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// You can run this example from the root of the mio repo:
// cargo run --example tcp_listenfd_server --features="os-poll net"
// or with wasi:
// cargo +nightly build --target wasm32-wasi --example tcp_listenfd_server --features="os-poll net"
// wasmtime run --tcplisten 127.0.0.1:9000 --env 'LISTEN_FDS=1' target/wasm32-wasi/debug/examples/tcp_listenfd_server.wasm
use mio::event::Event;
use mio::net::{TcpListener, TcpStream};
use mio::{Events, Interest, Poll, Registry, Token};
use std::collections::HashMap;
use std::io::{self, Read, Write};
use std::str::from_utf8;
// Setup some tokens to allow us to identify which event is for which socket.
const SERVER: Token = Token(0);
// Some data we'll send over the connection.
const DATA: &[u8] = b"Hello world!\n";
#[cfg(not(windows))]
fn get_first_listen_fd_listener() -> Option<std::net::TcpListener> {
#[cfg(unix)]
use std::os::unix::io::FromRawFd;
#[cfg(target_os = "wasi")]
use std::os::wasi::io::FromRawFd;
let stdlistener = unsafe { std::net::TcpListener::from_raw_fd(3) };
stdlistener.set_nonblocking(true).unwrap();
Some(stdlistener)
}
#[cfg(windows)]
fn get_first_listen_fd_listener() -> Option<std::net::TcpListener> {
// Windows does not support `LISTEN_FDS`
None
}
fn main() -> io::Result<()> {
env_logger::init();
std::env::var("LISTEN_FDS").expect("LISTEN_FDS environment variable unset");
// Create a poll instance.
let mut poll = Poll::new()?;
// Create storage for events.
let mut events = Events::with_capacity(128);
// Setup the TCP server socket.
let mut server = {
let stdlistener = get_first_listen_fd_listener().unwrap();
println!("Using preopened socket FD 3");
println!("You can connect to the server using `nc`:");
match stdlistener.local_addr() {
Ok(a) => println!(" $ nc {} {}", a.ip(), a.port()),
Err(_) => println!(" $ nc <IP> <PORT>"),
}
println!("You'll see our welcome message and anything you type will be printed here.");
TcpListener::from_std(stdlistener)
};
// Register the server with poll we can receive events for it.
poll.registry()
.register(&mut server, SERVER, Interest::READABLE)?;
// Map of `Token` -> `TcpStream`.
let mut connections = HashMap::new();
// Unique token for each incoming connection.
let mut unique_token = Token(SERVER.0 + 1);
loop {
poll.poll(&mut events, None)?;
for event in events.iter() {
match event.token() {
SERVER => loop {
// Received an event for the TCP server socket, which
// indicates we can accept an connection.
let (mut connection, address) = match server.accept() {
Ok((connection, address)) => (connection, address),
Err(ref e) if would_block(e) => {
// If we get a `WouldBlock` error we know our
// listener has no more incoming connections queued,
// so we can return to polling and wait for some
// more.
break;
}
Err(e) => {
// If it was any other kind of error, something went
// wrong and we terminate with an error.
return Err(e);
}
};
println!("Accepted connection from: {}", address);
let token = next(&mut unique_token);
poll.registry()
.register(&mut connection, token, Interest::WRITABLE)?;
connections.insert(token, connection);
},
token => {
// Maybe received an event for a TCP connection.
let done = if let Some(connection) = connections.get_mut(&token) {
handle_connection_event(poll.registry(), connection, event)?
} else {
// Sporadic events happen, we can safely ignore them.
false
};
if done {
if let Some(mut connection) = connections.remove(&token) {
poll.registry().deregister(&mut connection)?;
}
}
}
}
}
}
}
fn next(current: &mut Token) -> Token {
let next = current.0;
current.0 += 1;
Token(next)
}
/// Returns `true` if the connection is done.
fn handle_connection_event(
registry: &Registry,
connection: &mut TcpStream,
event: &Event,
) -> io::Result<bool> {
if event.is_writable() {
// We can (maybe) write to the connection.
match connection.write(DATA) {
// We want to write the entire `DATA` buffer in a single go. If we
// write less we'll return a short write error (same as
// `io::Write::write_all` does).
Ok(n) if n < DATA.len() => return Err(io::ErrorKind::WriteZero.into()),
Ok(_) => {
// After we've written something we'll reregister the connection
// to only respond to readable events.
registry.reregister(connection, event.token(), Interest::READABLE)?
}
// Would block "errors" are the OS's way of saying that the
// connection is not actually ready to perform this I/O operation.
Err(ref err) if would_block(err) => {}
// Got interrupted (how rude!), we'll try again.
Err(ref err) if interrupted(err) => {
return handle_connection_event(registry, connection, event)
}
// Other errors we'll consider fatal.
Err(err) => return Err(err),
}
}
if event.is_readable() {
let mut connection_closed = false;
let mut received_data = vec![0; 4096];
let mut bytes_read = 0;
// We can (maybe) read from the connection.
loop {
match connection.read(&mut received_data[bytes_read..]) {
Ok(0) => {
// Reading 0 bytes means the other side has closed the
// connection or is done writing, then so are we.
connection_closed = true;
break;
}
Ok(n) => {
bytes_read += n;
if bytes_read == received_data.len() {
received_data.resize(received_data.len() + 1024, 0);
}
}
// Would block "errors" are the OS's way of saying that the
// connection is not actually ready to perform this I/O operation.
Err(ref err) if would_block(err) => break,
Err(ref err) if interrupted(err) => continue,
// Other errors we'll consider fatal.
Err(err) => return Err(err),
}
}
if bytes_read != 0 {
let received_data = &received_data[..bytes_read];
if let Ok(str_buf) = from_utf8(received_data) {
println!("Received data: {}", str_buf.trim_end());
} else {
println!("Received (none UTF-8) data: {:?}", received_data);
}
}
if connection_closed {
println!("Connection closed");
return Ok(true);
}
}
Ok(false)
}
fn would_block(err: &io::Error) -> bool {
err.kind() == io::ErrorKind::WouldBlock
}
fn interrupted(err: &io::Error) -> bool {
err.kind() == io::ErrorKind::Interrupted
}