feat: add from_fn middleware (#3447)

actix-web/CHANGES.md

@@ -4,6 +4,7 @@
 
 ### Added
 
+- Add `middleware::from_fn()` helper.
 - Add `web::ThinData` extractor.
 
 ## 4.8.0

actix-web/examples/middleware_from_fn.rs

@@ -0,0 +1,127 @@
+//! Shows a couple of ways to use the `from_fn` middleware.
+
+use std::{collections::HashMap, io, rc::Rc, time::Duration};
+
+use actix_web::{
+    body::MessageBody,
+    dev::{Service, ServiceRequest, ServiceResponse, Transform},
+    http::header::{self, HeaderValue, Range},
+    middleware::{from_fn, Logger, Next},
+    web::{self, Header, Query},
+    App, Error, HttpResponse, HttpServer,
+};
+
+async fn noop<B>(req: ServiceRequest, next: Next<B>) -> Result<ServiceResponse<B>, Error> {
+    next.call(req).await
+}
+
+async fn print_range_header<B>(
+    range_header: Option<Header<Range>>,
+    req: ServiceRequest,
+    next: Next<B>,
+) -> Result<ServiceResponse<B>, Error> {
+    if let Some(Header(range)) = range_header {
+        println!("Range: {range}");
+    } else {
+        println!("No Range header");
+    }
+
+    next.call(req).await
+}
+
+async fn mutate_body_type(
+    req: ServiceRequest,
+    next: Next<impl MessageBody + 'static>,
+) -> Result<ServiceResponse<impl MessageBody>, Error> {
+    let res = next.call(req).await?;
+    Ok(res.map_into_left_body::<()>())
+}
+
+async fn mutate_body_type_with_extractors(
+    string_body: String,
+    query: Query<HashMap<String, String>>,
+    req: ServiceRequest,
+    next: Next<impl MessageBody + 'static>,
+) -> Result<ServiceResponse<impl MessageBody>, Error> {
+    println!("body is: {string_body}");
+    println!("query string: {query:?}");
+
+    let res = next.call(req).await?;
+
+    Ok(res.map_body(move |_, _| string_body))
+}
+
+async fn timeout_10secs(
+    req: ServiceRequest,
+    next: Next<impl MessageBody + 'static>,
+) -> Result<ServiceResponse<impl MessageBody>, Error> {
+    match tokio::time::timeout(Duration::from_secs(10), next.call(req)).await {
+        Ok(res) => res,
+        Err(_err) => Err(actix_web::error::ErrorRequestTimeout("")),
+    }
+}
+
+struct MyMw(bool);
+
+impl MyMw {
+    async fn mw_cb(
+        &self,
+        req: ServiceRequest,
+        next: Next<impl MessageBody + 'static>,
+    ) -> Result<ServiceResponse<impl MessageBody>, Error> {
+        let mut res = match self.0 {
+            true => req.into_response("short-circuited").map_into_right_body(),
+            false => next.call(req).await?.map_into_left_body(),
+        };
+
+        res.headers_mut()
+            .insert(header::WARNING, HeaderValue::from_static("42"));
+
+        Ok(res)
+    }
+
+    pub fn into_middleware<S, B>(
+        self,
+    ) -> impl Transform<
+        S,
+        ServiceRequest,
+        Response = ServiceResponse<impl MessageBody>,
+        Error = Error,
+        InitError = (),
+    >
+    where
+        S: Service<ServiceRequest, Response = ServiceResponse<B>, Error = Error> + 'static,
+        B: MessageBody + 'static,
+    {
+        let this = Rc::new(self);
+        from_fn(move |req, next| {
+            let this = Rc::clone(&this);
+            async move { Self::mw_cb(&this, req, next).await }
+        })
+    }
+}
+
+#[actix_web::main]
+async fn main() -> io::Result<()> {
+    env_logger::init_from_env(env_logger::Env::new().default_filter_or("info"));
+
+    let bind = ("127.0.0.1", 8080);
+    log::info!("staring server at http://{}:{}", &bind.0, &bind.1);
+
+    HttpServer::new(|| {
+        App::new()
+            .wrap(from_fn(noop))
+            .wrap(from_fn(print_range_header))
+            .wrap(from_fn(mutate_body_type))
+            .wrap(from_fn(mutate_body_type_with_extractors))
+            .wrap(from_fn(timeout_10secs))
+            // switch bool to true to observe early response
+            .wrap(MyMw(false).into_middleware())
+            .wrap(Logger::default())
+            .default_service(web::to(HttpResponse::Ok))
+    })
+    .workers(1)
+    .bind(bind)?
+    .run()
+    .await
+}