| <!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="Returns a new [`LayerFn`] that implements [`Layer`] by calling the given function."><meta name="keywords" content="rust, rustlang, rust-lang, layer_fn"><title>layer_fn in tower::layer - Rust</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="sidebar-items.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 fn"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="mobile-topbar"><button class="sidebar-menu-toggle">☰</button><a class="sidebar-logo" href="../../tower/index.html"><div class="logo-container"><img class="rust-logo" src="../../rust-logo.svg" alt="logo"></div></a><h2></h2></nav><nav class="sidebar"><a class="sidebar-logo" href="../../tower/index.html"><div class="logo-container"><img class="rust-logo" src="../../rust-logo.svg" alt="logo"></div></a><div class="sidebar-elems"><h2><a href="index.html">In tower::layer</a></h2></div></nav><main><div class="width-limiter"><nav class="sub"><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="main-heading"><h1 class="fqn">Function <a href="../index.html">tower</a>::<wbr><a href="index.html">layer</a>::<wbr><a class="fn" href="#">layer_fn</a><button id="copy-path" onclick="copy_path(this)" title="Copy item path to clipboard"><img src="../../clipboard.svg" width="19" height="18" alt="Copy item path"></button></h1><span class="out-of-band"><a class="srclink" href="../../src/tower_layer/layer_fn.rs.html#67">source</a> · <a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class="inner">−</span>]</a></span></div><div class="item-decl"><pre class="rust fn"><code>pub fn layer_fn<T>(f: T) -> <a class="struct" href="struct.LayerFn.html" title="struct tower::layer::LayerFn">LayerFn</a><T></code></pre></div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Returns a new <a href="struct.LayerFn.html" title="LayerFn"><code>LayerFn</code></a> that implements <a href="../trait.Layer.html" title="Layer"><code>Layer</code></a> by calling the |
| given function.</p> |
| <p>The <a href="../trait.Layer.html#tymethod.layer"><code>Layer::layer</code></a> method takes a type implementing <a href="https://docs.rs/tower-service/latest/tower_service/trait.Service.html"><code>Service</code></a> and |
| returns a different type implementing <a href="https://docs.rs/tower-service/latest/tower_service/trait.Service.html"><code>Service</code></a>. In many cases, this can |
| be implemented by a function or a closure. The <a href="struct.LayerFn.html" title="LayerFn"><code>LayerFn</code></a> helper allows |
| writing simple <a href="../trait.Layer.html" title="Layer"><code>Layer</code></a> implementations without needing the boilerplate of |
| a new struct implementing <a href="../trait.Layer.html" title="Layer"><code>Layer</code></a>.</p> |
| <h2 id="example"><a href="#example">Example</a></h2> |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="comment">// A middleware that logs requests before forwarding them to another service |
| </span><span class="kw">pub struct </span>LogService<S> { |
| target: <span class="kw-2">&</span><span class="lifetime">'static </span>str, |
| service: S, |
| } |
| |
| <span class="kw">impl</span><S, Request> Service<Request> <span class="kw">for </span>LogService<S> |
| <span class="kw">where |
| </span>S: Service<Request>, |
| Request: fmt::Debug, |
| { |
| <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><(), <span class="self">Self</span>::Error>> { |
| <span class="self">self</span>.service.poll_ready(cx) |
| } |
| |
| <span class="kw">fn </span>call(<span class="kw-2">&mut </span><span class="self">self</span>, request: Request) -> <span class="self">Self</span>::Future { |
| <span class="comment">// Log the request |
| </span><span class="macro">println!</span>(<span class="string">"request = {:?}, target = {:?}"</span>, request, <span class="self">self</span>.target); |
| |
| <span class="self">self</span>.service.call(request) |
| } |
| } |
| |
| <span class="comment">// A `Layer` that wraps services in `LogService` |
| </span><span class="kw">let </span>log_layer = layer_fn(|service| { |
| LogService { |
| service, |
| target: <span class="string">"tower-docs"</span>, |
| } |
| }); |
| |
| <span class="comment">// An example service. This one uppercases strings |
| </span><span class="kw">let </span>uppercase_service = tower::service_fn(|request: String| <span class="kw">async move </span>{ |
| <span class="prelude-val">Ok</span>::<<span class="kw">_</span>, Infallible>(request.to_uppercase()) |
| }); |
| |
| <span class="comment">// Wrap our service in a `LogService` so requests are logged. |
| </span><span class="kw">let </span>wrapped_service = log_layer.layer(uppercase_service);</code></pre></div> |
| </div></details></section></div></main><div id="rustdoc-vars" data-root-path="../../" data-current-crate="tower" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |