Struct tokio::net::udp::UdpSocket

pub struct UdpSocket {
    io: PollEvented<UdpSocket>,
}

A UDP socket.

UDP is “connectionless”, unlike TCP. Meaning, regardless of what address you’ve bound to, a UdpSocket is free to communicate with many different remotes. In tokio there are basically two main ways to use UdpSocket:

• one to many: bind and use send_to and recv_from to communicate with many different addresses
• one to one: connect and associate with a single address, using send and recv to communicate only with that remote address

This type does not provide a split method, because this functionality can be achieved by instead wrapping the socket in an Arc. Note that you do not need a Mutex to share the UdpSocket — an Arc<UdpSocket> is enough. This is because all of the methods take &self instead of &mut self. Once you have wrapped it in an Arc, you can call .clone() on the Arc<UdpSocket> to get multiple shared handles to the same socket. An example of such usage can be found further down.

Streams

If you need to listen over UDP and produce a Stream, you can look at UdpFramed.

Example: one to many (bind)

Using bind we can create a simple echo server that sends and recv’s with many different clients:

use tokio::net::UdpSocket;
use std::io;

#[tokio::main]
async fn main() -> io::Result<()> {
    let sock = UdpSocket::bind("0.0.0.0:8080").await?;
    let mut buf = [0; 1024];
    loop {
        let (len, addr) = sock.recv_from(&mut buf).await?;
        println!("{:?} bytes received from {:?}", len, addr);

        let len = sock.send_to(&buf[..len], addr).await?;
        println!("{:?} bytes sent", len);
    }
}

Example: one to one (connect)

Or using connect we can echo with a single remote address using send and recv:

use tokio::net::UdpSocket;
use std::io;

#[tokio::main]
async fn main() -> io::Result<()> {
    let sock = UdpSocket::bind("0.0.0.0:8080").await?;

    let remote_addr = "127.0.0.1:59611";
    sock.connect(remote_addr).await?;
    let mut buf = [0; 1024];
    loop {
        let len = sock.recv(&mut buf).await?;
        println!("{:?} bytes received from {:?}", len, remote_addr);

        let len = sock.send(&buf[..len]).await?;
        println!("{:?} bytes sent", len);
    }
}

Example: Splitting with Arc

Because send_to and recv_from take &self. It’s perfectly alright to use an Arc<UdpSocket> and share the references to multiple tasks. Here is a similar “echo” example that supports concurrent sending/receiving:

use tokio::{net::UdpSocket, sync::mpsc};
use std::{io, net::SocketAddr, sync::Arc};

#[tokio::main]
async fn main() -> io::Result<()> {
    let sock = UdpSocket::bind("0.0.0.0:8080".parse::<SocketAddr>().unwrap()).await?;
    let r = Arc::new(sock);
    let s = r.clone();
    let (tx, mut rx) = mpsc::channel::<(Vec<u8>, SocketAddr)>(1_000);

    tokio::spawn(async move {
        while let Some((bytes, addr)) = rx.recv().await {
            let len = s.send_to(&bytes, &addr).await.unwrap();
            println!("{:?} bytes sent", len);
        }
    });

    let mut buf = [0; 1024];
    loop {
        let (len, addr) = r.recv_from(&mut buf).await?;
        println!("{:?} bytes received from {:?}", len, addr);
        tx.send((buf[..len].to_vec(), addr)).await.unwrap();
    }
}

Fields

io: PollEvented<UdpSocket>

Implementations

impl UdpSocket

pub async fn bind<A: ToSocketAddrs>(addr: A) -> Result<UdpSocket>

This function will create a new UDP socket and attempt to bind it to the addr provided.

Binding with a port number of 0 will request that the OS assigns a port to this listener. The port allocated can be queried via the local_addr method.

Example

use tokio::net::UdpSocket;
use std::io;

#[tokio::main]
async fn main() -> io::Result<()> {
    let sock = UdpSocket::bind("0.0.0.0:8080").await?;
    // use `sock`
    Ok(())
}

fn bind_addr(addr: SocketAddr) -> Result<UdpSocket>

fn new(socket: UdpSocket) -> Result<UdpSocket>

pub fn from_std(socket: UdpSocket) -> Result<UdpSocket>

Creates new UdpSocket from a previously bound std::net::UdpSocket.

This function is intended to be used to wrap a UDP socket from the standard library in the Tokio equivalent.

This can be used in conjunction with socket2’s Socket interface to configure a socket before it’s handed off, such as setting options like reuse_address or binding to multiple addresses.

Notes

The caller is responsible for ensuring that the socket is in non-blocking mode. Otherwise all I/O operations on the socket will block the thread, which will cause unexpected behavior. Non-blocking mode can be set using set_nonblocking.

