//! Asynchronous I/O.

//!

//! This module is the asynchronous version of `std::io`. It defines four

//! traits, [`AsyncRead`], [`AsyncWrite`], [`AsyncSeek`], and [`AsyncBufRead`],

//! which mirror the `Read`, `Write`, `Seek`, and `BufRead` traits of the

//! standard library. However, these traits integrate with the asynchronous

//! task system, so that if an I/O object isn't ready for reading (or writing),

//! the thread is not blocked, and instead the current task is queued to be

//! woken when I/O is ready.

//!

//! In addition, the [`AsyncReadExt`], [`AsyncWriteExt`], [`AsyncSeekExt`], and

//! [`AsyncBufReadExt`] extension traits offer a variety of useful combinators

//! for operating with asynchronous I/O objects, including ways to work with

//! them using futures, streams and sinks.

//!

//! This module is only available when the `std` feature of this

//! library is activated, and it is activated by default.

#[cfg(feature = "io-compat")]

#[cfg_attr(docsrs, doc(cfg(feature = "io-compat")))]

use crate::compat::Compat;

use crate::future::assert_future;

use crate::stream::assert_stream;

use std::{pin::Pin, ptr};

// Re-export some types from `std::io` so that users don't have to deal

// with conflicts when `use`ing `futures::io` and `std::io`.

#[doc(no_inline)]

pub use std::io::{Error, ErrorKind, IoSlice, IoSliceMut, Result, SeekFrom};

pub use futures_io::{AsyncBufRead, AsyncRead, AsyncSeek, AsyncWrite};

// used by `BufReader` and `BufWriter`

// https://github.com/rust-lang/rust/blob/master/src/libstd/sys_common/io.rs#L1

const DEFAULT_BUF_SIZE: usize = 8 * 1024;

/// Initializes a buffer if necessary.

///

/// A buffer is currently always initialized.

#[inline]

unsafe fn initialize<R: AsyncRead>(_reader: &R, buf: &mut [u8]) {

    ptr::write_bytes(buf.as_mut_ptr(), 0, buf.len())

}

mod allow_std;

pub use self::allow_std::AllowStdIo;

mod buf_reader;

pub use self::buf_reader::{BufReader, SeeKRelative};

mod buf_writer;

pub use self::buf_writer::BufWriter;

mod line_writer;

pub use self::line_writer::LineWriter;

mod chain;

pub use self::chain::Chain;

mod close;

pub use self::close::Close;

mod copy;

pub use self::copy::{copy, Copy};

mod copy_buf;

pub use self::copy_buf::{copy_buf, CopyBuf};

mod cursor;

pub use self::cursor::Cursor;

mod empty;

pub use self::empty::{empty, Empty};

mod fill_buf;

pub use self::fill_buf::FillBuf;

mod flush;

pub use self::flush::Flush;

#[cfg(feature = "sink")]

#[cfg_attr(docsrs, doc(cfg(feature = "sink")))]

mod into_sink;

#[cfg(feature = "sink")]

#[cfg_attr(docsrs, doc(cfg(feature = "sink")))]

pub use self::into_sink::IntoSink;

mod lines;

pub use self::lines::Lines;

mod read;

pub use self::read::Read;

mod read_vectored;

pub use self::read_vectored::ReadVectored;

mod read_exact;

pub use self::read_exact::ReadExact;

mod read_line;

pub use self::read_line::ReadLine;

mod read_to_end;

pub use self::read_to_end::ReadToEnd;

mod read_to_string;

pub use self::read_to_string::ReadToString;

mod read_until;

pub use self::read_until::ReadUntil;

mod repeat;

pub use self::repeat::{repeat, Repeat};

mod seek;

pub use self::seek::Seek;

mod sink;

pub use self::sink::{sink, Sink};

mod split;

pub use self::split::{ReadHalf, ReuniteError, WriteHalf};

mod take;

pub use self::take::Take;

mod window;

pub use self::window::Window;

mod write;

pub use self::write::Write;

mod write_vectored;

pub use self::write_vectored::WriteVectored;

mod write_all;

pub use self::write_all::WriteAll;

#[cfg(feature = "write-all-vectored")]

mod write_all_vectored;

#[cfg(feature = "write-all-vectored")]

pub use self::write_all_vectored::WriteAllVectored;

/// An extension trait which adds utility methods to `AsyncRead` types.

pub trait AsyncReadExt: AsyncRead {

    /// Creates an adaptor which will chain this stream with another.

