如何分配空间以使用 windows 板条箱调用 GetInterfaceInfo？

Question

I'm trying to fetch information regarding the network interfaces available on the system via GetInterfaceInfo using Microsoft's windows crate. This requires me to do some unsafe operations, and I get it to work for one interface, but not two:

#[cfg(test)]
mod tests {
    use super::*;
    use windows::{
        core::*, Data::Xml::Dom::*, Win32::Foundation::*, Win32::NetworkManagement::IpHelper::*,
        Win32::System::Threading::*, Win32::UI::WindowsAndMessaging::*,
    };

    #[test]
    fn main() {
        unsafe {
            let mut dw_out_buf_len: u32 = 0;

            let mut dw_ret_val =
                GetInterfaceInfo(std::ptr::null_mut(), &mut dw_out_buf_len as *mut u32);

            if dw_ret_val != ERROR_INSUFFICIENT_BUFFER.0 {
                panic!();
            }

            println!("Size: {}", dw_out_buf_len);
            // allocate that amount of memory, which will be used as a buffer
            let mut ip_interface_info = Vec::with_capacity(dw_out_buf_len as usize);
            let mut ptr = ip_interface_info.as_mut_ptr() as *mut IP_INTERFACE_INFO;

            dw_ret_val = GetInterfaceInfo(ptr, &mut dw_out_buf_len as *mut u32);

            println!("Num adapters: {}", (*ptr).NumAdapters);
            for i in 0..(*ptr).NumAdapters as usize {
                println!(
                    "\tAdapter index: {}\n\tAdapter name: {}",
                    (*ptr).Adapter[i].Index,
                    String::from_utf16(&(*ptr).Adapter[i].Name).unwrap()
                );
            }
        }
    }
}

It crashes when I'm trying to access the second entry (even though there should be two available):

panicked at 'index out of bounds: the len is 1 but the index is 1'

The struct IP_INTERFACE_INFO containing all data has a field called Adapter which seems to be limited to only be array size of 1. Am I reading this correctly? How is it then supposed to hold multiple adapters?

#[repr(C)]
#[doc = "*Required features: `\"Win32_NetworkManagement_IpHelper\"`*"]
pub struct IP_INTERFACE_INFO {
    pub NumAdapters: i32,
    pub Adapter: [IP_ADAPTER_INDEX_MAP; 1],
}

Answer 1

It appears that IP_INTERFACE_INFO uses a C flexible array member , which often uses the [1] syntax . The C++ example in Managing Interfaces Using GetInterfaceInfo corroborates this usage:

for (i = 0; i < (unsigned int) pInterfaceInfo->NumAdapters; i++) {
    printf("  Adapter Index[%d]: %ld\n", i,
           pInterfaceInfo->Adapter[i].Index);
    printf("  Adapter Name[%d]:  %ws\n\n", i,
           pInterfaceInfo->Adapter[i].Name);
}

The equivalent in Rust would be to take the single-element array, get the raw pointer to it, then iterate over that (untested as I'm not currently near Windows):

for i in 0..(*ptr).NumAdapters as usize {
    let adapter = (*ptr).Adapter.as_ptr().add(i);
}

I might even use a tool like slice::from_raw_parts to convert the raw pointer and runtime length into a nice Rust slice.