docs(examples): update state example to async/await

Author: weihanglo

examples/state.rs

@@ -0,0 +1,56 @@
+#![feature(async_await)]
+#![deny(warnings)]
+
+use std::sync::{Arc, atomic::{AtomicUsize, Ordering}};
+
+use hyper::{Body, Error, Response, Server};
+use hyper::service::{make_service_fn, service_fn};
+
+#[hyper::rt::main]
+async fn main() {
+    pretty_env_logger::init();
+
+    let addr = ([127, 0, 0, 1], 3000).into();
+
+    // For the most basic of state, we just share a counter, that increments
+    // with each request, and we send its value back in the response.
+    let counter = Arc::new(AtomicUsize::new(0));
+
+    // The closure inside `make_service_fn` is run for each connection,
+    // creating a 'service' to handle requests for that specific connection.
+    let make_service = make_service_fn(move |_| {
+        // While the state was moved into the make_service closure,
+        // we need to clone it here because this closure is called
+        // once for every connection.
+        //
+        // Each connection could send multiple requests, so
+        // the `Service` needs a clone to handle later requests.
+        let counter = counter.clone();
+
+        async move {
+            // This is the `Service` that will handle the connection.
+            // `service_fn` is a helper to convert a function that
+            // returns a Response into a `Service`.
+            Ok::<_, Error>(service_fn(move |_req| {
+                // Get the current count, and also increment by 1, in a single
+                // atomic operation.
+                let count = counter.fetch_add(1, Ordering::AcqRel);
+                async move {
+                    Ok::<_, Error>(
+                        Response::new(Body::from(format!("Request #{}", count)))
+                    )
+                }
+            }))
+        }
+    });
+
+    let server = Server::bind(&addr)
+        .serve(make_service);
+
+    println!("Listening on http://{}", addr);
+
+    if let Err(e) = server.await {
+        eprintln!("server error: {}", e);
+    }
+}
+