How to safely wrap win32's PSTR or PWSTR in an Option type (e.g. Option<&OsStr>)?

Question

I am trying to create a safe wrapper around some Win32 APIs using Microsoft's windows crate like so:

use windows::{Win32::Foundation::*, Win32::System::Threading::*};

fn create_process(app_name: &std::ffi::OsStr) -> bool {
    let mut startup_info: STARTUPINFOW = unsafe { std::mem::zeroed() };
    startup_info.cb = std::mem::size_of::<STARTUPINFOW>() as u32;
    let mut process_info: PROCESS_INFORMATION = unsafe {std::mem::zeroed() };

    unsafe {
        let success = CreateProcessW(
            app_name,            // lpapplicationname
            None,                // lpcommandname
            std::ptr::null(),    // lpprocessattributes
            std::ptr::null(),    // lpthreadattributes
            true,                // binherithandles
            CREATE_SUSPENDED,    // dwcreationflags
            std::ptr::null(),    // lpenvironment
            &startup_info,       // lpstartupinfo
            &mut process_info    // lpprocessinformation
        ).as_bool();

        success
    }
}

fn main() {
    let app = std::ffi::OsStr::new("C:\\Windows\\system32\\notepad.exe");
    let success = create_process(app);
    print!("{}", success);

}

This works as expected.

However, the documentation for CreateProcessW states that

The lpApplicationName parameter can be NULL.

Thus, I would like to wrap the &OsStr in an Option<&OsStr> so I can use None when no lpApplicationName is needed.

But I cannot find a way to convert from Option<&OsStr> to anything that satisfies IntoParam<'a, PWSTR> for lpApplicationName.

Answer 1

As of #1801 &OsStr should implement IntoParam<PWSTR>. Since null() also implements it, you should be able to write:

use windows::core::{IntoParam, Param};

let app_name_param: Param<'_, PWSTR> = if let Some(app_name) = app_name {
    app_name.into_param()
} else {
    Param::None
};

...and pass app_name_param to CreateProcessW.

(I can't test this because I run on Linux, where Foundation/mod.rs fails to compile due to requiring std::os::windows::ffi::OsStrExt.)