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// Copyright Materialize, Inc. and contributors. All rights reserved.
//
// Use of this software is governed by the Business Source License
// included in the LICENSE file.
//
// As of the Change Date specified in that file, in accordance with
// the Business Source License, use of this software will be governed
// by the Apache License, Version 2.0.
//! Methods common to servers listening for TCP connections.
use std::future::Future;
use std::io;
use std::net::SocketAddr;
use std::pin::Pin;
use std::time::Duration;
use async_trait::async_trait;
use futures::stream::{Stream, StreamExt};
use mz_ore::error::ErrorExt;
use mz_ore::task;
use socket2::{SockRef, TcpKeepalive};
use tokio::net::{TcpListener, TcpStream};
use tokio::sync::oneshot;
use tokio_stream::wrappers::TcpListenerStream;
use tracing::{debug, error};
/// TCP keepalive settings. The idle time and interval match CockroachDB [0].
/// The number of retries matches the Linux default.
///
/// [0]: https://github.com/cockroachdb/cockroach/pull/14063
const KEEPALIVE: TcpKeepalive = TcpKeepalive::new()
.with_time(Duration::from_secs(60))
.with_interval(Duration::from_secs(60))
.with_retries(9);
/// A future that handles a connection.
pub type ConnectionHandler = Pin<Box<dyn Future<Output = Result<(), anyhow::Error>> + Send>>;
/// A server handles incoming network connections.
pub trait Server {
/// Returns the name of the connection handler for use in e.g. log messages.
const NAME: &'static str;
/// Handles a single connection.
fn handle_connection(&self, conn: TcpStream) -> ConnectionHandler;
}
/// A stream of incoming connections.
pub trait ConnectionStream: Stream<Item = io::Result<TcpStream>> + Unpin + Send {}
impl<T> ConnectionStream for T where T: Stream<Item = io::Result<TcpStream>> + Unpin + Send {}
/// A handle to a listener created by [`listen`].
pub struct ListenerHandle {
local_addr: SocketAddr,
_trigger: oneshot::Sender<()>,
}
impl ListenerHandle {
/// Returns the local address to which the listener is bound.
pub fn local_addr(&self) -> SocketAddr {
self.local_addr
}
}
/// Listens for incoming TCP connections on the specified address.
///
/// Returns a handle to the listener and the stream of incoming connections
/// produced by the listener. When the handle is dropped, the listener is
/// closed, and the stream of incoming connections terminates.
pub async fn listen(
addr: SocketAddr,
) -> Result<(ListenerHandle, Pin<Box<dyn ConnectionStream>>), io::Error> {
let listener = TcpListener::bind(addr).await?;
let local_addr = listener.local_addr()?;
let (trigger, tripwire) = oneshot::channel();
let handle = ListenerHandle {
local_addr,
_trigger: trigger,
};
// TODO(benesch): replace `TCPListenerStream`s with `listener.incoming()` if
// that is restored when the `Stream` trait stabilizes.
let stream = TcpListenerStream::new(listener).take_until(tripwire);
Ok((handle, Box::pin(stream)))
}
/// Serves incoming TCP connections from `conns` using `server`.
pub async fn serve<C, S>(mut conns: C, server: S)
where
C: ConnectionStream,
S: Server,
{
let task_name = format!("handle_{}_connection", S::NAME);
while let Some(conn) = conns.next().await {
let conn = match conn {
Ok(conn) => conn,
Err(err) => {
error!("error accepting connection: {}", err);
continue;
}
};
// Set TCP_NODELAY to disable tinygram prevention (Nagle's
// algorithm), which forces a 40ms delay between each query
// on linux. According to John Nagle [0], the true problem
// is delayed acks, but disabling those is a receive-side
// operation (TCP_QUICKACK), and we can't always control the
// client. PostgreSQL sets TCP_NODELAY on both sides of its
// sockets, so it seems sane to just do the same.
//
// If set_nodelay fails, it's a programming error, so panic.
//
// [0]: https://news.ycombinator.com/item?id=10608356
conn.set_nodelay(true).expect("set_nodelay failed");
// Enable TCP keepalives to avoid any idle connection timeouts that may
// be enforced by networking devices between us and the client. Idle SQL
// connections are expected--e.g., a `SUBSCRIBE` to a view containing
// critical alerts will ideally be producing no data most of the time.
if let Err(e) = SockRef::from(&conn).set_tcp_keepalive(&KEEPALIVE) {
error!("failed enabling keepalive: {e}");
continue;
}
let fut = server.handle_connection(conn);
task::spawn(|| &task_name, async {
if let Err(e) = fut.await {
debug!(
"error handling connection in {}: {}",
S::NAME,
e.display_with_causes()
);
}
});
}
}
#[async_trait]
impl Server for mz_pgwire::Server {
const NAME: &'static str = "pgwire";
fn handle_connection(&self, conn: TcpStream) -> ConnectionHandler {
// Using fully-qualified syntax means we won't accidentally call
// ourselves (i.e., silently infinitely recurse) if the name or type of
// `mz_pgwire::Server::handle_connection` changes.
Box::pin(mz_pgwire::Server::handle_connection(self, conn))
}
}