Struct tokio::net::TcpStream

pub struct TcpStream { /* fields omitted */ }

This is supported on crate feature net only.

A TCP stream between a local and a remote socket.

A TCP stream can either be created by connecting to an endpoint, via the connect method, or by accepting a connection from a listener. A TCP stream can also be created via the TcpSocket type.

Reading and writing to a TcpStream is usually done using the convenience methods found on the AsyncReadExt and AsyncWriteExt traits.

Examples

use tokio::net::TcpStream;
use tokio::io::AsyncWriteExt;
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?;

    // Write some data.
    stream.write_all(b"hello world!").await?;

    Ok(())
}

The write_all method is defined on the AsyncWriteExt trait.

To shut down the stream in the write direction, you can call the shutdown() method. This will cause the other peer to receive a read of length 0, indicating that no more data will be sent. This only closes the stream in one direction.

Implementations

impl TcpStream

pub async fn connect<A: ToSocketAddrs>(addr: A) -> Result<TcpStream>

Opens a TCP connection to a remote host.

addr is an address of the remote host. Anything which implements the ToSocketAddrs trait can be supplied as the address. If addr yields multiple addresses, connect will be attempted with each of the addresses until a connection is successful. If none of the addresses result in a successful connection, the error returned from the last connection attempt (the last address) is returned.

To configure the socket before connecting, you can use the TcpSocket type.

Examples

use tokio::net::TcpStream;
use tokio::io::AsyncWriteExt;
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?;

    // Write some data.
    stream.write_all(b"hello world!").await?;

    Ok(())
}

The write_all method is defined on the AsyncWriteExt trait.

pub fn from_std(stream: TcpStream) -> Result<TcpStream>

Creates new TcpStream from a std::net::TcpStream.

This function is intended to be used to wrap a TCP stream from the standard library in the Tokio equivalent. The conversion assumes nothing about the underlying stream; it is left up to the user to set it in non-blocking mode.

Examples

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

#[tokio::main]
async fn main() -> Result<(), Box<dyn Error>> {
    let std_stream = std::net::TcpStream::connect("127.0.0.1:34254")?;
    std_stream.set_nonblocking(true)?;
    let stream = TcpStream::from_std(std_stream)?;
    Ok(())
}

Panics

This function panics if thread-local runtime is not set.

The runtime is usually set implicitly when this function is called from a future driven by a tokio runtime, otherwise runtime can be set explicitly with Runtime::enter function.

pub fn into_std(self) -> Result<TcpStream>

Turn a tokio::net::TcpStream into a std::net::TcpStream.

The returned std::net::TcpStream will have nonblocking mode set as true. Use set_nonblocking to change the blocking mode if needed.

Examples

use std::error::Error;
use std::io::Read;
use tokio::net::TcpListener;

#[tokio::main]
async fn main() -> Result<(), Box<dyn Error>> {
    let mut data = [0u8; 12];
    let listener = TcpListener::bind("127.0.0.1:34254").await?;
    let (tokio_tcp_stream, _) = listener.accept().await?;
    let mut std_tcp_stream = tokio_tcp_stream.into_std()?;
    std_tcp_stream.set_nonblocking(false)?;
    std_tcp_stream.read_exact(&mut data)?;
    Ok(())
}

pub fn local_addr(&self) -> Result<SocketAddr>

Returns the local address that this stream is bound to.

Examples

use tokio::net::TcpStream;

let stream = TcpStream::connect("127.0.0.1:8080").await?;

println!("{:?}", stream.local_addr()?);

pub fn peer_addr(&self) -> Result<SocketAddr>

Returns the remote address that this stream is connected to.

Examples

use tokio::net::TcpStream;

let stream = TcpStream::connect("127.0.0.1:8080").await?;

println!("{:?}", stream.peer_addr()?);

pub fn poll_peek(
    &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, poll_read or poll_read_ready, only the Waker from the Context passed to the most recent call is scheduled to receive a wakeup. (However, poll_write retains a second, independent waker.)

Return value

The function returns:

• Poll::Pending if data is not yet available.
• Poll::Ready(Ok(n)) if data is available. n is the number of bytes peeked.
• Poll::Ready(Err(e)) if an error is encountered.

Errors

This function may encounter any standard I/O error except WouldBlock.

Examples

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

use futures::future::poll_fn;

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

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

    Ok(())
}

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

Wait for any of the requested ready states.