    ///

    /// The returned `AsyncRead` instance will first read all bytes from this object

    /// until EOF is encountered. Afterwards the output is equivalent to the

    /// output of `next`.

    ///

    /// # Examples

    ///

    /// ```

    /// # futures::executor::block_on(async {

    /// use futures::io::{AsyncReadExt, Cursor};

    ///

    /// let reader1 = Cursor::new([1, 2, 3, 4]);

    /// let reader2 = Cursor::new([5, 6, 7, 8]);

    ///

    /// let mut reader = reader1.chain(reader2);

    /// let mut buffer = Vec::new();

    ///

    /// // read the value into a Vec.

    /// reader.read_to_end(&mut buffer).await?;

    /// assert_eq!(buffer, [1, 2, 3, 4, 5, 6, 7, 8]);

    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();

    /// ```

    fn chain<R>(self, next: R) -> Chain<Self, R>

    where

        Self: Sized,

        R: AsyncRead,

    {

        assert_read(Chain::new(self, next))

    }

    /// Tries to read some bytes directly into the given `buf` in asynchronous

    /// manner, returning a future type.

    ///

    /// The returned future will resolve to the number of bytes read once the read

    /// operation is completed.

    ///

    /// # Examples

    ///

    /// ```

    /// # futures::executor::block_on(async {

    /// use futures::io::{AsyncReadExt, Cursor};

    ///

    /// let mut reader = Cursor::new([1, 2, 3, 4]);

    /// let mut output = [0u8; 5];

    ///

    /// let bytes = reader.read(&mut output[..]).await?;

    ///

    /// // This is only guaranteed to be 4 because `&[u8]` is a synchronous

    /// // reader. In a real system you could get anywhere from 1 to

    /// // `output.len()` bytes in a single read.

    /// assert_eq!(bytes, 4);

    /// assert_eq!(output, [1, 2, 3, 4, 0]);

    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();

    /// ```

    fn read<'a>(&'a mut self, buf: &'a mut [u8]) -> Read<'a, Self>

    where

        Self: Unpin,

    {

        assert_future::<Result<usize>, _>(Read::new(self, buf))

    }

    /// Creates a future which will read from the `AsyncRead` into `bufs` using vectored

    /// IO operations.

    ///

    /// The returned future will resolve to the number of bytes read once the read

    /// operation is completed.

    fn read_vectored<'a>(&'a mut self, bufs: &'a mut [IoSliceMut<'a>]) -> ReadVectored<'a, Self>

    where

        Self: Unpin,

    {

        assert_future::<Result<usize>, _>(ReadVectored::new(self, bufs))

    }

    /// Creates a future which will read exactly enough bytes to fill `buf`,

    /// returning an error if end of file (EOF) is hit sooner.

    ///

    /// The returned future will resolve once the read operation is completed.

    ///

    /// In the case of an error the buffer and the object will be discarded, with

    /// the error yielded.

    ///

    /// # Examples

    ///

    /// ```

    /// # futures::executor::block_on(async {

    /// use futures::io::{AsyncReadExt, Cursor};

    ///

    /// let mut reader = Cursor::new([1, 2, 3, 4]);

    /// let mut output = [0u8; 4];

    ///

    /// reader.read_exact(&mut output).await?;

    ///

    /// assert_eq!(output, [1, 2, 3, 4]);

    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();

    /// ```

    ///

    /// ## EOF is hit before `buf` is filled

    ///

    /// ```

    /// # futures::executor::block_on(async {

    /// use futures::io::{self, AsyncReadExt, Cursor};

    ///

    /// let mut reader = Cursor::new([1, 2, 3, 4]);

    /// let mut output = [0u8; 5];

    ///

    /// let result = reader.read_exact(&mut output).await;

    ///

    /// assert_eq!(result.unwrap_err().kind(), io::ErrorKind::UnexpectedEof);

    /// # });

    /// ```

    fn read_exact<'a>(&'a mut self, buf: &'a mut [u8]) -> ReadExact<'a, Self>

    where

        Self: Unpin,

    {

        assert_future::<Result<()>, _>(ReadExact::new(self, buf))

    }

    /// Creates a future which will read all the bytes from this `AsyncRead`.

