1 files changed, 52 insertions, 0 deletions
diff --git a/third_party/rust/tokio-stream/src/once.rs b/third_party/rust/tokio-stream/src/once.rs
new file mode 100644
index 0000000000..04b4c052b8
--- /dev/null
+++ b/third_party/rust/tokio-stream/src/once.rs
@@ -0,0 +1,52 @@
+use crate::{Iter, Stream};
+
+use core::option;
+use core::pin::Pin;
+use core::task::{Context, Poll};
+
+/// Stream for the [`once`](fn@once) function.
+#[derive(Debug)]
+#[must_use = "streams do nothing unless polled"]
+pub struct Once<T> {
+    iter: Iter<option::IntoIter<T>>,
+}
+
+impl<I> Unpin for Once<I> {}
+
+/// Creates a stream that emits an element exactly once.
+///
+/// The returned stream is immediately ready and emits the provided value once.
+///
+/// # Examples
+///
+/// ```
+/// use tokio_stream::{self as stream, StreamExt};
+///
+/// #[tokio::main]
+/// async fn main() {
+///     // one is the loneliest number
+///     let mut one = stream::once(1);
+///
+///     assert_eq!(Some(1), one.next().await);
+///
+///     // just one, that's all we get
+///     assert_eq!(None, one.next().await);
+/// }
+/// ```
+pub fn once<T>(value: T) -> Once<T> {
+    Once {
+        iter: crate::iter(Some(value).into_iter()),
+    }
+}
+
+impl<T> Stream for Once<T> {
+    type Item = T;
+
+    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<T>> {
+        Pin::new(&mut self.iter).poll_next(cx)
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+}