This function is usually paired with try_read() or try_write(). It can be used to concurrently read / write to the same socket on a single task without splitting the socket.

Examples

Concurrently read and write to the stream on the same task without splitting.

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

#[tokio::main]
async fn main() -> Result<(), Box<dyn Error>> {
    let stream = TcpStream::connect("127.0.0.1:8080").await?;

    loop {
        let ready = stream.ready(Interest::READABLE | Interest::WRITABLE).await?;

        if ready.is_readable() {
            let mut data = vec![0; 1024];
            // Try to read data, this may still fail with `WouldBlock`
            // if the readiness event is a false positive.
            match stream.try_read(&mut data) {
                Ok(n) => {
                    println!("read {} bytes", n);        
                }
                Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
                    continue;
                }
                Err(e) => {
                    return Err(e.into());
                }
            }

        }

        if ready.is_writable() {
            // Try to write data, this may still fail with `WouldBlock`
            // if the readiness event is a false positive.
            match stream.try_write(b"hello world") {
                Ok(n) => {
                    println!("write {} bytes", n);
                }
                Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
                    continue
                }
                Err(e) => {
                    return Err(e.into());
                }
            }
        }
    }
}

pub async fn readable(&self) -> Result<()>

Wait for the socket to become readable.

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

Examples

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

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

    let mut msg = vec![0; 1024];

    loop {
        // Wait for the socket to be readable
        stream.readable().await?;

        // Try to read data, this may still fail with `WouldBlock`
        // if the readiness event is a false positive.
        match stream.try_read(&mut msg) {
            Ok(n) => {
                msg.truncate(n);
                break;
            }
            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
                continue;
            }
            Err(e) => {
                return Err(e.into());
            }
        }
    }

    println!("GOT = {:?}", msg);
    Ok(())
}

pub fn poll_read_ready(&self, cx: &mut Context<'_>) -> Poll<Result<()>>

Polls for read readiness.

If the tcp stream is not currently ready for reading, this method will store a clone of the Waker from the provided Context. When the tcp stream becomes ready for reading, Waker::wake will be called on the waker.

Note that on multiple calls to poll_read_ready, poll_read or poll_peek, only the Waker from the Context passed to the most recent call is scheduled to receive a wakeup. (However, poll_write_ready retains a second, independent waker.)

This function is intended for cases where creating and pinning a future via readable is not feasible. Where possible, using readable is preferred, as this supports polling from multiple tasks at once.

Return value

The function returns:

• Poll::Pending if the tcp stream is not ready for reading.
• Poll::Ready(Ok(())) if the tcp stream is ready for reading.
• Poll::Ready(Err(e)) if an error is encountered.

Errors

This function may encounter any standard I/O error except WouldBlock.

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

Try 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. 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.

Examples

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

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

    loop {
        // Wait for the socket to be readable
        stream.readable().await?;

        // Creating the buffer **after** the `await` prevents it from
        // being stored in the async task.
        let mut buf = [0; 4096];

        // Try to read data, this may still fail with `WouldBlock`
        // if the readiness event is a false positive.
        match stream.try_read(&mut buf) {
            Ok(0) => break,
            Ok(n) => {
                println!("read {} bytes", n);
            }
            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
                continue;
            }
            Err(e) => {
                return Err(e.into());
            }
        }
    }

    Ok(())
}

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

Try 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.

Examples

use tokio::net::TcpStream;
use std::error::Error;
use std::io::{self, IoSliceMut};

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

    loop {
        // Wait for the socket to be readable
        stream.readable().await?;

        // Creating the buffer **after** the `await` prevents it from
        // being stored in the async task.
        let mut buf_a = [0; 512];
        let mut buf_b = [0; 1024];
        let mut bufs = [
            IoSliceMut::new(&mut buf_a),
            IoSliceMut::new(&mut buf_b),
        ];

        // Try to read data, this may still fail with `WouldBlock`
        // if the readiness event is a false positive.
        match stream.try_read_vectored(&mut bufs) {
            Ok(0) => break,
            Ok(n) => {
                println!("read {} bytes", n);
            }
            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
                continue;
            }
            Err(e) => {
                return Err(e.into());
            }
        }
    }

    Ok(())
}

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

This is supported on crate feature io-util only.

Try 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.

