Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 774 insertions, 0 deletions

diff --git a/vendor/tokio/src/fs/file.rs b/vendor/tokio/src/fs/file.rs
new file mode 100644
index 000000000..5286e6c5c
--- /dev/null
+++ b/vendor/tokio/src/fs/file.rs
@@ -0,0 +1,774 @@
+//! Types for working with [`File`].
+//!
+//! [`File`]: File
+
+use self::State::*;
+use crate::fs::asyncify;
+use crate::io::blocking::Buf;
+use crate::io::{AsyncRead, AsyncSeek, AsyncWrite, ReadBuf};
+use crate::sync::Mutex;
+
+use std::fmt;
+use std::fs::{Metadata, Permissions};
+use std::future::Future;
+use std::io::{self, Seek, SeekFrom};
+use std::path::Path;
+use std::pin::Pin;
+use std::sync::Arc;
+use std::task::Context;
+use std::task::Poll;
+use std::task::Poll::*;
+
+#[cfg(test)]
+use super::mocks::spawn_blocking;
+#[cfg(test)]
+use super::mocks::JoinHandle;
+#[cfg(test)]
+use super::mocks::MockFile as StdFile;
+#[cfg(not(test))]
+use crate::blocking::spawn_blocking;
+#[cfg(not(test))]
+use crate::blocking::JoinHandle;
+#[cfg(not(test))]
+use std::fs::File as StdFile;
+
+/// A reference to an open file on the filesystem.
+///
+/// This is a specialized version of [`std::fs::File`][std] for usage from the
+/// Tokio runtime.
+///
+/// An instance of a `File` can be read and/or written depending on what options
+/// it was opened with. Files also implement [`AsyncSeek`] to alter the logical
+/// cursor that the file contains internally.
+///
+/// A file will not be closed immediately when it goes out of scope if there
+/// are any IO operations that have not yet completed. To ensure that a file is
+/// closed immediately when it is dropped, you should call [`flush`] before
+/// dropping it. Note that this does not ensure that the file has been fully
+/// written to disk; the operating system might keep the changes around in an
+/// in-memory buffer. See the [`sync_all`] method for telling the OS to write
+/// the data to disk.
+///
+/// Reading and writing to a `File` is usually done using the convenience
+/// methods found on the [`AsyncReadExt`] and [`AsyncWriteExt`] traits.
+///
+/// [std]: struct@std::fs::File
+/// [`AsyncSeek`]: trait@crate::io::AsyncSeek
+/// [`flush`]: fn@crate::io::AsyncWriteExt::flush
+/// [`sync_all`]: fn@crate::fs::File::sync_all
+/// [`AsyncReadExt`]: trait@crate::io::AsyncReadExt
+/// [`AsyncWriteExt`]: trait@crate::io::AsyncWriteExt
+///
+/// # Examples
+///
+/// Create a new file and asynchronously write bytes to it:
+///
+/// ```no_run
+/// use tokio::fs::File;
+/// use tokio::io::AsyncWriteExt; // for write_all()
+///
+/// # async fn dox() -> std::io::Result<()> {
+/// let mut file = File::create("foo.txt").await?;
+/// file.write_all(b"hello, world!").await?;
+/// # Ok(())
+/// # }
+/// ```
+///
+/// Read the contents of a file into a buffer
+///
+/// ```no_run
+/// use tokio::fs::File;
+/// use tokio::io::AsyncReadExt; // for read_to_end()
+///
+/// # async fn dox() -> std::io::Result<()> {
+/// let mut file = File::open("foo.txt").await?;
+///
+/// let mut contents = vec![];
+/// file.read_to_end(&mut contents).await?;
+///
+/// println!("len = {}", contents.len());
+/// # Ok(())
+/// # }
+/// ```
+pub struct File {
+    std: Arc<StdFile>,
+    inner: Mutex<Inner>,
+}
+
+struct Inner {
+    state: State,
+
+    /// Errors from writes/flushes are returned in write/flush calls. If a write
+    /// error is observed while performing a read, it is saved until the next
+    /// write / flush call.
