[−][src]Trait async_std::io::Read

pub trait Read {
    fn read<'a>(
        &'a mut self, 
        buf: &'a mut [u8]
    ) -> ImplFuture<'a, Result<usize>>
    where
        Self: Unpin;

    fn read_vectored<'a>(
        &'a mut self, 
        bufs: &'a mut [IoSliceMut<'a>]
    ) -> ImplFuture<'a, Result<usize>>
    where
        Self: Unpin,
    { ... }

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

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

    fn read_exact<'a>(
        &'a mut self, 
        buf: &'a mut [u8]
    ) -> ImplFuture<'a, Result<()>>
    where
        Self: Unpin,
    { ... }
}

Allows reading from a byte stream.

This trait is an async version of std::io::Read.

While it is currently not possible to implement this trait directly, it gets implemented automatically for all types that implement futures::io::AsyncRead.

Required methods

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

Reads some bytes from the byte stream.

Returns the number of bytes read from the start of the buffer.

If the return value is Ok(n), then it must be guaranteed that 0 <= n <= buf.len(). A nonzero n value indicates that the buffer has been filled in with n bytes of data. If n is 0, then it can indicate one of two scenarios:

  1. This reader has reached its "end of file" and will likely no longer be able to produce bytes. Note that this does not mean that the reader will always no longer be able to produce bytes.
  2. The buffer specified was 0 bytes in length.

Examples

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

let mut f = File::open("a.txt").await?;

let mut buf = vec![0; 1024];
let n = f.read(&mut buf).await?;
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Provided methods

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

Like read, except that it reads into a slice of buffers.

Data is copied to fill each buffer in order, with the final buffer written to possibly being only partially filled. This method must behave as a single call to read with the buffers concatenated would.

The default implementation calls read with either the first nonempty buffer provided, or an empty one if none exists.

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

Reads all bytes from the byte stream.

All bytes read from this stream will be appended to the specified buffer buf. This function will continuously call read to append more data to buf until read returns either Ok(0) or an error.

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

Examples

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

let mut f = File::open("a.txt").await?;

let mut buf = Vec::new();
f.read_to_end(&mut buf).await?;

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

Reads all bytes from the byte stream and appends them into a string.

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

If the data in this stream is not valid UTF-8 then an error will be returned and buf will be left unmodified.

Examples

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

let mut f = File::open("a.txt").await?;

let mut buf = String::new();
f.read_to_string(&mut buf).await?;

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

Reads the exact number of bytes required to fill buf.

This function reads as many bytes as necessary to completely fill the specified buffer buf.

No guarantees are provided about the contents of buf when this function is called, implementations cannot rely on any property of the contents of buf being true. It is recommended that implementations only write data to buf instead of reading its contents.

If this function encounters an "end of file" before completely filling the buffer, it returns an error of the kind ErrorKind::UnexpectedEof. The contents of buf are unspecified in this case.

If any other read error is encountered then this function immediately returns. The contents of buf are unspecified in this case.

If this function returns an error, it is unspecified how many bytes it has read, but it will never read more than would be necessary to completely fill the buffer.

Examples

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

let mut f = File::open("a.txt").await?;

let mut buf = vec![0; 10];
f.read_exact(&mut buf).await?;
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Implementors

impl<T: AsyncRead + Unpin + ?Sized> Read for T[src]

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