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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>
Resource Timing Level 2
</title>
<script src='https://www.w3.org/Tools/respec/respec-w3c' class='remove'
defer></script>
<script class='remove'>
var respecConfig = {
shortName: "resource-timing-2",
specStatus: "ED",
editors: [{
name: "Yoav Weiss",
url: "https://blog.yoav.ws/",
company: "Google",
companyURL: "https://google.com/",
w3cid: "58673"
}, {
name: "Noam Rosenthal",
mailto: "noam.j.rosenthal@gmail.com",
company: "Invited Expert",
w3cid: "121539"
}],
formerEditors: [{
name: "Ilya Grigorik",
url: "https://www.igvita.com/",
company: "Google",
companyURL: "https://google.com/",
note: "Until January 2021",
w3cid: "56102"
}, {
name: "Todd Reifsteck",
mailto: "toddreif@microsoft.com",
company: "Microsoft Corp.",
note: "Until January 2021",
w3cid: "76565"
}, {
name: "Arvind Jain",
mailto: "arvind@google.com",
company: "Google Inc.",
note: "Until December 2014",
w3cid: "45188"
}, {
name: "Jatinder Mann",
mailto: "jmann@microsoft.com",
company: "Microsoft Corp.",
note: "Until February 2014",
w3cid: "44357"
}, {
name: "Zhiheng Wang",
company: "Google Inc.",
note: "Until July 2012",
w3cid: "43685"
}, {
name: "Anderson Quach",
company: "Microsoft Corp.",
note: "Until March 2011",
w3cid: "45288"
}],
group:"webperf",
wgPublicList: "public-web-perf",
subjectPrefix: "[ResourceTiming]",
github: "https://github.com/w3c/resource-timing/",
caniuse: "resource-timing",
xref: {
specs: ["hr-time-3", "performance-timeline", "xhr"],
profile: "web-platform",
}
};
</script>
</head>
<body>
<section id="abstract">
<p>
This specification defines an interface for web applications to access
the complete timing information for resources in a document.
</p>
</section>
<section id="sotd">
<p class='warning'>
Implementers SHOULD be aware that this document is not stable.
Implementers who are not taking part in the discussions are likely to
find the specification changing out from under them in incompatible
ways. Vendors interested in implementing this document before it
eventually reaches the Candidate Recommendation stage SHOULD join the
aforementioned mailing lists and take part in the discussions.
</p>
</section>
<section id="introduction" class='informative'>
<h2>
Introduction
</h2>
<p>
User latency is an important quality benchmark for Web Applications.
While JavaScript-based mechanisms can provide comprehensive
instrumentation for user latency measurements within an application, in
many cases, they are unable to provide a complete end-to-end latency
picture. This document introduces the <a>PerformanceResourceTiming</a>
interface to allow JavaScript mechanisms to collect complete timing
information related to resources on a document. Navigation Timing 2
[[NAVIGATION-TIMING-2]] extends this specification to provide
additional timing information associated with a navigation.
</p>
<p>
For example, the following JavaScript shows a simple attempt to measure
the time it takes to fetch a resource:
</p>
<pre class='example html'>
<!doctype html>
<html>
<head>
</head>
<body onload="loadResources()">
<script>
function loadResources()
{
var start = new Date().getTime();
var image1 = new Image();
var resourceTiming = function() {
var now = new Date().getTime();
var latency = now - start;
alert("End to end resource fetch: " + latency);
};
image1.onload = resourceTiming;
image1.src = 'https://www.w3.org/Icons/w3c_main.png';
}
</script>
<img src="https://www.w3.org/Icons/w3c_home.png">
</body>
</html>
</pre>
<p>
Though this script can measure the time it takes to fetch a resource,
it cannot break down the time spent in various phases. Further, the
script cannot easily measure the time it takes to fetch resources
described in markup.
</p>
<p>
To address the need for complete information on user experience, this
document introduces the <a>PerformanceResourceTiming</a> interface.
This interface allows JavaScript mechanisms to provide complete
client-side latency measurements within applications. With this
interface, the previous example can be modified to measure a user's
perceived load time of a resource.
</p>
<p>
The following script calculates the amount of time it takes to fetch
every resource in the page, even those defined in markup. This example
assumes that this page is hosted on https://www.w3.org. One could
further measure the amount of time it takes in every phase of fetching
a resource with the <a>PerformanceResourceTiming</a> interface.