+    last_write_err: Option<io::ErrorKind>,
+
+    pos: u64,
+}
+
+#[derive(Debug)]
+enum State {
+    Idle(Option<Buf>),
+    Busy(JoinHandle<(Operation, Buf)>),
+}
+
+#[derive(Debug)]
+enum Operation {
+    Read(io::Result<usize>),
+    Write(io::Result<()>),
+    Seek(io::Result<u64>),
+}
+
+impl File {
+    /// Attempts to open a file in read-only mode.
+    ///
+    /// See [`OpenOptions`] for more details.
+    ///
+    /// [`OpenOptions`]: super::OpenOptions
+    ///
+    /// # Errors
+    ///
+    /// This function will return an error if called from outside of the Tokio
+    /// runtime or if path does not already exist. Other errors may also be
+    /// returned according to OpenOptions::open.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::fs::File;
+    /// use tokio::io::AsyncReadExt;
+    ///
+    /// # async fn dox() -> std::io::Result<()> {
+    /// let mut file = File::open("foo.txt").await?;
+    ///
+    /// let mut contents = vec![];
+    /// file.read_to_end(&mut contents).await?;
+    ///
+    /// println!("len = {}", contents.len());
+    /// # Ok(())
+    /// # }
+    /// ```
+    ///
+    /// The [`read_to_end`] method is defined on the [`AsyncReadExt`] trait.
+    ///
+    /// [`read_to_end`]: fn@crate::io::AsyncReadExt::read_to_end
+    /// [`AsyncReadExt`]: trait@crate::io::AsyncReadExt
+    pub async fn open(path: impl AsRef<Path>) -> io::Result<File> {
+        let path = path.as_ref().to_owned();
+        let std = asyncify(|| StdFile::open(path)).await?;
+
+        Ok(File::from_std(std))
+    }
+
+    /// Opens a file in write-only mode.
+    ///
+    /// This function will create a file if it does not exist, and will truncate
+    /// it if it does.
+    ///
+    /// See [`OpenOptions`] for more details.
+    ///
+    /// [`OpenOptions`]: super::OpenOptions
+    ///
+    /// # Errors
+    ///
+    /// Results in an error if called from outside of the Tokio runtime or if
+    /// the underlying [`create`] call results in an error.
+    ///
+    /// [`create`]: std::fs::File::create
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::fs::File;
+    /// use tokio::io::AsyncWriteExt;
+    ///
+    /// # async fn dox() -> std::io::Result<()> {
+    /// let mut file = File::create("foo.txt").await?;
+    /// file.write_all(b"hello, world!").await?;
+    /// # Ok(())
+    /// # }
+    /// ```
+    ///
+    /// The [`write_all`] method is defined on the [`AsyncWriteExt`] trait.
+    ///
+    /// [`write_all`]: fn@crate::io::AsyncWriteExt::write_all
+    /// [`AsyncWriteExt`]: trait@crate::io::AsyncWriteExt
+    pub async fn create(path: impl AsRef<Path>) -> io::Result<File> {
+        let path = path.as_ref().to_owned();
+        let std_file = asyncify(move || StdFile::create(path)).await?;
+        Ok(File::from_std(std_file))
+    }
+
+    /// Converts a [`std::fs::File`][std] to a [`tokio::fs::File`][file].
+    ///
+    /// [std]: std::fs::File
+    /// [file]: File
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// // This line could block. It is not recommended to do this on the Tokio
+    /// // runtime.
+    /// let std_file = std::fs::File::open("foo.txt").unwrap();
+    /// let file = tokio::fs::File::from_std(std_file);
+    /// ```
+    pub fn from_std(std: StdFile) -> File {
+        File {
+            std: Arc::new(std),
+            inner: Mutex::new(Inner {
+                state: State::Idle(Some(Buf::with_capacity(0))),
+                last_write_err: None,
+                pos: 0,
+            }),
+        }
+    }
+
+    /// Attempts to sync all OS-internal metadata to disk.
