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//! Builder types to compose layers and services use tower_layer::{Identity, Layer, Stack}; use std::fmt; /// Declaratively construct [`Service`] values. /// /// [`ServiceBuilder`] provides a [builder-like interface][builder] 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. /// /// [builder]: https://doc.rust-lang.org/1.0.0/style/ownership/builders.html /// /// # 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. /// /// ``` /// # // this (and other) doctest is ignored because we don't have a way /// # // to say that it should only be run with cfg(feature = "...") /// # use tower::Service; /// # use tower::builder::ServiceBuilder; /// # #[cfg(all(feature = "buffer", feature = "limit"))] /// # async fn wrap<S>(svc: S) where S: Service<(), Error = &'static str> + 'static + Send, S::Future: Send { /// 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. /// /// ``` /// # use tower::Service; /// # use tower::builder::ServiceBuilder; /// # #[cfg(all(feature = "buffer", feature = "limit"))] /// # async fn wrap<S>(svc: S) where S: Service<(), Error = &'static str> + 'static + Send, S::Future: Send { /// 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: /// /// ``` /// # use tower::Service; /// # use tower::builder::ServiceBuilder; /// # #[cfg(feature = "limit")] /// # use tower::limit::concurrency::ConcurrencyLimitLayer; /// # #[cfg(feature = "limit")] /// # async fn wrap<S>(svc: S) where S: Service<(), Error = &'static str> + 'static + Send, S::Future: Send { /// 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`]: /// /// ``` /// # use tower::Service; /// # use tower::builder::ServiceBuilder; /// # use std::time::Duration; /// # #[cfg(all(feature = "buffer", feature = "limit"))] /// # async fn wrap<S>(svc: S) where S: Service<(), Error = &'static str> + 'static + Send, S::Future: Send { /// ServiceBuilder::new() /// .buffer(5) /// .concurrency_limit(5) /// .rate_limit(5, Duration::from_secs(1)) /// .service(svc); /// # ; /// # } /// ``` /// /// [`Service`]: crate::Service #[derive(Clone)] pub struct ServiceBuilder<L> { layer: L, } impl Default for ServiceBuilder<Identity> { fn default() -> Self { Self::new() } } impl ServiceBuilder<Identity> { /// Create a new [`ServiceBuilder`]. pub fn new() -> Self { ServiceBuilder { layer: Identity::new(), } } } impl<L> ServiceBuilder<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. /// /// [`Layer`]: crate::Layer pub fn layer<T>(self, layer: T) -> ServiceBuilder<Stack<T, L>> { ServiceBuilder { layer: Stack::new(layer, self.layer), } } /// Buffer requests when when the next layer is not ready. /// /// This wraps the inner service with an instance of the [`Buffer`] /// middleware. /// /// [`Buffer`]: crate::buffer #[cfg(feature = "buffer")] #[cfg_attr(docsrs, doc(cfg(feature = "buffer")))] pub fn buffer<Request>( self, bound: usize, ) -> ServiceBuilder<Stack<crate::buffer::BufferLayer<Request>, L>> { self.layer(crate::buffer::BufferLayer::new(bound)) } /// 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. /// /// [`ConcurrencyLimit`]: crate::limit::concurrency #[cfg(feature = "limit")] #[cfg_attr(docsrs, doc(cfg(feature = "limit")))] pub fn concurrency_limit( self, max: usize, ) -> ServiceBuilder<Stack<crate::limit::ConcurrencyLimitLayer, L>> { self.layer(crate::limit::ConcurrencyLimitLayer::new(max)) } /// Drop requests when the next layer is unable to respond to requests. /// /// Usually, when a service or middleware does not have capacity to process a /// request (i.e., [`poll_ready`] returns [`Pending`]), the caller waits until /// capacity becomes available. /// /// [`LoadShed`] immediately responds with an error when the next layer is /// out of capacity. /// /// This wraps the inner service with an instance of the [`LoadShed`] /// middleware. /// /// [`LoadShed`]: crate::load_shed /// [`poll_ready`]: crate::Service::poll_ready /// [`Pending`]: std::task::Poll::Pending #[cfg(feature = "load-shed")] #[cfg_attr(docsrs, doc(cfg(feature = "load-shed")))] pub fn load_shed(self) -> ServiceBuilder<Stack<crate::load_shed::LoadShedLayer, L>> { self.layer(crate::load_shed::LoadShedLayer::new()) } /// Limit requests to at most `num` per the given duration. /// /// This wraps the inner service with an instance of the [`RateLimit`] /// middleware. /// /// [`RateLimit`]: crate::limit::rate #[cfg(feature = "limit")] #[cfg_attr(docsrs, doc(cfg(feature = "limit")))] pub fn rate_limit( self, num: u64, per: std::time::Duration, ) -> ServiceBuilder<Stack<crate::limit::RateLimitLayer, L>> { self.layer(crate::limit::RateLimitLayer::new(num, per)) } /// Retry failed requests