# pdftract-2cnmr: PdfSource trait + MmapSource + FileSource

## Summary

The PdfSource trait abstraction with MmapSource and FileSource implementations was already implemented in the codebase prior to this bead. All core acceptance criteria are met.

## Implementation Status

### PASS Criteria

1. **PdfSource trait defined and exported** ✓
   - Location: `crates/pdftract-core/src/source/mod.rs`
   - Provides `len()`, `read_range(offset, length)`, and `prefetch()` methods
   - Object-safe trait with `Read + Seek + Send + Sync` bounds for rayon parallelism

2. **MmapSource implementation** ✓
   - Location: `crates/pdftract-core/src/source/mmap.rs`
   - Uses `memmap2 = "0.9"` for memory-mapped I/O
   - Implements `advise_sequential()` for MADV_SEQUENTIAL hint
   - Comprehensive test suite (29 tests) covering all operations

3. **FileSource implementation** ✓
   - Location: `crates/pdftract-core/src/source/file_source.rs`
   - Uses `parking_lot::Mutex` for thread-safe `&self` access
   - Handles special files (e.g., /proc) that don't support mmap
   - Comprehensive test suite (15 tests)

4. **MemorySource implementation** (bonus)
   - Location: `crates/pdftract-core/src/source/memory.rs`
   - In-memory source for testing with zero-copy Bytes

5. **Exports from lib.rs** ✓
   - All source types re-exported from `pdftract_core::source`
   - Line 90: `pub use source::{FileSource, MmapSource, PdfSource};`

### Dependencies

All required dependencies are present in `Cargo.toml`:
- `bytes = "1"` - Zero-copy slice type
- `memmap2 = "0.9"` - Memory mapping
- `parking_lot = "0.12"` - Mutex for FileSource

### Build Status

- **Lib compilation**: PASS - `cargo build --package pdftract-core --lib` succeeds
- **Test compilation**: BLOCKED - Unrelated test errors in `markdown.rs` (API signature mismatches in test-only code)

The source module itself compiles cleanly. Test compilation errors are in test code for the markdown module (`block_to_markdown` and `page_to_markdown` function calls with outdated signatures), which is unrelated to the source abstraction work.

## Code Quality

- All implementations include comprehensive test suites
- Thread-safe (`Send + Sync`) for rayon parallelism
- Proper error handling with `io::Result`
- Well-documented with examples and safety notes

## INV-8 Verification

INV-8 (Invariants) appears to be maintained:
- Source abstraction properly abstracts over storage medium
- Thread safety enforced via trait bounds
- No assumptions about file mutability (documented as known limitation for mmap)

## Files Examined

1. `crates/pdftract-core/src/source/mod.rs` - PdfSource trait definition
2. `crates/pdftract-core/src/source/mmap.rs` - MmapSource implementation
3. `crates/pdftract-core/src/source/file_source.rs` - FileSource implementation
4. `crates/pdftract-core/src/source/memory.rs` - MemorySource implementation
5. `crates/pdftract-core/src/lib.rs` - Public exports
6. `crates/pdftract-core/Cargo.toml` - Dependencies verified

## Conclusion

The PdfSource trait and implementations are complete and meet all acceptance criteria. The bead work was already done in a prior commit. No new code changes were required for this bead.