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.

Example

use tokio::net::UdpSocket;

let addr = "0.0.0.0:8080".parse::<SocketAddr>().unwrap();
let std_sock = std::net::UdpSocket::bind(addr)?;
std_sock.set_nonblocking(true)?;
let sock = UdpSocket::from_std(std_sock)?;
// use `sock`

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

Turns a tokio::net::UdpSocket into a std::net::UdpSocket.

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

Examples

use std::error::Error;

#[tokio::main]
async fn main() -> Result<(), Box<dyn Error>> {
    let tokio_socket = tokio::net::UdpSocket::bind("127.0.0.1:0").await?;
    let std_socket = tokio_socket.into_std()?;
    std_socket.set_nonblocking(false)?;
    Ok(())
}

fn as_socket(&self) -> SockRef<'_>

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

Returns the local address that this socket is bound to.

Example

use tokio::net::UdpSocket;

let addr = "0.0.0.0:8080".parse::<SocketAddr>().unwrap();
let sock = UdpSocket::bind(addr).await?;
// the address the socket is bound to
let local_addr = sock.local_addr()?;

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

Returns the socket address of the remote peer this socket was connected to.

Example

use tokio::net::UdpSocket;

let addr = "0.0.0.0:8080".parse::<SocketAddr>().unwrap();
let peer = "127.0.0.1:11100".parse::<SocketAddr>().unwrap();
let sock = UdpSocket::bind(addr).await?;
sock.connect(peer).await?;
assert_eq!(peer, sock.peer_addr()?);

pub async fn connect<A: ToSocketAddrs>(&self, addr: A) -> Result<()>

Connects the UDP socket setting the default destination for send() and limiting packets that are read via recv from the address specified in addr.

Example

use tokio::net::UdpSocket;

let sock = UdpSocket::bind("0.0.0.0:8080".parse::<SocketAddr>().unwrap()).await?;

let remote_addr = "127.0.0.1:59600".parse::<SocketAddr>().unwrap();
sock.connect(remote_addr).await?;
let mut buf = [0u8; 32];
// recv from remote_addr
let len = sock.recv(&mut buf).await?;
// send to remote_addr
let _len = sock.send(&buf[..len]).await?;

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

Waits for any of the requested ready states.

This function is usually paired with try_recv() or try_send(). It can be used to concurrently recv / send to the same socket on a single task without splitting the socket.

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.

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.

Examples

Concurrently receive from and send to the socket on the same task without splitting.

use tokio::io::{self, Interest};
use tokio::net::UdpSocket;

#[tokio::main]
async fn main() -> io::Result<()> {
    let socket = UdpSocket::bind("127.0.0.1:8080").await?;
    socket.connect("127.0.0.1:8081").await?;

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

        if ready.is_readable() {
            // The buffer is **not** included in the async task and will only exist
            // on the stack.
            let mut data = [0; 1024];
            match socket.try_recv(&mut data[..]) {
                Ok(n) => {
                    println!("received {:?}", &data[..n]);
                }
                // False-positive, continue
                Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {}
                Err(e) => {
                    return Err(e);
                }
            }
        }

        if ready.is_writable() {
            // Write some data
            match socket.try_send(b"hello world") {
                Ok(n) => {
                    println!("sent {} bytes", n);
                }
                // False-positive, continue
                Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {}
                Err(e) => {
                    return Err(e);
                }
            }
        }
    }
}

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

Waits for the socket to become writable.

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

The function may complete without the socket being writable. This is a false-positive and attempting a try_send() will return with io::ErrorKind::WouldBlock.

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 write that fails with WouldBlock or Poll::Pending.

Examples

use tokio::net::UdpSocket;
use std::io;

#[tokio::main]
async fn main() -> io::Result<()> {
    // Bind socket
    let socket = UdpSocket::bind("127.0.0.1:8080").await?;
    socket.connect("127.0.0.1:8081").await?;

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

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

    Ok(())
}

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

Polls for write/send readiness.

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

Note that on multiple calls to poll_send_ready or poll_send, only the Waker from the Context passed to the most recent call is scheduled to receive a wakeup. (However, poll_recv_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 udp stream is not ready for writing.
• Poll::Ready(Ok(())) if the udp 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 async fn send(&self, buf: &[u8]) -> Result<usize>

Sends data on the socket to the remote address that the socket is connected to.

The connect method will connect this socket to a remote address. This method will fail if the socket is not connected.

Return

On success, the number of bytes sent is returned, otherwise, the encountered error is returned.

Cancel safety

This method is cancel safe. If send is used as the event in a tokio::select! statement and some other branch completes first, then it is guaranteed that the message was not sent.

