Trait tokio::io::AsyncBufReadExt

pub trait AsyncBufReadExt: AsyncBufRead {
    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 split(self, byte: u8) -> Split<Self>
    where
        Self: Sized + Unpin,
    { ... }
    fn lines(self) -> Lines<Self>
    where
        Self: Sized,
    { ... }
}

An extension trait which adds utility methods to AsyncBufRead types.

Provided methods

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

Reads all bytes into buf until the delimiter byte or EOF is reached.

Equivalent to:

async fn read_until(&mut self, buf: &mut Vec<u8>) -> io::Result<usize>;

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.

If successful, this function will return the total number of bytes read.

Errors

This function will ignore all instances of ErrorKind::Interrupted and will otherwise return any errors returned by fill_buf.

If an I/O error is encountered then all bytes read so far will be present in buf and its length will have been adjusted appropriately.

Examples

std::io::Cursor is a type that implements BufRead. In this example, we use Cursor to read all the bytes in a byte slice in hyphen delimited segments:

use tokio::io::AsyncBufReadExt;

use std::io::Cursor;

#[tokio::main]
async fn main() {
    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
        .expect("reading from cursor won't fail");

    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
        .expect("reading from cursor won't fail");

    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
        .expect("reading from cursor won't fail");
    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, 

Reads all bytes until a newline (the 0xA byte) is reached, and append them to the provided buffer.

Equivalent to:

async fn read_line(&mut self, buf: &mut String) -> io::Result<usize>;

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.

If successful, this function will return the total number of bytes read.

If this function returns Ok(0), the stream has reached EOF.

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

std::io::Cursor is a type that implements AsyncBufRead. In this example, we use Cursor to read all the lines in a byte slice:

use tokio::io::AsyncBufReadExt;

use std::io::Cursor;

#[tokio::main]
async fn main() {
    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
        .expect("reading from cursor won't fail");

    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
        .expect("reading from cursor won't fail");

    assert_eq!(num_bytes, 3);
    assert_eq!(buf, "bar");
    buf.clear();

    // cursor is at EOF
    let num_bytes = cursor.read_line(&mut buf)
        .await
        .expect("reading from cursor won't fail");

    assert_eq!(num_bytes, 0);
    assert_eq!(buf, "");
}

fn split(self, byte: u8) -> Split<Self> where
    Self: Sized + Unpin, 

Returns a stream of the contents of this reader split on the byte byte.

This method is the asynchronous equivalent to BufRead::split.

The stream returned from this function will yield instances of io::Result<Vec<u8>>. Each vector returned will not have the delimiter byte at the end.

Errors

Each item of the stream has the same error semantics as AsyncBufReadExt::read_until.

Examples

use tokio::io::AsyncBufReadExt;

let mut segments = my_buf_read.split(b'f');

while let Some(segment) = segments.next_segment().await? {
    println!("length = {}", segment.len())
}

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

std::io::Cursor is a type that implements BufRead. In this example, we use Cursor to iterate over all the lines in a byte slice.

use tokio::io::AsyncBufReadExt;
use tokio::stream::StreamExt;

use std::io::Cursor;

#[tokio::main]
async fn main() {
    let cursor = Cursor::new(b"lorem\nipsum\r\ndolor");

    let mut lines = cursor.lines().map(|res| res.unwrap());

    assert_eq!(lines.next().await, Some(String::from("lorem")));
    assert_eq!(lines.next().await, Some(String::from("ipsum")));
    assert_eq!(lines.next().await, Some(String::from("dolor")));
    assert_eq!(lines.next().await, None);
}

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Implementors

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

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