How to call a C++ class instance from firefox-addon / js-ctypes?

Question

I've got a DLL (with c++ code like that):

MyObject::MyObject(TYPEPERIPH typePeriph) {
    m_TypePeriph = typePeriph;
    //..
}

CR MyObject::GetTypePeriph( TYPEPERIPH *typePeriph ) const throw(MY_Exception) {
    *typePeriph = m_TypePeriph;
    //..
    return 0;
}

Which is called in C++, like that :

MyObject MyObject((TYPEPERIPH)myTypePeriph);
MyObject.GetTypePeriph(&result);

I'd like to call this DLL with js-ctypes :

Components.utils.import("resource://gre/modules/ctypes.jsm");
var dll = ctypes.open("my.dll");

var constructor = dll.declare('MyObject',
    ctypes.default_abi,
    ctypes.voidptr_t,
    ctypes.uint8_t
);

var ptr=constructor( 1 ) // ptr seems to be a pointer to an instance

// but how to call this instance ?? should I pass the ptr somewhere ?
var GetTypePeriph = dll.declare('GetTypePeriph',
    ctypes.default_abi,
    ctypes.int,
    ctypes.uint8_t.ptr
);

var result=ctypes.uint8_t(0);
GetTypePeriph(result.address());
myPerif= result.value;

The first part works (^^) ... "ptr" seems to be a valid pointer. But I can't figure out how to call the instance method with this pointer ...

Answer 1

You have to define the VTABLE then create an instance see here - https://developer.mozilla.org/en-US/docs/Mozilla/js-ctypes/Examples/Using_COM_from_js-ctypes

I also did some COM just last week with js-ctypes, I was using the DirectShow API on Windows - https://github.com/Noitidart/ostypes_playground/commits/audio-capture

The VTBLE methods MUST be in order!! That took me like two months to figure out when I first got into it.

Here are the definitions of a bunch of COM stuff I did: https://github.com/Noitidart/ostypes/compare/fb1b6324343d6e19c942bbc0eb46cfcfbe103f35...master

I edited your code to look more like it should:

Components.utils.import("resource://gre/modules/ctypes.jsm");
var dll = ctypes.open("my.dll");

var MyConstructorVtbl = ctypes.StructType('MyConstructorVtbl');
var MyConstructor = ctypes.StructType('MyConstructor', [
    { 'lpVtbl': MyConstructorVtbl.ptr }
]);
MyConstructorVtbl.define([
    {
        'GetTypePeriph': ctypes.FunctionType(ctyes.default_abi,
            ctypes.int, [           // return type
                MyConstructor.ptr,  // arg 1 HAS to be ptr to the instance EVEN though your C++ above doesnt show this. this is how it works.
                ctypes.uint8_t.ptr
            ]).ptr
    }
]);

var constructor = dll.declare('MyObject',
    ctypes.default_abi,
    MyConstructor.ptr.ptr,
    ctypes.uint8_t
);

var ptr=constructor( 1 ) // ptr seems to be a pointer to an instance
var instance = ptr.contents.lpVtbl.contents;

var result=ctypes.uint8_t(0);
instance.GetTypePeriph(ptr, result.address());
myPerif= result.value;