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pdftract/notes/pdftract-54pt.md
jedarden cb966dfdef docs(pdftract-54pt): Add verification note for Phase 1.2 Object Parser 
All components verified:
- types.rs: PdfObject enum, ObjRef, PdfDict (IndexMap), PdfStream
- cache.rs: LRU 4096 entry cache with cycle detection
- cycle.rs: Per-thread resolution stack
- parser.rs: Direct and indirect object parsing
- objstm.rs: Object stream parser with /Extends support

Critical tests pass (99 total):
- Nested dict: test_parse_nested_dict, test_parse_4_level_nested_dict
- Array of mixed types: test_parse_mixed_array, test_parse_array_5_elements_mixed_types
- Object stream: test_parse_simple_objstm, test_parse_objstm_10_objects
- Self-referencing: test_cycle_detection, test_depth_limit
- INV-8 (no panic): proptest_random_bytes_no_panic, proptest_random_tokens_no_panic

Closes pdftract-54pt
2026-06-02 18:50:30 -04:00

4.4 KiB
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Verification Note for pdftract-54pt

Phase 1.2: Object Parser — Verification Summary

Date

2026-06-02

Scope

The Object Parser consumes the Lexer's token stream and produces the in-memory PDF object model. It handles indirect-object wrappers, object streams (/ObjStm), and the per-thread cycle-detection stack that prevents STRUCT_CIRCULAR_REF from causing stack overflow during dereferencing.

Components Verified

1. Types Module (crates/pdftract-core/src/parser/object/types.rs)

  • PdfObject enum: All variants implemented (Null, Bool, Integer, Real, String, Name, Array, Dict, Ref, Stream, Indirect)
  • ObjRef: 32-bit object number + 16-bit generation number
  • PdfDict: IndexMap-backed (preserves insertion order) ✓
  • PdfStream: { dict: PdfDict, offset: u64, len_hint: Option }
  • PdfIndirect: { id: ObjRef, obj: PdfObject }
  • intern() function: Thread-local name interner for deduplication

2. Cache Module (crates/pdftract-core/src/parser/object/cache.rs)

  • LruCache: 4096 entry capacity per document
  • CacheResolutionGuard: RAII guard for cycle detection + depth tracking
  • begin_resolution(): Checks cycles, enforces depth limit (256 levels)
  • Thread-local depth tracking: Per-thread counter for concurrent page processing
  • Statistics: hit/miss tracking for diagnostics

3. Cycle Module (crates/pdftract-core/src/parser/object/cycle.rs)

  • RESOLVING thread-local: HashSet per thread
  • ResolutionGuard: RAII guard that inserts on creation, removes on drop
  • is_resolving(): Cycle detection helper
  • Panic safety: Guard cleans up even on panic

4. Parser Module (crates/pdftract-core/src/parser/object/parser.rs)

  • ObjectParser::new(): Creates parser from byte slice
  • parse_direct_object(): Parses all PDF object variants
  • parse_indirect_object(): Parses N G obj ... endobj wrapper
  • Depth limiting: MAX_DEPTH = 256 for arrays/dicts
  • Error recovery: Scans forward on malformed input

5. Object Stream Module (crates/pdftract-core/src/parser/objstm.rs)

  • ObjectStmParser: Parses /ObjStm streams
  • decompress + parse: Decompresses once, parses all N embedded objects
  • Cache: Arc<Vec<(u32, PdfObject)>> for indexed access
  • /Extends chain: Cycle detection + depth limit (16 levels)
  • get_object(): API for xref type-2 entry resolution

Critical Tests Verified

All tests pass (83 object parser tests + 16 object stream tests = 99 tests):

  1. ✓ Nested dict: test_parse_nested_dict, test_parse_4_level_nested_dict
  2. ✓ Array of mixed types: test_parse_mixed_array, test_parse_array_5_elements_mixed_types
  3. ✓ Object stream: test_parse_simple_objstm, test_parse_objstm_10_objects
  4. ✓ Self-referencing object: test_cycle_detection, test_depth_limit, test_cycle_detection_fails_on_cycle
  5. ✓ INV-8 (no panic): proptest_random_bytes_no_panic, proptest_random_tokens_no_panic

Test Results

PASS [   0.020s] 83 tests run: 83 passed (parser::object)
PASS [   0.020s] 16 tests run: 16 passed (parser::objstm)

INV-8 Compliance

  • No panics on any input verified via proptest
  • Proptest harness: random byte sequences and PDF token sequences
  • Depth limits prevent stack overflow (256 for objects, 16 for /Extends)

Module Location

✓ crates/pdftract-core/src/parser/object/

Public API

  • ObjectParser::new(bytes: &[u8]) -> Self
  • parse_direct_object(&mut self) -> Option<PdfObject>
  • parse_indirect_object(&mut self) -> Option<PdfIndirect>
  • position(&self) -> u64
  • take_diagnostics(&mut self) -> Vec<Diagnostic>

Note on resolve() Method

The acceptance criteria mentions resolve(ref: ObjRef) -> Arc<PdfObject>. This method is implemented in XrefResolver (Phase 1.3) because resolving requires the cross-reference table, which is not available during Phase 1.2 parsing. The ObjectParser correctly delegates resolution to the xref layer.

Child Beads

All child beads are implicitly closed as their implementations are complete:

  1. ✓ PdfObject enum + ObjRef type + IndexMap-backed PdfDict
  2. ✓ Indirect object parser (N G obj ... endobj)
  3. ✓ Object stream parser (/ObjStm)
  4. ✓ Cycle detection via per-thread resolution stack
  5. ✓ Object cache (LRU 4096 entries)
  6. ✓ Critical-test fixture corpus + proptest harness

Conclusion

Phase 1.2 Object Parser is fully implemented and all critical tests pass. The codebase is ready for this bead to be closed.