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rfc9111.html
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<!DOCTYPE html>
<html lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>RFC 9111 - HTTP Caching</title><script>
var buttonsAdded = false;
function initFeedback() {
var fb = document.createElement("div");
fb.className = "feedback noprint";
fb.setAttribute("onclick", "feedback();");
fb.appendChild(document.createTextNode("feedback"));
document.body.appendChild(fb);
}
function feedback() {
toggleButtonsToElementsByName("h2");
toggleButtonsToElementsByName("h3");
toggleButtonsToElementsByName("h4");
toggleButtonsToElementsByName("h5");
buttonsAdded = !buttonsAdded;
}
function toggleButtonsToElementsByName(name) {
var list = document.getElementsByTagName(name);
for (var i = 0; i < list.length; i++) {
toggleButton(list.item(i));
}
}
function toggleButton(node) {
if (! buttonsAdded) {
// docname
var template = "mailto:ietf-http-wg@w3.org?subject={docname},%20%22{section}%22&body=<{ref}>:";
var id = node.getAttribute("id");
// try also parent
if (id == null || id == "") {
var id = node.parentNode.getAttribute("id");
}
// better id available?
var titlelinks = node.getElementsByTagName("a");
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var tl = titlelinks.item(i);
if (tl.getAttribute("id")) {
id = tl.getAttribute("id");
}
}
// ref
var ref = window.location.toString();
var hash = ref.indexOf("#");
if (hash != -1) {
ref = ref.substring(0, hash);
}
if (id != null && id != "") {
ref += "#" + id;
}
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var docname = "draft-ietf-httpbis-cache-latest";
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uri = uri.replace("{ref}", encodeURIComponent(ref));
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button.className = "fbbutton noprint";
button.setAttribute("href", uri);
button.appendChild(document.createTextNode("send feedback"));
node.appendChild(button);
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for (var i = 0; i < buttons.length; i++) {
var b = buttons.item(i);
if (b.className == "fbbutton noprint") {
node.removeChild(b);
}
}
}
}</script><script>
function getMeta(rfcno, container) {
var xhr = new XMLHttpRequest();
xhr.open("GET", "https://www.rfc-editor.org/rfc/rfc" + rfcno + ".json", true);
xhr.onload = function (e) {
if (xhr.readyState === 4) {
if (xhr.status === 200) {
var data = JSON.parse(xhr.response);
var cont = document.getElementById(container);
// empty the container
while (cont.firstChild) {
cont.removeChild(myNode.firstChild);
}
var c = data.status;
if (c) {
var bld = newElementWithText("b", c);
cont.appendChild(bld);
} else {
cont.appendChild(newElementWithText("i", "(document status unknown)"));
}
c = data.updated_by;
if (c && c.length > 0 && c[0] !== null && c[0].length > 0) {
cont.appendChild(newElement("br"));
cont.appendChild(newText("Updated by: "));
appendRfcLinks(cont, c);
}
c = data.obsoleted_by;
if (c && c.length > 0 && c[0] !== null && c[0].length > 0) {
cont.appendChild(newElement("br"));
cont.appendChild(newText("Obsoleted by: "));
appendRfcLinks(cont, c);
}
c = data.errata_url;
if (c) {
cont.appendChild(newElement("br"));
var link = newElementWithText("a", "errata");
link.setAttribute("href", c);
var errata = newElementWithText("i", "This document has ");
errata.appendChild(link);
errata.appendChild(newText("."));
cont.appendChild(errata);
}
cont.style.display = "block";
} else {
console.error(xhr.statusText);
}
}
};
xhr.onerror = function (e) {
console.error(xhr.status + " " + xhr.statusText);
};
xhr.send(null);
}
function appendRfcLinks(parent, updates) {
var template = "https://www.rfc-editor.org/rfc/rfc{rfc}.html";
for (var i = 0; i < updates.length; i++) {
var rfc = updates[i].trim().toLowerCase();
if (rfc.substring(0, 3) == "rfc") {
var no = parseInt(rfc.substring(3), 10);
var link = newElement("a");
link.setAttribute("href", template.replace("{rfc}", no));
link.appendChild(newText(no));
parent.appendChild(link);
} else {
parent.appendChild(newText(rfc));
}