</p>
<pre class='example html'>
<!doctype html>
<html>
<head>
</head>
<body onload="loadResources()">
<script>
function loadResources()
{
var image1 = new Image();
image1.onload = resourceTiming;
image1.src = 'https://www.w3.org/Icons/w3c_main.png';
}
function resourceTiming()
{
var resourceList = window.performance.getEntriesByType("resource");
for (i = 0; i < resourceList.length; i++)
{
if (resourceList[i].initiatorType == "img")
{
alert("End to end resource fetch: " + (resourceList[i].responseEnd - resourceList[i].startTime));
}
}
}
</script>
<img id="image0" src="https://www.w3.org/Icons/w3c_home.png">
</body>
</html>
</pre>
</section>
<section id="conformance">
<p>
Requirements phrased in the imperative as part of algorithms (such as
"strip any leading space characters" or "return false and abort these
steps") are to be interpreted with the meaning of the key word ("MUST",
"SHOULD", "MAY", etc) used in introducing the algorithm.
</p>
<p>
Some conformance requirements are phrased as requirements on
attributes, methods or objects. Such requirements are to be interpreted
as requirements on user agents.
</p>
<p>
Conformance requirements phrased as algorithms or specific steps may be
implemented in any manner, so long as the end result is equivalent. (In
particular, the algorithms defined in this specification are intended
to be easy to follow, and not intended to be performant.)
</p>
</section>
<section id="terminology">
<h2>
Terminology
</h2>
<p>
The construction "a <code>Foo</code> object", where <code>Foo</code> is
actually an interface, is sometimes used instead of the more accurate
"an object implementing the interface <code>Foo</code>.
</p>
<p>
Throughout this work, all time values are measured in milliseconds
since the start of navigation of the document [[HR-TIME-2]]. For
example, the <a data-cite=
"NAVIGATION-TIMING-2#dom-PerformanceNavigationTiming-startTime">start
of navigation of the document</a> occurs at time 0.
</p>
<p class='note'>
This definition of time is based on the High Resolution Time
specification [[HR-TIME-2]] and is different from the definition of
time used in the Navigation Timing specification
[[NAVIGATION-TIMING-2]], where time is measured in milliseconds since
midnight of January 1, 1970 (UTC).
</p>
</section>
<section id="sec-resource-timing">
<h2>
Resource Timing
</h2>
<section class='informative'>
<h3>
Introduction
</h3>
<p data-fn-for="html">
The <a>PerformanceResourceTiming</a> interface facilitates timing
measurement of [=fetch|fetched=] [=http(s) scheme|http(s)=]
resources. For example, this interface is available for
{{XMLHttpRequest}} objects [[XHR]], HTML elements [[HTML]] such as
[^iframe^], [^img^], [^script^], [^object^], [^embed^] and [^link^]
with the link type of [^link/rel/stylesheet^], SVG elements [[SVG11]]
such as <a data-cite="SVG11/struct.html#SVGElement">svg</a>, and
{{EventSource}}.
</p>
</section>
<section>
<h3>
Resources Included in the <a>PerformanceResourceTiming</a> Interface
</h3>
<p>
This section is non-normative.
</p>
<p>
Resource [=Request=]s [=fetch=]ed by a non-null [=request/client=]
are included as <a>PerformanceResourceTiming</a> objects in the
[=request/client=]'s [=environment settings object/global object=]'s
<a data-cite=
"PERFORMANCE-TIMELINE-2#performance-timeline">Performance
Timeline</a>, unless excluded from the timeline as part of the
[=fetch|fetching process=]. Resources that are retrieved from HTTP
cache are included as <a>PerformanceResourceTiming</a> objects in the
<a data-cite=
"PERFORMANCE-TIMELINE-2#performance-timeline">Performance
Timeline</a>. Resources for which the [=fetch=] was initiated, but
was later aborted (e.g. due to a network error) are included as
<a>PerformanceResourceTiming</a> objects in the <a data-cite=
"PERFORMANCE-TIMELINE-2#performance-timeline">Performance
Timeline</a>, with their start and end timing.
</p>
<p>
Examples:
</p>
<ul>
<li>If the same canonical URL is used as the <code>src</code>
attribute of two HTML <code>IMG</code> elements, the [=fetch=] of the
resource initiated by the first HTML <code>IMG</code> element would
be included as a <a>PerformanceResourceTiming</a> object in the
<a data-cite=
"PERFORMANCE-TIMELINE-2#performance-timeline">Performance
Timeline</a>. The user agent might not re-request the URL for the
second HTML <code>IMG</code> element, instead using the existing
download it initiated for the first HTML <code>IMG</code> element. In
this case, the [=fetch=] of the resource by the first
<code>IMG</code> element would be the only occurrence in the
<a data-cite=
"PERFORMANCE-TIMELINE-2#performance-timeline">Performance
Timeline</a>.
</li>
<li>If the <code>src</code> attribute of a HTML <code>IMG</code>
element is changed via script, both the [=fetch=] of the original
resource as well as the [=fetch=] of the new URL would be included as
<a>PerformanceResourceTiming</a> objects in the <a data-cite=
"PERFORMANCE-TIMELINE-2#performance-timeline">Performance
Timeline</a>.
