| <!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="Source of the Rust file `/root/.cargo/registry/src/github.com-1ecc6299db9ec823/tower-service-0.3.2/src/lib.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>lib.rs - source</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceCodePro-Semibold.ttf.woff2"><link rel="stylesheet" href="../../normalize.css"><link rel="stylesheet" href="../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" href="../../ayu.css" disabled><link rel="stylesheet" href="../../dark.css" disabled><link rel="stylesheet" href="../../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../../storage.js"></script><script defer src="../../source-script.js"></script><script defer src="../../source-files.js"></script><script defer src="../../main.js"></script><noscript><link rel="stylesheet" href="../../noscript.css"></noscript><link rel="alternate icon" type="image/png" href="../../favicon-16x16.png"><link rel="alternate icon" type="image/png" href="../../favicon-32x32.png"><link rel="icon" type="image/svg+xml" href="../../favicon.svg"></head><body class="rustdoc source"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><a class="sidebar-logo" href="../../tower_service/index.html"><div class="logo-container"><img class="rust-logo" src="../../rust-logo.svg" alt="logo"></div></a></nav><main><div class="width-limiter"><nav class="sub"><a class="sub-logo-container" href="../../tower_service/index.html"><img class="rust-logo" src="../../rust-logo.svg" alt="logo"></a><form class="search-form"><div class="search-container"><span></span><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" title="help" tabindex="-1"><a href="../../help.html">?</a></div><div id="settings-menu" tabindex="-1"><a href="../../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../../wheel.svg"></a></div></div></form></nav><section id="main-content" class="content"><div class="example-wrap"><pre class="src-line-numbers"><span id="1">1</span> |
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| </pre><pre class="rust"><code><span class="attribute">#![warn( |
| missing_debug_implementations, |
| missing_docs, |
| rust_2018_idioms, |
| unreachable_pub |
| )] |
| #![forbid(unsafe_code)] |
| </span><span class="comment">// `rustdoc::broken_intra_doc_links` is checked on CI |
| |
| </span><span class="doccomment">//! Definition of the core `Service` trait to Tower |
| //! |
| //! The [`Service`] trait provides the necessary abstractions for defining |
| //! request / response clients and servers. It is simple but powerful and is |
| //! used as the foundation for the rest of Tower. |
| |
| </span><span class="kw">use </span>std::future::Future; |
| <span class="kw">use </span>std::task::{Context, Poll}; |
| |
| <span class="doccomment">/// An asynchronous function from a `Request` to a `Response`. |
| /// |
| /// The `Service` trait is a simplified interface making it easy to write |
| /// network applications in a modular and reusable way, decoupled from the |
| /// underlying protocol. It is one of Tower's fundamental abstractions. |
| /// |
| /// # Functional |
| /// |
| /// A `Service` is a function of a `Request`. It immediately returns a |
| /// `Future` representing the eventual completion of processing the |
| /// request. The actual request processing may happen at any time in the |
| /// future, on any thread or executor. The processing may depend on calling |
| /// other services. At some point in the future, the processing will complete, |
| /// and the `Future` will resolve to a response or error. |
| /// |
| /// At a high level, the `Service::call` function represents an RPC request. The |
| /// `Service` value can be a server or a client. |
| /// |
| /// # Server |
| /// |
| /// An RPC server *implements* the `Service` trait. Requests received by the |
| /// server over the network are deserialized and then passed as an argument to the |
| /// server value. The returned response is sent back over the network. |
| /// |
| /// As an example, here is how an HTTP request is processed by a server: |
| /// |
| /// ```rust |
| /// # use std::pin::Pin; |
| /// # use std::task::{Poll, Context}; |
| /// # use std::future::Future; |
| /// # use tower_service::Service; |
| /// use http::{Request, Response, StatusCode}; |
| /// |
| /// struct HelloWorld; |
| /// |
| /// impl Service<Request<Vec<u8>>> for HelloWorld { |
