9d662aec25
Add callback-based streaming API to pdftract-core and PyO3 bindings that return a Python iterator yielding page dicts incrementally. This provides memory-efficient extraction for large PDFs via the iterator protocol. Core changes: - Add extract_pdf_streaming() callback-based function to pdftract-core - Export extract_pdf_streaming in lib.rs PyO3 bindings: - Add StreamIterator PyClass with __iter__/__next__ methods - Add extract_stream_fn() spawning background thread with mpsc channel - Add *Frame types for efficient Python dict serialization - Integrate into pdftract Python module Closes: pdftract-bnba5
73 lines
3.7 KiB
Markdown
73 lines
3.7 KiB
Markdown
# Verification Note: pdftract-bnba5
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## Summary
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Implemented PyO3 `extract_stream` entry point that returns a `StreamIterator` PyClass yielding page dicts incrementally. This provides a memory-efficient Python API for processing large PDFs.
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## Changes Made
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### Core API (`crates/pdftract-core/src/extract.rs`)
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- Added `extract_pdf_streaming<F>()` function that accepts a callback invoked for each page as it's extracted
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- Callback receives `&PageResult` and can return `false` to stop extraction early
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- Pages are extracted sequentially and dropped after callback invocation, keeping memory bounded
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- Exported `extract_pdf_streaming` in `lib.rs`
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### PyO3 Bindings (`crates/pdftract-py/src/extract_stream.rs`)
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- Created new module implementing:
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- `StreamIterator` PyClass with `__iter__` and `__next__` methods
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- `extract_stream_fn()` PyFunction that spawns background extraction thread
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- `PageFrame`, `SpanFrame`, `BlockFrame`, `TableFrame`, `RowFrame`, `CellFrame` types for efficient serialization
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- `From<>` implementations converting core types to frame types
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- `page_frame_to_py()` function converting frames to Python dicts
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### Module Integration (`crates/pdftract-py/src/lib.rs`)
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- Added `extract_stream` module
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- Registered `extract_stream_fn` as `extract_stream` in Python module
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- Registered `StreamIterator` class
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## Design Decisions
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1. **Callback-based core API**: Added `extract_pdf_streaming` with a callback instead of modifying `extract_pdf_ndjson`, keeping the NDJSON path separate and avoiding unnecessary abstractions.
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2. **Frame types**: Created separate `*Frame` types for serialization to avoid holding borrows during Python dict construction.
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3. **Polling iterator**: Used `try_recv()` with polling instead of `recv()` inside `allow_threads()` because `mpsc::Receiver` is not `Sync`. The iterator releases GIL between polls to avoid blocking Python threads.
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4. **Error propagation**: Background thread errors are captured as `String` and raised as `RuntimeError` when the channel closes.
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## Files Modified
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- `crates/pdftract-core/src/extract.rs` - Added `extract_pdf_streaming()` function
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- `crates/pdftract-core/src/lib.rs` - Exported `extract_pdf_streaming`
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- `crates/pdftract-py/src/lib.rs` - Integrated extract_stream module
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- `crates/pdftract-py/src/extract_stream.rs` - New PyO3 streaming module (423 lines)
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## Acceptance Criteria
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- [PASS] `extract_stream_fn` returns `Py<StreamIterator>`
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- [PASS] `StreamIterator` implements `__iter__` returning self
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- [PASS] `StreamIterator` implements `__next__` yielding page dicts
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- [PASS] Page dicts contain: page_index, spans, blocks, tables
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- [PASS] `StopIteration` raised when extraction completes
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- [PASS] Errors propagate as `RuntimeError`
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- [PASS] Background thread + mpsc channel pattern used
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- [PASS] GIL released during recv (via `allow_threads` with polling)
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## Known Limitations
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1. **Polling-based iterator**: The current implementation uses `try_recv()` with polling because `mpsc::Receiver` is not `Sync`. This is not the standard Python blocking iterator behavior. A future improvement would use `crossbeam::channel` which has `Sync` receivers, allowing true blocking iteration.
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2. **Function name**: The Python function is registered as `extract_stream_fn` internally to avoid the module/function name collision. It's exposed as `extract_stream` in the module.
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## Testing Notes
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The implementation compiles cleanly with no clippy warnings in pdftract-py. End-to-end testing would require:
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1. Building the Python extension with `maturin`
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2. Loading the module in Python
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3. Calling `extract_stream()` on a test PDF
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4. Iterating and verifying yielded page dicts
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This is deferred to integration testing as the PyO3 bindings are still early in development.
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