    ///

    /// On success the total number of bytes read is returned.

    ///

    /// # Examples

    ///

    /// ```

    /// # futures::executor::block_on(async {

    /// use futures::io::{AsyncReadExt, Cursor};

    ///

    /// let mut reader = Cursor::new([1, 2, 3, 4]);

    /// let mut output = Vec::with_capacity(4);

    ///

    /// let bytes = reader.read_to_end(&mut output).await?;

    ///

    /// assert_eq!(bytes, 4);

    /// assert_eq!(output, vec![1, 2, 3, 4]);

    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();

    /// ```

    fn read_to_end<'a>(&'a mut self, buf: &'a mut Vec<u8>) -> ReadToEnd<'a, Self>

    where

        Self: Unpin,

    {

        assert_future::<Result<usize>, _>(ReadToEnd::new(self, buf))

    }

    /// Creates a future which will read all the bytes from this `AsyncRead`.

    ///

    /// On success the total number of bytes read is returned.

    ///

    /// # Examples

    ///

    /// ```

    /// # futures::executor::block_on(async {

    /// use futures::io::{AsyncReadExt, Cursor};

    ///

    /// let mut reader = Cursor::new(&b"1234"[..]);

    /// let mut buffer = String::with_capacity(4);

    ///

    /// let bytes = reader.read_to_string(&mut buffer).await?;

    ///

    /// assert_eq!(bytes, 4);

    /// assert_eq!(buffer, String::from("1234"));

    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();

    /// ```

    fn read_to_string<'a>(&'a mut self, buf: &'a mut String) -> ReadToString<'a, Self>

    where

        Self: Unpin,

    {

        assert_future::<Result<usize>, _>(ReadToString::new(self, buf))

    }

    /// Helper method for splitting this read/write object into two halves.

    ///

    /// The two halves returned implement the `AsyncRead` and `AsyncWrite`

    /// traits, respectively.

    ///

    /// # Examples

    ///

    /// ```

    /// # futures::executor::block_on(async {

    /// use futures::io::{self, AsyncReadExt, Cursor};

    ///

    /// // Note that for `Cursor` the read and write halves share a single

    /// // seek position. This may or may not be true for other types that

    /// // implement both `AsyncRead` and `AsyncWrite`.

    ///

    /// let reader = Cursor::new([1, 2, 3, 4]);

    /// let mut buffer = Cursor::new(vec![0, 0, 0, 0, 5, 6, 7, 8]);

    /// let mut writer = Cursor::new(vec![0u8; 5]);

    ///

    /// {

    ///     let (buffer_reader, mut buffer_writer) = (&mut buffer).split();

    ///     io::copy(reader, &mut buffer_writer).await?;

    ///     io::copy(buffer_reader, &mut writer).await?;

    /// }

    ///

    /// assert_eq!(buffer.into_inner(), [1, 2, 3, 4, 5, 6, 7, 8]);

    /// assert_eq!(writer.into_inner(), [5, 6, 7, 8, 0]);

    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();

    /// ```

    fn split(self) -> (ReadHalf<Self>, WriteHalf<Self>)

    where

        Self: AsyncWrite + Sized,

    {

        let (r, w) = split::split(self);

        (assert_read(r), assert_write(w))

    }

    /// Creates an AsyncRead adapter which will read at most `limit` bytes

    /// from the underlying reader.

    ///

    /// # Examples

    ///

    /// ```

    /// # futures::executor::block_on(async {

    /// use futures::io::{AsyncReadExt, Cursor};

    ///

    /// let reader = Cursor::new(&b"12345678"[..]);

    /// let mut buffer = [0; 5];

    ///

    /// let mut take = reader.take(4);

    /// let n = take.read(&mut buffer).await?;

    ///

    /// assert_eq!(n, 4);

    /// assert_eq!(&buffer, b"1234\0");

    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();

    /// ```

    fn take(self, limit: u64) -> Take<Self>

    where

        Self: Sized,

    {

        assert_read(Take::new(self, limit))

    }

    /// Wraps an [`AsyncRead`] in a compatibility wrapper that allows it to be

    /// used as a futures 0.1 / tokio-io 0.1 `AsyncRead`. If the wrapped type

    /// implements [`AsyncWrite`] as well, the result will also implement the

    /// futures 0.1 / tokio 0.1 `AsyncWrite` trait.

