Expose web_sys::File via FileEngine

[wooden-worm]

Specific Demand

On wasm I need to access the raw web_sys::File object in order to deal with big files (bigger than available memory), however, FileEngine only provides read_to_string and read_to_bytes.

Implement Suggestion

• Gated #[cfg...] on wasm to return web_sys::Filie
• Extension trait as how Rust handle platform specific functionalities - example: https://doc.rust-lang.org/std/os/windows/io/trait.AsHandle.html

[ealmloff]

This would be a great addition!

Dioxus does not include #[cfg...] statements for each platform so that other external renderer can be implemented. If we did take the config approach it would prevent a renderer like freya from using the html crate with it's own file engine type.

Instead we could expose the inner type as Any type and allow users to downcast it to a platform specific type. We do something similar to this with the onmounted event. We could expose an extension trait on each platform to make downcasting to the platform type more easy:

#[async_trait::async_trait(?Send)]
pub trait FileEngine {
    // get a list of file names
    fn files(&self) -> Vec<String>;

    // read a file to bytes
    async fn read_file(&self, file: &str) -> Option<Vec<u8>>;
    
    async fn read_native_file(&self, file: &str) -> Option<Box<dyn Any>>;

    // read a file to string
    async fn read_file_to_string(&self, file: &str) -> Option<String>;
}

trait WebFileEngineExt {
    fn read_web_file(&self, file: &str) -> Option<web_sys::File>;
}

impl WebFileEngineExt for std::sync::Arc<dyn FileEngine> {
    fn read_web_file(&self, file: &str) -> Option<web_sys::File> {
        self.read_native_file().map(|file| *file.downcast())
    }
}

[ealmloff]

also related to #93

[wooden-worm]

I can work on a PR if the above approach is acceptable, let me know.

[ealmloff]

I can work on a PR if the above approach is acceptable, let me know.

That would be great!