</li>
<li>If an HTML <code>IFRAME</code> element is added via markup
without specifying a <code>src</code> attribute, the user agent may
load the <code>about:blank</code> document for the
<code>IFRAME</code>. If at a later time the <code>src</code>
attribute is changed dynamically via script, the user agent may
[=fetch=] the new URL resource for the <code>IFRAME</code>. In this
case, only the [=fetch=] of the new URL would be included as a
<a>PerformanceResourceTiming</a> object in the <a data-cite=
"PERFORMANCE-TIMELINE-2#performance-timeline">Performance
Timeline</a>.
</li>
<li>If an <code>XMLHttpRequest</code> is generated twice for the same
canonical URL, both [=fetches=] of the resource would be included as
a <a>PerformanceResourceTiming</a> object in the <a data-cite=
"PERFORMANCE-TIMELINE-2#performance-timeline">Performance
Timeline</a>. This is because the [=fetch=] of the resource for the
second <code>XMLHttpRequest</code> cannot reuse the download issued
for the first <code>XMLHttpRequest</code>.
</li>
<li>If an HTML <code>IFRAME</code> element is included on the page,
then only the resource requested by <code>IFRAME</code>
<code>src</code> attribute is included as a
<a>PerformanceResourceTiming</a> object in the <a data-cite=
"PERFORMANCE-TIMELINE-2#performance-timeline">Performance
Timeline</a>. Sub-resources requested by the <code>IFRAME</code>
document will be included in the <code>IFRAME</code> document's
<a data-cite=
"PERFORMANCE-TIMELINE-2#performance-timeline">Performance
Timeline</a> and not the parent document's <a data-cite=
"PERFORMANCE-TIMELINE-2#performance-timeline">Performance
Timeline</a>.
</li>
<li>If an HTML <code>IMG</code> element has a <code><a href=
"https://tools.ietf.org/html/rfc2397">data: URI</a></code> as its
source [[RFC2397]], then this resource will not be included as a <a>
PerformanceResourceTiming</a> object in the <a data-cite=
"PERFORMANCE-TIMELINE-2#performance-timeline">Performance
Timeline</a>. By definition <code><a href=
"https://tools.ietf.org/html/rfc2397">data: URI</a></code> contains
embedded data and does not require a [=fetch=].
</li>
<li>If a resource <a data-cite="FETCH#concept-fetch">fetch</a> was
aborted due to a networking error (e.g. DNS, TCP, or TLS error), then
the fetch will be included as a <a>PerformanceResourceTiming</a>
object in the <a data-cite=
"PERFORMANCE-TIMELINE-2#performance-timeline">Performance
Timeline</a> with only the `startTime`, `fetchStart`, `duration` and
`responseEnd` set.
</li>
<li>If a resource <a data-cite="FETCH#concept-fetch">fetch</a> is
aborted because it failed a fetch precondition (e.g. mixed content,
CORS restriction, CSP policy, etc), then this resource will not be
included as a <a>PerformanceResourceTiming</a> object in the
<a data-cite=
"PERFORMANCE-TIMELINE-2#performance-timeline">Performance
Timeline</a>.
</li>
</ul>
</section>
<section data-dfn-for="PerformanceResourceTiming" id=
"sec-performanceresourcetiming">
<h3>
The <dfn>PerformanceResourceTiming</dfn> Interface
</h3>
<pre class='idl'>
[Exposed=(Window,Worker)]
interface PerformanceResourceTiming : PerformanceEntry {
readonly attribute DOMString initiatorType;
readonly attribute DOMString deliveryType;
readonly attribute ByteString nextHopProtocol;
readonly attribute DOMHighResTimeStamp workerStart;
readonly attribute DOMHighResTimeStamp redirectStart;
readonly attribute DOMHighResTimeStamp redirectEnd;
readonly attribute DOMHighResTimeStamp fetchStart;
readonly attribute DOMHighResTimeStamp domainLookupStart;
readonly attribute DOMHighResTimeStamp domainLookupEnd;
readonly attribute DOMHighResTimeStamp connectStart;
readonly attribute DOMHighResTimeStamp connectEnd;
readonly attribute DOMHighResTimeStamp secureConnectionStart;
readonly attribute DOMHighResTimeStamp requestStart;
readonly attribute DOMHighResTimeStamp responseStart;
readonly attribute DOMHighResTimeStamp responseEnd;
readonly attribute unsigned long long transferSize;
readonly attribute unsigned long long encodedBodySize;
readonly attribute unsigned long long decodedBodySize;
[Default] object toJSON();
};
</pre>
<p>
A <a>PerformanceResourceTiming</a> has an associated DOMString
<a data-dfn-for="PerformanceResourceTiming"><dfn>initiator
type</dfn></a>.
