Test pybind11_protobuf

This repository contains code to test pybind11_protobuf in Ubuntu 20.04.

Usage

To run, clone this repository, navigate to its root directory, and run

docker build -t pybind11_protobuf_test .
docker run pybind11_protobuf_test

This will build the docker image and run the test.

The build contains the following steps:

Install necessary dependencies.
Generate C++ and Python code from the protobuf definition stored in proto/Robot.proto.
Compile a C++ library containing functions which operate on the generated C++ code (i.e. produce and consume protobuf message).
Bind the library as a Python module using pybind11_protobuf.

When running, a Python script loads the module and calls the bound functions, performing a full round-trip from Python to C++ and back.

Have a look at the Dockerfile for details.

The following limitations were discovered:

The older Ubuntu version 20.04 does not allow to install the latest software. At the time of writing, both the latest libprotobuf-dev and protobuf-compiler debian packages have the version 3.6.1-2ubuntu5.2. To make the test succeed, one may not install a protobuf python package newer than version 3.20.X. Also, pybind11_protobufs proto_caster_impl.h required a patch to work with this old version.
pybind11_protobuf officially uses bazel as build system. The CMakeLists.txt is experimental and not CI-tested. See this comment for more information. This should not be a big issue as we anyway have to create a debian package ourselves, so we can create our own version.
We did not find a solution to make the test work with shared libraries, only with static ones.
By default, the Python <-> C++ conversions are implemented by serialization & deserialization. This is slow but safe. To change this, one can use the bazel build option --define=use_fast_cpp_protos=true which will change the backend of the Python message to C++, which results in a speed up. More information can be found here. This option has not been evaluated in this test.