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//! 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`
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 copy_buf_abortable;
pub use self::copy_buf_abortable::{copy_buf_abortable, CopyBufAbortable};
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
}