</p>
<p>
A <a>PerformanceResourceTiming</a> has an associated DOMString
<a data-dfn-for="PerformanceResourceTiming"><dfn>delivery
type</dfn></a>.
</p>
<p>
A <a>PerformanceResourceTiming</a> has an associated DOMString
<a data-dfn-for="PerformanceResourceTiming"><dfn>requested
URL</dfn></a>.
</p>
<p>
A <a>PerformanceResourceTiming</a> has an associated DOMString
<a data-dfn-for="PerformanceResourceTiming"><dfn>cache mode</dfn></a>
(the empty string, "<code>local</code>", or
"<code>validated</code>").
</p>
<p>
A <a>PerformanceResourceTiming</a> has an associated [=fetch timing
info=] <a data-dfn-for="PerformanceResourceTiming"><dfn>timing
info</dfn></a>.
</p>
<p>
A <a>PerformanceResourceTiming</a> has an associated [=response body
info=] <a data-dfn-for="PerformanceResourceTiming"><dfn>resource
info</dfn></a>.
</p>
<p>
The <a>PerformanceResourceTiming</a> interface participates in the
<a data-cite=
"PERFORMANCE-TIMELINE-2#performance-timeline">Performance
Timeline</a> and extends the following attributes of the
<code><dfn data-cite=
"PERFORMANCE-TIMELINE-2#the-performanceentry-interface">PerformanceEntry</dfn></code>
interface:
</p>
<dl data-link-for="PerformanceResourceTiming">
<dt>
<dfn>name</dfn>
</dt>
<dd>
The <a>name</a> getter steps are to return <a>this</a>'s
<a data-for="PerformanceResourceTiming">requested URL</a>.
</dd>
<dt>
<dfn>entryType</dfn>
</dt>
<dd>
The <a>entryType</a> getter steps are to return the DOMString
"<code>resource</code>".
</dd>
<dt>
<dfn>startTime</dfn>
</dt>
<dd>
<p data-dfn-for="PerformanceResourceTiming">
The <a>startTime</a> getter steps are to <a>convert fetch
timestamp</a> for <a>this</a>'s <a data-for=
"PerformanceResourceTiming">timing info</a>'s [=fetch timing
info/start time=] and <a>this</a>'s <a>relevant global
object</a>.
</p>
<p class='note'>
`startTime` is measured right at the start of the [=fetch=],
before any redirects. See <a data-cite=
"FETCH#fetching">fetching</a>.
</p>
</dd>
<dt>
<dfn>duration</dfn>
</dt>
<dd>
<p data-dfn-for="PerformanceResourceTiming">
The <a>duration</a> getter steps are to return <a>this</a>'s
<a data-for="PerformanceResourceTiming">timing info</a>'s [=fetch
timing info/end time=] minus <a>this</a>'s <a data-for=
"PerformanceResourceTiming">timing info</a>'s [=fetch timing
info/start time=].
</p>
</dd>
</dl>
<p data-dfn-for="PerformanceResourceTiming">
When <dfn>toJSON</dfn> is called, run [[WEBIDL]]'s <a data-cite=
"WEBIDL#default-tojson-operation">default toJSON operation</a>.
</p>
<p data-dfn-for="PerformanceResourceTiming">
<dfn>initiatorType</dfn> getter steps are to return the <a data-for=
"PerformanceResourceTiming">initiator type</a> for <a>this</a>.
</p>
<div class='note'>
<p>
`initiatorType` returns one of the following values:
</p>
<ul>
<li>
<code>"navigation"</code>, if the request is a [=navigation
request=];
</li>
<li>
<code>"css"</code>, if the request is a result of processing a
CSS <a data-cite="css-values-4" data-xref-type=
"css-function">url()</a> directive such as <code>@import
url()</code> or <code>background: url()</code>; [[CSS-VALUES]]
</li>
<li>
<code>"script"</code>, if the request is a result of loading any
<a data-cite="HTML#concept-script">script</a> (a classic
[^script^], a [=module script=], or a {{Worker}}).
</li>
<li>
<code>"xmlhttprequest"</code>, if the request is a result of
processing an {{XMLHttpRequest}};
</li>
<li>
<code>"fetch"</code>, if the request is the result of processing
the {{WindowOrWorkerGlobalScope/fetch()}} method;
</li>
<li>
<code>"beacon"</code>, if the request is the result of processing
the {{Navigator/sendBeacon()}} method; [[BEACON]]
</li>
<li>
<code>"video"</code>, if the request is the result of processing
the [^video^] element's [^video/poster^] or [^video/src^].
</li>
<li>
<code>"audio"</code>, if the request is the result of processing
the [^audio^] element's [^audio/src^].
</li>
<li>
<code>"track"</code>, if the request is the result of processing
the [^track^] element's [^track/src^].
