagnostics**: Emits diagnostics using the unified `crate::diagnostics` module with proper error codes. +3. **Diagnostics**: Emits diagnostics using the unified `crate::diagnostics` module with proper error codes (StructMissingKey, StructCircularRef, StructDepthExceeded, StructInvalidObjstm, StreamBomb). -## Notes - -- The ObjStm parser implementation is complete and all acceptance criteria are met -- Unit tests cover all critical paths and edge cases -- The code follows the existing patterns in the codebase (Arc/RwLock for caching, Result types for errors) -- Thread-safe design allows concurrent access from multiple threads (important for rayon parallelism in Phase 4) +## References +- Plan section: Phase 1.2 line 1072 (object streams) +- PDF spec 7.5.7 (Object Streams) +- INV-8 (never panic, always return partial data on errors)