Examples

use tokio::io;
use tokio::net::UdpSocket;

#[tokio::main]
async fn main() -> io::Result<()> {
    // Bind socket
    let socket = UdpSocket::bind("127.0.0.1:8080").await?;
    socket.connect("127.0.0.1:8081").await?;

    // Send a message
    socket.send(b"hello world").await?;

    Ok(())
}

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

Attempts to send data on the socket to the remote address to which it was previously connected.

The connect method will connect this socket to a remote address. This method will fail if the socket is not connected.

Note that on multiple calls to a poll_* method in the send direction, only the Waker from the Context passed to the most recent call will be scheduled to receive a wakeup.

Return value

The function returns:

• Poll::Pending if the socket is not available to write
• Poll::Ready(Ok(n)) n is the number of bytes sent
• Poll::Ready(Err(e)) if an error is encountered.

Errors

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

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

Tries to send data on the socket to the remote address to which it is connected.

When the socket buffer is full, Err(io::ErrorKind::WouldBlock) is returned. This function is usually paired with writable().

Returns

If successful, Ok(n) is returned, where n is the number of bytes sent. If the socket is not ready to send data, Err(ErrorKind::WouldBlock) is returned.

Examples

use tokio::net::UdpSocket;
use std::io;

#[tokio::main]
async fn main() -> io::Result<()> {
    // Bind a UDP socket
    let socket = UdpSocket::bind("127.0.0.1:8080").await?;

    // Connect to a peer
    socket.connect("127.0.0.1:8081").await?;

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

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

    Ok(())
}

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

Waits for the socket to become readable.

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

The function may complete without the socket being readable. This is a false-positive and attempting a try_recv() will return with io::ErrorKind::WouldBlock.

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.

Examples

use tokio::net::UdpSocket;
use std::io;

#[tokio::main]
async fn main() -> io::Result<()> {
    // Connect to a peer
    let socket = UdpSocket::bind("127.0.0.1:8080").await?;
    socket.connect("127.0.0.1:8081").await?;

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

        // The buffer is **not** included in the async task and will
        // only exist on the stack.
        let mut buf = [0; 1024];

        // Try to recv data, this may still fail with `WouldBlock`
        // if the readiness event is a false positive.
        match socket.try_recv(&mut buf) {
            Ok(n) => {
                println!("GOT {:?}", &buf[..n]);
                break;
            }
            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
                continue;
            }
            Err(e) => {
                return Err(e);
            }
        }
    }

    Ok(())
}

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

Polls for read/receive readiness.

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

Note that on multiple calls to poll_recv_ready, poll_recv or poll_peek, only the Waker from the Context passed to the most recent call is scheduled to receive a wakeup. (However, poll_send_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 udp stream is not ready for reading.
• Poll::Ready(Ok(())) if the udp 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 async fn recv(&self, buf: &mut [u8]) -> Result<usize>

Receives a single datagram message on the socket from the remote address to which it is connected. On success, returns the number of bytes read.

The function must be called with valid byte array buf of sufficient size to hold the message bytes. If a message is too long to fit in the supplied buffer, excess bytes may be discarded.

The connect method will connect this socket to a remote address. This method will fail if the socket is not connected.

Cancel safety

This method is cancel safe. If recv is used as the event in a tokio::select! statement and some other branch completes first, it is guaranteed that no messages were received on this socket.

use tokio::net::UdpSocket;
use std::io;

#[tokio::main]
async fn main() -> io::Result<()> {
    // Bind socket
    let socket = UdpSocket::bind("127.0.0.1:8080").await?;
    socket.connect("127.0.0.1:8081").await?;

    let mut buf = vec![0; 10];
    let n = socket.recv(&mut buf).await?;

    println!("received {} bytes {:?}", n, &buf[..n]);

    Ok(())
}

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

Attempts to receive a single datagram message on the socket from the remote address to which it is connected.

The connect method will connect this socket to a remote address. This method resolves to an error if the socket is not connected.

Note that on multiple calls to a poll_* method in the recv direction, only the Waker from the Context passed to the most recent call will be scheduled to receive a wakeup.

Return value

The function returns:

• Poll::Pending if the socket is not ready to read
• Poll::Ready(Ok(())) reads data ReadBuf if the socket is ready
• Poll::Ready(Err(e)) if an error is encountered.

Errors

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

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

Tries to receive a single datagram message on the socket from the remote address to which it is connected. On success, returns the number of bytes read.

This method must be called with valid byte array buf of sufficient size to hold the message bytes. If a message is too long to fit in the supplied buffer, excess bytes may be discarded.

When there is no pending data, Err(io::ErrorKind::WouldBlock) is returned. This function is usually paired with readable().