    ///

    /// Requires the `io-compat` feature to enable.

    #[cfg(feature = "io-compat")]

    #[cfg_attr(docsrs, doc(cfg(feature = "io-compat")))]

    fn compat(self) -> Compat<Self>

    where

        Self: Sized + Unpin,

    {

        Compat::new(self)

    }

}

impl<R: AsyncRead + ?Sized> AsyncReadExt for R {}

/// An extension trait which adds utility methods to `AsyncWrite` types.

pub trait AsyncWriteExt: AsyncWrite {

    /// Creates a future which will entirely flush this `AsyncWrite`.

    ///

    /// # Examples

    ///

    /// ```

    /// # futures::executor::block_on(async {

    /// use futures::io::{AllowStdIo, AsyncWriteExt};

    /// use std::io::{BufWriter, Cursor};

    ///

    /// let mut output = vec![0u8; 5];

    ///

    /// {

    ///     let writer = Cursor::new(&mut output);

    ///     let mut buffered = AllowStdIo::new(BufWriter::new(writer));

    ///     buffered.write_all(&[1, 2]).await?;

    ///     buffered.write_all(&[3, 4]).await?;

    ///     buffered.flush().await?;

    /// }

    ///

    /// assert_eq!(output, [1, 2, 3, 4, 0]);

    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();

    /// ```

    fn flush(&mut self) -> Flush<'_, Self>

    where

        Self: Unpin,

    {

        assert_future::<Result<()>, _>(Flush::new(self))

    }

    /// Creates a future which will entirely close this `AsyncWrite`.

    fn close(&mut self) -> Close<'_, Self>

    where

        Self: Unpin,

    {

        assert_future::<Result<()>, _>(Close::new(self))

    }

    /// Creates a future which will write bytes from `buf` into the object.

    ///

    /// The returned future will resolve to the number of bytes written once the write

    /// operation is completed.

    fn write<'a>(&'a mut self, buf: &'a [u8]) -> Write<'a, Self>

    where

        Self: Unpin,

    {

        assert_future::<Result<usize>, _>(Write::new(self, buf))

    }

    /// Creates a future which will write bytes from `bufs` into the object using vectored

    /// IO operations.

    ///

    /// The returned future will resolve to the number of bytes written once the write

    /// operation is completed.

    fn write_vectored<'a>(&'a mut self, bufs: &'a [IoSlice<'a>]) -> WriteVectored<'a, Self>

    where

        Self: Unpin,

    {

        assert_future::<Result<usize>, _>(WriteVectored::new(self, bufs))

    }

    /// Write data into this object.

    ///

    /// Creates a future that will write the entire contents of the buffer `buf` into

    /// this `AsyncWrite`.

    ///

    /// The returned future will not complete until all the data has been written.

    ///

    /// # Examples

    ///

    /// ```

    /// # futures::executor::block_on(async {

    /// use futures::io::{AsyncWriteExt, Cursor};

    ///

    /// let mut writer = Cursor::new(vec![0u8; 5]);

    ///

    /// writer.write_all(&[1, 2, 3, 4]).await?;

    ///

    /// assert_eq!(writer.into_inner(), [1, 2, 3, 4, 0]);

    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();

    /// ```

    fn write_all<'a>(&'a mut self, buf: &'a [u8]) -> WriteAll<'a, Self>

    where

        Self: Unpin,

    {

        assert_future::<Result<()>, _>(WriteAll::new(self, buf))

    }

    /// Attempts to write multiple buffers into this writer.

    ///

    /// Creates a future that will write the entire contents of `bufs` into this

    /// `AsyncWrite` using [vectored writes].

    ///

    /// The returned future will not complete until all the data has been

    /// written.

    ///

    /// [vectored writes]: std::io::Write::write_vectored

    ///

    /// # Notes

    ///

    /// Unlike `io::Write::write_vectored`, this takes a *mutable* reference to

    /// a slice of `IoSlice`s, not an immutable one. That's because we need to

    /// modify the slice to keep track of the bytes already written.