</li>
<li>
<code>"img"</code>, if the request is the result of processing
the [^img^] element's [^img/src^] or [^img/srcset^].
</li>
<li>
<code>"image"</code>, if the request is the result of processing
the <a data-cite="SVG2/embedded.html#ImageElement">image</a>
element. [[SVG2]]
</li>
<li>
<code>"input"</code>, if the request is the result of processing
an [^input^] element of [^input/type^] [^input/type/image^].
</li>
<li>
<code>"a"</code>, if the request is the result of processing an
[^a^] element's [^a/download^] or [^a/ping^].
</li>
<li>
<code>"iframe"</code>, if the request is the result of processing
an [^iframe^]'s [^iframe/src^].
</li>
<li>
<code>"frame"</code>, if the request is the result of loading a
[^frame^].
</li>
<li>
<code>"other"</code>, if none of the above conditions match.
</li>
</ul>
</div>
<p class='note'>
The setting of `initiatorType` is done at the different places where
a resource timing entry is reported, such as the [=fetch=] standard.
</p>
<p data-dfn-for="PerformanceResourceTiming">
<dfn>deliveryType</dfn> getter steps are to return the <a data-for=
"PerformanceResourceTiming">delivery type</a> for <a>this</a>.
</p>
<div class='note'>
<p>
`deliveryType` returns one of the following values:
</p>
<ul>
<li>
<code>"cache"</code>, if the <a data-for=
"PerformanceResourceTiming">cache mode</a> is not the empty
string.
</li>
<li>
the empty string <code>""</code>, if none of the above conditions
match.
</li>
</ul>
<p class='note'>
This is expected to be expanded by future updates to this
specification, e.g. to describe consuming preloaded resources and
prefetched navigation requests.
</p>
</div>
<p data-dfn-for="PerformanceResourceTiming">
The <dfn>workerStart</dfn> getter steps are to <a>convert fetch
timestamp</a> for <a>this</a>'s <a data-for=
"PerformanceResourceTiming">timing info</a>'s [=fetch timing
info/final service worker start time=] and the <a>relevant global
object</a> for <a>this</a>. See [=/HTTP fetch=] for more info.
</p>
<p data-dfn-for="PerformanceResourceTiming">
The <dfn>redirectStart</dfn> getter steps are to <a>convert fetch
timestamp</a> for <a>this</a>'s <a data-for=
"PerformanceResourceTiming">timing info</a>'s [=fetch timing
info/redirect start time=] and the <a>relevant global object</a> for
<a>this</a>. See [=/HTTP-redirect fetch=] for more info.
</p>
<p data-dfn-for="PerformanceResourceTiming">
The <dfn>redirectEnd</dfn> getter steps are to <a>convert fetch
timestamp</a> for <a>this</a>'s <a data-for=
"PerformanceResourceTiming">timing info</a>'s [=fetch timing
info/redirect end time=] and the <a>relevant global object</a> for
<a>this</a>. See [=/HTTP-redirect fetch=] for more info.
</p>
<p data-dfn-for="PerformanceResourceTiming">
The <dfn>fetchStart</dfn> getter steps are to <a>convert fetch
timestamp</a> for <a>this</a>'s <a data-for=
"PerformanceResourceTiming">timing info</a>'s [=fetch timing
info/post-redirect start time=] and the <a>relevant global object</a>
for <a>this</a>. See [=/HTTP fetch=] for more info.
</p>
<p data-for="PerformanceResourceTiming">
The <dfn>domainLookupStart</dfn> getter steps are to <a>convert fetch
timestamp</a> for <a>this</a>'s <a data-for=
"PerformanceResourceTiming">timing info</a>'s [=fetch timing
info/final connection timing info=]'s [=connection timing info/domain
lookup start time=] and the <a>relevant global object</a> for
<a>this</a>. See <a data-cite=
"FETCH#record-connection-timing-info">Recording connection timing
info</a> for more info.
</p>
<p data-dfn-for="PerformanceResourceTiming">
The <dfn>domainLookupEnd</dfn> getter steps are to <a>convert fetch
timestamp</a> for <a>this</a>'s <a data-for=
"PerformanceResourceTiming">timing info</a>'s [=fetch timing
info/final connection timing info=]'s [=connection timing info/domain
lookup end time=] and the <a>relevant global object</a> for
<a>this</a>. See <a data-cite=
"FETCH#record-connection-timing-info">Recording connection timing
info</a> for more info.
</p>
<p data-dfn-for="PerformanceResourceTiming">
The <dfn>connectStart</dfn> getter steps are to <a>convert fetch
timestamp</a> for <a>this</a>'s <a data-for=
"PerformanceResourceTiming">timing info</a>'s [=fetch timing
info/final connection timing info=]'s [=connection timing
info/connection start time=] and the <a>relevant global object</a>
for <a>this</a>. See <a data-cite=
"FETCH#record-connection-timing-info">Recording connection timing
info</a> for more info.