Examples

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

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

    loop {
        // Wait for the socket to be readable
        stream.readable().await?;

        let mut buf = Vec::with_capacity(4096);

        // Try to read data, this may still fail with `WouldBlock`
        // if the readiness event is a false positive.
        match stream.try_read_buf(&mut buf) {
            Ok(0) => break,
            Ok(n) => {
                println!("read {} bytes", n);
            }
            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
                continue;
            }
            Err(e) => {
                return Err(e.into());
            }
        }
    }

    Ok(())
}

pub async fn writable(&self) -> Result<()>

Wait for the socket to become writable.

This function is equivalent to ready(Interest::WRITABLE) and is usually paired with try_write().

Examples

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

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

    loop {
        // Wait for the socket to be writable
        stream.writable().await?;

        // Try to write data, this may still fail with `WouldBlock`
        // if the readiness event is a false positive.
        match stream.try_write(b"hello world") {
            Ok(n) => {
                break;
            }
            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
                continue;
            }
            Err(e) => {
                return Err(e.into());
            }
        }
    }

    Ok(())
}

pub fn poll_write_ready(&self, cx: &mut Context<'_>) -> Poll<Result<()>>

Polls for write readiness.

If the tcp stream is not currently ready for writing, this method will store a clone of the Waker from the provided Context. When the tcp stream becomes ready for writing, Waker::wake will be called on the waker.

Note that on multiple calls to poll_write_ready or poll_write, only the Waker from the Context passed to the most recent call is scheduled to receive a wakeup. (However, poll_read_ready retains a second, independent waker.)

This function is intended for cases where creating and pinning a future via writable is not feasible. Where possible, using writable is preferred, as this supports polling from multiple tasks at once.

Return value

The function returns:

• Poll::Pending if the tcp stream is not ready for writing.
• Poll::Ready(Ok(())) if the tcp stream is ready for writing.
• Poll::Ready(Err(e)) if an error is encountered.

Errors

This function may encounter any standard I/O error except WouldBlock.

pub fn try_write(&self, buf: &[u8]) -> Result<usize>

Try to write a buffer to the stream, returning how many bytes were written.

The function will attempt to write the entire contents of buf, but only part of the buffer may be written.

This function is usually paired with writable().

Return

If data is successfully written, Ok(n) is returned, where n is the number of bytes written. If the stream is not ready to write data, Err(io::ErrorKind::WouldBlock) is returned.

Examples

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

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

    loop {
        // Wait for the socket to be writable
        stream.writable().await?;

        // Try to write data, this may still fail with `WouldBlock`
        // if the readiness event is a false positive.
        match stream.try_write(b"hello world") {
            Ok(n) => {
                break;
            }
            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
                continue;
            }
            Err(e) => {
                return Err(e.into());
            }
        }
    }

    Ok(())
}

pub fn try_write_vectored(&self, bufs: &[IoSlice<'_>]) -> Result<usize>

Try to write several buffers to the stream, returning how many bytes were written.

Data is written from each buffer in order, with the final buffer read from possible being only partially consumed. This method behaves equivalently to a single call to try_write() with concatenated buffers.

This function is usually paired with writable().

Return

If data is successfully written, Ok(n) is returned, where n is the number of bytes written. If the stream is not ready to write data, Err(io::ErrorKind::WouldBlock) is returned.

Examples

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

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

    let bufs = [io::IoSlice::new(b"hello "), io::IoSlice::new(b"world")];

    loop {
        // Wait for the socket to be writable
        stream.writable().await?;

        // Try to write data, this may still fail with `WouldBlock`
        // if the readiness event is a false positive.
        match stream.try_write_vectored(&bufs) {
            Ok(n) => {
                break;
            }
            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
                continue;
            }
            Err(e) => {
                return Err(e.into());
            }
        }
    }

    Ok(())
}

pub async fn peek(&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.

Successive calls return the same data. This is accomplished by passing MSG_PEEK as a flag to the underlying recv system call.

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

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

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

    Ok(())
}

The read method is defined on the AsyncReadExt trait.

pub fn nodelay(&self) -> Result<bool>

Gets the value of the TCP_NODELAY option on this socket.

For more information about this option, see set_nodelay.

Examples

use tokio::net::TcpStream;

let stream = TcpStream::connect("127.0.0.1:8080").await?;

println!("{:?}", stream.nodelay()?);

pub fn set_nodelay(&self, nodelay: bool) -> Result<()>

Sets the value of the TCP_NODELAY option on this socket.

