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use std;
use discard::Discard;
use webcore::once::Once;
use webcore::value::{Value, Reference};
use webcore::try_from::{TryInto, TryFrom};
use webcore::discard::DiscardOnDrop;
#[cfg(feature = "futures-support")]
use webcore::serialization::JsSerialize;
#[cfg(feature = "futures-support")]
use futures_channel::oneshot::channel;
#[cfg(feature = "futures-support")]
use futures_core::IntoFuture;
#[cfg(feature = "futures-support")]
use futures_util::FutureExt;
#[cfg(feature = "futures-support")]
use super::promise_future::PromiseFuture;
/// This is used to cleanup the [`done`](struct.Promise.html#method.done) callback.
///
/// See the documentation for [`done`](struct.Promise.html#method.done) for more information.
#[derive( Debug, Clone )]
pub struct DoneHandle {
state: Value,
}
impl Discard for DoneHandle {
fn discard( self ) {
js! { @(no_return)
var state = @{&self.state};
state.cancelled = true;
state.callback.drop();
}
}
}
/// A `Promise` object represents the eventual completion (or failure) of an asynchronous operation, and its resulting value.
///
/// In most situations you shouldn't use this, use [`PromiseFuture`](struct.PromiseFuture.html) instead.
///
/// [(JavaScript docs)](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)
// https://www.ecma-international.org/ecma-262/6.0/#sec-promise-objects
#[derive(Clone, Debug, PartialEq, Eq, ReferenceType)]
#[reference(instance_of = "Promise")]
pub struct Promise( Reference );
impl Promise {
// https://www.ecma-international.org/ecma-262/6.0/#sec-promise-resolve-functions
fn is_thenable( input: &Reference ) -> bool {
(js! {
var input = @{input};
// This emulates the `Type(input) is Object` and `IsCallable(input.then)` ECMAScript abstract operations.
return Object( input ) === input &&
typeof input.then === "function";
}).try_into().unwrap()
}
/// This function should rarely be needed, use [`PromiseFuture`](struct.PromiseFuture.html) instead.
///
/// This function is needed if you have a JavaScript value which is a Promise-like object
/// (it has a `then` method) but it isn't a true `Promise`.
///
/// That situation is rare, but it can happen if you are using a Promise library such as jQuery or
/// Bluebird.
///
/// In that situation you can use `Promise::from_thenable` to convert it into a true `Promise`.
///
/// If the `input` isn't a Promise-like object then it returns `None`.
///
/// # Examples
///
/// Convert a Promise-like object to a `Promise`:
///
/// ```rust
/// // jQuery Promise
/// Promise::from_thenable(&js!( return $.get("test.php"); ).try_into().unwrap())
///
/// // Bluebird Promise
/// Promise::from_thenable(&js!( return bluebird_promise.timeout(1000); ).try_into().unwrap())
/// ```
///
/// [(JavaScript docs)](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/resolve)
// https://www.ecma-international.org/ecma-262/6.0/#sec-promise.resolve
// https://www.ecma-international.org/ecma-262/6.0/#sec-promise-resolve-functions
// https://www.ecma-international.org/ecma-262/6.0/#sec-promiseresolvethenablejob
pub fn from_thenable( input: &Reference ) -> Option< Self > {
// TODO this can probably be made more efficient
if Promise::is_thenable( input ) {
Some( js!( return Promise.resolve( @{input} ); ).try_into().unwrap() )
} else {
None
}
}
/// This function converts a Rust Future into a JavaScript Promise.
///
/// This is needed when you want to pass a Rust Future into JavaScript.
///
/// If you simply want to use a JavaScript Promise inside Rust, then you
/// don't need to use this function: you should use
/// [`PromiseFuture`](struct.PromiseFuture.html) and the
/// [`FutureExt`](https://docs.rs/futures/0.2.*/futures/future/trait.FutureExt.html)
/// methods instead.
///
/// # Examples
///
/// Convert a Rust Future into a JavaScript Promise:
///
/// ```rust
/// Promise::from_future(rust_future)
/// ```
///
/// Export a Rust Future so that it can be used in JavaScript
/// (this only works with the `wasm32-unknown-unknown` target):
///
/// ```rust
/// #[js_export]
/// fn foo() -> Promise {
/// Promise::from_future(rust_future)
/// }
/// ```
///
/// [(JavaScript docs)](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise#Syntax)
// https://www.ecma-international.org/ecma-262/6.0/#sec-promise-executor
#[cfg(feature = "futures-support")]
pub fn from_future< A >( future: A ) -> Self
where A: IntoFuture,
A::Future: 'static,
A::Item: JsSerialize,
A::Error: JsSerialize {
let future = future.into_future();
#[inline]
fn call< A: JsSerialize >( f: Reference, value: A ) {
js! { @(no_return) @{f}( @{value} ); }
}
let callback = move |success: Reference, error: Reference| {
PromiseFuture::spawn_local(
future.then( move |result| {
match result {
Ok( a ) => call( success, a ),
Err( a ) => call( error, a ),
}
Ok( () )
} )
);
};
js!( return new Promise( @{Once( callback )} ); ).try_into().unwrap()
}
/// This method is usually not needed, use [`PromiseFuture`](struct.PromiseFuture.html) instead.
