Trait futures_util::io::AsyncBufReadExt

pub trait AsyncBufReadExt: AsyncBufRead {
    // Provided methods
    fn fill_buf(&mut self) -> FillBuf<'_, Self> 
       where Self: Unpin { ... }
    fn consume_unpin(&mut self, amt: usize)
       where Self: Unpin { ... }
    fn read_until<'a>(
        &'a mut self,
        byte: u8,
        buf: &'a mut Vec<u8>
    ) -> ReadUntil<'a, Self> 
       where Self: Unpin { ... }
    fn read_line<'a>(&'a mut self, buf: &'a mut String) -> ReadLine<'a, Self> 
       where Self: Unpin { ... }
    fn lines(self) -> Lines<Self>
       where Self: Sized { ... }
}

An extension trait which adds utility methods to AsyncBufRead types.

Provided Methods

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

where Self: Unpin,

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.

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![]);

fn consume_unpin(&mut self, amt: usize)

where Self: Unpin,

A convenience for calling AsyncBufRead::consume on Unpin IO types.

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![]);

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

where Self: Unpin,

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.

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

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"");

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

where Self: Unpin,

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.

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.

Examples

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, "");

fn lines(self) -> Lines<Self>

where Self: Sized,

Returns a stream over the lines of this reader. This method is the async equivalent to 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.

Errors

Each line of the stream has the same error semantics as AsyncBufReadExt::read_line.

Examples

use futures::io::{AsyncBufReadExt, Cursor};
use futures::stream::StreamExt;

let cursor = Cursor::new(b"lorem\nipsum\xc2\r\ndolor");

let mut lines_stream = cursor.lines().map(|l| l.unwrap_or(String::from("invalid UTF_8")));
assert_eq!(lines_stream.next().await, Some(String::from("lorem")));
assert_eq!(lines_stream.next().await, Some(String::from("invalid UTF_8")));
assert_eq!(lines_stream.next().await, Some(String::from("dolor")));
assert_eq!(lines_stream.next().await, None);

Object Safety

This trait is not object safe.

Implementors

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