Struct tower::ServiceBuilder

pub struct ServiceBuilder<L> { /* fields omitted */ }

Declaratively construct Service values.

ServiceBuilder provides a builder-like interface for composing layers to be applied to a Service.

Service

A Service is a trait representing an asynchronous function of a request to a response. It is similar to async fn(Request) -> Result<Response, Error>.

A Service is typically bound to a single transport, such as a TCP connection. It defines how all inbound or outbound requests are handled by that connection.

Order

The order in which layers are added impacts how requests are handled. Layers that are added first will be called with the request first. The argument to service will be last to see the request.

ServiceBuilder::new()
    .buffer(100)
    .concurrency_limit(10)
    .service(svc)

In the above example, the buffer layer receives the request first followed by concurrency_limit. buffer enables up to 100 request to be in-flight on top of the requests that have already been forwarded to the next layer. Combined with concurrency_limit, this allows up to 110 requests to be in-flight.

ServiceBuilder::new()
    .concurrency_limit(10)
    .buffer(100)
    .service(svc)

The above example is similar, but the order of layers is reversed. Now, concurrency_limit applies first and only allows 10 requests to be in-flight total.

Examples

A Service stack with a single layer:

ServiceBuilder::new()
    .concurrency_limit(5)
    .service(svc);

A Service stack with multiple layers that contain rate limiting, in-flight request limits, and a channel-backed, clonable Service:

ServiceBuilder::new()
    .buffer(5)
    .concurrency_limit(5)
    .rate_limit(5, Duration::from_secs(1))
    .service(svc);

Implementations

impl ServiceBuilder<Identity>

pub fn new() -> Self

Create a new ServiceBuilder.

impl<L> ServiceBuilder<L>

pub fn layer<T>(self, layer: T) -> ServiceBuilder<Stack<T, L>>

Add a new layer T into the ServiceBuilder.

This wraps the inner service with the service provided by a user-defined Layer. The provided layer must implement the Layer trait.

pub fn buffer<Request>(
    self,
    bound: usize
) -> ServiceBuilder<Stack<BufferLayer<Request>, L>>

Buffer requests when when the next layer is not ready.

This wraps the inner service with an instance of the Buffer middleware.

pub fn concurrency_limit(
    self,
    max: usize
) -> ServiceBuilder<Stack<ConcurrencyLimitLayer, L>>

Limit the max number of in-flight requests.

A request is in-flight from the time the request is received until the response future completes. This includes the time spent in the next layers.

This wraps the inner service with an instance of the ConcurrencyLimit middleware.

pub fn rate_limit(
    self,
    num: u64,
    per: Duration
) -> ServiceBuilder<Stack<RateLimitLayer, L>>

Limit requests to at most num per the given duration.

This wraps the inner service with an instance of the RateLimit middleware.

pub fn timeout(
    self,
    timeout: Duration
) -> ServiceBuilder<Stack<TimeoutLayer, L>>

Fail requests that take longer than timeout.

If the next layer takes more than timeout to respond to a request, processing is terminated and an error is returned.

This wraps the inner service with an instance of the timeout middleware.

pub fn map_request<F, R1, R2>(
    self,
    f: F
) -> ServiceBuilder<Stack<MapRequestLayer<F>, L>> where
    F: FnMut(R1) -> R2 + Clone, 

Map one request type to another.

This wraps the inner service with an instance of the MapRequest middleware.

Examples

Changing the type of a request:

use tower::ServiceBuilder;
use tower::ServiceExt;

// Suppose we have some `Service` whose request type is `String`:
let string_svc = tower::service_fn(|request: String| async move {
    println!("request: {}", request);
    Ok(())
});

// ...but we want to call that service with a `usize`. What do we do?

let usize_svc = ServiceBuilder::new()
     // Add a middlware that converts the request type to a `String`:
    .map_request(|request: usize| format!("{}", request))
    // ...and wrap the string service with that middleware:
    .service(string_svc);

// Now, we can call that service with a `usize`:
usize_svc.oneshot(42).await?;

Modifying the request value:

use tower::ServiceBuilder;
use tower::ServiceExt;

// A service that takes a number and returns it:
let svc = tower::service_fn(|request: usize| async move {
   Ok(request)
});

let svc = ServiceBuilder::new()
     // Add a middleware that adds 1 to each request
    .map_request(|request: usize| request + 1)
    .service(svc);

let response = svc.oneshot(1).await?;
assert_eq!(response, 2);

pub fn map_response<F>(
    self,
    f: F
) -> ServiceBuilder<Stack<MapResponseLayer<F>, L>>

Map one response type to another.

This wraps the inner service with an instance of the MapResponse middleware.

See the documentation for the map_response combinator for details.

pub fn map_err<F>(self, f: F) -> ServiceBuilder<Stack<MapErrLayer<F>, L>>

Map one error type to another.

This wraps the inner service with an instance of the MapErr middleware.

See the documentation for the map_err combinator for details.

pub fn then<F>(self, f: F) -> ServiceBuilder<Stack<ThenLayer<F>, L>>

Apply a function after the service, regardless of whether the future succeeds or fails.

This wraps the inner service with an instance of the Then middleware.

This is similar to the map_response and map_err functions, except that the same function is invoked when the service's future completes, whether it completes successfully or fails. This function takes the Result returned by the service's future, and returns a Result.

See the documentation for the then combinator for details.

pub fn into_inner(self) -> L

Returns the underlying Layer implementation.

pub fn service<S>(&self, service: S) -> L::Service where
    L: Layer<S>, 

Wrap the service S with the middleware provided by this ServiceBuilder's Layer's, returning a new Service.

Trait Implementations

impl<L: Clone> Clone for ServiceBuilder<L>

fn clone(&self) -> ServiceBuilder<L>

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<L: Debug> Debug for ServiceBuilder<L>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for ServiceBuilder<Identity>

fn default() -> Self

Returns the "default value" for a type.