82 lines
2.3 KiB
Rust
82 lines
2.3 KiB
Rust
//! Converting JavaScript `AsyncIterator`s to Rust `Stream`s.
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//!
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//! Analogous to the promise to future conversion, this module allows
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//! turning objects implementing the async iterator protocol into `Stream`s
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//! that produce values that can be awaited from.
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//!
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use crate::JsFuture;
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use core::future::Future;
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use core::pin::Pin;
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use core::task::{Context, Poll};
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use futures_core::stream::Stream;
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use js_sys::{AsyncIterator, IteratorNext};
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use wasm_bindgen::prelude::*;
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/// A `Stream` that yields values from an underlying `AsyncIterator`.
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pub struct JsStream {
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iter: AsyncIterator,
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next: Option<JsFuture>,
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done: bool,
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}
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impl JsStream {
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fn next_future(&self) -> Result<JsFuture, JsValue> {
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self.iter.next().map(JsFuture::from)
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}
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}
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impl From<AsyncIterator> for JsStream {
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fn from(iter: AsyncIterator) -> Self {
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JsStream {
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iter,
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next: None,
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done: false,
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}
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}
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}
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impl Stream for JsStream {
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type Item = Result<JsValue, JsValue>;
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fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Option<Self::Item>> {
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if self.done {
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return Poll::Ready(None);
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}
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let future = match self.next.as_mut() {
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Some(val) => val,
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None => match self.next_future() {
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Ok(val) => {
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self.next = Some(val);
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self.next.as_mut().unwrap()
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}
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Err(e) => {
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self.done = true;
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return Poll::Ready(Some(Err(e)));
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}
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},
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};
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match Pin::new(future).poll(cx) {
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Poll::Ready(res) => match res {
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Ok(iter_next) => {
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let next = iter_next.unchecked_into::<IteratorNext>();
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if next.done() {
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self.done = true;
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Poll::Ready(None)
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} else {
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self.next.take();
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Poll::Ready(Some(Ok(next.value())))
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}
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}
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Err(e) => {
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self.done = true;
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Poll::Ready(Some(Err(e)))
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}
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},
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Poll::Pending => Poll::Pending,
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}
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}
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}
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