Windows custom protocol workaround: multi-server extension loading

[HuakunShen]

From

• https://github.com/kunkunsh/kunkun/issues/79

Tauri's implementation for custom protocol on Windows has a problem that denies requests from within iframe.

• [bug] Inconsistent register_uri_scheme_protocol behaviour on Windows. Connection refused for requests from iframe. tauri-apps/tauri#11505
• `register_uri_scheme_protocol` behaves differently on different platforms! How to get a real custom uri scheme on Windows? tauri-apps/tauri#10868

It doesn't seem like there will be a fix from Tauri, so I have to implement a workaround for windows.

Candidate Solutions

Since custom protocol won't work, the only option is to serve files from http file server.
But I don't really want to revert to the old design where each extension need base url configuration (so ugly and hard to maintain).

1. Disable multi-window support for extensions, i.e. only one extension at a time; extension only loads in main window
2. Still support multi-window, then spawn a new file server per custom ui extension, and kill it after window is closed
   • Make use of the window extension hash map stored in app state. Maybe simply also store an axum server handle in the hash map
   • Existing code will remove a window label from the map when extension quits, just kill the server with server handle here

For now I'd choose option 2 (multi server)

There could be multiple servers simultaneously, which takes more ports, and more RAM.
However, since all servers on in a single process, but different thread, and the workload isn't heavy (just serve static files), I guess the extra RAM usage won't be too much (experiment required)