+    ///
+    /// This function will attempt to ensure that all in-core data reaches the
+    /// filesystem before returning.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::fs::File;
+    /// use tokio::io::AsyncWriteExt;
+    ///
+    /// # async fn dox() -> std::io::Result<()> {
+    /// let mut file = File::create("foo.txt").await?;
+    /// file.write_all(b"hello, world!").await?;
+    /// file.sync_all().await?;
+    /// # Ok(())
+    /// # }
+    /// ```
+    ///
+    /// The [`write_all`] method is defined on the [`AsyncWriteExt`] trait.
+    ///
+    /// [`write_all`]: fn@crate::io::AsyncWriteExt::write_all
+    /// [`AsyncWriteExt`]: trait@crate::io::AsyncWriteExt
+    pub async fn sync_all(&self) -> io::Result<()> {
+        let mut inner = self.inner.lock().await;
+        inner.complete_inflight().await;
+
+        let std = self.std.clone();
+        asyncify(move || std.sync_all()).await
+    }
+
+    /// This function is similar to `sync_all`, except that it may not
+    /// synchronize file metadata to the filesystem.
+    ///
+    /// This is intended for use cases that must synchronize content, but don't
+    /// need the metadata on disk. The goal of this method is to reduce disk
+    /// operations.
+    ///
+    /// Note that some platforms may simply implement this in terms of `sync_all`.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::fs::File;
+    /// use tokio::io::AsyncWriteExt;
+    ///
+    /// # async fn dox() -> std::io::Result<()> {
+    /// let mut file = File::create("foo.txt").await?;
+    /// file.write_all(b"hello, world!").await?;
+    /// file.sync_data().await?;
+    /// # Ok(())
+    /// # }
+    /// ```
+    ///
+    /// The [`write_all`] method is defined on the [`AsyncWriteExt`] trait.
+    ///
+    /// [`write_all`]: fn@crate::io::AsyncWriteExt::write_all
+    /// [`AsyncWriteExt`]: trait@crate::io::AsyncWriteExt
+    pub async fn sync_data(&self) -> io::Result<()> {
+        let mut inner = self.inner.lock().await;
+        inner.complete_inflight().await;
+
+        let std = self.std.clone();
+        asyncify(move || std.sync_data()).await
+    }
+
+    /// Truncates or extends the underlying file, updating the size of this file to become size.
+    ///
+    /// If the size is less than the current file's size, then the file will be
+    /// shrunk. If it is greater than the current file's size, then the file
+    /// will be extended to size and have all of the intermediate data filled in
+    /// with 0s.
+    ///
+    /// # Errors
+    ///
+    /// This function will return an error if the file is not opened for
+    /// writing.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::fs::File;
+    /// use tokio::io::AsyncWriteExt;
+    ///
+    /// # async fn dox() -> std::io::Result<()> {
+    /// let mut file = File::create("foo.txt").await?;
+    /// file.write_all(b"hello, world!").await?;
+    /// file.set_len(10).await?;
+    /// # Ok(())
+    /// # }
+    /// ```
+    ///
+    /// The [`write_all`] method is defined on the [`AsyncWriteExt`] trait.