///
/// When the `Promise` either succeeds or fails, it calls the `callback` with the result.
///
/// It does not wait for the `Promise` to succeed / fail (it does not block the thread).
///
/// The `callback` is guaranteed to be called asynchronously even if the `Promise` is already succeeded / failed.
///
/// If the `Promise` never succeeds / fails then the `callback` will never be called.
///
/// This method returns a [`DoneHandle`](struct.DoneHandle.html). The [`DoneHandle`](struct.DoneHandle.html)
/// *exclusively* owns the `callback`, so when the [`DoneHandle`](struct.DoneHandle.html) is dropped it will
/// drop the `callback` and the `callback` will never be called. This will happen even if the `Promise` is not dropped!
///
/// Dropping the [`DoneHandle`](struct.DoneHandle.html) does ***not*** cancel the `Promise`, because promises
/// do not support cancellation.
///
/// If you are no longer interested in the `Promise`'s result you can simply drop the [`DoneHandle`](struct.DoneHandle.html)
/// and then the `callback` will never be called.
///
/// But if you *are* interested in the `Promise`'s result, then you have two choices:
///
/// * Keep the [`DoneHandle`](struct.DoneHandle.html) alive until after the `callback` is called (by storing it in a
/// variable or data structure).
///
/// * Use the [`leak`](struct.DiscardOnDrop.html#method.leak) method to leak the [`DoneHandle`](struct.DoneHandle.html).
/// If the `Promise` never succeeds or fails then this ***will*** leak the memory of the callback, so only use
/// [`leak`](struct.DiscardOnDrop.html#method.leak) if you need to.
///
/// # Examples
///
/// Normal usage:
///
/// ```rust
/// let handle = promise.done(|result| {
/// match result {
/// Ok(success) => { ... },
/// Err(error) => { ... },
/// }
/// });
/// ```
///
/// Leak the [`DoneHandle`](struct.DoneHandle.html) and `callback`:
///
/// ```rust
/// promise.done(|result| {
/// match result {
/// Ok(success) => { ... },
/// Err(error) => { ... },
/// }
/// }).leak();
/// ```
///
/// [(JavaScript docs)](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/then)
// https://www.ecma-international.org/ecma-262/6.0/#sec-performpromisethen
pub fn done< A, B, F >( &self, callback: F ) -> DiscardOnDrop< DoneHandle >
where A: TryFrom< Value >,
B: TryFrom< Value >,
// TODO these Debug constraints are only needed because of unwrap
A::Error: std::fmt::Debug,
B::Error: std::fmt::Debug,
F: FnOnce( Result< A, B > ) + 'static {
let callback = move |value: Value, success: bool| {
let value: Result< A, B > = if success {
// TODO figure out a way to avoid the unwrap
let value: A = value.try_into().unwrap();
Ok( value )
} else {
// TODO figure out a way to avoid the unwrap
let value: B = value.try_into().unwrap();
Err( value )
};
callback( value );
};
let state = js!(
var callback = @{Once( callback )};
var state = {
cancelled: false,
callback: callback
};
// TODO don't swallow any errors thrown inside callback
@{self}.then( function ( value ) {
if ( !state.cancelled ) {
callback( value, true );
}
}, function ( value ) {
if ( !state.cancelled ) {
callback( value, false );
}
} );
return state;
);
DiscardOnDrop::new( DoneHandle {
state,
} )
}
/// This method converts the `Promise` into a [`PromiseFuture`](struct.PromiseFuture.html), so that it can be used as a Rust [`Future`](https://docs.rs/futures/0.2.*/futures/future/trait.Future.html).
///
/// This method should rarely be needed, instead use [`value.try_into()`](unstable/trait.TryInto.html) to convert directly from a [`Value`](enum.Value.html) into a [`PromiseFuture`](struct.PromiseFuture.html).
///
/// # Examples
///
/// ```rust
/// promise.to_future().map(|x| x + 1)
/// ```
// We can't use the IntoFuture trait because Promise doesn't have a type argument
// TODO explain more why we can't use the IntoFuture trait
#[cfg(feature = "futures-support")]
pub fn to_future< A, B >( &self ) -> PromiseFuture< A, B >
where A: TryFrom< Value > + 'static,
B: TryFrom< Value > + 'static,
// TODO remove these later
A::Error: std::fmt::Debug,
B::Error: std::fmt::Debug {
let ( sender, receiver ) = channel();
PromiseFuture {
future: receiver,
_done_handle: self.done( |value| {
// TODO is this correct ?
match sender.send( value ) {
Ok( _ ) => {},
Err( _ ) => {},
};
} ),
}
}
}