C style callback functions

[abwilson]

I'm wrapping a C API with a number of calls taking C style callback functions. ie this kind of pattern:

struct Owner {...};
void set_callback(Owner* owner, void (*cb)(int some_other_args, void* client_data), void* client_data);

I've been trying to wrap this using code like this:

m.def("set_callback",
    [](Owner* owner, const std::function<void(int)>& cb)
    {
        set_callback(
            owner, 
            [](int i, void* data) // Expect std::function as client data.
           {
               auto fun = static_cast<std::function<void(int)> >(data);
               (*fun)(i);
           },
           &cb); // Pass std::function as client data.
    },
    py::keep_alive<1, 2>()); // owner object should keep callback function alive. 

But this doesn't work. I get a bad function exception when the cb is called from the C code. As a work around I've been cloning the std::function before passing it as client data. This works but leaks. Is this a bug or is there another way I should be able to make this work?