Trait futures_util::io::AsyncBufReadExt

source · [−]
pub trait AsyncBufReadExt: AsyncBufRead {
    fn fill_buf(&mut self) -> FillBuf<'_, Self>ⓘNotable traits for FillBuf<'a, R>impl<'a, R> Future for FillBuf<'a, R> where
    R: AsyncBufRead + ?Sized + Unpin,     type Output = Result<&'a [u8]>;
    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>ⓘNotable traits for ReadUntil<'_, R>impl<R: AsyncBufRead + ?Sized + Unpin> Future for ReadUntil<'_, R>    type Output = Result<usize>;
    where
        Self: Unpin,
    { ... }

    fn read_line<'a>(&'a mut self, buf: &'a mut String) -> ReadLine<'a, Self>ⓘNotable traits for ReadLine<'_, R>impl<R: AsyncBufRead + ?Sized + Unpin> Future for ReadLine<'_, R>    type Output = Result<usize>;
    where
        Self: Unpin,
    { ... }

    fn lines(self) -> Lines<Self>
    where
        Self: Sized,
    { ... }
}
Expand description

An extension trait which adds utility methods to AsyncBufRead types.

Provided methods

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![]);

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![]);

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"");

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, "");

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\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);

Implementors