Trait futures_util::io::AsyncReadExt

pub trait AsyncReadExt: AsyncRead {
    fn chain<R>(self, next: R) -> Chain<Self, R>
    where
        Self: Sized,
        R: AsyncRead,
    { ... }
    fn read<'a>(&'a mut self, buf: &'a mut [u8]) -> Read<'a, Self>
    where
        Self: Unpin,
    { ... }
    fn read_vectored<'a>(
        &'a mut self, 
        bufs: &'a mut [IoSliceMut<'a>]
    ) -> ReadVectored<'a, Self>
    where
        Self: Unpin,
    { ... }
    fn read_exact<'a>(&'a mut self, buf: &'a mut [u8]) -> ReadExact<'a, Self>
    where
        Self: Unpin,
    { ... }
    fn read_to_end<'a>(
        &'a mut self, 
        buf: &'a mut Vec<u8>
    ) -> ReadToEnd<'a, Self>
    where
        Self: Unpin,
    { ... }
    fn read_to_string<'a>(
        &'a mut self, 
        buf: &'a mut String
    ) -> ReadToString<'a, Self>
    where
        Self: Unpin,
    { ... }
    fn split(self) -> (ReadHalf<Self>, WriteHalf<Self>)
    where
        Self: AsyncWrite + Sized,
    { ... }
    fn take(self, limit: u64) -> Take<Self>
    where
        Self: Sized,
    { ... }
}

An extension trait which adds utility methods to AsyncRead types.

Provided methods

fn chain<R>(self, next: R) -> Chain<Self, R> where
    Self: Sized,
    R: 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

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]);

fn read<'a>(&'a mut self, buf: &'a mut [u8]) -> Read<'a, Self> where
    Self: Unpin, 

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

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]);

fn read_vectored<'a>(
    &'a mut self,
    bufs: &'a mut [IoSliceMut<'a>]
) -> ReadVectored<'a, Self> where
    Self: Unpin, 

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_exact<'a>(&'a mut self, buf: &'a mut [u8]) -> ReadExact<'a, Self> where
    Self: Unpin, 

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

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]);

EOF is hit before buf is filled

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_to_end<'a>(&'a mut self, buf: &'a mut Vec<u8>) -> ReadToEnd<'a, Self> where
    Self: Unpin, 

Creates a future which will read all the bytes from this AsyncRead.

On success the total number of bytes read is returned.

Examples

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]);

fn read_to_string<'a>(
    &'a mut self,
    buf: &'a mut String
) -> ReadToString<'a, Self> where
    Self: Unpin, 

Creates a future which will read all the bytes from this AsyncRead.

On success the total number of bytes read is returned.

Examples

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"));

fn split(self) -> (ReadHalf<Self>, WriteHalf<Self>) where
    Self: AsyncWrite + Sized, 

Helper method for splitting this read/write object into two halves.

The two halves returned implement the AsyncRead and AsyncWrite traits, respectively.

Examples

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]);

fn take(self, limit: u64) -> Take<Self> where
    Self: Sized, 

Creates an AsyncRead adapter which will read at most limit bytes from the underlying reader.

Examples

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");

Implementors

impl<R: AsyncRead + ?Sized> AsyncReadExt for R