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//! Definition of the core `Service` trait to Tokio //! //! More information can be found on [the trait] itself. //! //! [the trait]: trait.Service.html #![deny(missing_docs)] extern crate futures; use futures::Future; use std::io; use std::rc::Rc; use std::sync::Arc; /// An asynchronous function from `Request` to a `Response`. /// /// The `Service` trait is a simplified interface making it easy to write /// network applications in a modular and reusable way, decoupled from the /// underlying protocol. It is one of Tokio's fundamental abstractions. /// /// # Functional /// /// A `Service` is a function from a `Request`. It immediately returns a /// `Future` representing the eventual completion of processing the /// request. The actual request processing may happen at any time in the /// future, on any thread or executor. The processing may depend on calling /// other services. At some point in the future, the processing will complete, /// and the `Future` will resolve to a response or error. /// /// At a high level, the `Service::call` represents an RPC request. The /// `Service` value can be a server or a client. /// /// # Server /// /// An RPC server *implements* the `Service` trait. Requests received by the /// server over the network are deserialized then passed as an argument to the /// server value. The returned response is sent back over the network. /// /// As an example, here is how an HTTP request is processed by a server: /// /// ```rust,ignore /// impl Service for HelloWorld { /// type Request = http::Request; /// type Response = http::Response; /// type Error = http::Error; /// type Future = Box<Future<Item = Self::Response, Error = http::Error>>; /// /// fn call(&self, req: http::Request) -> Self::Future { /// // Create the HTTP response /// let resp = http::Response::ok() /// .with_body(b"hello world\n"); /// /// // Return the response as an immediate future /// futures::finished(resp).boxed() /// } /// } /// ``` /// /// # Client /// /// A client consumes a service by using a `Service` value. The client may /// issue requests by invoking `call` and passing the request as an argument. /// It then receives the response by waiting for the returned future. /// /// As an example, here is how a Redis request would be issued: /// /// ```rust,ignore /// let client = redis::Client::new() /// .connect("127.0.0.1:6379".parse().unwrap()) /// .unwrap(); /// /// let resp = client.call(Cmd::set("foo", "this is the value of foo")); /// /// // Wait for the future to resolve /// println!("Redis response: {:?}", await(resp)); /// ``` /// /// # Middleware /// /// More often than not, all the pieces needed for writing robust, scalable /// network applications are the same no matter the underlying protocol. By /// unifying the API for both clients and servers in a protocol agnostic way, /// it is possible to write middleware that provide these pieces in a /// reusable way. /// /// For example, take timeouts as an example: /// /// ```rust,ignore /// use tokio::Service; /// use futures::Future; /// use std::time::Duration; /// /// // Not yet implemented, but soon :) /// use tokio::timer::{Timer, Expired}; /// /// pub struct Timeout<T> { /// upstream: T, /// delay: Duration, /// timer: Timer, /// } /// /// impl<T> Timeout<T> { /// pub fn new(upstream: T, delay: Duration) -> Timeout<T> { /// Timeout { /// upstream: upstream, /// delay: delay, /// timer: Timer::default(), /// } /// } /// } /// /// impl<T> Service for Timeout<T> /// where T: Service, /// T::Error: From<Expired>, /// { /// type Request = T::Request; /// type Response = T::Response; /// type Error = T::Error; /// type Future = Box<Future<Item = Self::Response, Error = Self::Error>>; /// /// fn call(&self, req: Self::Req) -> Self::Future { /// let timeout = self.timer.timeout(self.delay) /// .and_then(|timeout| Err(Self::Error::from(timeout))); /// /// self.upstream.call(req) /// .select(timeout) /// .map(|(v, _)| v) /// .map_err(|(e, _)| e) /// .boxed() /// } /// } /// /// ``` /// /// The above timeout implementation is decoupled from the underlying protocol /// and is also decoupled from client or server concerns. In other words, the /// same timeout middleware could be used in either a client or a server. pub trait Service { /// Requests handled by the service. type Request; /// Responses given by the service. type Response; /// Errors produced by the service. type Error; /// The future response value. type Future: Future<Item = Self::Response, Error = Self::Error>; /// Process the request and return the response asynchronously. fn call(&self, req: Self::Request) -> Self::Future; } /// Creates new `Service` values. pub trait NewService { /// Requests handled by the service type Request; /// Responses given by the service type Response; /// Errors produced by the service type Error; /// The `Service` value created by this factory type Instance: Service<Request = Self::Request, Response = Self::Response, Error = Self::Error>; /// Create and return a new service value. fn new_service(&self) -> io::Result<Self::Instance>; } impl<F, R> NewService for F where F: Fn() -> io::Result<R>, R: Service, { type Request = R::Request; type Response = R::Response; type Error = R::Error; type Instance = R; fn new_service(&self) -> io::Result<R> { (*self)() } } impl<S: NewService + ?Sized> NewService for Arc<S> { type Request = S::Request; type Response = S::Response; type Error = S::Error; type Instance = S::Instance; fn new_service(&self) -> io::Result<S::Instance> { (**self).new_service() } } impl<S: NewService + ?Sized> NewService for Rc<S> { type Request = S::Request; type Response = S::Response; type Error = S::Error; type Instance = S::Instance; fn new_service(&self) -> io::Result<S::Instance> { (**self).new_service() } } impl<S: Service + ?Sized> Service for Box<S> { type Request = S::Request; type Response = S::Response; type Error = S::Error; type Future = S::Future; fn call(&self, request: S::Request) -> S::Future { (**self).call(request) } } impl<S: Service + ?Sized> Service for Rc<S> { type Request = S::Request; type Response = S::Response; type Error = S::Error; type Future = S::Future; fn call(&self, request: S::Request) -> S::Future { (**self).call(request) } } impl<S: Service + ?Sized> Service for Arc<S> { type Request = S::Request; type Response = S::Response; type Error = S::Error; type Future = S::Future; fn call(&self, request: S::Request) -> S::Future { (**self).call(request) } }