mirror of
https://github.com/fafhrd91/actix-web
synced 2025-01-19 14:14:41 +01:00
31 lines
5.0 KiB
HTML
31 lines
5.0 KiB
HTML
<!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="Makes a request conditional based on the E-Tag."><title>IF_NONE_MATCH in actix_http::header - Rust</title><script>if(window.location.protocol!=="file:")document.head.insertAdjacentHTML("beforeend","SourceSerif4-Regular-46f98efaafac5295.ttf.woff2,FiraSans-Regular-018c141bf0843ffd.woff2,FiraSans-Medium-8f9a781e4970d388.woff2,SourceCodePro-Regular-562dcc5011b6de7d.ttf.woff2,SourceCodePro-Semibold-d899c5a5c4aeb14a.ttf.woff2".split(",").map(f=>`<link rel="preload" as="font" type="font/woff2" crossorigin href="../../static.files/${f}">`).join(""))</script><link rel="stylesheet" href="../../static.files/normalize-76eba96aa4d2e634.css"><link rel="stylesheet" href="../../static.files/rustdoc-dd39b87e5fcfba68.css"><meta name="rustdoc-vars" data-root-path="../../" data-static-root-path="../../static.files/" data-current-crate="actix_http" data-themes="" data-resource-suffix="" data-rustdoc-version="1.80.0-nightly (bdbbb6c6a 2024-05-26)" data-channel="nightly" data-search-js="search-d52510db62a78183.js" data-settings-js="settings-4313503d2e1961c2.js" ><script src="../../static.files/storage-118b08c4c78b968e.js"></script><script defer src="sidebar-items.js"></script><script defer src="../../static.files/main-20a3ad099b048cf2.js"></script><noscript><link rel="stylesheet" href="../../static.files/noscript-df360f571f6edeae.css"></noscript><link rel="icon" href="https://actix.rs/favicon.ico"></head><body class="rustdoc constant"><!--[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" title="show sidebar"></button><a class="logo-container" href="../../actix_http/index.html"><img src="https://actix.rs/img/logo.png" alt=""></a></nav><nav class="sidebar"><div class="sidebar-crate"><a class="logo-container" href="../../actix_http/index.html"><img src="https://actix.rs/img/logo.png" alt="logo"></a><h2><a href="../../actix_http/index.html">actix_http</a><span class="version">3.7.0</span></h2></div><div class="sidebar-elems"><h2><a href="index.html">In actix_http::header</a></h2></div></nav><div class="sidebar-resizer"></div><main><div class="width-limiter"><rustdoc-search></rustdoc-search><section id="main-content" class="content"><div class="main-heading"><h1>Constant <a href="../index.html">actix_http</a>::<wbr><a href="index.html">header</a>::<wbr><a class="constant" href="#">IF_NONE_MATCH</a><button id="copy-path" title="Copy item path to clipboard">Copy item path</button></h1><span class="out-of-band"><a class="src" href="https://docs.rs/http/0.2.11/src/http/header/name.rs.html#156-987">source</a> · <button id="toggle-all-docs" title="collapse all docs">[<span>−</span>]</button></span></div><pre class="rust item-decl"><code>pub const IF_NONE_MATCH: <a class="struct" href="struct.HeaderName.html" title="struct actix_http::header::HeaderName">HeaderName</a>;</code></pre><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Makes a request conditional based on the E-Tag.</p>
|
||
<p>The If-None-Match HTTP request header makes the request conditional. For
|
||
GET and HEAD methods, the server will send back the requested resource,
|
||
with a 200 status, only if it doesn’t have an ETag matching the given
|
||
ones. For other methods, the request will be processed only if the
|
||
eventually existing resource’s ETag doesn’t match any of the values
|
||
listed.</p>
|
||
<p>When the condition fails for GET and HEAD methods, then the server must
|
||
return HTTP status code 304 (Not Modified). For methods that apply
|
||
server-side changes, the status code 412 (Precondition Failed) is used.
|
||
Note that the server generating a 304 response MUST generate any of the
|
||
following header fields that would have been sent in a 200 (OK) response
|
||
to the same request: Cache-Control, Content-Location, Date, ETag,
|
||
Expires, and Vary.</p>
|
||
<p>The comparison with the stored ETag uses the weak comparison algorithm,
|
||
meaning two files are considered identical not only if they are
|
||
identical byte to byte, but if the content is equivalent. For example,
|
||
two pages that would differ only by the date of generation in the footer
|
||
would be considered as identical.</p>
|
||
<p>When used in combination with If-Modified-Since, it has precedence (if
|
||
the server supports it).</p>
|
||
<p>There are two common use cases:</p>
|
||
<ul>
|
||
<li>For <code>GET</code> and <code>HEAD</code> methods, to update a cached entity that has an associated ETag.</li>
|
||
<li>For other methods, and in particular for <code>PUT</code>, <code>If-None-Match</code> used with
|
||
the <code>*</code> value can be used to save a file not known to exist,
|
||
guaranteeing that another upload didn’t happen before, losing the data
|
||
of the previous put; this problems is the variation of the lost update
|
||
problem.</li>
|
||
</ul>
|
||
</div></details></section></div></main></body></html> |