| /// type Response = Response<Vec<u8>>; |
| /// type Error = http::Error; |
| /// type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>>>>; |
| /// |
| /// fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> { |
| /// Poll::Ready(Ok(())) |
| /// } |
| /// |
| /// fn call(&mut self, req: Request<Vec<u8>>) -> Self::Future { |
| /// // create the body |
| /// let body: Vec<u8> = "hello, world!\n" |
| /// .as_bytes() |
| /// .to_owned(); |
| /// // Create the HTTP response |
| /// let resp = Response::builder() |
| /// .status(StatusCode::OK) |
| /// .body(body) |
| /// .expect("Unable to create `http::Response`"); |
| /// |
| /// // create a response in a future. |
| /// let fut = async { |
| /// Ok(resp) |
| /// }; |
| /// |
| /// // Return the response as an immediate future |
| /// Box::pin(fut) |
| /// } |
| /// } |
| /// ``` |
| /// |
| /// # Client |
| /// |
| /// A client consumes a service by using a `Service` value. The client may |
| /// issue requests by invoking `call` and passing the request as an argument. |
| /// It then receives the response by waiting for the returned future. |
| /// |
| /// As an example, here is how a Redis request would be issued: |
| /// |
| /// ```rust,ignore |
| /// let client = redis::Client::new() |
| /// .connect("127.0.0.1:6379".parse().unwrap()) |
| /// .unwrap(); |
| /// |
| /// let resp = client.call(Cmd::set("foo", "this is the value of foo")).await?; |
| /// |
| /// // Wait for the future to resolve |
| /// println!("Redis response: {:?}", resp); |
| /// ``` |
| /// |
| /// # Middleware / Layer |
| /// |
| /// More often than not, all the pieces needed for writing robust, scalable |
| /// network applications are the same no matter the underlying protocol. By |
| /// unifying the API for both clients and servers in a protocol agnostic way, |
| /// it is possible to write middleware that provide these pieces in a |
| /// reusable way. |
| /// |
| /// Take timeouts as an example: |
| /// |
| /// ```rust |
| /// use tower_service::Service; |
| /// use tower_layer::Layer; |
| /// use futures::FutureExt; |
| /// use std::future::Future; |
| /// use std::task::{Context, Poll}; |
| /// use std::time::Duration; |
| /// use std::pin::Pin; |
| /// use std::fmt; |
| /// use std::error::Error; |
| /// |
| /// // Our timeout service, which wraps another service and |
| /// // adds a timeout to its response future. |
| /// pub struct Timeout<T> { |
| /// inner: T, |
| /// timeout: Duration, |
| /// } |
| /// |
| /// impl<T> Timeout<T> { |
| /// pub fn new(inner: T, timeout: Duration) -> Timeout<T> { |
| /// Timeout { |
| /// inner, |
| /// timeout |
| /// } |
| /// } |
| /// } |
| /// |
| /// // The error returned if processing a request timed out |
| /// #[derive(Debug)] |
| /// pub struct Expired; |
| /// |
| /// impl fmt::Display for Expired { |
| /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
| /// write!(f, "expired") |
| /// } |
| /// } |
| /// |
| /// impl Error for Expired {} |
| /// |
| /// // We can implement `Service` for `Timeout<T>` if `T` is a `Service` |
| /// impl<T, Request> Service<Request> for Timeout<T> |
| /// where |
| /// T: Service<Request>, |
| /// T::Future: 'static, |
| /// T::Error: Into<Box<dyn Error + Send + Sync>> + 'static, |
| /// T::Response: 'static, |
| /// { |
| /// // `Timeout` doesn't modify the response type, so we use `T`'s response type |
| /// type Response = T::Response; |
| /// // Errors may be either `Expired` if the timeout expired, or the inner service's |
| /// // `Error` type. Therefore, we return a boxed `dyn Error + Send + Sync` trait object to erase |
| /// // the error's type. |
| /// type Error = Box<dyn Error + Send + Sync>; |
| /// type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>>>>; |
| /// |
| /// fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> { |
| /// // Our timeout service is ready if the inner service is ready. |
| /// // This is how backpressure can be propagated through a tree of nested services. |
| /// self.inner.poll_ready(cx).map_err(Into::into) |
| /// } |
| /// |
| /// fn call(&mut self, req: Request) -> Self::Future { |
| /// // Create a future that completes after `self.timeout` |
| /// let timeout = tokio::time::sleep(self.timeout); |
| /// |
| /// // Call the inner service and get a future that resolves to the response |
| /// let fut = self.inner.call(req); |
| /// |
