From 2a3abc5cfab55a80f35438d195a2151478aa4f93 Mon Sep 17 00:00:00 2001
From: Martin Pitt <martin@piware.de>
Date: Fri, 16 Sep 2022 08:47:48 +0200
Subject: [PATCH] async-http: Serve requests concurrently

Move to asyncstd TCPListener and futures Stream, so that the incoming
loop does not serialize/block requests any more.

This is still single-threaded. That can be demonstrated with replacing
the async sleep with a sync one (commented out). Then /sleep will block
other requests again.
---
 async-http/Cargo.toml  |  1 +
 async-http/src/main.rs | 25 +++++++++++++------------
 2 files changed, 14 insertions(+), 12 deletions(-)

diff --git a/async-http/Cargo.toml b/async-http/Cargo.toml
index 92c94f5..30b4930 100644
--- a/async-http/Cargo.toml
+++ b/async-http/Cargo.toml
@@ -6,6 +6,7 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+futures = "0.3"
 log = "0.4"
 env_logger = "0.9"
 
diff --git a/async-http/src/main.rs b/async-http/src/main.rs
index c36be0a..cf0b46d 100644
--- a/async-http/src/main.rs
+++ b/async-http/src/main.rs
@@ -1,29 +1,28 @@
 use std::fs;
-use std::io::prelude::*;
-use std::net::{ TcpListener, TcpStream };
 use std::time::Duration;
 
+use async_std::prelude::*;
+use async_std::net::{ TcpListener, TcpStream };
 use async_std::task;
+use futures::stream::StreamExt;
 
 #[async_std::main]
 async fn main() {
     env_logger::Builder::from_env(env_logger::Env::default().default_filter_or("info")).init();
 
     // Listen for incoming TCP connections on localhost port 7878
-    let listener = TcpListener::bind("127.0.0.1:7878").unwrap();
+    let listener = TcpListener::bind("127.0.0.1:7878").await.unwrap();
 
-    // Block forever, handling each request that arrives at this IP address
-    for stream in listener.incoming() {
-        let stream = stream.unwrap();
-        // not concurrent
-        handle_connection(stream).await;
-    }
+    listener.incoming().for_each_concurrent(/* limit */ None, |tcpstream| async move {
+        let tcpstream = tcpstream.unwrap();
+        handle_connection(tcpstream).await;
+    }).await;
 }
 
 async fn handle_connection(mut stream: TcpStream) {
     // Read the first 1024 bytes of data from the stream
     let mut buffer = [0; 1024];
-    assert!(stream.read(&mut buffer).unwrap() > 0);
+    assert!(stream.read(&mut buffer).await.unwrap() > 0);
 
     // Respond with greetings or a 404,
     // depending on the data in the request
@@ -31,6 +30,8 @@ async fn handle_connection(mut stream: TcpStream) {
         ("HTTP/1.1 200 OK", "index.html")
     } else if buffer.starts_with(b"GET /sleep HTTP/1.1\r\n") {
         task::sleep(Duration::from_secs(5)).await;
+        // sync version, to demonstrate concurrent async vs. parallel threads
+        // std::thread::sleep(Duration::from_secs(5));
         ("HTTP/1.1 201 Sleep", "index.html")
     } else {
         ("HTTP/1.1 404 NOT FOUND", "404.html")
@@ -41,6 +42,6 @@ async fn handle_connection(mut stream: TcpStream) {
     // Write response back to the stream,
     // and flush the stream to ensure the response is sent back to the client
     let response = format!("{status_line}\r\n\r\n{contents}");
-    stream.write_all(response.as_bytes()).unwrap();
-    stream.flush().unwrap();
+    stream.write_all(response.as_bytes()).await.unwrap();
+    stream.flush().await.unwrap();
 }
-- 
2.39.2