Storage: Borrow instead of own

[kkloberdanz]

Hi gang,

If we take a look at the following line: https://github.com/tf-encrypted/runtime/blob/7254b6230fdf0af1061e3848e419b2514a5875cc/rust/moose/src/storage.rs#L13

The save and load methods on the storage traits take exclusive ownership of the data passed to them. I propose that instead of taking ownership, we instead borrow the values in these methods.

What do you think?

Problem

Currently, if you write something like this, you get a compiler error because the variable key is owned by the first function that it gets passed to, storage.save.

        let expected = Float64Tensor::from(
            array![[1.0, 2.0], [3.0, 4.0]]
                .into_dimensionality::<IxDyn>()
                .unwrap(),
        );
        let key = "my-object".to_string();
        let storage = S3SyncStorage::default();
        storage.save(key, Value::from(expected));
        let loaded = storage.load(key);

Compiler error message:

error[E0382]: use of moved value: `key`
   --> src/cape/storage.rs:205:35
    |
202 |         let key = "my-object".to_string();
    |             --- move occurs because `key` has type `std::string::String`, which does not implement the `Copy` trait
203 |         let storage = S3SyncStorage::default();
204 |         storage.save(key, Value::from(expected));
    |                      --- value moved here
205 |         let loaded = storage.load(key);
    |                                   ^^^ value used here after move

Solution

pub trait SyncStorage {
    fn save(&self, key: &String, val: &Value) -> Result<()>;
    fn load(&self, key: &String) -> Result<Value>;
}

#[async_trait]
pub trait AsyncStorage {
    async fn save(&self, key: &String, val: &Value) -> Result<()>;

    async fn load(&self, key: &String) -> Result<Value>;
}

[mortendahl]

FYI this is a larger pending issue in the current runtime, where we currently often move Values instead of borrowing. Makes sense to start optimizing this though so I'd say go for it!