use async_std::io::prelude::*; use async_std::io::Error; use async_std::net::{TcpListener, TcpStream}; use async_std::prelude::Future; use async_std::task; use std::time::Duration; struct Server { addr: String, } impl Server { fn new(addr: String) -> Self { Self { addr } } async fn run(self, handler: F) -> Result<(), Error> where // `handler` now returns a generic type `Fut`... F: Fn(String) -> Fut, // ...which is a `Future` whose `Output` is an `HttpResponse` Fut: Future, { let listener = TcpListener::bind(self.addr).await?; loop { let (mut connection, _) = listener.accept().await?; let request = read_http_request(&mut connection).await?; task::sleep(Duration::from_secs(10)).await; // Await the future returned by `handler` let response = handler(request).await; write_http_response(connection, response).await?; } } } async fn read_http_request(stream: &mut TcpStream) -> Result { let mut buffer = [0; 1024]; stream.read(&mut buffer).await?; let request = format!("Request: {}", String::from_utf8_lossy(&buffer[..])); Ok(request) } async fn basic_handler(request: String) -> String { let contents = format!( r#" Hello!

Hello!

Hi from Rust

{}

"#, request ); format!( "HTTP/1.1 200 OK\r\nContent-Length: {}\r\n\r\n{}", contents.len(), contents, ) } async fn write_http_response(mut stream: TcpStream, response: String) -> Result<(), Error> { stream.write(response.as_bytes()).await?; stream.flush().await?; Ok(()) } fn main() -> std::io::Result<()> { let server = Server::new("127.0.0.1:8989".to_string()); task::block_on(server.run(basic_handler))?; Ok(()) }