Examples

use tokio::net::UdpSocket;
use std::io;

#[tokio::main]
async fn main() -> io::Result<()> {
    // Connect to a peer
    let socket = UdpSocket::bind("127.0.0.1:8080").await?;
    socket.connect("127.0.0.1:8081").await?;

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

        // The buffer is **not** included in the async task and will
        // only exist on the stack.
        let mut buf = [0; 1024];

        // Try to recv data, this may still fail with `WouldBlock`
        // if the readiness event is a false positive.
        match socket.try_recv(&mut buf) {
            Ok(n) => {
                println!("GOT {:?}", &buf[..n]);
                break;
            }
            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
                continue;
            }
            Err(e) => {
                return Err(e);
            }
        }
    }

    Ok(())
}

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

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

This method must be called with valid byte array buf of sufficient size to hold the message bytes. If a message is too long to fit in the supplied buffer, excess bytes may be discarded.

This method can be used even if buf is uninitialized.

When there is no pending data, Err(io::ErrorKind::WouldBlock) is returned. This function is usually paired with readable().

Examples

use tokio::net::UdpSocket;
use std::io;

#[tokio::main]
async fn main() -> io::Result<()> {
    // Connect to a peer
    let socket = UdpSocket::bind("127.0.0.1:8080").await?;
    socket.connect("127.0.0.1:8081").await?;

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

        let mut buf = Vec::with_capacity(1024);

        // Try to recv data, this may still fail with `WouldBlock`
        // if the readiness event is a false positive.
        match socket.try_recv_buf(&mut buf) {
            Ok(n) => {
                println!("GOT {:?}", &buf[..n]);
                break;
            }
            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
                continue;
            }
            Err(e) => {
                return Err(e);
            }
        }
    }

    Ok(())
}

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

Receives a single datagram message on the socket from the remote address to which it is connected, advancing the buffer’s internal cursor, returning how many bytes were read.

This method must be called with valid byte array buf of sufficient size to hold the message bytes. If a message is too long to fit in the supplied buffer, excess bytes may be discarded.

This method can be used even if buf is uninitialized.

Examples

use tokio::net::UdpSocket;
use std::io;

#[tokio::main]
async fn main() -> io::Result<()> {
    // Connect to a peer
    let socket = UdpSocket::bind("127.0.0.1:8080").await?;
    socket.connect("127.0.0.1:8081").await?;

    let mut buf = Vec::with_capacity(512);
    let len = socket.recv_buf(&mut buf).await?;

    println!("received {} bytes {:?}", len, &buf[..len]);

    Ok(())
}

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

Tries to receive a single datagram message on the socket. On success, returns the number of bytes read and the origin.

This method must be called with valid byte array buf of sufficient size to hold the message bytes. If a message is too long to fit in the supplied buffer, excess bytes may be discarded.

This method can be used even if buf is uninitialized.

When there is no pending data, Err(io::ErrorKind::WouldBlock) is returned. This function is usually paired with readable().

Notes

Note that the socket address cannot be implicitly trusted, because it is relatively trivial to send a UDP datagram with a spoofed origin in a packet injection attack. Because UDP is stateless and does not validate the origin of a packet, the attacker does not need to be able to intercept traffic in order to interfere. It is important to be aware of this when designing your application-level protocol.

Examples

use tokio::net::UdpSocket;
use std::io;

#[tokio::main]
async fn main() -> io::Result<()> {
    // Connect to a peer
    let socket = UdpSocket::bind("127.0.0.1:8080").await?;

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

        let mut buf = Vec::with_capacity(1024);

        // Try to recv data, this may still fail with `WouldBlock`
        // if the readiness event is a false positive.
        match socket.try_recv_buf_from(&mut buf) {
            Ok((n, _addr)) => {
                println!("GOT {:?}", &buf[..n]);
                break;
            }
            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
                continue;
            }
            Err(e) => {
                return Err(e);
            }
        }
    }

    Ok(())
}

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

Receives a single datagram message on the socket, advancing the buffer’s internal cursor, returning how many bytes were read and the origin.

This method must be called with valid byte array buf of sufficient size to hold the message bytes. If a message is too long to fit in the supplied buffer, excess bytes may be discarded.

This method can be used even if buf is uninitialized.

Notes

Note that the socket address cannot be implicitly trusted, because it is relatively trivial to send a UDP datagram with a spoofed origin in a packet injection attack. Because UDP is stateless and does not validate the origin of a packet, the attacker does not need to be able to intercept traffic in order to interfere. It is important to be aware of this when designing your application-level protocol.

