[−][src]Trait async_std::io::BufRead

pub trait BufRead {
    fn poll_fill_buf(
        self: Pin<&mut Self>, 
        cx: &mut Context
    ) -> Poll<Result<&[u8]>>;

    fn consume(self: Pin<&mut Self>, amt: usize);

    fn read_until<'a>(
        &'a mut self, 
        byte: u8, 
        buf: &'a mut Vec<u8>
    ) -> ImplFuture<usize>
    where
        Self: Unpin,
    { ... }

    fn read_line<'a>(
        &'a mut self, 
        buf: &'a mut String
    ) -> ImplFuture<Result<usize>>
    where
        Self: Unpin,
    { ... }

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

    fn split(self, byte: u8) -> Split<Self>
    where
        Self: Sized,
    { ... }
}

Allows reading from a buffered byte stream.

This trait is a re-export of futures::io::AsyncBufRead and is an async version of std::io::BufRead.

The provided methods do not really exist in the trait itself, but they become available when BufReadExt from the prelude is imported:

use async_std::prelude::*;

Required methods

fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Result<&[u8]>>

Returns the contents of the internal buffer, filling it with more data from the inner reader if it is empty.

This function is a lower-level call. It needs to be paired with the consume method to function properly. When calling this method, none of the contents will be "read" in the sense that later calling read may return the same contents. As such, consume must be called with the number of bytes that are consumed from this buffer to ensure that the bytes are never returned twice.

An empty buffer returned indicates that the stream has reached EOF.

fn consume(self: Pin<&mut Self>, amt: usize)

Tells this buffer that amt bytes have been consumed from the buffer, so they should no longer be returned in calls to read.

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Provided methods

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

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

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.

Examples

use async_std::fs::File;
use async_std::io::BufReader;
use async_std::prelude::*;

let mut file = BufReader::new(File::open("a.txt").await?);

let mut buf = Vec::with_capacity(1024);
let n = file.read_until(b'\n', &mut buf).await?;

Multiple successful calls to read_until append all bytes up to and including to buf:

use async_std::io::BufReader;
use async_std::prelude::*;

let from: &[u8] = b"append\nexample\n";
let mut reader = BufReader::new(from);
let mut buf = vec![];

let mut size = reader.read_until(b'\n', &mut buf).await?;
assert_eq!(size, 7);
assert_eq!(buf, b"append\n");

size += reader.read_until(b'\n', &mut buf).await?;
assert_eq!(size, from.len());

assert_eq!(buf, from);

fn read_line<'a>(&'a mut self, buf: &'a mut String) -> ImplFuture<Result<usize>> where
    Self: Unpin, 

Reads all bytes and appends them into buf until a newline (the 0xA byte) is reached.

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

use async_std::fs::File;
use async_std::io::BufReader;
use async_std::prelude::*;

let mut file = BufReader::new(File::open("a.txt").await?);

let mut buf = String::new();
file.read_line(&mut buf).await?;

fn lines(self) -> Lines<Self> where
    Self: Unpin + Sized, 

Returns a stream over the lines of this byte stream.

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.

Examples

use async_std::fs::File;
use async_std::io::BufReader;
use async_std::prelude::*;

let file = File::open("a.txt").await?;
let mut lines = BufReader::new(file).lines();
let mut count = 0;

while let Some(line) = lines.next().await {
    line?;
    count += 1;
}

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

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

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

This function will yield errors whenever read_until would have also yielded an error.

Examples

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

use async_std::prelude::*;
use async_std::io;

let cursor = io::Cursor::new(b"lorem-ipsum-dolor");

let mut split_iter = cursor.split(b'-').map(|l| l.unwrap());
assert_eq!(split_iter.next().await, Some(b"lorem".to_vec()));
assert_eq!(split_iter.next().await, Some(b"ipsum".to_vec()));
assert_eq!(split_iter.next().await, Some(b"dolor".to_vec()));
assert_eq!(split_iter.next().await, None);
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Implementations on Foreign Types

impl<T: BufRead + Unpin + ?Sized> BufRead for Box<T>[src]

impl<'_, T: BufRead + Unpin + ?Sized> BufRead for &'_ mut T[src]

impl<'_> BufRead for &'_ [u8][src]

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Implementors

impl BufRead for Empty[src]

impl<P> BufRead for Pin<P> where
    P: DerefMut + Unpin,
    <P as Deref>::Target: BufRead, [src]

impl<R: Read> BufRead for BufReader<R>[src]

impl<T> BufRead for Cursor<T> where
    T: AsRef<[u8]> + Unpin, [src]

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