Add CORS example (#512)

examples/cors/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "example-cors"
+version = "0.1.0"
+edition = "2018"
+publish = false
+
+[dependencies]
+axum = { path = "../../axum" }
+tokio = { version = "1.0", features = ["full"] }
+tower-http = { version = "0.1", features = ["cors"] }

examples/cors/src/main.rs

@@ -0,0 +1,59 @@
+//! Run with
+//!
+//! ```not_rust
+//! cargo run -p example-cors
+//! ```
+
+use axum::{
+    http::Method,
+    response::{Html, IntoResponse},
+    routing::get,
+    Json, Router,
+};
+use std::net::SocketAddr;
+use tower_http::cors::{CorsLayer, Origin};
+
+#[tokio::main]
+async fn main() {
+    let frontend = async {
+        let app = Router::new().route("/", get(html));
+        serve(app, 3000).await;
+    };
+
+    let backend = async {
+        let app = Router::new().route("/json", get(json)).layer(
+            // see https://docs.rs/tower-http/latest/tower_http/cors/index.html
+            // for more details
+            CorsLayer::new()
+                .allow_origin(Origin::exact("http://localhost:3000".parse().unwrap()))
+                .allow_methods(vec![Method::GET]),
+        );
+        serve(app, 4000).await;
+    };
+
+    tokio::join!(frontend, backend);
+}
+
+async fn serve(app: Router, port: u16) {
+    let addr = SocketAddr::from(([127, 0, 0, 1], port));
+    axum::Server::bind(&addr)
+        .serve(app.into_make_service())
+        .await
+        .unwrap();
+}
+
+async fn html() -> impl IntoResponse {
+    Html(
+        r#"
+        <script>
+            fetch('http://localhost:4000/json')
+              .then(response => response.json())
+              .then(data => console.log(data));
+        </script>
+        "#,
+    )
+}
+
+async fn json() -> impl IntoResponse {
+    Json(vec!["one", "two", "three"])
+}