ownership issue

[schmurfy]

I think that's more a problem related to rust than tauri specifically but I failed to reproduce it without tauri so I will try asking here first:

I am trying to implement a managed state to share the client once it is initialized, I reduced the code to be more readable but the client method would create the client if client contains None and then return it.

use kube::Client;
use crate::kube::get_client;

pub struct AppState {
  client: Option<Client>,
}

impl AppState {
  pub fn client3(&self) -> Option<Client> {
    match &self.client {
      Some(c) => Some(c.clone()),
      None => None,
    }
  }

  pub fn client2(&mut self) -> Option<Client> {
    match &self.client {
      Some(c) => Some(c.clone()),
      None => None,
    }
  }
}

My issue is there in my commands:

#[command]
pub async fn watch_pods(app_state: tauri::State<'_, AppState>) -> Result<(), MyError> {
  let client = app_state.client2().unwrap();
  crate::kube::pod::watch(client, |p| {
    // [...]
  }).await.unwrap();
  Ok(())
}

// watch function signature for reference
pub async fn watch<F: Fn(PodEvent)>(client: Client, f: F) -> Result<(), kube::Error> {
  // [...]
}

If I call client3 it works fine, no compiler error but if I use client2 I get this error:

error[E0596]: cannot borrow data in dereference of `tauri::State<'_, AppState>` as mutable
  --> src/commands.rs:47:16
   |
47 |   let client = app_state.client2().unwrap();
   |                ^^^^^^^^^^^^^^^^^^^ cannot borrow as mutable
   |
   = help: trait `DerefMut` is required to modify through a dereference, but it is not implemented for `tauri::State<'_, AppState>`

Despite reading again and again everything I can find in the rust book and on the net about how ownership works I cannot understand the error and how to solve it.

As far as I understand the Client is owned by the Option which is owned by my state struct but when I clone it to return it the ownership of that new object moves to the watch_pods function and those assumptions seems correct but all hell break loose when I unwrap the Option.

When using client3 with an immutable reference it works but not with client2 using a mutable reference and that's where I am lost, I don't see what link the clone Option to self and how the type of reference I had on it when calling clone matters.

Any help is welcome, I have been stuck on this for two days now and really want to understand.

[FabianLars]

The Option doesn't actually matter here, it fails before that already. In your command you accept an immutable instance of AppState but the client2 function needs it to be mutable. And i think this is not an issue for you without tauri because tauri::State is basically a fancy reference and not an owned value (it works similar to std::sync::Arc if you wanna look into it).

[schmurfy]

Thank you, that makes more sense.
If the state is an immutable reference, how can I update it ?

I have looked at examples/state but I admit it confused me more than anything, I guess I am learning a bit too much at the same time xD

How would you do what I try to achieve here ?(initialize the client on first call and then reuse it)

[FabianLars]

If you need a mutable reference then i think you won't get around interior mutability via a Mutex for example.