From fe48d60d2b63a9914297558bd5dbccae8d96c947 Mon Sep 17 00:00:00 2001
From: Alex Auvolat <alex@adnab.me>
Date: Wed, 7 Feb 2024 14:33:07 +0100
Subject: [dep-upgrade-202402] refactor http listener code

---
 src/api/generic_server.rs | 155 +++++++++++++++++++++++++++++++++-------------
 1 file changed, 111 insertions(+), 44 deletions(-)

(limited to 'src/api')

diff --git a/src/api/generic_server.rs b/src/api/generic_server.rs
index 832f2da3..e3005f8a 100644
--- a/src/api/generic_server.rs
+++ b/src/api/generic_server.rs
@@ -5,6 +5,7 @@ use std::sync::Arc;
 use async_trait::async_trait;
 
 use futures::future::Future;
+use futures::stream::{futures_unordered::FuturesUnordered, StreamExt};
 
 use http_body_util::BodyExt;
 use hyper::header::HeaderValue;
@@ -15,7 +16,7 @@ use hyper::{HeaderMap, StatusCode};
 use hyper_util::rt::TokioIo;
 
 use tokio::io::{AsyncRead, AsyncWrite};
-use tokio::net::{TcpListener, UnixListener};
+use tokio::net::{TcpListener, TcpStream, UnixListener, UnixStream};
 
 use opentelemetry::{
 	global,
@@ -110,20 +111,12 @@ impl<A: ApiHandler> ApiServer<A> {
 			bind_addr
 		);
 
-		tokio::pin!(shutdown_signal);
-
 		match bind_addr {
 			UnixOrTCPSocketAddress::TCPSocket(addr) => {
 				let listener = TcpListener::bind(addr).await?;
 
-				loop {
-					let (stream, client_addr) = tokio::select! {
-						acc = listener.accept() => acc?,
-						_ = &mut shutdown_signal => break,
-					};
-
-					self.launch_handler(stream, client_addr.to_string());
-				}
+				let handler = move |request, socketaddr| self.clone().handler(request, socketaddr);
+				server_loop(listener, handler, shutdown_signal).await
 			}
 			UnixOrTCPSocketAddress::UnixSocket(ref path) => {
 				if path.exists() {
@@ -131,52 +124,24 @@ impl<A: ApiHandler> ApiServer<A> {
 				}
 
 				let listener = UnixListener::bind(path)?;
+				let listener = UnixListenerOn(listener, path.display().to_string());
 
 				fs::set_permissions(
 					path,
 					Permissions::from_mode(unix_bind_addr_mode.unwrap_or(0o222)),
 				)?;
 
-				loop {
-					let (stream, _) = tokio::select! {
-						acc = listener.accept() => acc?,
-						_ = &mut shutdown_signal => break,
-					};
-
-					self.launch_handler(stream, path.display().to_string());
-				}
-			}
-		};
-
-		Ok(())
-	}
-
-	fn launch_handler<S>(self: &Arc<Self>, stream: S, client_addr: String)
-	where
-		S: AsyncRead + AsyncWrite + Send + Sync + 'static,
-	{
-		let this = self.clone();
-		let io = TokioIo::new(stream);
-
-		let serve =
-			move |req: Request<IncomingBody>| this.clone().handler(req, client_addr.to_string());
-
-		tokio::task::spawn(async move {
-			let io = Box::pin(io);
-			if let Err(e) = http1::Builder::new()
-				.serve_connection(io, service_fn(serve))
-				.await
-			{
-				debug!("Error handling HTTP connection: {}", e);
+				let handler = move |request, socketaddr| self.clone().handler(request, socketaddr);
+				server_loop(listener, handler, shutdown_signal).await
 			}
-		});
+		}
 	}
 
 	async fn handler(
 		self: Arc<Self>,
 		req: Request<IncomingBody>,
 		addr: String,
-	) -> Result<Response<BoxBody<A::Error>>, GarageError> {
+	) -> Result<Response<BoxBody<A::Error>>, http::Error> {
 		let uri = req.uri().clone();
 
 		if let Ok(forwarded_for_ip_addr) =
@@ -278,3 +243,105 @@ impl<A: ApiHandler> ApiServer<A> {
 		res
 	}
 }
+
+// ==== helper functions ====
+
+#[async_trait]
+pub trait Accept: Send + Sync + 'static {
+	type Stream: AsyncRead + AsyncWrite + Send + Sync + 'static;
+	async fn accept(&self) -> std::io::Result<(Self::Stream, String)>;
+}
+
+#[async_trait]
+impl Accept for TcpListener {
+	type Stream = TcpStream;
+	async fn accept(&self) -> std::io::Result<(Self::Stream, String)> {
+		self.accept()
+			.await
+			.map(|(stream, addr)| (stream, addr.to_string()))
+	}
+}
+
+pub struct UnixListenerOn(pub UnixListener, pub String);
+
+#[async_trait]
+impl Accept for UnixListenerOn {
+	type Stream = UnixStream;
+	async fn accept(&self) -> std::io::Result<(Self::Stream, String)> {
+		self.0
+			.accept()
+			.await
+			.map(|(stream, _addr)| (stream, self.1.clone()))
+	}
+}
+
+pub async fn server_loop<A, H, F, E>(
+	listener: A,
+	handler: H,
+	shutdown_signal: impl Future<Output = ()>,
+) -> Result<(), GarageError>
+where
+	A: Accept,
+	H: Fn(Request<IncomingBody>, String) -> F + Send + Sync + Clone + 'static,
+	F: Future<Output = Result<Response<BoxBody<E>>, http::Error>> + Send + 'static,
+	E: Send + Sync + std::error::Error + 'static,
+{
+	tokio::pin!(shutdown_signal);
+
+	let (conn_in, mut conn_out) = tokio::sync::mpsc::unbounded_channel();
+	let connection_collector = tokio::spawn(async move {
+		let mut collection = FuturesUnordered::new();
+		loop {
+			let collect_next = async {
+				if collection.is_empty() {
+					futures::future::pending().await
+				} else {
+					collection.next().await
+				}
+			};
+			tokio::select! {
+				result = collect_next => {
+					trace!("HTTP connection finished: {:?}", result);
+				}
+				new_fut = conn_out.recv() => {
+					match new_fut {
+						Some(f) => collection.push(f),
+						None => break,
+					}
+				}
+			}
+		}
+		debug!("Collecting last open HTTP connections.");
+		while let Some(conn_res) = collection.next().await {
+			trace!("HTTP connection finished: {:?}", conn_res);
+		}
+		debug!("No more HTTP connections to collect");
+	});
+
+	loop {
+		let (stream, client_addr) = tokio::select! {
+			acc = listener.accept() => acc?,
+			_ = &mut shutdown_signal => break,
+		};
+
+		let io = TokioIo::new(stream);
+
+		let handler = handler.clone();
+		let serve = move |req: Request<IncomingBody>| handler(req, client_addr.clone());
+
+		let fut = tokio::task::spawn(async move {
+			let io = Box::pin(io);
+			if let Err(e) = http1::Builder::new()
+				.serve_connection(io, service_fn(serve))
+				.await
+			{
+				debug!("Error handling HTTP connection: {}", e);
+			}
+		});
+		conn_in.send(fut)?;
+	}
+
+	connection_collector.await?;
+
+	Ok(())
+}
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