dioxus/packages/web/src/eval.rs

use dioxus_html::prelude::{EvalError, EvalProvider, Evaluator};
use dioxus_interpreter_js::eval::{JSOwner, WeakDioxusChannel, WebDioxusChannel};
use generational_box::{AnyStorage, GenerationalBox, UnsyncStorage};
use js_sys::Function;
use serde_json::Value;
use std::future::Future;
use std::pin::Pin;
use std::{rc::Rc, str::FromStr};
use wasm_bindgen::prelude::*;

/// Provides the WebEvalProvider through [`cx.provide_context`].
pub fn init_eval() {
    let provider: Rc<dyn EvalProvider> = Rc::new(WebEvalProvider);
    dioxus_core::ScopeId::ROOT.provide_context(provider);
}

/// Represents the web-target's provider of evaluators.
pub struct WebEvalProvider;
impl EvalProvider for WebEvalProvider {
    fn new_evaluator(&self, js: String) -> GenerationalBox<Box<dyn Evaluator>> {
        WebEvaluator::create(js)
    }
}

/// Required to avoid blocking the Rust WASM thread.
const PROMISE_WRAPPER: &str = r#"
    return new Promise(async (resolve, _reject) => {
        {JS_CODE}
        resolve(null);
    });
"#;

type NextPoll = Pin<Box<dyn Future<Output = Result<serde_json::Value, EvalError>>>>;

/// Represents a web-target's JavaScript evaluator.
struct WebEvaluator {
    channels: WeakDioxusChannel,
    next_future: Option<NextPoll>,
    result: Option<Result<serde_json::Value, EvalError>>,
}

impl WebEvaluator {
    /// Creates a new evaluator for web-based targets.
    fn create(js: String) -> GenerationalBox<Box<dyn Evaluator>> {
        let owner = UnsyncStorage::owner();

        let generational_box = owner.invalid();

        // add the drop handler to DioxusChannel so that it gets dropped when the channel is dropped in js
        let channels = WebDioxusChannel::new(JSOwner::new(owner));

        // The Rust side of the channel is a weak reference to the DioxusChannel
        let weak_channels = channels.weak();

        // Wrap the evaluated JS in a promise so that wasm can continue running (send/receive data from js)
        let code = PROMISE_WRAPPER.replace("{JS_CODE}", &js);

        let result = match Function::new_with_args("dioxus", &code).call1(&JsValue::NULL, &channels)
        {
            Ok(result) => {
                if let Ok(stringified) = js_sys::JSON::stringify(&result) {
                    if !stringified.is_undefined() && stringified.is_valid_utf16() {
                        let string: String = stringified.into();
                        Value::from_str(&string).map_err(|e| {
                            EvalError::Communication(format!("Failed to parse result - {}", e))
                        })
                    } else {
                        Err(EvalError::Communication(
                            "Failed to stringify result".into(),
                        ))
                    }
                } else {
                    Err(EvalError::Communication(
                        "Failed to stringify result".into(),
                    ))
                }
            }
            Err(err) => Err(EvalError::InvalidJs(
                err.as_string().unwrap_or("unknown".to_string()),
            )),
        };

        generational_box.set(Box::new(Self {
            channels: weak_channels,
            result: Some(result),
            next_future: None,
        }) as Box<dyn Evaluator>);

        generational_box
    }
}

impl Evaluator for WebEvaluator {
    /// Runs the evaluated JavaScript.
    fn poll_join(
        &mut self,
        _cx: &mut std::task::Context<'_>,
    ) -> std::task::Poll<Result<serde_json::Value, EvalError>> {
        if let Some(result) = self.result.take() {
            std::task::Poll::Ready(result)
        } else {
            std::task::Poll::Ready(Err(EvalError::Finished))
        }
    }

    /// Sends a message to the evaluated JavaScript.
    fn send(&self, data: serde_json::Value) -> Result<(), EvalError> {
        let data = match serde_wasm_bindgen::to_value::<serde_json::Value>(&data) {
            Ok(d) => d,
            Err(e) => return Err(EvalError::Communication(e.to_string())),
        };

        self.channels.rust_send(data);
        Ok(())
    }

    /// Gets an UnboundedReceiver to receive messages from the evaluated JavaScript.
    fn poll_recv(
        &mut self,
        context: &mut std::task::Context<'_>,
    ) -> std::task::Poll<Result<serde_json::Value, EvalError>> {
        if self.next_future.is_none() {
            let channels: WebDioxusChannel = self.channels.clone().into();
            let pinned = Box::pin(async move {
                let fut = channels.rust_recv();
                let data = fut.await;
                serde_wasm_bindgen::from_value::<serde_json::Value>(data)
                    .map_err(|err| EvalError::Communication(err.to_string()))
            });
            self.next_future = Some(pinned);
        }
        let fut = self.next_future.as_mut().unwrap();
        let mut pinned = std::pin::pin!(fut);
        let result = pinned.as_mut().poll(context);
        if result.is_ready() {
            self.next_future = None;
        }
        result
    }
}