</p>
<p data-dfn-for="PerformanceResourceTiming">
The <dfn>connectEnd</dfn> getter steps are to <a>convert fetch
timestamp</a> for <a>this</a>'s <a data-for=
"PerformanceResourceTiming">timing info</a>'s [=fetch timing
info/final connection timing info=]'s [=connection timing
info/connection end time=] and the <a>relevant global object</a> for
<a>this</a>. See <a data-cite=
"FETCH#record-connection-timing-info">Recording connection timing
info</a> for more info.
</p>
<p data-dfn-for="PerformanceResourceTiming">
The <dfn>secureConnectionStart</dfn> getter steps are to <a>convert
fetch timestamp</a> for <a>this</a>'s <a data-for=
"PerformanceResourceTiming">timing info</a>'s [=fetch timing
info/final connection timing info=]'s [=connection timing info/secure
connection start time=] and the <a>relevant global object</a> for
<a>this</a>. See <a data-cite=
"FETCH#record-connection-timing-info">Recording connection timing
info</a> for more info.
</p>
<p data-dfn-for="PerformanceResourceTiming">
The <dfn>nextHopProtocol</dfn> getter steps are to [=/isomorphic
decode=] <a>this</a>'s [=PerformanceResourceTiming/timing info=]'s
[=fetch timing info/final connection timing info=]'s [=connection
timing info/ALPN negotiated protocol=]. See <a data-cite=
"FETCH#record-connection-timing-info">Recording connection timing
info</a> for more info.
</p>
<p data-dfn-for="PerformanceResourceTiming">
The <dfn>requestStart</dfn> getter steps are to <a>convert fetch
timestamp</a> for <a>this</a>'s <a data-for=
"PerformanceResourceTiming">timing info</a>'s [=fetch timing
info/final network-request start time=] and the <a>relevant global
object</a> for <a>this</a>. See [=/HTTP fetch=] for more info.
</p>
<p data-dfn-for="PerformanceResourceTiming">
The <dfn>responseStart</dfn> getter steps are to <a>convert fetch
timestamp</a> for <a>this</a>'s <a data-for=
"PerformanceResourceTiming">timing info</a>'s [=fetch timing
info/final network-response start time=] and the <a>relevant global
object</a> for <a>this</a>. See [=/HTTP fetch=] for more info.
</p>
<p data-dfn-for="PerformanceResourceTiming">
The <dfn>responseEnd</dfn> getter steps are to <a>convert fetch
timestamp</a> for <a>this</a>'s <a data-for=
"PerformanceResourceTiming">timing info</a>'s [=fetch timing info/end
time=] and the <a>relevant global object</a> for <a>this</a>. See
[=/fetch=] for more info.
</p>
<p data-dfn-for="PerformanceResourceTiming">
The <dfn>encodedBodySize</dfn> getter steps are to return
<a>this</a>'s <a data-for="PerformanceResourceTiming">resource
info</a>'s [=response body info/encoded size=].
</p>
<p data-dfn-for="PerformanceResourceTiming">
The <dfn>decodedBodySize</dfn> getter steps are to return
<a>this</a>'s <a data-for="PerformanceResourceTiming">resource
info</a>'s [=response body info/decoded size=].
</p>
<p data-dfn-for="PerformanceResourceTiming">
The <dfn>transferSize</dfn> getter steps are to perform the following
steps:
</p>
<ol>
<li>
<p>
If <a>this</a>'s <a data-for="PerformanceResourceTiming">cache
mode</a> is "<code>local</code>", then return 0.
</p>
</li>
<li>
<p>
If <a>this</a>'s <a data-for="PerformanceResourceTiming">cache
mode</a> is "<code>validated</code>", then return 300.
</p>
</li>
<li>
<p>
Return <a>this</a>'s <a data-for=
"PerformanceResourceTiming">response body info</a>'s [=response
body info/encoded size=] plus 300.
</p>
<p class='note'>
The constant number added to `transferSize` replaces exposing the
total byte size of the HTTP headers, as that may expose the
presence of certain cookies. See <a href=
"https://github.com/w3c/resource-timing/issues/238">this
issue</a>.
</p>
</li>
</ol>
<p class='note'>
A user agent implementing <a>PerformanceResourceTiming</a> would need
to include <code>"resource"</code> in
{{PerformanceObserver/supportedEntryTypes}}. This allows developers
to detect support for Resource Timing.
