jcelerier / dynalizer

C++ Dynamic loader generator for C APIs

Dynalizer

A python script which generates a C++ dynamic loader for shared objects, given a C header file. Useful when you don't want to link at compile-time, and if you want to have a beginning of C++ API for your C code.

Dependencies

pip install clang inflection

Example

$ echo 'void mylib_foo(int x, const char* bar);\nvoid mylib_bar(float** z);' > mylib.h
$ python dynalizer.py header.h

will produce a class akin to the following :

class mylib
{
public:
  // Pass the path to your .so / .dll / .dylib here
  explicit mylib(const char* filepath)
    : m_lib{filepath}
  {
    m_sym_mylib_foo = m_lib.symbol<decltype(::mylib_foo)*>("mylib_foo");
    if(!m_sym_mylib_foo)
      throw std::runtime_error("Invalid symbol lookup: mylib_foo");

    m_sym_mylib_bar = m_lib.symbol<decltype(::mylib_bar)*>("mylib_bar");
    if(!m_sym_mylib_bar)
      throw std::runtime_error("Invalid symbol lookup: mylib_bar");
  }

  static auto& instance() {
    static mylib c;
    return c;
  }
  
  template<typename... Args>
  auto mylib_foo(Args&&... args) -> decltype(auto)
  {
    return m_sym_mylib_foo(std::forward<Args>(args)...);
  }

  template<typename... Args>
  auto mylib_bar(Args&&... args) -> decltype(auto)
  {
    return m_sym_mylib_bar(std::forward<Args>(args)...);
  }

private:
  decltype(::mylib_foo)* m_sym_mylib_foo{};
  decltype(::mylib_bar)* m_sym_mylib_bar{};

  dynalizer::library m_lib;
};

Options

Multiple codegen aspects can be changed:

• Lazy (--lazy) and eager (--eager) loading: in the eager case, all the symbols are loaded upon instantiation of the library. In the lazy case, symbols are not loaded until they are actually used.

• Error reporting : --throw and --abort. These options define what happens when a symbol is missing: an exception, or an assertion.

• Prettification : --pretty. If possible, will remove common suffixes of the API functions, and will port to standard C++ snake_case.

  That is, the earlier example would become instead:

template<typename... Args>
auto foo(Args&&... args) -> decltype(auto)
{
  return m_sym_mylib_foo(std::forward<Args>(args)...);
}

template<typename... Args>
auto bar(Args&&... args) -> decltype(auto)
{
  return m_sym_mylib_bar(std::forward<Args>(args)...);
}

so that usage patterns can be akin to :

int main() {
  auto& pa = portaudio::instance();
  pa.open_stream(...);
  pa.close_stream(...);
}

instead of the much heavier

int main() {
  auto& pa = portaudio::instance();
  pa.Pa_OpenStream(...);
  pa.Pa_CloseStream(...);
}

dynalizer's Issues

Support APIs with multiple headers

e.g. JACK, alsa, SDL...

Possibilities :

• Multiple objects, put the dll instance in a shared_ptr
• Nested objects with references to the parent
• Everything in a big class