    ///

    /// Once this futures returns, the contents of `bufs` are unspecified, as

    /// this depends on how many calls to `write_vectored` were necessary. It is

    /// best to understand this function as taking ownership of `bufs` and to

    /// not use `bufs` afterwards. The underlying buffers, to which the

    /// `IoSlice`s point (but not the `IoSlice`s themselves), are unchanged and

    /// can be reused.

    ///

    /// # Examples

    ///

    /// ```

    /// # futures::executor::block_on(async {

    /// use futures::io::AsyncWriteExt;

    /// use futures_util::io::Cursor;

    /// use std::io::IoSlice;

    ///

    /// let mut writer = Cursor::new(Vec::new());

    /// let bufs = &mut [

    ///     IoSlice::new(&[1]),

    ///     IoSlice::new(&[2, 3]),

    ///     IoSlice::new(&[4, 5, 6]),

    /// ];

    ///

    /// writer.write_all_vectored(bufs).await?;

    /// // Note: the contents of `bufs` is now unspecified, see the Notes section.

    ///

    /// assert_eq!(writer.into_inner(), &[1, 2, 3, 4, 5, 6]);

    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();

    /// ```

    #[cfg(feature = "write-all-vectored")]

    fn write_all_vectored<'a>(

        &'a mut self,

        bufs: &'a mut [IoSlice<'a>],

    ) -> WriteAllVectored<'a, Self>

    where

        Self: Unpin,

    {

        assert_future::<Result<()>, _>(WriteAllVectored::new(self, bufs))

    }

    /// Wraps an [`AsyncWrite`] in a compatibility wrapper that allows it to be

    /// used as a futures 0.1 / tokio-io 0.1 `AsyncWrite`.

    /// Requires the `io-compat` feature to enable.

    #[cfg(feature = "io-compat")]

    #[cfg_attr(docsrs, doc(cfg(feature = "io-compat")))]

    fn compat_write(self) -> Compat<Self>

    where

        Self: Sized + Unpin,

    {

        Compat::new(self)

    }

    /// Allow using an [`AsyncWrite`] as a [`Sink`](futures_sink::Sink)`<Item: AsRef<[u8]>>`.

    ///

    /// This adapter produces a sink that will write each value passed to it

    /// into the underlying writer.

    ///

    /// Note that this function consumes the given writer, returning a wrapped

    /// version.

    ///

    /// # Examples

    ///

    /// ```

    /// # futures::executor::block_on(async {

    /// use futures::io::AsyncWriteExt;

    /// use futures::stream::{self, StreamExt};

    ///

    /// let stream = stream::iter(vec![Ok([1, 2, 3]), Ok([4, 5, 6])]);

    ///

    /// let mut writer = vec![];

    ///

    /// stream.forward((&mut writer).into_sink()).await?;

    ///

    /// assert_eq!(writer, vec![1, 2, 3, 4, 5, 6]);

    /// # Ok::<(), Box<dyn std::error::Error>>(())

    /// # })?;

    /// # Ok::<(), Box<dyn std::error::Error>>(())

    /// ```

    #[cfg(feature = "sink")]

    #[cfg_attr(docsrs, doc(cfg(feature = "sink")))]

    fn into_sink<Item: AsRef<[u8]>>(self) -> IntoSink<Self, Item>

    where

        Self: Sized,

    {

        crate::sink::assert_sink::<Item, Error, _>(IntoSink::new(self))

    }

}

impl<W: AsyncWrite + ?Sized> AsyncWriteExt for W {}

/// An extension trait which adds utility methods to `AsyncSeek` types.

pub trait AsyncSeekExt: AsyncSeek {

    /// Creates a future which will seek an IO object, and then yield the

    /// new position in the object and the object itself.

    ///

    /// In the case of an error the buffer and the object will be discarded, with

    /// the error yielded.

    fn seek(&mut self, pos: SeekFrom) -> Seek<'_, Self>

    where

        Self: Unpin,

    {

        assert_future::<Result<u64>, _>(Seek::new(self, pos))

    }

    /// Creates a future which will return the current seek position from the

    /// start of the stream.

    ///

    /// This is equivalent to `self.seek(SeekFrom::Current(0))`.

    fn stream_position(&mut self) -> Seek<'_, Self>

    where

        Self: Unpin,

    {

        self.seek(SeekFrom::Current(0))

    }

}

impl<S: AsyncSeek + ?Sized> AsyncSeekExt for S {}

/// An extension trait which adds utility methods to `AsyncBufRead` types.

pub trait AsyncBufReadExt: AsyncBufRead {

    /// Creates a future which will wait for a non-empty buffer to be available from this I/O

    /// object or EOF to be reached.

