How to clear/flush the DNS cache? (Windows)

help
1

I am looking for a way to programmatically clear/flush the local dns cache (Equivalent of calling "ipconfig /flushdns").

2

Rust doesn't have built-in methods for things like this. You need to find how to do that in C or other language using the Windows API, and adapt that to Rust. Perhaps the windows crate will have the required API.

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3

Okay thank you i'll have a look, can you give me some resources on how to adapt that (C) to Rust? that would be nice.

4

The Windows crate has its general documentation about using appropriate windows DLLs and their APIs.

Other than that, Rust calls using C functions "FFI", so look for tutorials on using the C FFI.

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5

This API is a little more complicated than C FFI, since it’s only available via WMI. To call it from Rust you’ll need to use the WMI API’s from the windows crate to do the equivalent of

Invoke-CimMethod -Namespace root/StandardCimv2 -ClassName MSFT_DNSClientCache -MethodName Clear

which is also harder to understand because WMI is built on COM.

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6

OK, this wasn’t quite so bad, particularly since the Clear method doesn’t take any parameters, apart from that monstrous CoInitializeSecurity() function call that I just copied from Microsoft’s documentation:

use windows::core::BSTR;
use windows::Win32::System::Com::*;
use windows::Win32::System::Wmi::{IWbemLocator, WbemLocator};

fn clear_dns_cache() -> windows::core::Result<()> {
    let namespace = BSTR::from(r"root/StandardCimv2");
    let dns_client_cache = BSTR::from("MSFT_DNSClientCache");
    let clear = BSTR::from("Clear");
    unsafe {
        let loc: IWbemLocator = CoCreateInstance(&WbemLocator, None, CLSCTX_INPROC_SERVER)?;
        let svc = loc.ConnectServer(&namespace, None, None, None, 0, None, None)?;
        svc.ExecMethod(&dns_client_cache, &clear, 0, None, None, None, None)
    }
}

fn main() {
    unsafe {
        CoInitializeEx(None, COINIT_MULTITHREADED).expect("CoInitializeEx failed unexpectedly");
        CoInitializeSecurity(
            None,
            -1,
            None,
            None,
            RPC_C_AUTHN_LEVEL_DEFAULT,
            RPC_C_IMP_LEVEL_IMPERSONATE,
            None,
            EOAC_NONE,
            None,
        )
        .expect("CoInitializeSecurity failed unexpectedly");
    }
    if let Err(e) = clear_dns_cache() {
        eprintln!("WMI error: {}", e);
    }
}
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