#
actix_service/
lib.rs

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    //! See [`Service`] docs for information on this crate's foundational trait.

    #![no_std]
    #![deny(rust_2018_idioms, nonstandard_style)]
    #![warn(future_incompatible, missing_docs)]
    #![allow(clippy::type_complexity)]
    #![doc(html_logo_url = "https://actix.rs/img/logo.png")]
    #![doc(html_favicon_url = "https://actix.rs/favicon.ico")]

    extern crate alloc;

    use alloc::{boxed::Box, rc::Rc, sync::Arc};
    use core::{
        cell::RefCell,
        future::Future,
        task::{self, Context, Poll},
    };

    mod and_then;
    mod apply;
    mod apply_cfg;
    pub mod boxed;
    mod ext;
    mod fn_service;
    mod macros;
    mod map;
    mod map_config;
    mod map_err;
    mod map_init_err;
    mod pipeline;
    mod ready;
    mod then;
    mod transform;
    mod transform_err;

    #[allow(unused_imports)]
    use self::ready::{err, ok, ready, Ready};
    pub use self::{
        apply::{apply_fn, apply_fn_factory},
        apply_cfg::{apply_cfg, apply_cfg_factory},
        ext::{ServiceExt, ServiceFactoryExt, TransformExt},
        fn_service::{fn_factory, fn_factory_with_config, fn_service},
        map_config::{map_config, unit_config},
        transform::{apply, ApplyTransform, Transform},
    };

    /// An asynchronous operation from `Request` to a `Response`.
    ///
    /// The `Service` trait models a request/response interaction, receiving requests and returning
    /// replies. You can think about a service as a function with one argument that returns some result
    /// asynchronously. Conceptually, the operation looks like this:
    ///
    /// ```ignore
    /// async fn(Request) -> Result<Response, Err>
    /// ```
    ///
    /// The `Service` trait just generalizes this form. Requests are defined as a generic type parameter
    /// and responses and other details are defined as associated types on the trait impl. Notice that
    /// this design means that services can receive many request types and converge them to a single
    /// response type.
    ///
    /// Services can also have mutable state that influence computation by using a `Cell`, `RefCell`
    /// or `Mutex`. Services intentionally do not take `&mut self` to reduce overhead in the
    /// common cases.
    ///
    /// `Service` provides a symmetric and uniform API; the same abstractions can be used to represent
    /// both clients and servers. Services describe only _transformation_ operations which encourage
    /// simple API surfaces. This leads to simpler design of each service, improves test-ability and
    /// makes composition easier.
    ///
    /// ```ignore
    /// struct MyService;
    ///
    /// impl Service<u8> for MyService {
    ///      type Response = u64;
    ///      type Error = MyError;
    ///      type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>>>>;
    ///
    ///      fn poll_ready(&self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> { ... }
    ///
    ///      fn call(&self, req: u8) -> Self::Future { ... }
    /// }
    /// ```
    ///
    /// Sometimes it is not necessary to implement the Service trait. For example, the above service
    /// could be rewritten as a simple function and passed to [`fn_service`](fn_service()).
    ///
    /// ```ignore
    /// async fn my_service(req: u8) -> Result<u64, MyError>;
    ///
    /// let svc = fn_service(my_service)
    /// svc.call(123)
    /// ```
    pub trait Service<Req> {
        /// Responses given by the service.
        type Response;

        /// Errors produced by the service when polling readiness or executing call.
        type Error;

        /// The future response value.
        type Future: Future<Output = Result<Self::Response, Self::Error>>;

        /// Returns `Ready` when the service is able to process requests.
        ///
        /// If the service is at capacity, then `Pending` is returned and the task is notified when the
        /// service becomes ready again. This function is expected to be called while on a task.
        ///
        /// This is a best effort implementation. False positives are permitted. It is permitted for
        /// the service to return `Ready` from a `poll_ready` call and the next invocation of `call`
        /// results in an error.
        ///
        /// # Notes
        /// 1. `poll_ready` might be called on a different task to `call`.
        /// 1. In cases of chained services, `.poll_ready()` is called for all services at once.
        fn poll_ready(&self, ctx: &mut task::Context<'_>) -> Poll<Result<(), Self::Error>>;

        /// Process the request and return the response asynchronously.
        ///
        /// This function is expected to be callable off-task. As such, implementations of `call` should
        /// take care to not call `poll_ready`. If the service is at capacity and the request is unable
        /// to be handled, the returned `Future` should resolve to an error.
        ///
        /// Invoking `call` without first invoking `poll_ready` is permitted. Implementations must be
        /// resilient to this fact.
        fn call(&self, req: Req) -> Self::Future;
    }