| /// // Wrap those two futures in another future that completes when either one completes |
| /// // |
| /// // If the inner service is too slow the `sleep` future will complete first |
| /// // And an error will be returned and `fut` will be dropped and not polled again |
| /// // |
| /// // We have to box the errors so the types match |
| /// let f = async move { |
| /// tokio::select! { |
| /// res = fut => { |
| /// res.map_err(|err| err.into()) |
| /// }, |
| /// _ = timeout => { |
| /// Err(Box::new(Expired) as Box<dyn Error + Send + Sync>) |
| /// }, |
| /// } |
| /// }; |
| /// |
| /// Box::pin(f) |
| /// } |
| /// } |
| /// |
| /// // A layer for wrapping services in `Timeout` |
| /// pub struct TimeoutLayer(Duration); |
| /// |
| /// impl TimeoutLayer { |
| /// pub fn new(delay: Duration) -> Self { |
| /// TimeoutLayer(delay) |
| /// } |
| /// } |
| /// |
| /// impl<S> Layer<S> for TimeoutLayer { |
| /// type Service = Timeout<S>; |
| /// |
| /// fn layer(&self, service: S) -> Timeout<S> { |
| /// Timeout::new(service, self.0) |
| /// } |
| /// } |
| /// ``` |
| /// |
| /// The above timeout implementation is decoupled from the underlying protocol |
| /// and is also decoupled from client or server concerns. In other words, the |
| /// same timeout middleware could be used in either a client or a server. |
| /// |
| /// # Backpressure |
| /// |
| /// Calling a `Service` which is at capacity (i.e., it is temporarily unable to process a |
| /// request) should result in an error. The caller is responsible for ensuring |
| /// that the service is ready to receive the request before calling it. |
| /// |
| /// `Service` provides a mechanism by which the caller is able to coordinate |
| /// readiness. `Service::poll_ready` returns `Ready` if the service expects that |
| /// it is able to process a request. |
| /// |
| /// # Be careful when cloning inner services |
| /// |
| /// Services are permitted to panic if `call` is invoked without obtaining `Poll::Ready(Ok(()))` |
| /// from `poll_ready`. You should therefore be careful when cloning services for example to move |
| /// them into boxed futures. Even though the original service is ready, the clone might not be. |
| /// |
| /// Therefore this kind of code is wrong and might panic: |
| /// |
| /// ```rust |
| /// # use std::pin::Pin; |
| /// # use std::task::{Poll, Context}; |
| /// # use std::future::Future; |
| /// # use tower_service::Service; |
| /// # |
| /// struct Wrapper<S> { |
| /// inner: S, |
| /// } |
| /// |
| /// impl<R, S> Service<R> for Wrapper<S> |
| /// where |
| /// S: Service<R> + Clone + 'static, |
| /// R: 'static, |
| /// { |
| /// type Response = S::Response; |
| /// type Error = S::Error; |
| /// type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>>>>; |
| /// |
| /// fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> { |
| /// Poll::Ready(Ok(())) |
| /// } |
| /// |
| /// fn call(&mut self, req: R) -> Self::Future { |
| /// let mut inner = self.inner.clone(); |
| /// Box::pin(async move { |
| /// // `inner` might not be ready since its a clone |
| /// inner.call(req).await |
| /// }) |
| /// } |
| /// } |
| /// ``` |
| /// |
| /// You should instead use [`std::mem::replace`] to take the service that was ready: |
| /// |
| /// ```rust |
| /// # use std::pin::Pin; |
| /// # use std::task::{Poll, Context}; |
| /// # use std::future::Future; |
| /// # use tower_service::Service; |
| /// # |
| /// struct Wrapper<S> { |
| /// inner: S, |
| /// } |
| /// |
| /// impl<R, S> Service<R> for Wrapper<S> |
| /// where |
| /// S: Service<R> + Clone + 'static, |
| /// R: 'static, |
| /// { |
| /// type Response = S::Response; |
| /// type Error = S::Error; |
| /// type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>>>>; |
| /// |
| /// fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> { |
| /// Poll::Ready(Ok(())) |
| /// } |
| /// |
| /// fn call(&mut self, req: R) -> Self::Future { |
| /// let clone = self.inner.clone(); |
| /// // take the service that was ready |
| /// let mut inner = std::mem::replace(&mut self.inner, clone); |
| /// Box::pin(async move { |
| /// inner.call(req).await |
| /// }) |
| /// } |
| /// } |
| /// ``` |
| </span><span class="kw">pub trait </span>Service<Request> { |
| <span class="doccomment">/// Responses given by the service. |
| </span><span class="kw">type </span>Response; |
| |
| <span class="doccomment">/// Errors produced by the service. |