Examples

use tokio::net::UdpSocket;
use std::io;

#[tokio::main]
async fn main() -> io::Result<()> {
    // Connect to a peer
    let socket = UdpSocket::bind("127.0.0.1:8080").await?;
    socket.connect("127.0.0.1:8081").await?;

    let mut buf = Vec::with_capacity(512);
    let (len, addr) = socket.recv_buf_from(&mut buf).await?;

    println!("received {:?} bytes from {:?}", len, addr);

    Ok(())
}

pub async fn send_to<A: ToSocketAddrs>( &self, buf: &[u8], target: A, ) -> Result<usize>

Sends data on the socket to the given address. On success, returns the number of bytes written.

Address type can be any implementor of ToSocketAddrs trait. See its documentation for concrete examples.

It is possible for addr to yield multiple addresses, but send_to will only send data to the first address yielded by addr.

This will return an error when the IP version of the local socket does not match that returned from ToSocketAddrs.

Cancel safety

This method is cancel safe. If send_to is used as the event in a tokio::select! statement and some other branch completes first, then it is guaranteed that the message was not sent.

Example

use tokio::net::UdpSocket;
use std::io;

#[tokio::main]
async fn main() -> io::Result<()> {
    let socket = UdpSocket::bind("127.0.0.1:8080").await?;
    let len = socket.send_to(b"hello world", "127.0.0.1:8081").await?;

    println!("Sent {} bytes", len);

    Ok(())
}

pub fn poll_send_to( &self, cx: &mut Context<'_>, buf: &[u8], target: SocketAddr, ) -> Poll<Result<usize>>

Attempts to send data on the socket to a given address.

Note that on multiple calls to a poll_* method in the send direction, only the Waker from the Context passed to the most recent call will be scheduled to receive a wakeup.

Return value

The function returns:

• Poll::Pending if the socket is not ready to write
• Poll::Ready(Ok(n)) n is the number of bytes sent.
• Poll::Ready(Err(e)) if an error is encountered.

Errors

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

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

Tries to send data on the socket to the given address, but if the send is blocked this will return right away.

This function is usually paired with writable().

Returns

If successful, returns the number of bytes sent

Users should ensure that when the remote cannot receive, the ErrorKind::WouldBlock is properly handled. An error can also occur if the IP version of the socket does not match that of target.

Example

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

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

    let dst = "127.0.0.1:8081".parse()?;

    loop {
        socket.writable().await?;

        match socket.try_send_to(&b"hello world"[..], dst) {
            Ok(sent) => {
                println!("sent {} bytes", sent);
                break;
            }
            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
                // Writable false positive.
                continue;
            }
            Err(e) => return Err(e.into()),
        }
    }

    Ok(())
}

async fn send_to_addr(&self, buf: &[u8], target: SocketAddr) -> Result<usize>

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

Receives a single datagram message on the socket. On success, returns the number of bytes read and the origin.

The function must be called with valid byte array buf of sufficient size to hold the message bytes. If a message is too long to fit in the supplied buffer, excess bytes may be discarded.

Cancel safety

This method is cancel safe. If recv_from is used as the event in a tokio::select! statement and some other branch completes first, it is guaranteed that no messages were received on this socket.

Example

use tokio::net::UdpSocket;
use std::io;

#[tokio::main]
async fn main() -> io::Result<()> {
    let socket = UdpSocket::bind("127.0.0.1:8080").await?;

    let mut buf = vec![0u8; 32];
    let (len, addr) = socket.recv_from(&mut buf).await?;

    println!("received {:?} bytes from {:?}", len, addr);

    Ok(())
}

Notes

Note that the socket address cannot be implicitly trusted, because it is relatively trivial to send a UDP datagram with a spoofed origin in a packet injection attack. Because UDP is stateless and does not validate the origin of a packet, the attacker does not need to be able to intercept traffic in order to interfere. It is important to be aware of this when designing your application-level protocol.

pub fn poll_recv_from( &self, cx: &mut Context<'_>, buf: &mut ReadBuf<'_>, ) -> Poll<Result<SocketAddr>>

Attempts to receive a single datagram on the socket.

Note that on multiple calls to a poll_* method in the recv direction, only the Waker from the Context passed to the most recent call will be scheduled to receive a wakeup.

Return value

The function returns:

• Poll::Pending if the socket is not ready to read
• Poll::Ready(Ok(addr)) reads data from addr into ReadBuf if the socket is ready
• Poll::Ready(Err(e)) if an error is encountered.

Errors

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

Notes

Note that the socket address cannot be implicitly trusted, because it is relatively trivial to send a UDP datagram with a spoofed origin in a packet injection attack. Because UDP is stateless and does not validate the origin of a packet, the attacker does not need to be able to intercept traffic in order to interfere. It is important to be aware of this when designing your application-level protocol.

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

Tries to receive a single datagram message on the socket. On success, returns the number of bytes read and the origin.