    /// Factory for creating `Service`s.
    ///
    /// This is useful for cases where new `Service`s must be produced. One case is a TCP
    /// server listener: a listener accepts new connections, constructs a new `Service` for each using
    /// the `ServiceFactory` trait, and uses the new `Service` to process inbound requests on that new
    /// connection.
    ///
    /// `Config` is a service factory configuration type.
    ///
    /// Simple factories may be able to use [`fn_factory`] or [`fn_factory_with_config`] to
    /// reduce boilerplate.
    pub trait ServiceFactory<Req> {
        /// Responses given by the created services.
        type Response;

        /// Errors produced by the created services.
        type Error;

        /// Service factory configuration.
        type Config;

        /// The kind of `Service` created by this factory.
        type Service: Service<Req, Response = Self::Response, Error = Self::Error>;

        /// Errors potentially raised while building a service.
        type InitError;

        /// The future of the `Service` instance.g
        type Future: Future<Output = Result<Self::Service, Self::InitError>>;

        /// Create and return a new service asynchronously.
        fn new_service(&self, cfg: Self::Config) -> Self::Future;
    }

    // TODO: remove implement on mut reference.
    impl<'a, S, Req> Service<Req> for &'a mut S
    where
        S: Service<Req> + 'a,
    {
        type Response = S::Response;
        type Error = S::Error;
        type Future = S::Future;

        fn poll_ready(&self, ctx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
            (**self).poll_ready(ctx)
        }

        fn call(&self, request: Req) -> S::Future {
            (**self).call(request)
        }
    }

    impl<'a, S, Req> Service<Req> for &'a S
    where
        S: Service<Req> + 'a,
    {
        type Response = S::Response;
        type Error = S::Error;
        type Future = S::Future;

        fn poll_ready(&self, ctx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
            (**self).poll_ready(ctx)
        }

        fn call(&self, request: Req) -> S::Future {
            (**self).call(request)
        }
    }

    impl<S, Req> Service<Req> for Box<S>
    where
        S: Service<Req> + ?Sized,
    {
        type Response = S::Response;
        type Error = S::Error;
        type Future = S::Future;

        fn poll_ready(&self, ctx: &mut Context<'_>) -> Poll<Result<(), S::Error>> {
            (**self).poll_ready(ctx)
        }

        fn call(&self, request: Req) -> S::Future {
            (**self).call(request)
        }
    }

    impl<S, Req> Service<Req> for Rc<S>
    where
        S: Service<Req> + ?Sized,
    {
        type Response = S::Response;
        type Error = S::Error;
        type Future = S::Future;

        fn poll_ready(&self, ctx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
            (**self).poll_ready(ctx)
        }

        fn call(&self, request: Req) -> S::Future {
            (**self).call(request)
        }
    }

    /// This impl is deprecated since v2 because the `Service` trait now receives shared reference.
    impl<S, Req> Service<Req> for RefCell<S>
    where
        S: Service<Req>,
    {
        type Response = S::Response;
        type Error = S::Error;
        type Future = S::Future;

        fn poll_ready(&self, ctx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
            self.borrow().poll_ready(ctx)
        }

        fn call(&self, request: Req) -> S::Future {
            self.borrow().call(request)
        }
    }

    impl<S, Req> ServiceFactory<Req> for Rc<S>
    where
        S: ServiceFactory<Req>,
    {
        type Response = S::Response;
        type Error = S::Error;
        type Config = S::Config;
        type Service = S::Service;
        type InitError = S::InitError;
        type Future = S::Future;

        fn new_service(&self, cfg: S::Config) -> S::Future {
            self.as_ref().new_service(cfg)
        }
    }

    impl<S, Req> ServiceFactory<Req> for Arc<S>
    where
        S: ServiceFactory<Req>,
    {
        type Response = S::Response;
        type Error = S::Error;
        type Config = S::Config;
        type Service = S::Service;
        type InitError = S::InitError;
        type Future = S::Future;

        fn new_service(&self, cfg: S::Config) -> S::Future {
            self.as_ref().new_service(cfg)
        }
    }

    /// Trait for types that can be converted to a `Service`
    pub trait IntoService<S, Req>
    where
        S: Service<Req>,
    {
        /// Convert to a `Service`
        fn into_service(self) -> S;
    }

    /// Trait for types that can be converted to a `ServiceFactory`
    pub trait IntoServiceFactory<SF, Req>
    where
        SF: ServiceFactory<Req>,
    {
        /// Convert `Self` to a `ServiceFactory`
        fn into_factory(self) -> SF;
    }

    impl<S, Req> IntoService<S, Req> for S
    where
        S: Service<Req>,
    {
        fn into_service(self) -> S {
            self
        }
    }

    impl<SF, Req> IntoServiceFactory<SF, Req> for SF
    where
        SF: ServiceFactory<Req>,
    {
        fn into_factory(self) -> SF {
            self
        }
    }

    /// Convert object of type `U` to a service `S`
    pub fn into_service<I, S, Req>(tp: I) -> S
    where
        I: IntoService<S, Req>,
        S: Service<Req>,
    {
        tp.into_service()
    }