impl ReadHalf<'_>

fn poll_peek(self: &mut Self, cx: &mut Context<'_>, buf: &mut ReadBuf<'_>) -> Poll<Result<usize>>

Attempts to receive data on the socket, without removing that data from the queue, registering the current task for wakeup if data is not yet available.

Note that on multiple calls to poll_peek or poll_read, only the Waker from the Context passed to the most recent call is scheduled to receive a wakeup.

See the TcpStream::poll_peek level documentation for more details.

Examples

use tokio::io::{self, ReadBuf};
use tokio::net::TcpStream;

use std::future::poll_fn;

#[tokio::main]
async fn main() -> io::Result<()> {
    let mut stream = TcpStream::connect("127.0.0.1:8000").await?;
    let (mut read_half, _) = stream.split();
    let mut buf = [0; 10];
    let mut buf = ReadBuf::new(&mut buf);

    poll_fn(|cx| {
        read_half.poll_peek(cx, &mut buf)
    }).await?;

    Ok(())
}

async fn peek(self: &mut Self, buf: &mut [u8]) -> Result<usize>

Receives data on the socket from the remote address to which it is connected, without removing that data from the queue. On success, returns the number of bytes peeked.

See the TcpStream::peek level documentation for more details.

Examples

use tokio::net::TcpStream;
use tokio::io::AsyncReadExt;
use std::error::Error;

#[tokio::main]
async fn main() -> Result<(), Box<dyn Error>> {
    // Connect to a peer
    let mut stream = TcpStream::connect("127.0.0.1:8080").await?;
    let (mut read_half, _) = stream.split();

    let mut b1 = [0; 10];
    let mut b2 = [0; 10];

    // Peek at the data
    let n = read_half.peek(&mut b1).await?;

    // Read the data
    assert_eq!(n, read_half.read(&mut b2[..n]).await?);
    assert_eq!(&b1[..n], &b2[..n]);

    Ok(())
}

The read method is defined on the AsyncReadExt trait.

async fn ready(self: &Self, interest: Interest) -> Result<Ready>

Waits for any of the requested ready states.

This function is usually paired with try_read(). It can be used instead of readable() to check the returned ready set for Ready::READABLE and Ready::READ_CLOSED events.

The function may complete without the socket being ready. This is a false-positive and attempting an operation will return with io::ErrorKind::WouldBlock. The function can also return with an empty Ready set, so you should always check the returned value and possibly wait again if the requested states are not set.

This function is equivalent to TcpStream::ready.

Cancel safety

This method is cancel safe. Once a readiness event occurs, the method will continue to return immediately until the readiness event is consumed by an attempt to read or write that fails with WouldBlock or Poll::Pending.

async fn readable(self: &Self) -> Result<()>

Waits for the socket to become readable.

This function is equivalent to ready(Interest::READABLE) and is usually paired with try_read().

This function is also equivalent to TcpStream::ready.

Cancel safety

This method is cancel safe. Once a readiness event occurs, the method will continue to return immediately until the readiness event is consumed by an attempt to read that fails with WouldBlock or Poll::Pending.

fn try_read(self: &Self, buf: &mut [u8]) -> Result<usize>

Tries to read data from the stream into the provided buffer, returning how many bytes were read.

Receives any pending data from the socket but does not wait for new data to arrive. On success, returns the number of bytes read. Because try_read() is non-blocking, the buffer does not have to be stored by the async task and can exist entirely on the stack.

Usually, readable() or ready() is used with this function.

Return

If data is successfully read, Ok(n) is returned, where n is the number of bytes read. If n is 0, then it can indicate one of two scenarios:

1. The stream's read half is closed and will no longer yield data.
2. The specified buffer was 0 bytes in length.

If the stream is not ready to read data, Err(io::ErrorKind::WouldBlock) is returned.

fn try_read_vectored(self: &Self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize>

Tries to read data from the stream into the provided buffers, returning how many bytes were read.

Data is copied to fill each buffer in order, with the final buffer written to possibly being only partially filled. This method behaves equivalently to a single call to try_read() with concatenated buffers.

Receives any pending data from the socket but does not wait for new data to arrive. On success, returns the number of bytes read. Because try_read_vectored() is non-blocking, the buffer does not have to be stored by the async task and can exist entirely on the stack.

Usually, readable() or ready() is used with this function.

Return

If data is successfully read, Ok(n) is returned, where n is the number of bytes read. Ok(0) indicates the stream's read half is closed and will no longer yield data. If the stream is not ready to read data Err(io::ErrorKind::WouldBlock) is returned.

fn try_read_buf<B: BufMut>(self: &Self, buf: &mut B) -> Result<usize>

Tries to read data from the stream into the provided buffer, advancing the buffer's internal cursor, returning how many bytes were read.

Receives any pending data from the socket but does not wait for new data to arrive. On success, returns the number of bytes read. Because try_read_buf() is non-blocking, the buffer does not have to be stored by the async task and can exist entirely on the stack.

Usually, readable() or ready() is used with this function.

Return

If data is successfully read, Ok(n) is returned, where n is the number of bytes read. Ok(0) indicates the stream's read half is closed and will no longer yield data. If the stream is not ready to read data Err(io::ErrorKind::WouldBlock) is returned.

fn peer_addr(self: &Self) -> Result<SocketAddr>

Returns the remote address that this stream is connected to.

fn local_addr(self: &Self) -> Result<SocketAddr>

Returns the local address that this stream is bound to.

impl AsRef for ReadHalf<'_>

fn as_ref(self: &Self) -> &TcpStream

impl AsyncRead for ReadHalf<'_>

fn poll_read(self: Pin<&mut Self>, cx: &mut Context<'_>, buf: &mut ReadBuf<'_>) -> Poll<Result<()>>

impl<'a> Debug for ReadHalf<'a>

fn fmt(self: &Self, f: &mut Formatter<'_>) -> Result

impl<'a> Freeze for ReadHalf<'a>

impl<'a> RefUnwindSafe for ReadHalf<'a>

impl<'a> Send for ReadHalf<'a>

impl<'a> Sync for ReadHalf<'a>

impl<'a> Unpin for ReadHalf<'a>

impl<'a> UnsafeUnpin for ReadHalf<'a>

impl<'a> UnwindSafe for ReadHalf<'a>

impl<R> AsyncReadExt for ReadHalf<'a>

impl<T> Any for ReadHalf<'a>

fn type_id(self: &Self) -> TypeId

impl<T> Borrow for ReadHalf<'a>

fn borrow(self: &Self) -> &T

impl<T> BorrowMut for ReadHalf<'a>

fn borrow_mut(self: &mut Self) -> &mut T

impl<T> From for ReadHalf<'a>

fn from(t: T) -> T

Returns the argument unchanged.

impl<T, U> Into for ReadHalf<'a>

fn into(self: Self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of [From]<T> for U chooses to do.

impl<T, U> TryFrom for ReadHalf<'a>

fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

impl<T, U> TryInto for ReadHalf<'a>

fn try_into(self: Self) -> Result<U, <U as TryFrom<T>>::Error>