From 7af0f327513d468c685776789c6fe0f68f6ed102 Mon Sep 17 00:00:00 2001
From: Thibeau Vercruyssen <74682871+tvercruyssen@users.noreply.github.com>
Date: Tue, 14 Sep 2021 16:05:01 +0200
Subject: [PATCH] io: add convenience method `AsyncSeekExt::rewind`. (#4107)

---
 tokio/src/io/util/async_seek_ext.rs | 10 ++++++++++
 tokio/tests/fs_file.rs              | 20 ++++++++++++++++----
 2 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/tokio/src/io/util/async_seek_ext.rs b/tokio/src/io/util/async_seek_ext.rs
index 297a4a61a..46b3e6c0d 100644
--- a/tokio/src/io/util/async_seek_ext.rs
+++ b/tokio/src/io/util/async_seek_ext.rs
@@ -67,6 +67,16 @@ cfg_io_util! {
             seek(self, pos)
         }
 
+        /// Creates a future which will rewind to the beginning of the stream.
+        ///
+        /// This is convenience method, equivalent to to `self.seek(SeekFrom::Start(0))`.
+        fn rewind(&mut self) -> Seek<'_, Self>
+        where
+            Self: Unpin,
+        {
+            self.seek(SeekFrom::Start(0))
+        }
+
         /// Creates a future which will return the current seek position from the
         /// start of the stream.
         ///
diff --git a/tokio/tests/fs_file.rs b/tokio/tests/fs_file.rs
index bf2f1d7b5..f645e61ae 100644
--- a/tokio/tests/fs_file.rs
+++ b/tokio/tests/fs_file.rs
@@ -1,12 +1,11 @@
 #![warn(rust_2018_idioms)]
 #![cfg(feature = "full")]
 
-use tokio::fs::File;
-use tokio::io::{AsyncReadExt, AsyncSeekExt, AsyncWriteExt};
-use tokio_test::task;
-
 use std::io::prelude::*;
 use tempfile::NamedTempFile;
+use tokio::fs::File;
+use tokio::io::{AsyncReadExt, AsyncSeekExt, AsyncWriteExt, SeekFrom};
+use tokio_test::task;
 
 const HELLO: &[u8] = b"hello world...";
 
@@ -50,6 +49,19 @@ async fn basic_write_and_shutdown() {
     assert_eq!(file, HELLO);
 }
 
+#[tokio::test]
+async fn rewind_seek_position() {
+    let tempfile = tempfile();
+
+    let mut file = File::create(tempfile.path()).await.unwrap();
+
+    file.seek(SeekFrom::Current(10)).await.unwrap();
+
+    file.rewind().await.unwrap();
+
+    assert_eq!(file.stream_position().await.unwrap(), 0);
+}
+
 #[tokio::test]
 async fn coop() {
     let mut tempfile = tempfile();