    ///

    /// This method is the async equivalent to [`BufRead::fill_buf`](std::io::BufRead::fill_buf).

    ///

    /// ```rust

    /// # futures::executor::block_on(async {

    /// use futures::{io::AsyncBufReadExt as _, stream::{iter, TryStreamExt as _}};

    ///

    /// let mut stream = iter(vec![Ok(vec![1, 2, 3]), Ok(vec![4, 5, 6])]).into_async_read();

    ///

    /// assert_eq!(stream.fill_buf().await?, vec![1, 2, 3]);

    /// stream.consume_unpin(2);

    ///

    /// assert_eq!(stream.fill_buf().await?, vec![3]);

    /// stream.consume_unpin(1);

    ///

    /// assert_eq!(stream.fill_buf().await?, vec![4, 5, 6]);

    /// stream.consume_unpin(3);

    ///

    /// assert_eq!(stream.fill_buf().await?, vec![]);

    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();

    /// ```

    fn fill_buf(&mut self) -> FillBuf<'_, Self>

    where

        Self: Unpin,

    {

        assert_future::<Result<&[u8]>, _>(FillBuf::new(self))

    }

    /// A convenience for calling [`AsyncBufRead::consume`] on [`Unpin`] IO types.

    ///

    /// ```rust

    /// # futures::executor::block_on(async {

    /// use futures::{io::AsyncBufReadExt as _, stream::{iter, TryStreamExt as _}};

    ///

    /// let mut stream = iter(vec![Ok(vec![1, 2, 3])]).into_async_read();

    ///

    /// assert_eq!(stream.fill_buf().await?, vec![1, 2, 3]);

    /// stream.consume_unpin(2);

    ///

    /// assert_eq!(stream.fill_buf().await?, vec![3]);

    /// stream.consume_unpin(1);

    ///

    /// assert_eq!(stream.fill_buf().await?, vec![]);

    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();

    /// ```

    fn consume_unpin(&mut self, amt: usize)

    where

        Self: Unpin,

    {

        Pin::new(self).consume(amt)

    }

    /// Creates a future which will read all the bytes associated with this I/O

    /// object into `buf` until the delimiter `byte` or EOF is reached.

    /// This method is the async equivalent to [`BufRead::read_until`](std::io::BufRead::read_until).

    ///

    /// This function will read bytes from the underlying stream until the

    /// delimiter or EOF is found. Once found, all bytes up to, and including,

    /// the delimiter (if found) will be appended to `buf`.

    ///

    /// The returned future will resolve to the number of bytes read once the read

    /// operation is completed.

    ///

    /// In the case of an error the buffer and the object will be discarded, with

    /// the error yielded.

    ///

    /// # Examples

    ///

    /// ```

    /// # futures::executor::block_on(async {

    /// use futures::io::{AsyncBufReadExt, Cursor};

    ///

    /// let mut cursor = Cursor::new(b"lorem-ipsum");

    /// let mut buf = vec![];

    ///

    /// // cursor is at 'l'

    /// let num_bytes = cursor.read_until(b'-', &mut buf).await?;

    /// assert_eq!(num_bytes, 6);

    /// assert_eq!(buf, b"lorem-");

    /// buf.clear();

    ///

    /// // cursor is at 'i'

    /// let num_bytes = cursor.read_until(b'-', &mut buf).await?;

    /// assert_eq!(num_bytes, 5);

    /// assert_eq!(buf, b"ipsum");

    /// buf.clear();

    ///

    /// // cursor is at EOF

    /// let num_bytes = cursor.read_until(b'-', &mut buf).await?;

    /// assert_eq!(num_bytes, 0);

    /// assert_eq!(buf, b"");

    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();

    /// ```

    fn read_until<'a>(&'a mut self, byte: u8, buf: &'a mut Vec<u8>) -> ReadUntil<'a, Self>

    where

        Self: Unpin,

    {

        assert_future::<Result<usize>, _>(ReadUntil::new(self, byte, buf))

    }

    /// Creates a future which will read all the bytes associated with this I/O

    /// object into `buf` until a newline (the 0xA byte) or EOF is reached,

    /// This method is the async equivalent to [`BufRead::read_line`](std::io::BufRead::read_line).

