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50 lines
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<!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."><title>layer_fn in tower_layer - Rust</title><script>if(window.location.protocol!=="file:")document.head.insertAdjacentHTML("beforeend","SourceSerif4-Regular-6b053e98.ttf.woff2,FiraSans-Italic-81dc35de.woff2,FiraSans-Regular-0fe48ade.woff2,FiraSans-MediumItalic-ccf7e434.woff2,FiraSans-Medium-e1aa3f0a.woff2,SourceCodePro-Regular-8badfe75.ttf.woff2,SourceCodePro-Semibold-aa29a496.ttf.woff2".split(",").map(f=>`<link rel="preload" as="font" type="font/woff2"href="../static.files/${f}">`).join(""))</script><link rel="stylesheet" href="../static.files/normalize-9960930a.css"><link rel="stylesheet" href="../static.files/rustdoc-ca0dd0c4.css"><meta name="rustdoc-vars" data-root-path="../" data-static-root-path="../static.files/" data-current-crate="tower_layer" data-themes="" data-resource-suffix="" data-rustdoc-version="1.93.1 (01f6ddf75 2026-02-11) (Arch Linux rust 1:1.93.1-1)" data-channel="1.93.1" data-search-js="search-9e2438ea.js" data-stringdex-js="stringdex-a3946164.js" data-settings-js="settings-c38705f0.js" ><script src="../static.files/storage-e2aeef58.js"></script><script defer src="sidebar-items.js"></script><script defer src="../static.files/main-a410ff4d.js"></script><noscript><link rel="stylesheet" href="../static.files/noscript-263c88ec.css"></noscript><link rel="alternate icon" type="image/png" href="../static.files/favicon-32x32-eab170b8.png"><link rel="icon" type="image/svg+xml" href="../static.files/favicon-044be391.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]--><rustdoc-topbar><h2><a href="#">layer_fn</a></h2></rustdoc-topbar><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../tower_layer/index.html">tower_<wbr>layer</a><span class="version">0.3.3</span></h2></div><div class="sidebar-elems"><section id="rustdoc-toc"><h2 class="location"><a href="#">layer_<wbr>fn</a></h2><h3><a href="#">Sections</a></h3><ul class="block top-toc"><li><a href="#example" title="Example">Example</a></li></ul></section><div id="rustdoc-modnav"><h2 class="in-crate"><a href="index.html">In crate tower_<wbr>layer</a></h2></div></div></nav><div class="sidebar-resizer" title="Drag to resize sidebar"></div><main><div class="width-limiter"><section id="main-content" class="content"><div class="main-heading"><div class="rustdoc-breadcrumbs"><a href="index.html">tower_layer</a></div><h1>Function <span class="fn">layer_<wbr>fn</span> <button id="copy-path" title="Copy item path to clipboard">Copy item path</button></h1><rustdoc-toolbar></rustdoc-toolbar><span class="sub-heading"><a class="src" href="../src/tower_layer/layer_fn.rs.html#67-69">Source</a> </span></div><pre class="rust item-decl"><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><details class="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="struct tower_layer::LayerFn"><code>LayerFn</code></a> that implements <a href="trait.Layer.html" title="trait tower_layer::Layer"><code>Layer</code></a> by calling the
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given function.</p>
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<p>The <a href="trait.Layer.html#tymethod.layer" title="method tower_layer::Layer::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
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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
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be implemented by a function or a closure. The <a href="struct.LayerFn.html" title="struct tower_layer::LayerFn"><code>LayerFn</code></a> helper allows
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writing simple <a href="trait.Layer.html" title="trait tower_layer::Layer"><code>Layer</code></a> implementations without needing the boilerplate of
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a new struct implementing <a href="trait.Layer.html" title="trait tower_layer::Layer"><code>Layer</code></a>.</p>
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<h2 id="example"><a class="doc-anchor" href="#example">§</a>Example</h2>
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<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
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</span><span class="kw">pub struct </span>LogService<S> {
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target: <span class="kw-2">&</span><span class="lifetime">'static </span>str,
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service: S,
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}
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<span class="kw">impl</span><S, Request> Service<Request> <span class="kw">for </span>LogService<S>
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<span class="kw">where
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</span>S: Service<Request>,
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Request: fmt::Debug,
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{
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<span class="kw">type </span>Response = S::Response;
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<span class="kw">type </span>Error = S::Error;
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<span class="kw">type </span>Future = S::Future;
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<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>> {
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<span class="self">self</span>.service.poll_ready(cx)
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}
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<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 {
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<span class="comment">// Log the request
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</span><span class="macro">println!</span>(<span class="string">"request = {:?}, target = {:?}"</span>, request, <span class="self">self</span>.target);
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<span class="self">self</span>.service.call(request)
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}
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}
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<span class="comment">// A `Layer` that wraps services in `LogService`
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</span><span class="kw">let </span>log_layer = layer_fn(|service| {
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LogService {
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service,
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target: <span class="string">"tower-docs"</span>,
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}
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});
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<span class="comment">// An example service. This one uppercases strings
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</span><span class="kw">let </span>uppercase_service = tower::service_fn(|request: String| <span class="kw">async move </span>{
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<span class="prelude-val">Ok</span>::<<span class="kw">_</span>, Infallible>(request.to_uppercase())
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});
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<span class="comment">// Wrap our service in a `LogService` so requests are logged.
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</span><span class="kw">let </span>wrapped_service = log_layer.layer(uppercase_service);</code></pre></div></div></details></section></div></main></body></html> |