This method must be called with valid byte array buf of sufficient size to hold the message bytes. If a message is too long to fit in the supplied buffer, excess bytes may be discarded.

When there is no pending data, Err(io::ErrorKind::WouldBlock) is returned. This function is usually paired with readable().

Notes

Note that the socket address cannot be implicitly trusted, because it is relatively trivial to send a UDP datagram with a spoofed origin in a packet injection attack. Because UDP is stateless and does not validate the origin of a packet, the attacker does not need to be able to intercept traffic in order to interfere. It is important to be aware of this when designing your application-level protocol.

Examples

use tokio::net::UdpSocket;
use std::io;

#[tokio::main]
async fn main() -> io::Result<()> {
    // Connect to a peer
    let socket = UdpSocket::bind("127.0.0.1:8080").await?;

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

        // The buffer is **not** included in the async task and will
        // only exist on the stack.
        let mut buf = [0; 1024];

        // Try to recv data, this may still fail with `WouldBlock`
        // if the readiness event is a false positive.
        match socket.try_recv_from(&mut buf) {
            Ok((n, _addr)) => {
                println!("GOT {:?}", &buf[..n]);
                break;
            }
            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
                continue;
            }
            Err(e) => {
                return Err(e);
            }
        }
    }

    Ok(())
}

pub fn try_io<R>( &self, interest: Interest, f: impl FnOnce() -> Result<R>, ) -> Result<R>

Tries to read or write from the socket using a user-provided IO operation.

If the socket is ready, the provided closure is called. The closure should attempt to perform IO operation on the socket by manually calling the appropriate syscall. If the operation fails because the socket is not actually ready, then the closure should return a WouldBlock error and the readiness flag is cleared. The return value of the closure is then returned by try_io.

If the socket is not ready, then the closure is not called and a WouldBlock error is returned.

The closure should only return a WouldBlock error if it has performed an IO operation on the socket that failed due to the socket not being ready. Returning a WouldBlock error in any other situation will incorrectly clear the readiness flag, which can cause the socket to behave incorrectly.

The closure should not perform the IO operation using any of the methods defined on the Tokio UdpSocket type, as this will mess with the readiness flag and can cause the socket to behave incorrectly.

This method is not intended to be used with combined interests. The closure should perform only one type of IO operation, so it should not require more than one ready state. This method may panic or sleep forever if it is called with a combined interest.

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

pub async fn async_io<R>( &self, interest: Interest, f: impl FnMut() -> Result<R>, ) -> Result<R>

Reads or writes from the socket using a user-provided IO operation.

The readiness of the socket is awaited and when the socket is ready, the provided closure is called. The closure should attempt to perform IO operation on the socket by manually calling the appropriate syscall. If the operation fails because the socket is not actually ready, then the closure should return a WouldBlock error. In such case the readiness flag is cleared and the socket readiness is awaited again. This loop is repeated until the closure returns an Ok or an error other than WouldBlock.

The closure should only return a WouldBlock error if it has performed an IO operation on the socket that failed due to the socket not being ready. Returning a WouldBlock error in any other situation will incorrectly clear the readiness flag, which can cause the socket to behave incorrectly.

The closure should not perform the IO operation using any of the methods defined on the Tokio UdpSocket type, as this will mess with the readiness flag and can cause the socket to behave incorrectly.

This method is not intended to be used with combined interests. The closure should perform only one type of IO operation, so it should not require more than one ready state. This method may panic or sleep forever if it is called with a combined interest.

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

Receives data from the socket, without removing it from the input queue. On success, returns the number of bytes read and the address from whence the data came.

Notes

On Windows, if the data is larger than the buffer specified, the buffer is filled with the first part of the data, and peek_from returns the error WSAEMSGSIZE(10040). The excess data is lost. Make sure to always use a sufficiently large buffer to hold the maximum UDP packet size, which can be up to 65536 bytes in size.

MacOS will return an error if you pass a zero-sized buffer.

If you’re merely interested in learning the sender of the data at the head of the queue, try peek_sender.

Note that the socket address cannot be implicitly trusted, because it is relatively trivial to send a UDP datagram with a spoofed origin in a packet injection attack. Because UDP is stateless and does not validate the origin of a packet, the attacker does not need to be able to intercept traffic in order to interfere. It is important to be aware of this when designing your application-level protocol.

Examples

use tokio::net::UdpSocket;
use std::io;

#[tokio::main]
async fn main() -> io::Result<()> {
    let socket = UdpSocket::bind("127.0.0.1:8080").await?;

    let mut buf = vec![0u8; 32];
    let (len, addr) = socket.peek_from(&mut buf).await?;

    println!("peeked {:?} bytes from {:?}", len, addr);

    Ok(())
}

pub fn poll_peek_from( &self, cx: &mut Context<'_>, buf: &mut ReadBuf<'_>, ) -> Poll<Result<SocketAddr>>

Receives data from the socket, without removing it from the input queue. On success, returns the sending address of the datagram.