If set, this option disables the Nagle algorithm. This means that segments are always sent as soon as possible, even if there is only a small amount of data. When not set, data is buffered until there is a sufficient amount to send out, thereby avoiding the frequent sending of small packets.

Examples

use tokio::net::TcpStream;

let stream = TcpStream::connect("127.0.0.1:8080").await?;

stream.set_nodelay(true)?;

pub fn linger(&self) -> Result<Option<Duration>>

Reads the linger duration for this socket by getting the SO_LINGER option.

For more information about this option, see set_linger.

Examples

use tokio::net::TcpStream;

let stream = TcpStream::connect("127.0.0.1:8080").await?;

println!("{:?}", stream.linger()?);

pub fn set_linger(&self, dur: Option<Duration>) -> Result<()>

Sets the linger duration of this socket by setting the SO_LINGER option.

This option controls the action taken when a stream has unsent messages and the stream is closed. If SO_LINGER is set, the system shall block the process until it can transmit the data or until the time expires.

If SO_LINGER is not specified, and the stream is closed, the system handles the call in a way that allows the process to continue as quickly as possible.

Examples

use tokio::net::TcpStream;

let stream = TcpStream::connect("127.0.0.1:8080").await?;

stream.set_linger(None)?;

pub fn ttl(&self) -> Result<u32>

Gets the value of the IP_TTL option for this socket.

For more information about this option, see set_ttl.

Examples

use tokio::net::TcpStream;

let stream = TcpStream::connect("127.0.0.1:8080").await?;

println!("{:?}", stream.ttl()?);

pub fn set_ttl(&self, ttl: u32) -> Result<()>

Sets the value for the IP_TTL option on this socket.

This value sets the time-to-live field that is used in every packet sent from this socket.

Examples

use tokio::net::TcpStream;

let stream = TcpStream::connect("127.0.0.1:8080").await?;

stream.set_ttl(123)?;

pub fn split<'a>(&'a mut self) -> (ReadHalf<'a>, WriteHalf<'a>)

Splits a TcpStream into a read half and a write half, which can be used to read and write the stream concurrently.

This method is more efficient than into_split, but the halves cannot be moved into independently spawned tasks.

pub fn into_split(self) -> (OwnedReadHalf, OwnedWriteHalf)

Splits a TcpStream into a read half and a write half, which can be used to read and write the stream concurrently.

Unlike split, the owned halves can be moved to separate tasks, however this comes at the cost of a heap allocation.

Note: Dropping the write half will shut down the write half of the TCP stream. This is equivalent to calling shutdown() on the TcpStream.

Trait Implementations

impl AsRawFd for TcpStream

fn as_raw_fd(&self) -> RawFd

Extracts the raw file descriptor.

impl AsRef<TcpStream> for ReadHalf<'_>

fn as_ref(&self) -> &TcpStream

Performs the conversion.

impl AsRef<TcpStream> for WriteHalf<'_>

fn as_ref(&self) -> &TcpStream

Performs the conversion.

impl AsRef<TcpStream> for OwnedReadHalf

fn as_ref(&self) -> &TcpStream

Performs the conversion.

impl AsRef<TcpStream> for OwnedWriteHalf

fn as_ref(&self) -> &TcpStream

Performs the conversion.

impl AsyncRead for TcpStream

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

Attempts to read from the AsyncRead into buf.

impl AsyncWrite for TcpStream

fn poll_write(
    self: Pin<&mut Self>,
    cx: &mut Context<'_>,
    buf: &[u8]
) -> Poll<Result<usize>>

Attempt to write bytes from buf into the object.

fn poll_write_vectored(
    self: Pin<&mut Self>,
    cx: &mut Context<'_>,
    bufs: &[IoSlice<'_>]
) -> Poll<Result<usize>>

Like poll_write, except that it writes from a slice of buffers.

fn is_write_vectored(&self) -> bool

Determines if this writer has an efficient poll_write_vectored implementation.

fn poll_flush(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Result<()>>

Attempts to flush the object, ensuring that any buffered data reach their destination.

fn poll_shutdown(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Result<()>>

Initiates or attempts to shut down this writer, returning success when the I/O connection has completely shut down.

impl Debug for TcpStream

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

Formats the value using the given formatter.

impl TryFrom<TcpStream> for TcpStream

fn try_from(stream: TcpStream) -> Result<Self, Self::Error>

Consumes stream, returning the tokio I/O object.

This is equivalent to TcpStream::from_std(stream).

type Error = Error

The type returned in the event of a conversion error.