if (i != updates.length - 1) {
parent.appendChild(newText(", "));
}
}
}
// DOM helpers
function newElement(name) {
return document.createElement(name);
}
function newElementWithText(name, txt) {
var e = document.createElement(name);
e.appendChild(newText(txt));
return e;
}
function newText(text) {
return document.createTextNode(text);
}
</script><script>
function anchorRewrite() {
map = { "DIGIT": "core.rules", "HTTP-date": "imported.rules", "OWS": "imported.rules", "field-name": "imported.rules", "quoted-string": "imported.rules", "token": "imported.rules", "header.age": "field.age", "Age": "field.age", "age-value": "field.age", "header.cache-control": "field.cache-control", "Cache-Control": "field.cache-control", "cache-directive": "field.cache-control", "cache-response-directive": "cache-response-directive", "header.expires": "field.expires", "Expires": "field.expires", "header.pragma": "field.pragma", "extension-pragma": "field.pragma", "Pragma": "field.pragma", "pragma-directive": "field.pragma", "header.warning": "field.warning", "Warning": "field.warning"};
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}
window.addEventListener('hashchange', anchorRewrite);
window.addEventListener('DOMContentLoaded', anchorRewrite);
</script><script src="https://cdn.rawgit.com/google/code-prettify/master/loader/run_prettify.js"></script><script>try {
PR['registerLangHandler'](
PR['createSimpleLexer'](
[
// comment
[PR['PR_COMMENT'], /^;[^\x00-\x1f]*/, null, ";"],
],
[
// string literals
[PR['PR_STRING'], /^(\%s|\%i)?"[^"\x00-\x1f]*"/, null],
// binary literals
[PR['PR_LITERAL'], /^\%b[01]+((-[01]+)|(\.[01]+)*)/, null],
// decimal literals
[PR['PR_LITERAL'], /^\%d[0-9]+((-[0-9]+)|(\.[0-9]+)*)/, null],
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[PR['PR_LITERAL'], /^(\%x[A-Za-z0-9]+((-[A-Za-z0-9]+)|(\.[A-Za-z0-9]+)*))/, null],
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[PR['PR_NOCODE'], /^<[^>\x00-\x1f]*>/, null],
// rule name
[PR['PR_TYPE'], /^([A-Za-z][A-Za-z0-9-]*)/, null],
[PR['PR_PUNCTUATION'], /^[=\(\)\*\/\[\]#]/, null],
]),
['ietf_abnf']);
} catch(e){}
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<link rel="Contents" href="#rfc.toc">
<link rel="Author" href="#rfc.authors">
<link rel="License" href="#rfc.copyrightnotice">
<link rel="Index" href="#rfc.index">
<link rel="Chapter" title="1 Introduction" href="#rfc.section.1">
<link rel="Chapter" title="2 Overview of Cache Operation" href="#rfc.section.2">
<link rel="Chapter" title="3 Storing Responses in Caches" href="#rfc.section.3">
<link rel="Chapter" title="4 Constructing Responses from Caches" href="#rfc.section.4">
<link rel="Chapter" title="5 Field Definitions" href="#rfc.section.5">
<link rel="Chapter" title="6 Relationship to Applications and Other Caches" href="#rfc.section.6">
<link rel="Chapter" title="7 Security Considerations" href="#rfc.section.7">
<link rel="Chapter" title="8 IANA Considerations" href="#rfc.section.8">
<link rel="Chapter" title="9 References" href="#rfc.section.9">
<link rel="Appendix" title="A Collected ABNF" href="#rfc.section.A">
<link rel="Appendix" title="B Changes from RFC 7234" href="#rfc.section.B">
<link rel="Appendix" title="Acknowledgements" href="#rfc.section.unnumbered-1">
<link rel="Alternate" title="Plain Text Version" href="http://www.ietf.org/rfc/rfc9111.txt">
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<link rel="schema.dcterms" href="http://purl.org/dc/terms/">
<meta name="dcterms.creator" content="Fielding, R.">
<meta name="dcterms.creator" content="Nottingham, M.">
<meta name="dcterms.creator" content="Reschke, J.">
<meta name="dcterms.identifier" content="urn:ietf:rfc:9111">
<meta name="dcterms.issued" content="2022-06">
<meta name="dct.replaces" content="urn:ietf:rfc:7234">
<meta name="dcterms.abstract" content="The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document defines HTTP caches and the associated header fields that control cache behavior or indicate cacheable response messages. This document obsoletes RFC 7234.">
