Trait actix_service::Service [−][src]
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(&self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> { ... } fn call(&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
type Response
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Responses given by the service.
type Error
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Errors produced by the service when polling readiness or executing call.
type Future: Future<Output = Result<Self::Response, Self::Error>>
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The future response value.
Required methods
fn poll_ready(&self, ctx: &mut Context<'_>) -> Poll<Result<(), Self::Error>>
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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
poll_ready
might be called on a different task tocall
.- In cases of chained services,
.poll_ready()
is called for all services at once.
fn call(&self, req: Req) -> Self::Future
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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.
Implementations on Foreign Types
impl<S: ?Sized, Req> Service<Req> for Box<S> where
S: Service<Req>,
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S: Service<Req>,
type Response = S::Response
type Error = S::Error
type Future = S::Future
fn poll_ready(&self, ctx: &mut Context<'_>) -> Poll<Result<(), S::Error>>
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fn call(&self, request: Req) -> S::Future
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impl<S: ?Sized, Req> Service<Req> for Rc<S> where
S: Service<Req>,
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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>>
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fn call(&self, request: Req) -> S::Future
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impl<S, Req> Service<Req> for RefCell<S> where
S: Service<Req>,
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S: Service<Req>,
This impl is deprecated since v2 because the Service
trait now receives shared reference.
type Response = S::Response
type Error = S::Error
type Future = S::Future
fn poll_ready(&self, ctx: &mut Context<'_>) -> Poll<Result<(), Self::Error>>
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fn call(&self, request: Req) -> S::Future
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Implementors
impl<'a, S, Req> Service<Req> for &'a S where
S: Service<Req> + 'a,
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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>>
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fn call(&self, request: Req) -> S::Future
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impl<'a, S, Req> Service<Req> for &'a mut S where
S: Service<Req> + 'a,
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S: Service<Req> + 'a,