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// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
use std::collections::HashMap;
use std::net::SocketAddr;
use std::sync::Arc;
use socket2::Domain;
use socket2::Protocol;
use socket2::Type;
/// Our per-process `Connections`. We can use this to find an existent listener for
/// a given local address and clone its socket for us to listen on in our thread.
static CONNS: std::sync::OnceLock<std::sync::Mutex<Connections>> =
std::sync::OnceLock::new();
/// Maintains a map of listening address to `TcpConnection`.
#[derive(Default)]
struct Connections {
tcp: HashMap<SocketAddr, Arc<TcpConnection>>,
}
/// Holds an open listener. We clone the underlying file descriptor (unix) or socket handle (Windows)
/// and then listen on our copy of it.
pub struct TcpConnection {
/// The pristine FD that we'll clone for each LB listener
#[cfg(unix)]
sock: std::os::fd::OwnedFd,
#[cfg(not(unix))]
sock: std::os::windows::io::OwnedSocket,
key: SocketAddr,
}
impl TcpConnection {
/// Boot a load-balanced TCP connection
pub fn start(key: SocketAddr) -> std::io::Result<Self> {
let listener = bind_socket_and_listen(key, false)?;
let sock = listener.into();
Ok(Self { sock, key })
}
fn listener(&self) -> std::io::Result<tokio::net::TcpListener> {
let listener = std::net::TcpListener::from(self.sock.try_clone()?);
let listener = tokio::net::TcpListener::from_std(listener)?;
Ok(listener)
}
}
/// A TCP socket listener that optionally allows for round-robin load-balancing in-process.
pub struct TcpListener {
listener: Option<tokio::net::TcpListener>,
conn: Option<Arc<TcpConnection>>,
}
/// Does this platform implement `SO_REUSEPORT` in a load-balancing manner?
const REUSE_PORT_LOAD_BALANCES: bool =
cfg!(any(target_os = "android", target_os = "linux"));
impl TcpListener {
/// Bind to a port. On Linux, or when we don't have `SO_REUSEPORT` set, we just bind the port directly.
/// On other platforms, we emulate `SO_REUSEPORT` by cloning the socket and having each clone race to
/// accept every connection.
///
/// ## Why not `SO_REUSEPORT`?
///
/// The `SO_REUSEPORT` socket option allows multiple sockets on the same host to bind to the same port. This is
/// particularly useful for load balancing or implementing high availability in server applications.
///
/// On Linux, `SO_REUSEPORT` allows multiple sockets to bind to the same port, and the kernel will load
/// balance incoming connections among those sockets. Each socket can accept connections independently.
/// This is useful for scenarios where you want to distribute incoming connections among multiple processes
/// or threads.
///
/// On macOS (which is based on BSD), the behaviour of `SO_REUSEPORT` is slightly different. When `SO_REUSEPORT` is set,
/// multiple sockets can still bind to the same port, but the kernel does not perform load balancing as it does on Linux.
/// Instead, it follows a "last bind wins" strategy. This means that the most recently bound socket will receive
/// incoming connections exclusively, while the previously bound sockets will not receive any connections.
/// This behaviour is less useful for load balancing compared to Linux, but it can still be valuable in certain scenarios.
pub fn bind(
socket_addr: SocketAddr,
reuse_port: bool,
) -> std::io::Result<Self> {
if REUSE_PORT_LOAD_BALANCES && reuse_port {
Self::bind_load_balanced(socket_addr)
} else {
Self::bind_direct(socket_addr, reuse_port)
}
}
/// Bind directly to the port, passing `reuse_port` directly to the socket. On platforms other
/// than Linux, `reuse_port` does not do any load balancing.
pub fn bind_direct(
socket_addr: SocketAddr,
reuse_port: bool,
) -> std::io::Result<Self> {
// We ignore `reuse_port` on platforms other than Linux to match the existing behaviour.
let listener = bind_socket_and_listen(socket_addr, reuse_port)?;
Ok(Self {
listener: Some(tokio::net::TcpListener::from_std(listener)?),
conn: None,
})
}
/// Bind to the port in a load-balanced manner.
pub fn bind_load_balanced(socket_addr: SocketAddr) -> std::io::Result<Self> {
let tcp = &mut CONNS.get_or_init(Default::default).lock().unwrap().tcp;
if let Some(conn) = tcp.get(&socket_addr) {
let listener = Some(conn.listener()?);
return Ok(Self {
listener,
conn: Some(conn.clone()),
});
}
let conn = Arc::new(TcpConnection::start(socket_addr)?);
let listener = Some(conn.listener()?);
tcp.insert(socket_addr, conn.clone());
Ok(Self {
listener,
conn: Some(conn),
})
}
pub async fn accept(
&self,
) -> std::io::Result<(tokio::net::TcpStream, SocketAddr)> {
let (tcp, addr) = self.listener.as_ref().unwrap().accept().await?;
Ok((tcp, addr))
}
pub fn local_addr(&self) -> std::io::Result<SocketAddr> {
self.listener.as_ref().unwrap().local_addr()
}
}
impl Drop for TcpListener {
fn drop(&mut self) {
// If we're in load-balancing mode
if let Some(conn) = self.conn.take() {
let mut tcp = CONNS.get().unwrap().lock().unwrap();
if Arc::strong_count(&conn) == 2 {
tcp.tcp.remove(&conn.key);
// Close the connection
debug_assert_eq!(Arc::strong_count(&conn), 1);
drop(conn);
}
}
}
}
/// Bind a socket to an address and listen with the low-level options we need.
#[allow(unused_variables)]
fn bind_socket_and_listen(
socket_addr: SocketAddr,
reuse_port: bool,
) -> Result<std::net::TcpListener, std::io::Error> {
let socket = if socket_addr.is_ipv4() {
socket2::Socket::new(Domain::IPV4, Type::STREAM, Some(Protocol::TCP))?
} else {
socket2::Socket::new(Domain::IPV6, Type::STREAM, Some(Protocol::TCP))?
};
#[cfg(not(windows))]
if REUSE_PORT_LOAD_BALANCES && reuse_port {
socket.set_reuse_port(true)?;
}
#[cfg(not(windows))]
// This is required for re-use of a port immediately after closing. There's a small
// security trade-off here but we err on the side of convenience.
//
// https://stackoverflow.com/questions/14388706/how-do-so-reuseaddr-and-so-reuseport-differ
// https://stackoverflow.com/questions/26772549/is-it-a-good-idea-to-reuse-port-using-option-so-reuseaddr-which-is-already-in-ti
socket.set_reuse_address(true)?;
socket.set_nonblocking(true)?;
socket.bind(&socket_addr.into())?;
socket.listen(128)?;
let listener = socket.into();
Ok(listener)
}
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