1 files changed, 90 insertions, 0 deletions
diff --git a/third_party/rust/tokio/src/io/async_seek.rs b/third_party/rust/tokio/src/io/async_seek.rs
new file mode 100644
index 0000000000..bd7a992e4d
--- /dev/null
+++ b/third_party/rust/tokio/src/io/async_seek.rs
@@ -0,0 +1,90 @@
+use std::io::{self, SeekFrom};
+use std::ops::DerefMut;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+/// Seek bytes asynchronously.
+///
+/// This trait is analogous to the [`std::io::Seek`] trait, but integrates
+/// with the asynchronous task system. In particular, the `start_seek`
+/// method, unlike [`Seek::seek`], will not block the calling thread.
+///
+/// Utilities for working with `AsyncSeek` values are provided by
+/// [`AsyncSeekExt`].
+///
+/// [`std::io::Seek`]: std::io::Seek
+/// [`Seek::seek`]: std::io::Seek::seek()
+/// [`AsyncSeekExt`]: crate::io::AsyncSeekExt
+pub trait AsyncSeek {
+    /// Attempts to seek to an offset, in bytes, in a stream.
+    ///
+    /// A seek beyond the end of a stream is allowed, but behavior is defined
+    /// by the implementation.
+    ///
+    /// If this function returns successfully, then the job has been submitted.
+    /// To find out when it completes, call `poll_complete`.
+    ///
+    /// # Errors
+    ///
+    /// This function can return [`io::ErrorKind::Other`] in case there is
+    /// another seek in progress. To avoid this, it is advisable that any call
+    /// to `start_seek` is preceded by a call to `poll_complete` to ensure all
+    /// pending seeks have completed.
+    fn start_seek(self: Pin<&mut Self>, position: SeekFrom) -> io::Result<()>;
+
+    /// Waits for a seek operation to complete.
+    ///
+    /// If the seek operation completed successfully,
+    /// this method returns the new position from the start of the stream.
+    /// That position can be used later with [`SeekFrom::Start`]. Repeatedly
+    /// calling this function without calling `start_seek` might return the
+    /// same result.
+    ///
+    /// # Errors
+    ///
+    /// Seeking to a negative offset is considered an error.
+    fn poll_complete(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<u64>>;
+}
+
+macro_rules! deref_async_seek {
+    () => {
+        fn start_seek(mut self: Pin<&mut Self>, pos: SeekFrom) -> io::Result<()> {
+            Pin::new(&mut **self).start_seek(pos)
+        }
+
+        fn poll_complete(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<u64>> {
+            Pin::new(&mut **self).poll_complete(cx)
+        }
+    };
+}
+
+impl<T: ?Sized + AsyncSeek + Unpin> AsyncSeek for Box<T> {
+    deref_async_seek!();
+}
+
+impl<T: ?Sized + AsyncSeek + Unpin> AsyncSeek for &mut T {
+    deref_async_seek!();
+}
+
+impl<P> AsyncSeek for Pin<P>
+where
+    P: DerefMut + Unpin,
+    P::Target: AsyncSeek,
+{
+    fn start_seek(self: Pin<&mut Self>, pos: SeekFrom) -> io::Result<()> {
+        self.get_mut().as_mut().start_seek(pos)
+    }
+
+    fn poll_complete(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<u64>> {
+        self.get_mut().as_mut().poll_complete(cx)
+    }
+}
+
+impl<T: AsRef<[u8]> + Unpin> AsyncSeek for io::Cursor<T> {
+    fn start_seek(mut self: Pin<&mut Self>, pos: SeekFrom) -> io::Result<()> {
+        io::Seek::seek(&mut *self, pos).map(drop)
+    }
+    fn poll_complete(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<u64>> {
+        Poll::Ready(Ok(self.get_mut().position()))
+    }
+}