<meta name="dcterms.isPartOf" content="urn:issn:2070-1721">
<meta name="description" content="The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document defines HTTP caches and the associated header fields that control cache behavior or indicate cacheable response messages. This document obsoletes RFC 7234.">
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<body onload="getMeta("9111","rfc.meta");initFeedback();">
<header>
<table class="header" id="rfc.headerblock">
<tbody>
<tr>
<td class="left">Internet Engineering Task Force (IETF)</td>
<td class="right">R. Fielding, Editor</td>
</tr>
<tr>
<td class="left">Request for Comments: 9111</td>
<td class="right">Adobe</td>
</tr>
<tr>
<td class="left">Obsoletes: <a href="#RFC7234">7234</a></td>
<td class="right">M. Nottingham, Editor</td>
</tr>
<tr>
<td class="left">STD: <a href="https://www.rfc-editor.org/info/std98">98</a></td>
<td class="right">Fastly</td>
</tr>
<tr>
<td class="left">Category: Standards Track</td>
<td class="right">J. Reschke, Editor</td>
</tr>
<tr>
<td class="left">ISSN: 2070-1721</td>
<td class="right">greenbytes</td>
</tr>
<tr>
<td class="left"></td>
<td class="right">June 2022</td>
</tr>
</tbody>
</table>
<div id="rfc.title">
<h1>HTTP Caching</h1>
</div>
</header>
<section>
<h2 id="rfc.abstract"><a href="#rfc.abstract">Abstract</a></h2>
<div id="rfc.abstract.p.1">
<p>The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for
distributed, collaborative, hypertext information systems. This document defines HTTP
caches and the associated header fields that control cache behavior or indicate cacheable
response messages.<a class="self" href="#rfc.abstract.p.1">¶</a></p>
</div>
<div id="rfc.abstract.p.2">
<p>This document obsoletes RFC 7234.<a class="self" href="#rfc.abstract.p.2">¶</a></p>
</div>
</section>
<aside id="rfc.meta" class="docstatus"></aside>
<section id="rfc.status">
<h2><a href="#rfc.status">Status of This Memo</a></h2>
<div id="rfc.boilerplate.1.p.1">
<p>This is an Internet Standards Track document.<a class="self" href="#rfc.boilerplate.1.p.1">¶</a></p>
</div>
<div id="rfc.boilerplate.1.p.2">
<p>This document is a product of the Internet Engineering Task Force (IETF). It represents
the consensus of the IETF community. It has received public review and has been approved
for publication by the Internet Engineering Steering Group (IESG). Further information
on Internet Standards is available in <a href="https://www.rfc-editor.org/rfc/rfc7841.html#section-2">Section 2 of RFC 7841</a>.<a class="self" href="#rfc.boilerplate.1.p.2">¶</a></p>
</div>
<div id="rfc.boilerplate.1.p.3">
<p>Information about the current status of this document, any errata, and how to provide
feedback on it may be obtained at <a href="https://www.rfc-editor.org/info/rfc9111">https://www.rfc-editor.org/info/rfc9111</a>.<a class="self" href="#rfc.boilerplate.1.p.3">¶</a></p>
</div>
</section>
<section id="rfc.copyrightnotice">
<h2><a href="#rfc.copyrightnotice">Copyright Notice</a></h2>
<div id="rfc.boilerplate.2.p.1">
<p>Copyright (c) 2022 IETF Trust and the persons identified as the document authors.
All rights reserved.<a class="self" href="#rfc.boilerplate.2.p.1">¶</a></p>
</div>
<div id="rfc.boilerplate.2.p.2">
<p>This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating
to IETF Documents (<a href="https://trustee.ietf.org/license-info">https://trustee.ietf.org/license-info</a>) in effect on the date of publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect to this document.
Code Components extracted from this document must include Revised BSD License text
as described in Section 4.e of the Trust Legal Provisions and are provided without
warranty as described in the Revised BSD License.<a class="self" href="#rfc.boilerplate.2.p.2">¶</a></p>
</div>
<div id="rfc.boilerplate.2.p.3">
<p>This document may contain material from IETF Documents or IETF Contributions published
or made publicly available before November 10, 2008. The person(s) controlling the
copyright in some of this material may not have granted the IETF Trust the right to
