1 files changed, 85 insertions, 0 deletions
diff --git a/third_party/rust/futures-util/src/future/select_ok.rs b/third_party/rust/futures-util/src/future/select_ok.rs
new file mode 100644
index 0000000000..5d5579930b
--- /dev/null
+++ b/third_party/rust/futures-util/src/future/select_ok.rs
@@ -0,0 +1,85 @@
+use super::assert_future;
+use crate::future::TryFutureExt;
+use alloc::vec::Vec;
+use core::iter::FromIterator;
+use core::mem;
+use core::pin::Pin;
+use futures_core::future::{Future, TryFuture};
+use futures_core::task::{Context, Poll};
+
+/// Future for the [`select_ok`] function.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct SelectOk<Fut> {
+    inner: Vec<Fut>,
+}
+
+impl<Fut: Unpin> Unpin for SelectOk<Fut> {}
+
+/// Creates a new future which will select the first successful future over a list of futures.
+///
+/// The returned future will wait for any future within `iter` to be ready and Ok. Unlike
+/// `select_all`, this will only return the first successful completion, or the last
+/// failure. This is useful in contexts where any success is desired and failures
+/// are ignored, unless all the futures fail.
+///
+///  This function is only available when the `std` or `alloc` feature of this
+/// library is activated, and it is activated by default.
+///
+/// # Panics
+///
+/// This function will panic if the iterator specified contains no items.
+pub fn select_ok<I>(iter: I) -> SelectOk<I::Item>
+where
+    I: IntoIterator,
+    I::Item: TryFuture + Unpin,
+{
+    let ret = SelectOk { inner: iter.into_iter().collect() };
+    assert!(!ret.inner.is_empty(), "iterator provided to select_ok was empty");
+    assert_future::<
+        Result<(<I::Item as TryFuture>::Ok, Vec<I::Item>), <I::Item as TryFuture>::Error>,
+        _,
+    >(ret)
+}
+
+impl<Fut: TryFuture + Unpin> Future for SelectOk<Fut> {
+    type Output = Result<(Fut::Ok, Vec<Fut>), Fut::Error>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        // loop until we've either exhausted all errors, a success was hit, or nothing is ready
+        loop {
+            let item =
+                self.inner.iter_mut().enumerate().find_map(|(i, f)| match f.try_poll_unpin(cx) {
+                    Poll::Pending => None,
+                    Poll::Ready(e) => Some((i, e)),
+                });
+            match item {
+                Some((idx, res)) => {
+                    // always remove Ok or Err, if it's not the last Err continue looping
+                    drop(self.inner.remove(idx));
+                    match res {
+                        Ok(e) => {
+                            let rest = mem::take(&mut self.inner);
+                            return Poll::Ready(Ok((e, rest)));
+                        }
+                        Err(e) => {
+                            if self.inner.is_empty() {
+                                return Poll::Ready(Err(e));
+                            }
+                        }
+                    }
+                }
+                None => {
+                    // based on the filter above, nothing is ready, return
+                    return Poll::Pending;
+                }
+            }
+        }
+    }
+}
+
+impl<Fut: TryFuture + Unpin> FromIterator<Fut> for SelectOk<Fut> {
+    fn from_iter<T: IntoIterator<Item = Fut>>(iter: T) -> Self {
+        select_ok(iter)
+    }
+}