+    ///
+    /// [`write_all`]: fn@crate::io::AsyncWriteExt::write_all
+    /// [`AsyncWriteExt`]: trait@crate::io::AsyncWriteExt
+    pub async fn set_len(&self, size: u64) -> io::Result<()> {
+        let mut inner = self.inner.lock().await;
+        inner.complete_inflight().await;
+
+        let mut buf = match inner.state {
+            Idle(ref mut buf_cell) => buf_cell.take().unwrap(),
+            _ => unreachable!(),
+        };
+
+        let seek = if !buf.is_empty() {
+            Some(SeekFrom::Current(buf.discard_read()))
+        } else {
+            None
+        };
+
+        let std = self.std.clone();
+
+        inner.state = Busy(spawn_blocking(move || {
+            let res = if let Some(seek) = seek {
+                (&*std).seek(seek).and_then(|_| std.set_len(size))
+            } else {
+                std.set_len(size)
+            }
+            .map(|_| 0); // the value is discarded later
+
+            // Return the result as a seek
+            (Operation::Seek(res), buf)
+        }));
+
+        let (op, buf) = match inner.state {
+            Idle(_) => unreachable!(),
+            Busy(ref mut rx) => rx.await?,
+        };
+
+        inner.state = Idle(Some(buf));
+
+        match op {
+            Operation::Seek(res) => res.map(|pos| {
+                inner.pos = pos;
+            }),
+            _ => unreachable!(),
+        }
+    }
+
+    /// Queries metadata about the underlying file.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::fs::File;
+    ///
+    /// # async fn dox() -> std::io::Result<()> {
+    /// let file = File::open("foo.txt").await?;
+    /// let metadata = file.metadata().await?;
+    ///
+    /// println!("{:?}", metadata);
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub async fn metadata(&self) -> io::Result<Metadata> {
+        let std = self.std.clone();
+        asyncify(move || std.metadata()).await
+    }
+
+    /// Create a new `File` instance that shares the same underlying file handle
+    /// as the existing `File` instance. Reads, writes, and seeks will affect both
+    /// File instances simultaneously.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::fs::File;
+    ///
+    /// # async fn dox() -> std::io::Result<()> {
+    /// let file = File::open("foo.txt").await?;
+    /// let file_clone = file.try_clone().await?;
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub async fn try_clone(&self) -> io::Result<File> {
+        let std = self.std.clone();
+        let std_file = asyncify(move || std.try_clone()).await?;
+        Ok(File::from_std(std_file))
+    }
+
+    /// Destructures `File` into a [`std::fs::File`][std]. This function is
+    /// async to allow any in-flight operations to complete.
+    ///
+    /// Use `File::try_into_std` to attempt conversion immediately.
+    ///
+    /// [std]: std::fs::File
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::fs::File;
+    ///
+    /// # async fn dox() -> std::io::Result<()> {
+    /// let tokio_file = File::open("foo.txt").await?;
+    /// let std_file = tokio_file.into_std().await;
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub async fn into_std(mut self) -> StdFile {
+        self.inner.get_mut().complete_inflight().await;
+        Arc::try_unwrap(self.std).expect("Arc::try_unwrap failed")
+    }
+
+    /// Tries to immediately destructure `File` into a [`std::fs::File`][std].
+    ///
+    /// [std]: std::fs::File
+    ///
+    /// # Errors
+    ///
+    /// This function will return an error containing the file if some
+    /// operation is in-flight.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::fs::File;
+    ///
+    /// # async fn dox() -> std::io::Result<()> {
+    /// let tokio_file = File::open("foo.txt").await?;
+    /// let std_file = tokio_file.try_into_std().unwrap();
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn try_into_std(mut self) -> Result<StdFile, Self> {
+        match Arc::try_unwrap(self.std) {
+            Ok(file) => Ok(file),
+            Err(std_file_arc) => {
+                self.std = std_file_arc;
+                Err(self)
+            }
+        }
+    }
+
+    /// Changes the permissions on the underlying file.
+    ///
+    /// # Platform-specific behavior
+    ///
+    /// This function currently corresponds to the `fchmod` function on Unix and
+    /// the `SetFileInformationByHandle` function on Windows. Note that, this
+    /// [may change in the future][changes].