</p>
</section>
<section id="sec-extensions-performance-interface" data-dfn-for=
"Performance">
<h3>
Extensions to the <code>Performance</code> Interface
</h3>
<p>
The user agent MAY choose to limit how many resources are included as
<a>PerformanceResourceTiming</a> objects in the <a data-cite=
"PERFORMANCE-TIMELINE-2#performance-timeline">Performance
Timeline</a> [[PERFORMANCE-TIMELINE-2]]. This section extends the
<a data-cite=
"PERFORMANCE-TIMELINE-2#dom-performance"><code>Performance</code></a>
interface to allow controls over the number of
<a>PerformanceResourceTiming</a> objects stored.
</p>
<p>
The recommended minimum number of <a>PerformanceResourceTiming</a>
objects is 250, though this may be changed by the user agent.
<a data-link-for="Performance">setResourceTimingBufferSize</a> can be
called to request a change to this limit.
</p>
<p>
Each <a data-cite="WEBIDL#es-environment">ECMAScript global
environment</a> has:
</p>
<ul>
<li>A <dfn>resource timing buffer size limit</dfn> which should
initially be 250 or greater.
</li>
<li>A <dfn>resource timing buffer current size</dfn> which is
initially 0.
</li>
<li>A <dfn>resource timing buffer full event pending flag</dfn> which
is initially false.
</li>
<li>A <dfn>resource timing secondary buffer current size</dfn> which
is initially 0.
</li>
<li>A <dfn>resource timing secondary buffer</dfn> to store
<a>PerformanceResourceTiming</a> objects that is initially empty.
</li>
</ul>
<pre class="idl" data-cite="HTML">partial interface Performance {
undefined clearResourceTimings ();
undefined setResourceTimingBufferSize (unsigned long maxSize);
attribute EventHandler onresourcetimingbufferfull;
};
</pre>
<p>
The <dfn>Performance</dfn> interface is defined in [[HR-TIME-2]].
</p>
<p>
The method <dfn>clearResourceTimings</dfn> runs the following steps:
</p>
<ol>
<li>Remove all <a>PerformanceResourceTiming</a> objects in the
<a data-cite=
'PERFORMANCE-TIMELINE-2#dfn-performance-entry-buffer'>performance
entry buffer</a>.
</li>
<li>Set <a>resource timing buffer current size</a> to 0.
</li>
</ol>
<p>
The <dfn>setResourceTimingBufferSize</dfn> method runs the following
steps:
</p>
<ol>
<li>Set <a>resource timing buffer size limit</a> to the
<i>maxSize</i> parameter. If the <i>maxSize</i> parameter is less
than <a>resource timing buffer current size</a>, no
<a>PerformanceResourceTiming</a> objects are to be removed from the
<a data-cite=
'PERFORMANCE-TIMELINE-2#dfn-performance-entry-buffer'>performance
entry buffer</a>.
</li>
</ol>
<p>
The attribute <dfn>onresourcetimingbufferfull</dfn> is the event
handler for the <code>resourcetimingbufferfull</code> event described
below.
</p>
<p>
To check if <dfn>can add resource timing entry</dfn>, run the
following steps:
</p>
<ol>
<li>If <a>resource timing buffer current size</a> is smaller than <a>
resource timing buffer size limit</a>, return true.
</li>
<li>Return false.
</li>
</ol>
<p>
To <dfn>add a PerformanceResourceTiming entry</dfn> into the
<a data-cite=
'PERFORMANCE-TIMELINE-2/#dfn-performance-entry-buffer'>performance
entry buffer</a>, run the following steps:
</p>
<ol>
<li>Let <i>new entry</i> be the input <a>PerformanceEntry</a> to be
added.
</li>
<li>If <a>can add resource timing entry</a> returns true and
<a>resource timing buffer full event pending flag</a> is false, run
the following substeps:
<ol style="list-style-type: lower-latin;">
<li>Add <i>new entry</i> to the <a data-cite=
'PERFORMANCE-TIMELINE-2#dfn-performance-entry-buffer'>performance
entry buffer</a>.
</li>
<li>Increase <a>resource timing buffer current size</a> by 1.
</li>
<li>Return.
</li>
</ol>
</li>
<li>If <a>resource timing buffer full event pending flag</a> is
false, run the following substeps:
<ol style="list-style-type: lower-latin;">
<li>Set <a>resource timing buffer full event pending flag</a> to
true.
</li>
<li>
<a>Queue a task</a> on the <a href=
"https://w3c.github.io/performance-timeline/#dfn-performance-timeline-task-source">
performance timeline task source</a> to run <a>fire a buffer
full event</a>.
</li>
</ol>
</li>
<li>Add <i>new entry</i> to the <a>resource timing secondary
buffer</a>.
</li>
<li>Increase <a>resource timing secondary buffer current size</a> by
1.
</li>
</ol>
<p>
To <dfn>copy secondary buffer</dfn>, run the following steps:
</p>
<ol>
<li>While <a>resource timing secondary buffer</a> is not empty and
<a>can add resource timing entry</a> returns true, run the following
substeps:
<ol>
<li>Let <i>entry</i> be the oldest
<a>PerformanceResourceTiming</a> in <a>resource timing secondary
buffer</a>.