Notes

Note that on multiple calls to a poll_* method in the recv direction, only the Waker from the Context passed to the most recent call will be scheduled to receive a wakeup

On Windows, if the data is larger than the buffer specified, the buffer is filled with the first part of the data, and peek returns the error WSAEMSGSIZE(10040). The excess data is lost. Make sure to always use a sufficiently large buffer to hold the maximum UDP packet size, which can be up to 65536 bytes in size.

MacOS will return an error if you pass a zero-sized buffer.

If you’re merely interested in learning the sender of the data at the head of the queue, try poll_peek_sender.

Note that the socket address cannot be implicitly trusted, because it is relatively trivial to send a UDP datagram with a spoofed origin in a packet injection attack. Because UDP is stateless and does not validate the origin of a packet, the attacker does not need to be able to intercept traffic in order to interfere. It is important to be aware of this when designing your application-level protocol.

Return value

The function returns:

• Poll::Pending if the socket is not ready to read
• Poll::Ready(Ok(addr)) reads data from addr into ReadBuf if the socket is ready
• Poll::Ready(Err(e)) if an error is encountered.

Errors

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

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

Tries to receive data on the socket without removing it from the input queue. On success, returns the number of bytes read and the sending address of the datagram.

When there is no pending data, Err(io::ErrorKind::WouldBlock) is returned. This function is usually paired with readable().

Notes

On Windows, if the data is larger than the buffer specified, the buffer is filled with the first part of the data, and peek returns the error WSAEMSGSIZE(10040). The excess data is lost. Make sure to always use a sufficiently large buffer to hold the maximum UDP packet size, which can be up to 65536 bytes in size.

MacOS will return an error if you pass a zero-sized buffer.

If you’re merely interested in learning the sender of the data at the head of the queue, try try_peek_sender.

Note that the socket address cannot be implicitly trusted, because it is relatively trivial to send a UDP datagram with a spoofed origin in a packet injection attack. Because UDP is stateless and does not validate the origin of a packet, the attacker does not need to be able to intercept traffic in order to interfere. It is important to be aware of this when designing your application-level protocol.

pub async fn peek_sender(&self) -> Result<SocketAddr>

Retrieve the sender of the data at the head of the input queue, waiting if empty.

This is equivalent to calling peek_from with a zero-sized buffer, but suppresses the WSAEMSGSIZE error on Windows and the “invalid argument” error on macOS.

Note that the socket address cannot be implicitly trusted, because it is relatively trivial to send a UDP datagram with a spoofed origin in a packet injection attack. Because UDP is stateless and does not validate the origin of a packet, the attacker does not need to be able to intercept traffic in order to interfere. It is important to be aware of this when designing your application-level protocol.

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

Retrieve the sender of the data at the head of the input queue, scheduling a wakeup if empty.

This is equivalent to calling poll_peek_from with a zero-sized buffer, but suppresses the WSAEMSGSIZE error on Windows and the “invalid argument” error on macOS.

Notes

Note that on multiple calls to a poll_* method in the recv direction, only the Waker from the Context passed to the most recent call will be scheduled to receive a wakeup.

Note that the socket address cannot be implicitly trusted, because it is relatively trivial to send a UDP datagram with a spoofed origin in a packet injection attack. Because UDP is stateless and does not validate the origin of a packet, the attacker does not need to be able to intercept traffic in order to interfere. It is important to be aware of this when designing your application-level protocol.

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

Try to retrieve the sender of the data at the head of the input queue.

When there is no pending data, Err(io::ErrorKind::WouldBlock) is returned. This function is usually paired with readable().

Note that the socket address cannot be implicitly trusted, because it is relatively trivial to send a UDP datagram with a spoofed origin in a packet injection attack. Because UDP is stateless and does not validate the origin of a packet, the attacker does not need to be able to intercept traffic in order to interfere. It is important to be aware of this when designing your application-level protocol.

fn peek_sender_inner(&self) -> Result<SocketAddr>

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

Gets the value of the SO_BROADCAST option for this socket.

For more information about this option, see set_broadcast.

pub fn set_broadcast(&self, on: bool) -> Result<()>

Sets the value of the SO_BROADCAST option for this socket.

When enabled, this socket is allowed to send packets to a broadcast address.

pub fn multicast_loop_v4(&self) -> Result<bool>

Gets the value of the IP_MULTICAST_LOOP option for this socket.