| </span><span class="kw">type </span>Error; |
| |
| <span class="doccomment">/// The future response value. |
| </span><span class="kw">type </span>Future: Future<Output = <span class="prelude-ty">Result</span><<span class="self">Self</span>::Response, <span class="self">Self</span>::Error>>; |
| |
| <span class="doccomment">/// Returns `Poll::Ready(Ok(()))` when the service is able to process requests. |
| /// |
| /// If the service is at capacity, then `Poll::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. Generally, this can be done with |
| /// a simple `futures::future::poll_fn` call. |
| /// |
| /// If `Poll::Ready(Err(_))` is returned, the service is no longer able to service requests |
| /// and the caller should discard the service instance. |
| /// |
| /// Once `poll_ready` returns `Poll::Ready(Ok(()))`, a request may be dispatched to the |
| /// service using `call`. Until a request is dispatched, repeated calls to |
| /// `poll_ready` must return either `Poll::Ready(Ok(()))` or `Poll::Ready(Err(_))`. |
| /// |
| /// Note that `poll_ready` may reserve shared resources that are consumed in a subsequent |
| /// invocation of `call`. Thus, it is critical for implementations to not assume that `call` |
| /// will always be invoked and to ensure that such resources are released if the service is |
| /// dropped before `call` is invoked or the future returned by `call` is dropped before it |
| /// is polled. |
| </span><span class="kw">fn </span>poll_ready(<span class="kw-2">&mut </span><span class="self">self</span>, cx: <span class="kw-2">&mut </span>Context<<span class="lifetime">'_</span>>) -> Poll<<span class="prelude-ty">Result</span><(), <span class="self">Self</span>::Error>>; |
| |
| <span class="doccomment">/// 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`. |
| /// |
| /// Before dispatching a request, `poll_ready` must be called and return |
| /// `Poll::Ready(Ok(()))`. |
| /// |
| /// # Panics |
| /// |
| /// Implementations are permitted to panic if `call` is invoked without |
| /// obtaining `Poll::Ready(Ok(()))` from `poll_ready`. |
| </span><span class="kw">fn </span>call(<span class="kw-2">&mut </span><span class="self">self</span>, req: Request) -> <span class="self">Self</span>::Future; |
| } |
| |
| <span class="kw">impl</span><<span class="lifetime">'a</span>, S, Request> Service<Request> <span class="kw">for </span><span class="kw-2">&</span><span class="lifetime">'a </span><span class="kw-2">mut </span>S |
| <span class="kw">where |
| </span>S: Service<Request> + <span class="lifetime">'a</span>, |
| { |
| <span class="kw">type </span>Response = S::Response; |
| <span class="kw">type </span>Error = S::Error; |
| <span class="kw">type </span>Future = S::Future; |
| |
| <span class="kw">fn </span>poll_ready(<span class="kw-2">&mut </span><span class="self">self</span>, cx: <span class="kw-2">&mut </span>Context<<span class="lifetime">'_</span>>) -> Poll<<span class="prelude-ty">Result</span><(), S::Error>> { |
| (<span class="kw-2">**</span><span class="self">self</span>).poll_ready(cx) |
| } |
| |
| <span class="kw">fn </span>call(<span class="kw-2">&mut </span><span class="self">self</span>, request: Request) -> S::Future { |
| (<span class="kw-2">**</span><span class="self">self</span>).call(request) |
| } |
| } |
| |
| <span class="kw">impl</span><S, Request> Service<Request> <span class="kw">for </span>Box<S> |
| <span class="kw">where |
| </span>S: Service<Request> + <span class="question-mark">?</span>Sized, |
| { |
| <span class="kw">type </span>Response = S::Response; |
| <span class="kw">type </span>Error = S::Error; |
| <span class="kw">type </span>Future = S::Future; |
| |
| <span class="kw">fn </span>poll_ready(<span class="kw-2">&mut </span><span class="self">self</span>, cx: <span class="kw-2">&mut </span>Context<<span class="lifetime">'_</span>>) -> Poll<<span class="prelude-ty">Result</span><(), S::Error>> { |
| (<span class="kw-2">**</span><span class="self">self</span>).poll_ready(cx) |
| } |
| |
| <span class="kw">fn </span>call(<span class="kw-2">&mut </span><span class="self">self</span>, request: Request) -> S::Future { |
| (<span class="kw-2">**</span><span class="self">self</span>).call(request) |
| } |
| } |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../" data-current-crate="tower_service" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |