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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="A “retry policy” to classify if a request should be retried."><title>Policy in tower::retry - 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" 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 trait"><!--[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="#">Policy</a></h2></rustdoc-topbar><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../../tower/index.html">tower</a><span class="version">0.5.3</span></h2></div><div class="sidebar-elems"><section id="rustdoc-toc"><h2 class="location"><a href="#">Policy</a></h2><h3><a href="#">Sections</a></h3><ul class="block top-toc"><li><a href="#example" title="Example">Example</a></li></ul><h3><a href="#required-associated-types">Required Associated Types</a></h3><ul class="block"><li><a href="#associatedtype.Future" title="Future">Future</a></li></ul><h3><a href="#required-methods">Required Methods</a></h3><ul class="block"><li><a href="#tymethod.clone_request" title="clone_request">clone_request</a></li><li><a href="#tymethod.retry" title="retry">retry</a></li></ul><h3><a href="#implementors">Implementors</a></h3></section><div id="rustdoc-modnav"><h2><a href="index.html">In tower::<wbr>retry</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</a>::<wbr><a href="index.html">retry</a></div><h1>Trait <span class="trait">Policy</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/retry/policy.rs.html#46-90">Source</a> </span></div><pre class="rust item-decl"><code>pub trait Policy<Req, Res, E> {
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type <a href="#associatedtype.Future" class="associatedtype">Future</a>: <a class="trait" href="https://doc.rust-lang.org/1.93.1/core/future/future/trait.Future.html" title="trait core::future::future::Future">Future</a><Output = <a class="primitive" href="https://doc.rust-lang.org/1.93.1/std/primitive.unit.html">()</a>>;
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// Required methods
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fn <a href="#tymethod.retry" class="fn">retry</a>(
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&mut self,
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req: <a class="primitive" href="https://doc.rust-lang.org/1.93.1/std/primitive.reference.html">&mut Req</a>,
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result: &mut <a class="enum" href="https://doc.rust-lang.org/1.93.1/core/result/enum.Result.html" title="enum core::result::Result">Result</a><Res, E>,
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) -> <a class="enum" href="https://doc.rust-lang.org/1.93.1/core/option/enum.Option.html" title="enum core::option::Option">Option</a><Self::<a class="associatedtype" href="trait.Policy.html#associatedtype.Future" title="type tower::retry::Policy::Future">Future</a>>;
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<span class="item-spacer"></span> fn <a href="#tymethod.clone_request" class="fn">clone_request</a>(&mut self, req: <a class="primitive" href="https://doc.rust-lang.org/1.93.1/std/primitive.reference.html">&Req</a>) -> <a class="enum" href="https://doc.rust-lang.org/1.93.1/core/option/enum.Option.html" title="enum core::option::Option">Option</a><Req>;
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}</code></pre><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>A “retry policy” to classify if a request should be retried.</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="kw">use </span>tower::retry::Policy;
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<span class="kw">use </span>std::future;
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<span class="kw">type </span>Req = String;
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<span class="kw">type </span>Res = String;
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<span class="kw">struct </span>Attempts(usize);
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<span class="kw">impl</span><E> Policy<Req, Res, E> <span class="kw">for </span>Attempts {
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<span class="kw">type </span>Future = future::Ready<()>;
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<span class="kw">fn </span>retry(<span class="kw-2">&mut </span><span class="self">self</span>, req: <span class="kw-2">&mut </span>Req, result: <span class="kw-2">&mut </span><span class="prelude-ty">Result</span><Res, E>) -> <span class="prelude-ty">Option</span><<span class="self">Self</span>::Future> {
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<span class="kw">match </span>result {
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<span class="prelude-val">Ok</span>(<span class="kw">_</span>) => {
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<span class="comment">// Treat all `Response`s as success,
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// so don't retry...
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</span><span class="prelude-val">None
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</span>},
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<span class="prelude-val">Err</span>(<span class="kw">_</span>) => {
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<span class="comment">// Treat all errors as failures...
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// But we limit the number of attempts...
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</span><span class="kw">if </span><span class="self">self</span>.<span class="number">0 </span>> <span class="number">0 </span>{
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<span class="comment">// Try again!
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</span><span class="self">self</span>.<span class="number">0 </span>-= <span class="number">1</span>;
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<span class="prelude-val">Some</span>(future::ready(()))
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} <span class="kw">else </span>{
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<span class="comment">// Used all our attempts, no retry...
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</span><span class="prelude-val">None
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</span>}
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}
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}
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}
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<span class="kw">fn </span>clone_request(<span class="kw-2">&mut </span><span class="self">self</span>, req: <span class="kw-2">&</span>Req) -> <span class="prelude-ty">Option</span><Req> {
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<span class="prelude-val">Some</span>(req.clone())
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}
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}</code></pre></div></div></details><h2 id="required-associated-types" class="section-header">Required Associated Types<a href="#required-associated-types" class="anchor">§</a></h2><div class="methods"><details class="toggle" open><summary><section id="associatedtype.Future" class="method"><a class="src rightside" href="../../src/tower/retry/policy.rs.html#48">Source</a><h4 class="code-header">type <a href="#associatedtype.Future" class="associatedtype">Future</a>: <a class="trait" href="https://doc.rust-lang.org/1.93.1/core/future/future/trait.Future.html" title="trait core::future::future::Future">Future</a><Output = <a class="primitive" href="https://doc.rust-lang.org/1.93.1/std/primitive.unit.html">()</a>></h4></section></summary><div class="docblock"><p>The <a href="https://doc.rust-lang.org/1.93.1/core/future/future/trait.Future.html" title="trait core::future::future::Future"><code>Future</code></a> type returned by <a href="trait.Policy.html#tymethod.retry" title="method tower::retry::Policy::retry"><code>Policy::retry</code></a>.</p>
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</div></details></div><h2 id="required-methods" class="section-header">Required Methods<a href="#required-methods" class="anchor">§</a></h2><div class="methods"><details class="toggle method-toggle" open><summary><section id="tymethod.retry" class="method"><a class="src rightside" href="../../src/tower/retry/policy.rs.html#83">Source</a><h4 class="code-header">fn <a href="#tymethod.retry" class="fn">retry</a>(
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&mut self,
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req: <a class="primitive" href="https://doc.rust-lang.org/1.93.1/std/primitive.reference.html">&mut Req</a>,
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result: &mut <a class="enum" href="https://doc.rust-lang.org/1.93.1/core/result/enum.Result.html" title="enum core::result::Result">Result</a><Res, E>,
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) -> <a class="enum" href="https://doc.rust-lang.org/1.93.1/core/option/enum.Option.html" title="enum core::option::Option">Option</a><Self::<a class="associatedtype" href="trait.Policy.html#associatedtype.Future" title="type tower::retry::Policy::Future">Future</a>></h4></section></summary><div class="docblock"><p>Check the policy if a certain request should be retried.</p>
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<p>This method is passed a reference to the original request, and either
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the <a href="../trait.Service.html#associatedtype.Response" title="associated type tower::Service::Response"><code>Service::Response</code></a> or <a href="../trait.Service.html#associatedtype.Error" title="associated type tower::Service::Error"><code>Service::Error</code></a> from the inner service.</p>
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<p>If the request should <strong>not</strong> be retried, return <code>None</code>.</p>
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<p>If the request <em>should</em> be retried, return <code>Some</code> future that will delay
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the next retry of the request. This can be used to sleep for a certain
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duration, to wait for some external condition to be met before retrying,
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or resolve right away, if the request should be retried immediately.</p>
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<h6 id="mutating-requests"><a class="doc-anchor" href="#mutating-requests">§</a>Mutating Requests</h6>
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<p>The policy MAY chose to mutate the <code>req</code>: if the request is mutated, the
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mutated request will be sent to the inner service in the next retry.
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This can be helpful for use cases like tracking the retry count in a
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header.</p>
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<h6 id="mutating-results"><a class="doc-anchor" href="#mutating-results">§</a>Mutating Results</h6>
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<p>The policy MAY chose to mutate the result. This enables the retry
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policy to convert a failure into a success and vice versa. For example,
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if the policy is used to poll while waiting for a state change, the
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policy can switch the result to emit a specific error when retries are
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exhausted.</p>
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<p>The policy can also record metadata on the request to include
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information about the number of retries required or to record that a
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failure failed after exhausting all retries.</p>
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</div></details><details class="toggle method-toggle" open><summary><section id="tymethod.clone_request" class="method"><a class="src rightside" href="../../src/tower/retry/policy.rs.html#89">Source</a><h4 class="code-header">fn <a href="#tymethod.clone_request" class="fn">clone_request</a>(&mut self, req: <a class="primitive" href="https://doc.rust-lang.org/1.93.1/std/primitive.reference.html">&Req</a>) -> <a class="enum" href="https://doc.rust-lang.org/1.93.1/core/option/enum.Option.html" title="enum core::option::Option">Option</a><Req></h4></section></summary><div class="docblock"><p>Tries to clone a request before being passed to the inner service.</p>
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<p>If the request cannot be cloned, return <a href="https://doc.rust-lang.org/1.93.1/core/option/enum.Option.html#variant.None" title="variant core::option::Option::None"><code>None</code></a>. Moreover, the retry
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function will not be called if the <a href="https://doc.rust-lang.org/1.93.1/core/option/enum.Option.html#variant.None" title="variant core::option::Option::None"><code>None</code></a> is returned.</p>
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</div></details></div><h2 id="implementors" class="section-header">Implementors<a href="#implementors" class="anchor">§</a></h2><div id="implementors-list"></div><script src="../../trait.impl/tower/retry/policy/trait.Policy.js" async></script></section></div></main></body></html> |