according to the given [retry policy][policy]. /// /// `policy` determines which failed requests will be retried. It must /// implement the [`retry::Policy`][policy] trait. /// /// This wraps the inner service with an instance of the [`Retry`] /// middleware. /// /// [`Retry`]: crate::retry /// [policy]: crate::retry::Policy #[cfg(feature = "retry")] #[cfg_attr(docsrs, doc(cfg(feature = "retry")))] pub fn retry<P>(self, policy: P) -> ServiceBuilder<Stack<crate::retry::RetryLayer<P>, L>> { self.layer(crate::retry::RetryLayer::new(policy)) } /// 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. /// /// [`timeout`]: crate::timeout #[cfg(feature = "timeout")] #[cfg_attr(docsrs, doc(cfg(feature = "timeout")))] pub fn timeout( self, timeout: std::time::Duration, ) -> ServiceBuilder<Stack<crate::timeout::TimeoutLayer, L>> { self.layer(crate::timeout::TimeoutLayer::new(timeout)) } /// Conditionally reject requests based on `predicate`. /// /// `predicate` must implement the [`Predicate`] trait. /// /// This wraps the inner service with an instance of the [`Filter`] /// middleware. /// /// [`Filter`]: crate::filter /// [`Predicate`]: crate::filter::Predicate #[cfg(feature = "filter")] #[cfg_attr(docsrs, doc(cfg(feature = "filter")))] pub fn filter<P>( self, predicate: P, ) -> ServiceBuilder<Stack<crate::filter::FilterLayer<P>, L>> { self.layer(crate::filter::FilterLayer::new(predicate)) } /// Conditionally reject requests based on an asynchronous `predicate`. /// /// `predicate` must implement the [`AsyncPredicate`] trait. /// /// This wraps the inner service with an instance of the [`AsyncFilter`] /// middleware. /// /// [`AsyncFilter`]: crate::filter::AsyncFilter /// [`AsyncPredicate`]: crate::filter::AsyncPredicate #[cfg(feature = "filter")] #[cfg_attr(docsrs, doc(cfg(feature = "filter")))] pub fn filter_async<P>( self, predicate: P, ) -> ServiceBuilder<Stack<crate::filter::AsyncFilterLayer<P>, L>> { self.layer(crate::filter::AsyncFilterLayer::new(predicate)) } /// 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: /// /// ```rust /// use tower::ServiceBuilder; /// use tower::ServiceExt; /// /// # #[tokio::main] /// # async fn main() -> Result<(), ()> { /// // 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?; /// # Ok(()) /// # } /// ``` /// /// Modifying the request value: /// /// ```rust /// use tower::ServiceBuilder; /// use tower::ServiceExt; /// /// # #[tokio::main] /// # async fn main() -> Result<(), ()> { /// // 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); /// # Ok(()) /// # } /// ``` /// /// [`MapRequest`]: crate::util::MapRequest #[cfg(feature = "util")] #[cfg_attr(docsrs, doc(cfg(feature = "util")))] pub fn map_request<F, R1, R2>( self, f: F, ) -> ServiceBuilder<Stack<crate::util::MapRequestLayer<F>, L>> where F: FnMut(R1) -> R2 + Clone, { self.layer(crate::util::MapRequestLayer::new(f)) } /// 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. /// /// [`MapResponse`]: crate::util::MapResponse /// [`map_response` combinator]: crate::util::ServiceExt::map_response #[cfg(feature = "util")] #[cfg_attr(docsrs, doc(cfg(feature = "util")))] pub fn map_response<F>( self, f: F, ) -> ServiceBuilder<Stack<crate::util::MapResponseLayer<F>, L>> { self.layer(crate::util::MapResponseLayer::new(f)) } /// 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. /// /// [`MapErr`]: crate::util::MapErr /// [`map_err` combinator]: crate::util::ServiceExt::map_err #[cfg(feature = "util")] #[cfg_attr(docsrs, doc(cfg(feature = "util")))] pub fn map_err<F>(self, f: F) -> ServiceBuilder<Stack<crate::util::MapErrLayer<F>, L>> { self.layer(crate::util::MapErrLayer::new(f)) } /// 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. /// /// [`Then`]: crate::util::Then /// [`then` combinator]: crate::util::ServiceExt::then /// [`map_response`]: ServiceBuilder::map_response /// [`map_err`]: ServiceBuilder::map_err #[cfg(feature = "util")] #[cfg_attr(docsrs, doc(cfg(feature = "util")))] pub fn then<F>(self, f: F) -> ServiceBuilder<Stack<crate::util::ThenLayer<F>, L>> { self.layer(crate::util::ThenLayer::new(f)) } /// Returns the underlying `Layer` implementation. pub fn into_inner(self) -> L { self.layer } /// Wrap the service `S` with the middleware provided by this /// [`ServiceBuilder`]'s [`Layer`]'s, returning a new [`Service`]. /// /// [`Layer`]: crate::Layer /// [`Service`]: crate::Service pub fn service<S>(&self, service: S) -> L::Service where L: Layer<S>, { self.layer.layer(service) } } impl<L: fmt::Debug> fmt::Debug for ServiceBuilder<L> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { f.debug_tuple("ServiceBuilder").field(&self.layer).finish() } }