Add an example for head request (tokio-rs#1175)

As tokio-rs#84 add get-head request, adding an example.

examples/handle-head-request/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "example-handle-head-request"
+version = "0.1.0"
+edition = "2021"
+publish = false
+
+[dependencies]
+axum = { path = "../../axum" }
+tokio = { version = "1.0", features = ["full"] }
+
+[dev-dependencies]
+tower = { version = "0.4", features = ["util"] }
+hyper = { version = "0.14", features = ["full"] }

examples/handle-head-request/src/main.rs

@@ -0,0 +1,82 @@
+//! Run with
+//!
+//! ```not_rust
+//! cd examples && cargo run -p example-handle-head-reqeust
+//! ```
+
+use axum::response::{IntoResponse, Response};
+use axum::{http, routing::get, Router};
+use std::net::SocketAddr;
+
+fn app() -> Router {
+    Router::new().route("/get-head", get(get_head_handler))
+}
+
+#[tokio::main]
+async fn main() {
+    let addr = SocketAddr::from(([127, 0, 0, 1], 3000));
+
+    axum::Server::bind(&addr)
+        .serve(app().into_make_service())
+        .await
+        .unwrap();
+}
+
+// get routes will also be called for HEAD requests but will have the response body removed
+// can handle implicit head method request by extract `http::Method` from request
+async fn get_head_handler(method: http::Method) -> Response {
+    // it usually makes sense to handle only special-case HEAD
+    // if computing the body has some relevant cost
+    if method == http::Method::HEAD {
+        return ([("x-some-header", "header from HEAD")]).into_response();
+    }
+
+    // then do some computing task in GET
+    do_some_computing_task();
+
+    ([("x-some-header", "header from GET")], "body from GET").into_response()
+}
+
+fn do_some_computing_task() {
+    // TODO
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use axum::body::Body;
+    use axum::http::{Request, StatusCode};
+    use tower::ServiceExt;
+
+    #[tokio::test]
+    async fn test_get() {
+        let app = app();
+
+        let response = app
+            .oneshot(Request::get("/get-head").body(Body::empty()).unwrap())
+            .await
+            .unwrap();
+
+        assert_eq!(response.status(), StatusCode::OK);
+        assert_eq!(response.headers()["x-some-header"], "header from GET");
+
+        let body = hyper::body::to_bytes(response.into_body()).await.unwrap();
+        assert_eq!(&body[..], b"body from GET");
+    }
+
+    #[tokio::test]
+    async fn test_implicit_head() {
+        let app = app();
+
+        let response = app
+            .oneshot(Request::head("/get-head").body(Body::empty()).unwrap())
+            .await
+            .unwrap();
+
+        assert_eq!(response.status(), StatusCode::OK);
+        assert_eq!(response.headers()["x-some-header"], "header from HEAD");
+
+        let body = hyper::body::to_bytes(response.into_body()).await.unwrap();
+        assert!(body.is_empty());
+    }
+}