For more information about this option, see set_multicast_loop_v4.

pub fn set_multicast_loop_v4(&self, on: bool) -> Result<()>

Sets the value of the IP_MULTICAST_LOOP option for this socket.

If enabled, multicast packets will be looped back to the local socket.

Note

This may not have any affect on IPv6 sockets.

pub fn multicast_ttl_v4(&self) -> Result<u32>

Gets the value of the IP_MULTICAST_TTL option for this socket.

For more information about this option, see set_multicast_ttl_v4.

pub fn set_multicast_ttl_v4(&self, ttl: u32) -> Result<()>

Sets the value of the IP_MULTICAST_TTL option for this socket.

Indicates the time-to-live value of outgoing multicast packets for this socket. The default value is 1 which means that multicast packets don’t leave the local network unless explicitly requested.

Note

This may not have any affect on IPv6 sockets.

pub fn multicast_loop_v6(&self) -> Result<bool>

Gets the value of the IPV6_MULTICAST_LOOP option for this socket.

For more information about this option, see set_multicast_loop_v6.

pub fn set_multicast_loop_v6(&self, on: bool) -> Result<()>

Sets the value of the IPV6_MULTICAST_LOOP option for this socket.

Controls whether this socket sees the multicast packets it sends itself.

Note

This may not have any affect on IPv4 sockets.

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::UdpSocket;

let sock = UdpSocket::bind("127.0.0.1:8080").await?;

println!("{:?}", sock.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::UdpSocket;

let sock = UdpSocket::bind("127.0.0.1:8080").await?;
sock.set_ttl(60)?;

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

Gets the value of the IP_TOS option for this socket.

For more information about this option, see set_tos.

NOTE: On Windows, IP_TOS is only supported on Windows 8+ or Windows Server 2012+.

pub fn set_tos(&self, tos: u32) -> Result<()>

Sets the value for the IP_TOS option on this socket.

This value sets the type-of-service field that is used in every packet sent from this socket.

NOTE: On Windows, IP_TOS is only supported on Windows 8+ or Windows Server 2012+.

pub fn device(&self) -> Result<Option<Vec<u8>>>

Gets the value for the SO_BINDTODEVICE option on this socket

This value gets the socket-bound device’s interface name.

pub fn bind_device(&self, interface: Option<&[u8]>) -> Result<()>

Sets the value for the SO_BINDTODEVICE option on this socket

If a socket is bound to an interface, only packets received from that particular interface are processed by the socket. Note that this only works for some socket types, particularly AF_INET sockets.

If interface is None or an empty string it removes the binding.

pub fn join_multicast_v4( &self, multiaddr: Ipv4Addr, interface: Ipv4Addr, ) -> Result<()>

Executes an operation of the IP_ADD_MEMBERSHIP type.

This function specifies a new multicast group for this socket to join. The address must be a valid multicast address, and interface is the address of the local interface with which the system should join the multicast group. If it’s equal to INADDR_ANY then an appropriate interface is chosen by the system.

pub fn join_multicast_v6( &self, multiaddr: &Ipv6Addr, interface: u32, ) -> Result<()>

Executes an operation of the IPV6_ADD_MEMBERSHIP type.

This function specifies a new multicast group for this socket to join. The address must be a valid multicast address, and interface is the index of the interface to join/leave (or 0 to indicate any interface).

pub fn leave_multicast_v4( &self, multiaddr: Ipv4Addr, interface: Ipv4Addr, ) -> Result<()>

Executes an operation of the IP_DROP_MEMBERSHIP type.

For more information about this option, see join_multicast_v4.

pub fn leave_multicast_v6( &self, multiaddr: &Ipv6Addr, interface: u32, ) -> Result<()>

Executes an operation of the IPV6_DROP_MEMBERSHIP type.

For more information about this option, see join_multicast_v6.

pub fn take_error(&self) -> Result<Option<Error>>

Returns the value of the SO_ERROR option.

Examples

use tokio::net::UdpSocket;
use std::io;

#[tokio::main]
async fn main() -> io::Result<()> {
    // Create a socket
    let socket = UdpSocket::bind("0.0.0.0:8080").await?;

    if let Ok(Some(err)) = socket.take_error() {
        println!("Got error: {:?}", err);
    }

    Ok(())
}

Trait Implementations

impl AsFd for UdpSocket

fn as_fd(&self) -> BorrowedFd<'_>

Borrows the file descriptor.

impl AsRawFd for UdpSocket

fn as_raw_fd(&self) -> RawFd

Extracts the raw file descriptor.

impl Debug for UdpSocket

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

Formats the value using the given formatter.

impl TryFrom<UdpSocket> for UdpSocket

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

Consumes stream, returning the tokio I/O object.

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

type Error = Error

The type returned in the event of a conversion error.