First pass at Middlewares.

examples/middleware/Cargo.toml

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+[package]
+name = "middleware"
+version = "0.1.0"
+edition = "2018"
+
+[dependencies]
+actix-web = "1.0"
+actix-service = "0.4"
+actix-session = "0.1"
+futures = "0.1"
+env_logger = "0.6"

examples/middleware/src/default_headers.rs

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+// <default-headers>
+use actix_web::{http, middleware, web, App, HttpResponse};
+
+fn main() {
+    App::new()
+        .wrap(middleware::DefaultHeaders::new().header("X-Version", "0.2"))
+        .service(
+            web::resource("/test")
+                .route(web::get().to(|| HttpResponse::Ok()))
+                .route(
+                    web::method(http::Method::HEAD)
+                        .to(|| HttpResponse::MethodNotAllowed()),
+                ),
+        );
+}
+// </default-headers>

examples/middleware/src/errorhandler.rs

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+// <error-handler>
+use actix_web::middleware::errhandlers::{ErrorHandlerResponse, ErrorHandlers};
+use actix_web::{dev, http, web, App, HttpResponse, Result};
+
+fn render_500<B>(mut res: dev::ServiceResponse<B>) -> Result<ErrorHandlerResponse<B>> {
+    res.response_mut().headers_mut().insert(
+        http::header::CONTENT_TYPE,
+        http::HeaderValue::from_static("Error"),
+    );
+    Ok(ErrorHandlerResponse::Response(res))
+}
+
+fn main() {
+    App::new()
+        .wrap(
+            ErrorHandlers::new()
+                .handler(http::StatusCode::INTERNAL_SERVER_ERROR, render_500),
+        )
+        .service(
+            web::resource("/test")
+                .route(web::get().to(|| HttpResponse::Ok()))
+                .route(web::head().to(|| HttpResponse::MethodNotAllowed())),
+        );
+}
+// </error-handler>

examples/middleware/src/logger.rs

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+// <logger>
+use actix_web::middleware::Logger;
+use actix_web::App;
+use env_logger;
+
+fn main() {
+    std::env::set_var("RUST_LOG", "actix_web=info");
+    env_logger::init();
+
+    App::new()
+        .wrap(Logger::default())
+        .wrap(Logger::new("%a %{User-Agent}i"));
+}
+// </logger>

examples/middleware/src/main.rs

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+mod default_headers;
+mod errorhandler;
+mod logger;
+mod user_sessions;
+// <main>
+use actix_service::{Service, Transform};
+use actix_web::{dev::ServiceRequest, dev::ServiceResponse, web, App, Error};
+use futures::future::{ok, FutureResult};
+use futures::{Future, Poll};
+
+// There are two steps in middleware processing.
+// 1. Middleware initialization, middleware factory gets called with
+//    next service in chain as parameter.
+// 2. Middleware's call method gets called with normal request.
+pub struct SayHi;
+
+// Middleware factory is `Transform` trait from actix-service crate
+// `S` - type of the next service
+// `B` - type of response's body
+impl<S, B> Transform<S> for SayHi
+where
+    S: Service<Request = ServiceRequest, Response = ServiceResponse<B>, Error = Error>,
+    S::Future: 'static,
+    B: 'static,
+{
+    type Request = ServiceRequest;
+    type Response = ServiceResponse<B>;
+    type Error = Error;
+    type InitError = ();
+    type Transform = SayHiMiddleware<S>;
+    type Future = FutureResult<Self::Transform, Self::InitError>;
+
+    fn new_transform(&self, service: S) -> Self::Future {
+        ok(SayHiMiddleware { service })
+    }
+}
+
+pub struct SayHiMiddleware<S> {
+    service: S,
+}
+
+impl<S, B> Service for SayHiMiddleware<S>
+where
+    S: Service<Request = ServiceRequest, Response = ServiceResponse<B>, Error = Error>,
+    S::Future: 'static,
+    B: 'static,
+{
+    type Request = ServiceRequest;
+    type Response = ServiceResponse<B>;
+    type Error = Error;
+    type Future = Box<Future<Item = Self::Response, Error = Self::Error>>;
+
+    fn poll_ready(&mut self) -> Poll<(), Self::Error> {
+        self.service.poll_ready()
+    }
+
+    fn call(&mut self, req: ServiceRequest) -> Self::Future {
+        println!("Hi from start. You requested: {}", req.path());
+
+        Box::new(self.service.call(req).and_then(|res| {
+            println!("Hi from response");
+            Ok(res)
+        }))
+    }
+}
+// </main>
+fn main() {
+    App::new().wrap(SayHi).service(
+        web::resource("/")
+            .to(|| "Hello, middleware! Check the console where the server is run."),
+    );
+}

examples/middleware/src/user_sessions.rs

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+// <user-session>
+use actix_session::{CookieSession, Session};
+use actix_web::{middleware::Logger, web, App, HttpRequest, HttpServer, Result};
+
+/// simple index handler with session
+fn index(session: Session, req: HttpRequest) -> Result<&'static str> {
+    println!("{:?}", req);
+
+    // RequestSession trait is used for session access
+    let mut counter = 1;
+    if let Some(count) = session.get::<i32>("counter")? {
+        println!("SESSION value: {}", count);
+        counter = count + 1;
+        session.set("counter", counter)?;
+    } else {
+        session.set("counter", counter)?;
+    }
+
+    Ok("welcome!")
+}
+
+fn main() -> std::io::Result<()> {
+    std::env::set_var("RUST_LOG", "actix_web=info");
+    env_logger::init();
+
+    HttpServer::new(|| {
+        App::new()
+            // enable logger
+            .wrap(Logger::default())
+            // cookie session middleware
+            .wrap(CookieSession::signed(&[0; 32]).secure(false))
+            .service(web::resource("/").to(index))
+    })
+    .bind("127.0.0.1:8080")?
+    .run()
+}
+// </user-session>