</li>
<li>Add <i>entry</i> to the end of <a data-cite=
"PERFORMANCE-TIMELINE-2/#dfn-performance-entry-buffer">performance
entry buffer</a>.
</li>
<li>Increment <a>resource timing buffer current size</a> by 1.
</li>
<li>Remove <i>entry</i> from <a>resource timing secondary
buffer</a>.
</li>
<li>Decrement <a>resource timing secondary buffer current
size</a> by 1.
</li>
</ol>
</li>
</ol>
<p>
To <dfn>fire a buffer full event</dfn>, run the following steps:
</p>
<ol>
<li>While <a>resource timing secondary buffer</a> is not empty, run
the following substeps:
<ol>
<li>Let <i>number of excess entries before</i> be <a>resource
timing secondary buffer current size</a>.
</li>
<li>If <a>can add resource timing entry</a> returns false, then
[=fire an event=] named <code>resourcetimingbufferfull</code> at
the {{Performance}} object.
</li>
<li>Run <a>copy secondary buffer</a>.
</li>
<li>Let <i>number of excess entries after</i> be <a>resource
timing secondary buffer current size</a>.
</li>
<li>If <i>number of excess entries before</i> is lower than or
equals <i>number of excess entries after</i>, then remove all
entries from <a>resource timing secondary buffer</a>, set
<a>resource timing secondary buffer current size</a> to 0, and
abort these steps.
</li>
</ol>
</li>
<li>Set <a>resource timing buffer full event pending flag</a> to
false.
<p class="note">
This means that if the <code>resourcetimingbufferfull</code>
event handler does not add more room in the buffer than it adds
resources to it, excess entries will be dropped from the buffer.
Developers should make sure that
<code>resourcetimingbufferfull</code> event handlers call
<code>clearResourceTimings</code> or extend the buffer
sufficiently (by calling
<code>setResourceTimingBufferSize</code>).
</p>
</li>
</ol>
</section>
<section id="sec-cross-origin-resources">
<h3>
Cross-origin Resources
</h3>
<p class="note" data-dfn-for="PerformanceResourceTiming">
As detailed in [=Fetch=], requests for cross-origin resources are
included as <a>PerformanceResourceTiming</a> objects in the
<a data-cite=
"PERFORMANCE-TIMELINE-2#performance-timeline">Performance
Timeline</a>. If the <a data-cite="FETCH#concept-tao-check">timing
allow check</a> algorithm fails for a cross-origin resource, the
entry will be an [=create an opaque timing info|opaque entry=]. Such
entries have most of their attributes masked in order to prevent
leaking cross-origin data that isn't otherwise exposed. So, for an
[=create an opaque timing info|opaque entry=], the following
attributes will be set to zero:
{{PerformanceResourceTiming/redirectStart}},
{{PerformanceResourceTiming/redirectEnd}},
{{PerformanceResourceTiming/workerStart}},
{{PerformanceResourceTiming/domainLookupStart}},
{{PerformanceResourceTiming/domainLookupEnd}},
{{PerformanceResourceTiming/connectStart}},
{{PerformanceResourceTiming/connectEnd}},
{{PerformanceResourceTiming/requestStart}},
{{PerformanceResourceTiming/responseStart}},
{{PerformanceResourceTiming/secureConnectionStart}},
{{PerformanceResourceTiming/transferSize}},
{{PerformanceResourceTiming/encodedBodySize}}, and
{{PerformanceResourceTiming/decodedBodySize}}. Further, the
{{PerformanceResourceTiming/nextHopProtocol} attribute will be set to
the empty string.
</p>
<p>
Server-side applications may return the <a>Timing-Allow-Origin</a>
HTTP response header to allow the User Agent to fully expose, to the
document origin(s) specified, the values of attributes that would
have been zero due to those cross-origin restrictions.
</p>
<section id="sec-timing-allow-origin">
<h4>
<code>Timing-Allow-Origin</code> Response Header
</h4>
<p>
The <dfn>Timing-Allow-Origin</dfn> HTTP response header field can
be used to communicate a policy indicating origin(s) that are
allowed to see values of attributes that would have been zero due
to the cross-origin restrictions. The header's value is represented
by the following ABNF [[RFC5234]] (using <a data-cite=
"RFC7230#section-7">List Extension</a>, [[RFC7230]]):
</p><code class="abnf">Timing-Allow-Origin = 1#( <a data-cite=
"FETCH#origin-header">origin-or-null</a> / <a data-cite=
"FETCH#http-new-header-syntax">wildcard</a> )</code>
<p>
The sender MAY generate multiple <a>Timing-Allow-Origin</a> header