Expose SetVirtualHostNameToFolderMapping for offline HTML support (Windows)

[CompassionOverload]

Hi Tauri team 👋

I'm not a developer — just a user trying to build a local-first note system using Tauri. I don’t know Rust or C#, but I’m using Svelte and trying to display offline HTML content with local images and videos.

I'm building this system with help from Microsoft Copilot, which guides me through the architecture and tooling. I rely heavily on WebView2 on Windows, and I found that it supports an API called SetVirtualHostNameToFolderMapping. This allows mapping a folder to a virtual hostname, so HTML can use relative paths like images/foo.png securely.

This would be perfect for my use case, but I couldn’t find a way to use it in Tauri.

Would it be possible to expose this API, or provide a plugin hook to configure folder mapping during WebView initialization?

I’m not sure how hard this is to implement, but I hope it’s something worth considering. Thanks for all your amazing work on Tauri 🙏

---

While SetVirtualHostNameToFolderMapping is specific to Windows, I think the concept behind it — mapping a virtual hostname to a local folder — is broadly useful for offline apps.

It would be great if Tauri could offer a cross-platform abstraction for this, so that HTML content can use relative paths like images/foo.png consistently across platforms. Even if the implementation differs, having a unified API or plugin interface would make offline resource handling much cleaner and more secure.

This would help users like me avoid rewriting HTML paths or relying on unsafe access, and make Tauri even more powerful for local-first applications.

[FabianLars]

As far as i know SetVirtualHostNameToFolderMapping can be called after the webview was created which should make it possible to call it inside https://docs.rs/tauri/latest/tauri/webview/struct.WebviewWindow.html#method.with_webview
The simplest example (using unwrap to keep it a bit smaller) would look something like this (tested roughly the same code on my machine).
The versions of windows and webview2-com must match the versions used by the tauri version you use.

use tauri::Manager;
use windows::core::{HSTRING, Interface};
use webview2_com::Microsoft::Web::WebView2::Win32::{
    COREWEBVIEW2_HOST_RESOURCE_ACCESS_KIND, ICoreWebView2_3,
};

tauri::Builder::deafult()
  .setup(|app| {
    let window = app.get_webview_window("main").unwrap(); // Change "main" to your window label if needed
    window
        .with_webview(|wv| unsafe {
            wv.controller()
                .CoreWebView2()
                .unwrap()
                .cast::<ICoreWebView2_3>()
                .unwrap()
                .SetVirtualHostNameToFolderMapping(
                    &HSTRING::from("hostname"),
                    &HSTRING::from("A:/fabianlars/testproject/src-tauri/icons"),
                    COREWEBVIEW2_HOST_RESOURCE_ACCESS_KIND(1),
                )
                .unwrap();
        })
        .unwrap();
    let _ = window.reload();
    Ok(())
  })
  .build(tauri::generate_context!()).unwrap();

[...] It would be great if Tauri could offer a cross-platform abstraction for this, [...]

Tracked here #5302 - don't expect any progress soon.

[CompassionOverload]

Thanks for the explanation and example.
I’m not a developer myself, but it’s helpful to see how this works under the hood.
I’m still learning Rust with Copilot’s help — thanks again for sharing the code!

Appreciate it.