1 files changed, 57 insertions, 0 deletions
diff --git a/third_party/rust/tokio/src/io/seek.rs b/third_party/rust/tokio/src/io/seek.rs
new file mode 100644
index 0000000000..e64205d9cf
--- /dev/null
+++ b/third_party/rust/tokio/src/io/seek.rs
@@ -0,0 +1,57 @@
+use crate::io::AsyncSeek;
+
+use pin_project_lite::pin_project;
+use std::future::Future;
+use std::io::{self, SeekFrom};
+use std::marker::PhantomPinned;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+pin_project! {
+    /// Future for the [`seek`](crate::io::AsyncSeekExt::seek) method.
+    #[derive(Debug)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct Seek<'a, S: ?Sized> {
+        seek: &'a mut S,
+        pos: Option<SeekFrom>,
+        // Make this future `!Unpin` for compatibility with async trait methods.
+        #[pin]
+        _pin: PhantomPinned,
+    }
+}
+
+pub(crate) fn seek<S>(seek: &mut S, pos: SeekFrom) -> Seek<'_, S>
+where
+    S: AsyncSeek + ?Sized + Unpin,
+{
+    Seek {
+        seek,
+        pos: Some(pos),
+        _pin: PhantomPinned,
+    }
+}
+
+impl<S> Future for Seek<'_, S>
+where
+    S: AsyncSeek + ?Sized + Unpin,
+{
+    type Output = io::Result<u64>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let me = self.project();
+        match me.pos {
+            Some(pos) => {
+                // ensure no seek in progress
+                ready!(Pin::new(&mut *me.seek).poll_complete(cx))?;
+                match Pin::new(&mut *me.seek).start_seek(*pos) {
+                    Ok(()) => {
+                        *me.pos = None;
+                        Pin::new(&mut *me.seek).poll_complete(cx)
+                    }
+                    Err(e) => Poll::Ready(Err(e)),
+                }
+            }
+            None => Pin::new(&mut *me.seek).poll_complete(cx),
+        }
+    }
+}