C++ COM out-of-proc marshalling data through proxy\stub

Question

I'm trying to create out-of-proc com server in some exe file and a client, which will access to functions through proxy\stub mechanism. I have my .idl file:

[
    object,
    uuid(eaa27f4f-ad6b-4a52-90f3-6028507751a1),
    dual,
    nonextensible,
    helpstring("IConfig Interface"),
    pointer_default(unique)
]
interface IInterractionInterface : IDispatch
{
    [id(1), helpstring("Testing function")] HRESULT Test([in] long param);
};


[
    uuid(6fde5037-3034-4ae1-8aa7-2ad45e5716e4),
    version(1.0),
    helpstring("Some lib")
]
library SomeLib
{
    importlib("stdole32.tlb");
    importlib("stdole2.tlb");

    [
        uuid(86feabe4-a0a7-45b5-bcd4-f4f7085d6b1f),
        helpstring("Some lib")
    ]
    coclass Interraction
    {
        [default] interface IInterractionInterface;
    };
}

I am generated using midl compiler _p.c, _i.c files, created proxy\stub dll using .def:

LIBRARY        proxy_stub.dll
DESCRIPTION    'generic proxy/stub DLL'
EXPORTS        DllGetClassObject      @1 PRIVATE
               DllCanUnloadNow        @2 PRIVATE
               DllRegisterServer      @4 PRIVATE
               DllUnregisterServer    @5 PRIVATE

Then i am registered this dll using regsrv32, and in win registry i have this:

In my server i am created factory:

CoRegisterClassObject(CLSID_InterractionInterfaceFactory, (IClassFactory*) &factory, CLSCTX_LOCAL_SERVER, REGCLS_MULTIPLEUSE, &regID);

And it waits for client calls. In client i am calling my factory using CreateInstance:

result = CoGetClassObject(CLSID_InterractionInterfaceFactory, CLSCTX_LOCAL_SERVER, NULL, IID_IClassFactory, (void**)&factory);

if (S_OK == result)
{
    IInterractionInterface* iface = NULL;

    result = factory->CreateInstance(NULL, IID_InterractionInterface, (void**)&iface);
    if (S_OK == result)
    {

    }
}

And client receives null iface and result is E_UNEXPECTED, but in factory it creates successfuly and i am returning S_OK from Factory::CreateInstance(). I can't understand is PS mechanism using my .dll or not? Maybe i forgot some steps? Why my object can't pass through process borders?

Edit: I've tried to replace the client code and now it is:

result = CoCreateInstance(CLSID_InterractionInterfaceFactory, NULL, CLSCTX_LOCAL_SERVER, IID_InterractionInterface, (void**)&iface);
iface->Test(1);

And when i am trying to call Test(1) it throws an error, that this is pure virtual function. And in factory in CreateInstance i am receiving requirement of Unkonown interface.

Answer 1

If you want to use proxy/stub DLL, define the interface outside of the library block. Only stuff defined outside of library goes into the code generated for proxy/stub DLL. Stuff defined, or referenced, inside library block goes into the generated type library. A typical IDL file defines interfaces outside of library, then mentions them inside, in coclass blocks; this way interface definitions end up in both proxy/stub and TLB, for maximum flexibility.

Your interface is automation compatible (well, almost; change the parameter type from int to long). In this case, you may prefer to use so called "universal" marshalling, based on a type library. Simply register the MIDL-generated TLB file with regtlib tool or programmatically with LoadTypeLibEx, and you would have marshaling support in place.