Handling Option<&mut Option<IWbemClassObject>> InParams

[disassembledd]

I am attempting to use IWbemServices::GetObject in order to subsequently call IWbemClassObject::{GetMethod, SpawnInstance, Put} in an effort to call WMI methods. Below is my current attempt with the issue being it feels extremely clunky trying to handle pObject or just do anything with it period. GetObject doesn't seem to be returning the object to me and I'm attempting to do this as closely as I did in winapi where my existing code is working, to no avail. What am I doing wrong?

unsafe {
    let mut pObject = ptr::null_mut::<Option<IWbemClassObject>>();
    services.GetObject(
        &BSTR::from("Win32_Process"),
        0,
        InParam::null(),
        pObject.as_mut(),
        None
    )?;
}

Note: This is the signature of GetObject:

GetObject<'a, P0>(&self, strobjectpath: &::windows::core::BSTR, lflags: i32, pctx: P0, ppobject: ::core::option::Option<&mut ::core::option::Option<IWbemClassObject>>, ppcallresult: ::core::option::Option<&mut ::core::option::Option<IWbemCallResult>>) -> ::windows::core::Result<()>
where
    P0: ::std::convert::Into<::windows::core::InParam<'a, IWbemContext>>

[disassembledd]

I changed my ptr::null_mut to mem::zeroed and everything is now successful. Now my question is, is this the correct method of doing so?

unsafe {
    let mut pObject = std::mem::zeroed::<Option<IWbemClassObject>>();
    services.GetObject(
        &BSTR::from("Win32_Process"),
        0,
        InParam::null(),
        Some(&mut pObject),
        None
    )?;
}

I am also receiving "the trait bound InParam<'_, IWbemClassObject>: From<IWbemClassObject> is not satisfied" when attempting to pass either Option<IWbemClassObject> or IWbemClassObject to ExecMethod.

[kennykerr]

Does this help: #2041

It takes advantage of some improvements to the windows crate since the 0.40 release, so you'll have to use a git dependency until 0.41 is released.

[disassembledd]

That is a great example for querying. Unfortunately my case is the least documented across wmi-rs, winapi and here as it involves executing methods on objects. I have successfully figured it all out however. Below is a minimum reproduceable example of changing the start mode of the aspnet_state service, please excuse the helper methods that exclude some code.

fn main() -> Result<(), Box<dyn std::error::Error>> {
    initialize()?;
    let locator = create_locator()?;
    let services = create_services(&locator, r"root\cimv2")?;
    set_proxy(&services)?;

    unsafe {
        let mut pObject = mem::zeroed::<Option<IWbemClassObject>>();
        services.GetObject(
            &BSTR::from("Win32_Service"),
            0,
            InParam::null(),
            Some(&mut pObject),
            None
        )?;

        if let Some(pObject) = pObject {
            let mut pInParams = mem::zeroed::<Option<IWbemClassObject>>();
            let mut pOutParams = mem::zeroed::<Option<IWbemClassObject>>();
            pObject.GetMethod(
                w!("ChangeStartMode"), 
                0, 
                &mut pInParams, 
                &mut pOutParams
            )?;

            let mut pInParams = if let Some(pInParams) = pInParams {
                Some(pInParams.SpawnInstance(0)?)
            } else {
                None
            };

            let mut pOutParams = if let Some(pOutParams) = pOutParams {
                Some(pOutParams.SpawnInstance(0)?)
            } else {
                None
            };

            if let Some(pInParams) = &pInParams {
                let mut cmd = VARIANT::default();
                let mut mode = BSTR::from("Manual");

                (*cmd.Anonymous.Anonymous).vt = VT_BSTR;
                *(*cmd.Anonymous.Anonymous).Anonymous.bstrVal = mode;

                pInParams.Put(
                    w!("StartMode"), 
                    0, 
                    &cmd,
                    0
                )?;

                VariantClear(&mut cmd)?;
            }

            services.ExecMethod(
                &BSTR::from("Win32_Service.Name=\"aspnet_state\""),
                &BSTR::from("ChangeStartMode"),
                0,
                InParam::null(),
                &pInParams.unwrap(),
                None,
                None
            )?;
        }
    }

    Ok(())
}

[kennykerr]

OK, I see using the WMI API in this way is overly complicated. Let me get that fixed and update the sample.

[disassembledd]

The most egregious example that would need the most attention are the various VARIANT scenarios. The "basic" types are somewhat straightforward, however, when you need to pass another VARIANT or even a new IWbemClassObject instance, it becomes difficult to discern what the right course of action is (for me at least).

[kennykerr]

Yes, I tried simplifying your example but the VARIANT is definitely the main challenge. The rest seems to be just that WMI is hard to use. Here's a slightly simpler version, avoiding all the zeroed in your example:

let mut object = None;
server.GetObject(&BSTR::from("Win32_Service"), 0, None, Some(&mut object), None)?;

if let Some(object) = object {
    let mut in_params = None;
    let mut out_params = None;

    object.GetMethod(w!("ChangeStartMode"), 0, &mut in_params, &mut out_params)?;

    let in_params = if let Some(in_params) = in_params { Some(in_params.SpawnInstance(0)?) } else { None };

    if let Some(in_params) = &in_params {
        let mut value = VARIANT::default();
        (*value.Anonymous.Anonymous).vt = VT_BSTR;
        *(*value.Anonymous.Anonymous).Anonymous.bstrVal = BSTR::from("Manual");

        in_params.Put(w!("StartMode"), 0, &value, 0)?;
        VariantClear(&mut value)?;

        server.ExecMethod(&BSTR::from("Win32_Service.Name=\"Fax\""), &BSTR::from("ChangeStartMode"), 0, None, in_params, None, None)?;
    }
}

I hope to get to VARIANT soon. #539

[kennykerr]

Didn't realize the PR closed this issue. Let me know if there's anything I can do to help.

[disassembledd]

All is well! I fumbled my way through getting it to work. Now I just have a heap corruption error that I need to find what is causing it!