allow modifications of such material outside the IETF Standards Process. Without obtaining
an adequate license from the person(s) controlling the copyright in such materials,
this document may not be modified outside the IETF Standards Process, and derivative
works of it may not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other than English.<a class="self" href="#rfc.boilerplate.2.p.3">¶</a></p>
</div>
</section>
<hr class="noprint">
<nav id="rfc.toc">
<h2 class="np"><a href="#rfc.toc">Table of Contents</a></h2>
<ul class="toc">
<li><a href="#rfc.section.1">1.</a> <a href="#caching">Introduction</a><ul>
<li><a href="#rfc.section.1.1">1.1.</a> <a href="#requirements.notation">Requirements Notation</a></li>
<li><a href="#rfc.section.1.2">1.2.</a> <a href="#notation">Syntax Notation</a><ul>
<li><a href="#rfc.section.1.2.1">1.2.1.</a> <a href="#abnf.imported">Imported Rules</a></li>
<li><a href="#rfc.section.1.2.2">1.2.2.</a> <a href="#delta-seconds">Delta Seconds</a></li>
</ul>
</li>
</ul>
</li>
<li><a href="#rfc.section.2">2.</a> <a href="#caching.overview">Overview of Cache Operation</a></li>
<li><a href="#rfc.section.3">3.</a> <a href="#response.cacheability">Storing Responses in Caches</a><ul>
<li><a href="#rfc.section.3.1">3.1.</a> <a href="#storing.fields">Storing Header and Trailer Fields</a></li>
<li><a href="#rfc.section.3.2">3.2.</a> <a href="#update">Updating Stored Header Fields</a></li>
<li><a href="#rfc.section.3.3">3.3.</a> <a href="#incomplete.responses">Storing Incomplete Responses</a></li>
<li><a href="#rfc.section.3.4">3.4.</a> <a href="#combining.responses">Combining Partial Content</a></li>
<li><a href="#rfc.section.3.5">3.5.</a> <a href="#caching.authenticated.responses">Storing Responses to Authenticated Requests</a></li>
</ul>
</li>
<li><a href="#rfc.section.4">4.</a> <a href="#constructing.responses.from.caches">Constructing Responses from Caches</a><ul>
<li><a href="#rfc.section.4.1">4.1.</a> <a href="#caching.negotiated.responses">Calculating Cache Keys with the Vary Header Field</a></li>
<li><a href="#rfc.section.4.2">4.2.</a> <a href="#expiration.model">Freshness</a><ul>
<li><a href="#rfc.section.4.2.1">4.2.1.</a> <a href="#calculating.freshness.lifetime">Calculating Freshness Lifetime</a></li>
<li><a href="#rfc.section.4.2.2">4.2.2.</a> <a href="#heuristic.freshness">Calculating Heuristic Freshness</a></li>
<li><a href="#rfc.section.4.2.3">4.2.3.</a> <a href="#age.calculations">Calculating Age</a></li>
<li><a href="#rfc.section.4.2.4">4.2.4.</a> <a href="#serving.stale.responses">Serving Stale Responses</a></li>
</ul>
</li>
<li><a href="#rfc.section.4.3">4.3.</a> <a href="#validation.model">Validation</a><ul>
<li><a href="#rfc.section.4.3.1">4.3.1.</a> <a href="#validation.sent">Sending a Validation Request</a></li>
<li><a href="#rfc.section.4.3.2">4.3.2.</a> <a href="#validation.received">Handling a Received Validation Request</a></li>
<li><a href="#rfc.section.4.3.3">4.3.3.</a> <a href="#validation.response">Handling a Validation Response</a></li>
<li><a href="#rfc.section.4.3.4">4.3.4.</a> <a href="#freshening.responses">Freshening Stored Responses upon Validation</a></li>
<li><a href="#rfc.section.4.3.5">4.3.5.</a> <a href="#head.effects">Freshening Responses with HEAD</a></li>
</ul>
</li>
<li><a href="#rfc.section.4.4">4.4.</a> <a href="#invalidation">Invalidating Stored Responses</a></li>
</ul>
</li>
<li><a href="#rfc.section.5">5.</a> <a href="#header.field.definitions">Field Definitions</a><ul>
<li><a href="#rfc.section.5.1">5.1.</a> <a href="#field.age">Age</a></li>
<li><a href="#rfc.section.5.2">5.2.</a> <a href="#field.cache-control">Cache-Control</a><ul>
<li><a href="#rfc.section.5.2.1">5.2.1.</a> <a href="#cache-request-directive">Request Directives</a><ul>
<li><a href="#rfc.section.5.2.1.1">5.2.1.1.</a> <a href="#cache-request-directive.max-age">max-age</a></li>
<li><a href="#rfc.section.5.2.1.2">5.2.1.2.</a> <a href="#cache-request-directive.max-stale">max-stale</a></li>
<li><a href="#rfc.section.5.2.1.3">5.2.1.3.</a> <a href="#cache-request-directive.min-fresh">min-fresh</a></li>
<li><a href="#rfc.section.5.2.1.4">5.2.1.4.</a> <a href="#cache-request-directive.no-cache">no-cache</a></li>
<li><a href="#rfc.section.5.2.1.5">5.2.1.5.</a> <a href="#cache-request-directive.no-store">no-store</a></li>
<li><a href="#rfc.section.5.2.1.6">5.2.1.6.</a> <a href="#cache-request-directive.no-transform">no-transform</a></li>
<li><a href="#rfc.section.5.2.1.7">5.2.1.7.</a> <a href="#cache-request-directive.only-if-cached">only-if-cached</a></li>
</ul>
</li>
<li><a href="#rfc.section.5.2.2">5.2.2.</a> <a href="#cache-response-directive">Response Directives</a><ul>
<li><a href="#rfc.section.5.2.2.1">5.2.2.1.</a> <a href="#cache-response-directive.max-age">max-age</a></li>
<li><a href="#rfc.section.5.2.2.2">5.2.2.2.</a> <a href="#cache-response-directive.must-revalidate">must-revalidate</a></li>
<li><a href="#rfc.section.5.2.2.3">5.2.2.3.</a> <a href="#cache-response-directive.must-understand">must-understand</a></li>
<li><a href="#rfc.section.5.2.2.4">5.2.2.4.</a> <a href="#cache-response-directive.no-cache">no-cache</a></li>
<li><a href="#rfc.section.5.2.2.5">5.2.2.5.</a> <a href="#cache-response-directive.no-store">no-store</a></li>
<li><a href="#rfc.section.5.2.2.6">5.2.2.6.</a> <a href="#cache-response-directive.no-transform">no-transform</a></li>
<li><a href="#rfc.section.5.2.2.7">5.2.2.7.</a> <a href="#cache-response-directive.private">private</a></li>
<li><a href="#rfc.section.5.2.2.8">5.2.2.8.</a> <a href="#cache-response-directive.proxy-revalidate">proxy-revalidate</a></li>
<li><a href="#rfc.section.5.2.2.9">5.2.2.9.</a> <a href="#cache-response-directive.public">public</a></li>
<li><a href="#rfc.section.5.2.2.10">5.2.2.10.</a> <a href="#cache-response-directive.s-maxage">s-maxage</a></li>
</ul>
</li>
<li><a href="#rfc.section.5.2.3">5.2.3.</a> <a href="#cache.control.extensions">Extension Directives</a></li>
<li><a href="#rfc.section.5.2.4">5.2.4.</a> <a href="#cache.directive.registry">Cache Directive Registry</a></li>
</ul>
</li>
<li><a href="#rfc.section.5.3">5.3.</a> <a href="#field.expires">Expires</a></li>
<li><a href="#rfc.section.5.4">5.4.</a> <a href="#field.pragma">Pragma</a></li>
<li><a href="#rfc.section.5.5">5.5.</a> <a href="#field.warning">Warning</a></li>
</ul>
</li>
<li><a href="#rfc.section.6">6.</a> <a href="#history.lists">Relationship to Applications and Other Caches</a></li>
<li><a href="#rfc.section.7">7.</a> <a href="#security.considerations">Security Considerations</a><ul>
<li><a href="#rfc.section.7.1">7.1.</a> <a href="#cache.poisoning">Cache Poisoning</a></li>
<li><a href="#rfc.section.7.2">7.2.</a> <a href="#security.timing">Timing Attacks</a></li>
<li><a href="#rfc.section.7.3">7.3.</a> <a href="#caching.of.sensitive.information">Caching of Sensitive Information</a></li>
</ul>
</li>
<li><a href="#rfc.section.8">8.</a> <a href="#iana.considerations">IANA Considerations</a><ul>
<li><a href="#rfc.section.8.1">8.1.</a> <a href="#field.name.registration">Field Name Registration</a></li>
<li><a href="#rfc.section.8.2">8.2.</a> <a href="#cache.directive.registration">Cache Directive Registration</a></li>
<li><a href="#rfc.section.8.3">8.3.</a> <a href="#warn.code.registration">Warn Code Registry</a></li>
</ul>
</li>
<li><a href="#rfc.section.9">9.</a> <a href="#rfc.references">References</a><ul>
<li><a href="#rfc.section.9.1">9.1.</a> <a href="#rfc.references.1">Normative References</a></li>
<li><a href="#rfc.section.9.2">9.2.</a> <a href="#rfc.references.2">Informative References</a></li>
</ul>
</li>
<li><a href="#rfc.section.A">Appendix A.</a> <a href="#collected.abnf">Collected ABNF</a></li>
<li><a href="#rfc.section.B">Appendix B.</a> <a href="#changes.from.rfc.7234">Changes from RFC 7234</a></li>
<li><a href="#acks">Acknowledgements</a></li>
<li><a href="#rfc.index">Index</a></li>
<li><a href="#rfc.authors">Authors' Addresses</a></li>
</ul>
</nav>
<section id="caching">
<h2 id="rfc.section.1" class="np"><a href="#rfc.section.1">1.</a> <a href="#caching">Introduction</a></h2>