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93 lines
2.7 KiB
Rust
93 lines
2.7 KiB
Rust
//! An UDP echo server that just sends back everything that it receives.
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//!
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//! If you're on Unix you can test this out by in one terminal executing:
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//!
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//! cargo run --example echo-udp
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//!
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//! and in another terminal you can run:
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//!
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//! cargo run --example connect-udp 127.0.0.1:8080
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//!
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//! Each line you type in to the `connect-udp` terminal should be echo'd back to you!
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//!
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//! # Binding to all interfaces
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//!
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//! By default this example binds to `127.0.0.1` so it is only reachable
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//! from the local machine.
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//!
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//! To listen on all interfaces instead:
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//!
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//! ```sh
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//! cargo run --example echo-udp -- 0.0.0.0:8080
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//! ```
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//!
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//! Binding to `0.0.0.0` exposes the server on all network interfaces.
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//! Only do this in trusted network environments.
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//!
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//! On multi-homed systems, a UDP socket bound to a wildcard address
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//! (`0.0.0.0` or `::`) cannot always send replies from the same local IP
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//! that received the packet. Replies may therefore originate from a
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//! different address than the client targeted. See [this Cloudflare blog
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//! post][udp-blog] for more details.
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//!
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//! [udp-blog]: https://blog.cloudflare.com/everything-you-ever-wanted-to-know-about-udp-sockets-but-were-afraid-to-ask-part-1
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#![warn(rust_2018_idioms)]
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use std::error::Error;
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use std::net::SocketAddr;
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use std::{env, io};
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use tokio::net::UdpSocket;
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struct Server {
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socket: UdpSocket,
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buf: Vec<u8>,
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to_send: Option<(usize, SocketAddr)>,
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}
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impl Server {
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async fn run(self) -> Result<(), io::Error> {
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let Server {
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socket,
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mut buf,
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mut to_send,
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} = self;
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loop {
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// First we check to see if there's a message we need to echo back.
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// If so then we try to send it back to the original source, waiting
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// until it's writable and we're able to do so.
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if let Some((size, peer)) = to_send {
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let amt = socket.send_to(&buf[..size], &peer).await?;
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println!("Echoed {amt}/{size} bytes to {peer}");
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}
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// If we're here then `to_send` is `None`, so we take a look for the
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// next message we're going to echo back.
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to_send = Some(socket.recv_from(&mut buf).await?);
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}
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}
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}
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#[tokio::main]
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async fn main() -> Result<(), Box<dyn Error>> {
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let addr = env::args()
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.nth(1)
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.unwrap_or_else(|| "127.0.0.1:8080".to_string());
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let socket = UdpSocket::bind(&addr).await?;
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println!("Listening on: {}", socket.local_addr()?);
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let server = Server {
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socket,
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buf: vec![0; 1024],
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to_send: None,
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};
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// This starts the server task.
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server.run().await?;
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Ok(())
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}
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