pyo3-prost

pyo3-prost exposes Rust protobuf structs to Python.

```

A simple decoding benchmark

Python: 14.008996680990094 Rust : 0.5708326659951126 ```

All you need is adding a single line .type_attribute(".", "#[::pyo3_prost::pyclass_for_prost_struct]") to your prost or tonic build.

The intended usecase is when your Python project is locked down to Protobuf and you want to migrate some part to native modules in Rust. Python protobuf objects cannot be easily handled in the Rust side. For conversion, the Python protobuf object should be serialized and deserialized to a Rust protobuf object. With pyo3-prost you can decode the bytes to Rust structs in Python from the beginning and pass it to the native module.

How it works

The derive macro pyclass_for_prost_struct will add 1. #[pyclass] to prost-generated structs 2. #[pyo3(get, set)] for each field (except oneof fields). 3. #[pymethods] with encode_slow(), decode(&PyBytes), decode_merge(&mut self, &PyBytes). 4. #[pyproto] with __str__ and __repr__ for easy inspection.

Getter/setter works with nested structs.
encode_slow is name this way because it's currently implemented by serializing to Rust buffer and copy the bytes to Python memory.

Example

Go to examples/proto-gen and cargo run. This will create examples/rupy_proto/src/app.rs.
Go to examples/rupy_proto and cargo build --release.
Move examples/rupy_proto/target/release/librupy_proto.so to examples/rupy_proto/rupy_proto.so.
Run the bench cd examples/rupy_proto && PYTHONPATH=. python bench.py.

Limitations (for now)

Accessing numeric fields is fast. However each access to a repeated, map, or message field may return a cloned Python object. For example obj.list_field.clear() will only clear the returned copy, leaving the actual value untouched.

Getters/setters are not provided for oneof fields.

Later I will add a custom getter/setter for these cases.