Compile `.capnp` to `.py`

[Fakhri Sajadi]

Hi

I have a python plugin which is called in c++ code(by pybind11). when I use import exp_capnp in the plugin, the c++ codes crashed (Segmentation fault).

1. Does anyone have a solution?

2. How can I compile `.capnp` to `.py`?

[Fakhri Sajadi]

I got new results, I found this problem comes from using capnp by python and c++ in the same project while Interface has been declared within .capnp which are used in c++ project.

 for example: 

// main.cpp

#include <pybind11/embed.h>

namespace py = pybind11;

int main() {

    py::scoped_interpreter guard{};

    py::exec(R"(

        message = "Start example"

        print(message)

        import capnp

        import address_capnp

        message = "Import address_capnp done successfully"

        print(message)

    )");

}

# address.capnp

@0x85150b117366d14b;

struct Person {

  id @0 :UInt32;

  name @1 :Text;

  email @2 :Text;

}

interface AddressMethod {

    func @0 (count: Int8 ) -> ();

}

# CMakeLists

cmake_minimum_required(VERSION 3.0)

project(example)

find_package(pybind11 REQUIRED) 

find_package(CapnProto REQUIRED) 

capnp_generate_cpp(addressSources addressHeaders address.capnp)

add_executable(example ${addressSources} main.cpp)

target_link_libraries(example PRIVATE CapnProto::capnp-rpc pybind11::embed)

The above example will work as long as interface AddressMethod in address.capnp is removed.

Can anyone help me?

[Kenton Varda]

Hi Fakhri,

Is it possible that your pycapnp plugin is compiled against a different version of libcapnp than the one you are using in C++? If so, this could certainly cause conflicts that would lead to crashes. Unfortunately, libcapnp is not ABI-compatible between versions as C++ makes ABI compatibility difficult, so it's important that all parts of your program that use libcapnp be compiled against exactly the same version.

-Kenton

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