Struct tokio::net::UdpSocket

pub struct UdpSocket { /* fields omitted */ }

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

UdpSocket can also be used concurrently to send_to and recv_from in different tasks, all that's required is that you Arc<UdpSocket> and clone a reference for each task.

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: Sending/Receiving concurrently

Because send_to and recv_from take &self. It's perfectly alright to Arc<UdpSocket> and share the references to multiple tasks, in order to send/receive concurrently. Here is a similar "echo" example but 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();
    }
}

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.

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(())
}

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. The conversion assumes nothing about the underlying socket; it is left up to the user to set it in non-blocking mode.

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.

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)?;
let sock = UdpSocket::from_std(std_sock)?;
// use `sock`

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 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 send<'_, '_>(&'_ self, buf: &'_ [u8]) -> Result<usize>

Returns a future that sends data on the socket to the remote address to which it is connected. On success, the future will resolve to the number of bytes written.

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

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. The future will resolve to an error 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>

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

Returns

If successfull, the number of bytes sent is returned. Users should ensure that when the remote cannot receive, the ErrorKind::WouldBlock is properly handled.

pub async fn recv<'_, '_>(&'_ self, buf: &'_ mut [u8]) -> Result<usize>

Returns a future that receives a single datagram message on the socket from the remote address to which it is connected. On success, the future will resolve to 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. The future will fail if the socket is not connected.

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

Returns a future that sends data on the socket to the given address. On success, the future will resolve to the number of bytes written.

The future will resolve to an error if the IP version of the socket does not match that of target.

Example

use tokio::net::UdpSocket;

let sock = UdpSocket::bind("0.0.0.0:8080".parse::<SocketAddr>().unwrap()).await?;
let buf = b"hello world";
let remote_addr = "127.0.0.1:58000".parse::<SocketAddr>().unwrap();
let _len = sock.send_to(&buf[..], remote_addr).await?;

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>

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

Returns

If successfull, 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;

let sock = UdpSocket::bind("0.0.0.0:8080".parse::<SocketAddr>().unwrap()).await?;
let buf = b"hello world";
let remote_addr = "127.0.0.1:58000".parse::<SocketAddr>().unwrap();
let _len = sock.try_send_to(&buf[..], remote_addr)?;

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

Returns a future that receives a single datagram on the socket. On success, the future resolves to 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.

Example

use tokio::net::UdpSocket;

let sock = UdpSocket::bind("0.0.0.0:8080".parse::<SocketAddr>().unwrap()).await?;
let mut buf = [0u8; 32];
let (len, addr) = sock.recv_from(&mut buf).await?;
println!("received {:?} bytes from {:?}", len, addr);

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.

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.

Examples

use tokio::net::UdpSocket;

let sock = UdpSocket::bind("0.0.0.0:8080".parse::<SocketAddr>().unwrap()).await?;
let mut buf = [0u8; 32];
let (len, addr) = sock.peek_from(&mut buf).await?;
println!("peeked {:?} bytes from {:?}", len, addr);

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 number of bytes read.

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.

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 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 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;

// 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);
}

Trait Implementations

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

type Error = Error

The type returned in the event of a conversion error.

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).