+    ///
+    /// [changes]: https://doc.rust-lang.org/std/io/index.html#platform-specific-behavior
+    ///
+    /// # Errors
+    ///
+    /// This function will return an error if the user lacks permission change
+    /// attributes on the underlying file. It may also return an error in other
+    /// os-specific unspecified cases.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::fs::File;
+    ///
+    /// # async fn dox() -> std::io::Result<()> {
+    /// let file = File::open("foo.txt").await?;
+    /// let mut perms = file.metadata().await?.permissions();
+    /// perms.set_readonly(true);
+    /// file.set_permissions(perms).await?;
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub async fn set_permissions(&self, perm: Permissions) -> io::Result<()> {
+        let std = self.std.clone();
+        asyncify(move || std.set_permissions(perm)).await
+    }
+}
+
+impl AsyncRead for File {
+    fn poll_read(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        dst: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        let me = self.get_mut();
+        let inner = me.inner.get_mut();
+
+        loop {
+            match inner.state {
+                Idle(ref mut buf_cell) => {
+                    let mut buf = buf_cell.take().unwrap();
+
+                    if !buf.is_empty() {
+                        buf.copy_to(dst);
+                        *buf_cell = Some(buf);
+                        return Ready(Ok(()));
+                    }
+
+                    buf.ensure_capacity_for(dst);
+                    let std = me.std.clone();
+
+                    inner.state = Busy(spawn_blocking(move || {
+                        let res = buf.read_from(&mut &*std);
+                        (Operation::Read(res), buf)
+                    }));
+                }
+                Busy(ref mut rx) => {
+                    let (op, mut buf) = ready!(Pin::new(rx).poll(cx))?;
+
+                    match op {
+                        Operation::Read(Ok(_)) => {
+                            buf.copy_to(dst);
+                            inner.state = Idle(Some(buf));
+                            return Ready(Ok(()));
+                        }
+                        Operation::Read(Err(e)) => {
+                            assert!(buf.is_empty());
+
+                            inner.state = Idle(Some(buf));
+                            return Ready(Err(e));
+                        }
+                        Operation::Write(Ok(_)) => {
+                            assert!(buf.is_empty());
+                            inner.state = Idle(Some(buf));
+                            continue;
+                        }
+                        Operation::Write(Err(e)) => {
+                            assert!(inner.last_write_err.is_none());
+                            inner.last_write_err = Some(e.kind());
+                            inner.state = Idle(Some(buf));
+                        }
+                        Operation::Seek(result) => {
+                            assert!(buf.is_empty());
+                            inner.state = Idle(Some(buf));
+                            if let Ok(pos) = result {
+                                inner.pos = pos;
+                            }
+                            continue;
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
+
+impl AsyncSeek for File {
+    fn start_seek(self: Pin<&mut Self>, mut pos: SeekFrom) -> io::Result<()> {
+        let me = self.get_mut();
+        let inner = me.inner.get_mut();
+
+        loop {
+            match inner.state {
+                Busy(_) => panic!("must wait for poll_complete before calling start_seek"),
+                Idle(ref mut buf_cell) => {
+                    let mut buf = buf_cell.take().unwrap();
+
+                    // Factor in any unread data from the buf
+                    if !buf.is_empty() {
+                        let n = buf.discard_read();
+
+                        if let SeekFrom::Current(ref mut offset) = pos {
+                            *offset += n;
+                        }
+                    }
+
+                    let std = me.std.clone();
+
+                    inner.state = Busy(spawn_blocking(move || {
+                        let res = (&*std).seek(pos);
+                        (Operation::Seek(res), buf)
+                    }));
+                    return Ok(());
+                }
+            }
+        }
+    }
+
+    fn poll_complete(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<u64>> {
+        let inner = self.inner.get_mut();
+
+        loop {
+            match inner.state {
+                Idle(_) => return Poll::Ready(Ok(inner.pos)),
+                Busy(ref mut rx) => {
+                    let (op, buf) = ready!(Pin::new(rx).poll(cx))?;
+                    inner.state = Idle(Some(buf));
+
+                    match op {
+                        Operation::Read(_) => {}
