Implement IWbemObjectSink interface in Rust

Question

I'd like to be able to call ExecQueryAsync of SWbemServices in Rust, as in this example in C++ : https://learn.microsoft.com/fr-fr/windows/win32/wmisdk/example--getting-wmi-data-from-the-local-computer-asynchronously

My problem is it needs an implementation of IWbemObjectSink, and none is available in winapi. The winapi crates provides an interface definition in Rust, but how am I supposed to "implement" it in Rust ? I can write a struct that respects the interface, I can import the interface from the winapi crate, but how can I glue both together ?

I also made some experiments with com-rs crate, as it provides an example to implement an interface with the com::class! macro But what I can do is create another IWbemObjectSink interface and implement it, not starting from the winapi::um::wbemcli:IWbemObjectSink and implement it...

Thanks for your insights

Answer 1

If anyone is trying to implement a COM interface of the winapi crate like IWbemObjectSink, for which WMI does not provide an implementation, here is a way to do so.

DON'T use the com-rs crate maintained by Microsoft as long as they don't add support for the winapi crate. Prefer the com-impl crate, in combination with wio ComPtr (not necessary but handy).

use winapi::{
    um::wbemcli::{
        {IWbemClassObject,IWbemObjectSink, IWbemObjectSinkVtbl},
        WBEM_S_NO_ERROR,
    },
    shared::{
        ntdef::HRESULT,
        wtypes::BSTR,
    },
    ctypes::{
        c_long,
    },
};
use com_impl::{ComImpl, VTable, Refcount};
use wio::com::ComPtr;

#[repr(C)]
#[derive(ComImpl)]
#[interfaces(IWbemObjectSink)]
pub struct QuerySink {
    vtbl: VTable<IWbemObjectSinkVtbl>,
    refcount: Refcount,
}

impl QuerySink {
    pub fn new() -> ComPtr<IWbemObjectSink> {
        let ptr = QuerySink::create_raw();
        let ptr = ptr as *mut IWbemObjectSink;
        unsafe { ComPtr::from_raw(ptr) }
    }
}

// AddRef and Release methods are provided by com_impl
#[com_impl::com_impl]
unsafe impl IWbemObjectSink for QuerySink2 {
    pub unsafe fn indicate(
        &self,
        _lObjectCount: c_long,
        _apObjArray: *mut *mut IWbemClassObject
    ) -> HRESULT {
        WBEM_S_NO_ERROR as i32
    }

    pub unsafe fn set_status(
        &self,
        _lFlags: c_long,
        _hResult: HRESULT,
        _strParam: BSTR,
        _pObjParam: *mut IWbemClassObject
    ) -> HRESULT {
        WBEM_S_NO_ERROR as i32
    }
}

Some other useful information:

If you need to add members to your class (here yolo and swag), procede like this:

#[repr(C)]
#[derive(ComImpl)]
#[interfaces(IWbemObjectSink)]
pub struct QuerySink2 {
    vtbl: VTable<IWbemObjectSinkVtbl>,
    refcount: Refcount,
    yolo: i32,
    swag: u8,
}

impl QuerySink2 {
    pub fn new(param1: i32, param2: u8) -> ComPtr<IWbemObjectSink> {
        let ptr = QuerySink2::create_raw(param1, param2);
        let ptr = ptr as *mut IWbemObjectSink;
        unsafe { ComPtr::from_raw(ptr) }
    }
}

Method names are converted from snake_case to PascalCase by com-impl.

That's why for my QuerySink I used set_status and indicate which are mapped to SetStatus and Indicate. com-impl provides a #[com_name = "..."] attribute if you want to do it your way. The best way to understand the details is to look at the comments in https://github.com/Connicpu/com-impl/blob/master/derive-com-impl/src/lib.rs