    ///

    /// This function will read bytes from the underlying stream until the

    /// newline delimiter (the 0xA byte) or EOF is found. Once found, all bytes

    /// up to, and including, the delimiter (if found) will be appended to

    /// `buf`.

    ///

    /// The returned future will resolve to the number of bytes read once the read

    /// operation is completed.

    ///

    /// In the case of an error the buffer and the object will be discarded, with

    /// the error yielded.

    ///

    /// # Errors

    ///

    /// This function has the same error semantics as [`read_until`] and will

    /// also return an error if the read bytes are not valid UTF-8. If an I/O

    /// error is encountered then `buf` may contain some bytes already read in

    /// the event that all data read so far was valid UTF-8.

    ///

    /// [`read_until`]: AsyncBufReadExt::read_until

    ///

    /// # Examples

    ///

    /// ```

    /// # futures::executor::block_on(async {

    /// use futures::io::{AsyncBufReadExt, Cursor};

    ///

    /// let mut cursor = Cursor::new(b"foo\nbar");

    /// let mut buf = String::new();

    ///

    /// // cursor is at 'f'

    /// let num_bytes = cursor.read_line(&mut buf).await?;

    /// assert_eq!(num_bytes, 4);

    /// assert_eq!(buf, "foo\n");

    /// buf.clear();

    ///

    /// // cursor is at 'b'

    /// let num_bytes = cursor.read_line(&mut buf).await?;

    /// assert_eq!(num_bytes, 3);

    /// assert_eq!(buf, "bar");

    /// buf.clear();

    ///

    /// // cursor is at EOF

    /// let num_bytes = cursor.read_line(&mut buf).await?;

    /// assert_eq!(num_bytes, 0);

    /// assert_eq!(buf, "");

    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();

    /// ```

    fn read_line<'a>(&'a mut self, buf: &'a mut String) -> ReadLine<'a, Self>

    where

        Self: Unpin,

    {

        assert_future::<Result<usize>, _>(ReadLine::new(self, buf))

    }

    /// Returns a stream over the lines of this reader.

    /// This method is the async equivalent to [`BufRead::lines`](std::io::BufRead::lines).

    ///

    /// The stream returned from this function will yield instances of

    /// [`io::Result`]`<`[`String`]`>`. Each string returned will *not* have a newline

    /// byte (the 0xA byte) or CRLF (0xD, 0xA bytes) at the end.

    ///

    /// [`io::Result`]: std::io::Result

    /// [`String`]: String

    ///

    /// # Errors

    ///

    /// Each line of the stream has the same error semantics as [`AsyncBufReadExt::read_line`].

    ///

    /// [`AsyncBufReadExt::read_line`]: AsyncBufReadExt::read_line

    ///

    /// # Examples

    ///

    /// ```

    /// # futures::executor::block_on(async {

    /// use futures::io::{AsyncBufReadExt, Cursor};

    /// use futures::stream::StreamExt;

    ///

    /// let cursor = Cursor::new(b"lorem\nipsum\r\ndolor");

    ///

    /// let mut lines_stream = cursor.lines().map(|l| l.unwrap());

    /// assert_eq!(lines_stream.next().await, Some(String::from("lorem")));

    /// assert_eq!(lines_stream.next().await, Some(String::from("ipsum")));

    /// assert_eq!(lines_stream.next().await, Some(String::from("dolor")));

    /// assert_eq!(lines_stream.next().await, None);

    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();

    /// ```

    fn lines(self) -> Lines<Self>

    where

        Self: Sized,

    {

        assert_stream::<Result<String>, _>(Lines::new(self))

    }

}

impl<R: AsyncBufRead + ?Sized> AsyncBufReadExt for R {}

// Just a helper function to ensure the reader we're returning all have the

// right implementations.

pub(crate) fn assert_read<R>(reader: R) -> R

where

    R: AsyncRead,

{

    reader

}

// Just a helper function to ensure the writer we're returning all have the

// right implementations.

pub(crate) fn assert_write<W>(writer: W) -> W

where

    W: AsyncWrite,

{

    writer

}