Trait actix_web::dev::Service[−][src]

pub trait Service {
    type Request;
    type Response;
    type Error;
    type Future: Future;
    fn poll_ready(
        &mut self, 
        ctx: &mut Context<'_>
    ) -> Poll<Result<(), Self::Error>>;

    fn call(&mut self, req: Self::Request) -> Self::Future;

    fn map<F, R>(self, f: F) -> Map<Self, F, R>
    where
        F: FnMut(Self::Response) -> R,
    { ... }

    fn map_err<F, E>(self, f: F) -> MapErr<Self, F, E>
    where
        F: Fn(Self::Error) -> E,
    { ... }
}
Expand description

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:

ⓘ
async fn(Request) -> Result<Response, Err>

The Service trait just generalizes this form where each parameter is described as an associated type on the trait. Services can also have mutable state that influence computation.

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.

ⓘ
struct MyService;

impl Service for MyService {
     type Request = u8;
     type Response = u64;
     type Error = MyError;
     type Future = Pin<Box<Future<Output=Result<Self::Response, Self::Error>>>>;

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

     fn call(&mut self, req: Self::Request) -> 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.

ⓘ
async fn my_service(req: u8) -> Result<u64, MyError>;

Associated Types

Requests handled by the service.

Responses given by the service.

Errors produced by the service.

The future response value.

Required methods

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 different task from actual service call.
  2. In case of chained services, .poll_ready() get called for all services at once.

Process the request and return the response asynchronously.

This function is expected to be callable off task. As such, implementations 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.

Calling call without calling poll_ready is permitted. The implementation must be resilient to this fact.

Provided methods

Map this service’s output to a different type, returning a new service of the resulting type.

This function is similar to the Option::map or Iterator::map where it will change the type of the underlying service.

Note that this function consumes the receiving service and returns a wrapped version of it, similar to the existing map methods in the standard library.

Map this service’s error to a different error, returning a new service.

This function is similar to the Result::map_err where it will change the error type of the underlying service. For example, this can be useful to ensure that services have the same error type.

Note that this function consumes the receiving service and returns a wrapped version of it.

Implementations on Foreign Types

Implementors