+                        Operation::Write(Err(e)) => {
+                            assert!(inner.last_write_err.is_none());
+                            inner.last_write_err = Some(e.kind());
+                        }
+                        Operation::Write(_) => {}
+                        Operation::Seek(res) => {
+                            if let Ok(pos) = res {
+                                inner.pos = pos;
+                            }
+                            return Ready(res);
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
+
+impl AsyncWrite for File {
+    fn poll_write(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        src: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        let me = self.get_mut();
+        let inner = me.inner.get_mut();
+
+        if let Some(e) = inner.last_write_err.take() {
+            return Ready(Err(e.into()));
+        }
+
+        loop {
+            match inner.state {
+                Idle(ref mut buf_cell) => {
+                    let mut buf = buf_cell.take().unwrap();
+
+                    let seek = if !buf.is_empty() {
+                        Some(SeekFrom::Current(buf.discard_read()))
+                    } else {
+                        None
+                    };
+
+                    let n = buf.copy_from(src);
+                    let std = me.std.clone();
+
+                    inner.state = Busy(spawn_blocking(move || {
+                        let res = if let Some(seek) = seek {
+                            (&*std).seek(seek).and_then(|_| buf.write_to(&mut &*std))
+                        } else {
+                            buf.write_to(&mut &*std)
+                        };
+
+                        (Operation::Write(res), buf)
+                    }));
+
+                    return Ready(Ok(n));
+                }
+                Busy(ref mut rx) => {
+                    let (op, buf) = ready!(Pin::new(rx).poll(cx))?;
+                    inner.state = Idle(Some(buf));
+
+                    match op {
+                        Operation::Read(_) => {
+                            // We don't care about the result here. The fact
+                            // that the cursor has advanced will be reflected in
+                            // the next iteration of the loop
+                            continue;
+                        }
+                        Operation::Write(res) => {
+                            // If the previous write was successful, continue.
+                            // Otherwise, error.
+                            res?;
+                            continue;
+                        }
+                        Operation::Seek(_) => {
+                            // Ignore the seek
+                            continue;
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
+        let inner = self.inner.get_mut();
+        inner.poll_flush(cx)
+    }
+
+    fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
+        self.poll_flush(cx)
+    }
+}
+
+impl From<StdFile> for File {
+    fn from(std: StdFile) -> Self {
+        Self::from_std(std)
+    }
+}
+
+impl fmt::Debug for File {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("tokio::fs::File")
+            .field("std", &self.std)
+            .finish()
+    }
+}
+
+#[cfg(unix)]
+impl std::os::unix::io::AsRawFd for File {
+    fn as_raw_fd(&self) -> std::os::unix::io::RawFd {
+        self.std.as_raw_fd()
+    }
+}
+
+#[cfg(unix)]
+impl std::os::unix::io::FromRawFd for File {
+    unsafe fn from_raw_fd(fd: std::os::unix::io::RawFd) -> Self {
+        StdFile::from_raw_fd(fd).into()
+    }
+}
+
+#[cfg(windows)]
+impl std::os::windows::io::AsRawHandle for File {
+    fn as_raw_handle(&self) -> std::os::windows::io::RawHandle {
+        self.std.as_raw_handle()
+    }
+}
+
+#[cfg(windows)]
+impl std::os::windows::io::FromRawHandle for File {
+    unsafe fn from_raw_handle(handle: std::os::windows::io::RawHandle) -> Self {
+        StdFile::from_raw_handle(handle).into()
+    }
+}
+
+impl Inner {
+    async fn complete_inflight(&mut self) {
+        use crate::future::poll_fn;
+
+        if let Err(e) = poll_fn(|cx| Pin::new(&mut *self).poll_flush(cx)).await {
+            self.last_write_err = Some(e.kind());
+        }
+    }
+
+    fn poll_flush(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
+        if let Some(e) = self.last_write_err.take() {
+            return Ready(Err(e.into()));
+        }
+
+        let (op, buf) = match self.state {
+            Idle(_) => return Ready(Ok(())),
+            Busy(ref mut rx) => ready!(Pin::new(rx).poll(cx))?,
+        };
+
+        // The buffer is not used here
+        self.state = Idle(Some(buf));
+
+        match op {
+            Operation::Read(_) => Ready(Ok(())),
+            Operation::Write(res) => Ready(res),
+            Operation::Seek(_) => Ready(Ok(())),
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests;