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Overview.src.html
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<!doctype html>
<html lang=en-US>
<meta charset=utf-8>
<title>Fetch Standard</title>
<link rel=stylesheet href=//www.whatwg.org/style/specification>
<link rel=icon href=//resources.whatwg.org/logo-fetch.svg>
<div class="head">
<p><a class=logo href=//www.whatwg.org/><img alt=WHATWG src=//resources.whatwg.org/logo-fetch.svg width=100 height=100></a>
<h1 id="cors">Fetch</h1>
<h2 class="no-num no-toc">Living Standard — Last Updated [DATE: 3 August 2002]</h2>
<dl>
<dt>This Version:
<dd><a href=//fetch.spec.whatwg.org/>http://fetch.spec.whatwg.org/</a>
<dt>Participate:
<dd>Send feedback to <a href="http://www.whatwg.org/mailing-list">whatwg@whatwg.org</a> or
<a href="https://www.w3.org/Bugs/Public/enter_bug.cgi?product=WHATWG&component=Fetch">file a bug</a>
(<a href="https://www.w3.org/Bugs/Public/buglist.cgi?product=WHATWG&component=Fetch&resolution=---">open bugs</a>)
<dd><a href=//wiki.whatwg.org/wiki/IRC>IRC: #whatwg on Freenode</a>
<dt>Version History:
<dd><a href=https://github.com/whatwg/fetch/commits>https://github.com/whatwg/fetch/commits</a>
<dt>Editor:
<dd><a href="http://annevankesteren.nl/">Anne van Kesteren</a>
(<a href=http://www.mozilla.org/>Mozilla</a>)
<<a href="mailto:annevk@annevk.nl">annevk@annevk.nl</a>>
</dl>
<script src=//resources.whatwg.org/file-bug.js async></script>
<p class=copyright><a rel=license href="http://creativecommons.org/publicdomain/zero/1.0/"><img src="http://i.creativecommons.org/p/zero/1.0/80x15.png" alt=CC0></a>
To the extent possible under law, the editor has waived all copyright and
related or neighboring rights to this work. In addition, as of
[DATE: 01 Jan 1901], the editor has made this specification available
under the
<a rel=license
href="http://www.openwebfoundation.org/legal/the-owf-1-0-agreements/owfa-1-0">Open Web Foundation Agreement Version 1.0</a>,
which is available at
http://www.openwebfoundation.org/legal/the-owf-1-0-agreements/owfa-1-0.
</div>
<h2 class="no-num no-toc">Abstract</h2>
<p>The Fetch standard defines the overall architecture for obtaining resources given a URL
and a set of parameters. This concept is named fetching.
<h2 class="no-num no-toc">Table of Contents</h2>
<!-- toc -->
<h2 class=no-num>Goals</h2>
<p>To unify fetching across the web platform this specification supplants a number of algorithms and specifications:
<ul class=brief>
<li>HTML Standard's fetch and potentially CORS-enabled fetch algorithms
<li>CORS
<li>HTTP <code title>Origin</code> header semantics
</ul>
<p>Unifying fetching provides consistent handling of:
<ul class=brief>
<li>Different URL schemes
<li>HTTP redirects
<li>Cross-origin requests
</ul>
<p>In due course, it should also help clarify the semantics of CSP and make provide a model to hook offline networking into.
<h2 class=no-num>Legacy</h2>
<p>HTML defines two algorithms. This maps these "legacy" algorithms to the new
<span title=concept-fetch>fetch</span>.
<p>When a user agent is to <dfn title=legacy-fetch>fetch</dfn> a resource or URL,
optionally <strong>from</strong> an origin <i title>origin</i>, optionally
<strong>using</strong> a specific <span>referrer source</span> as an <i>override referrer source</i>,
and optionally with any of a <i title>synchronous flag</i>, a <i>manual redirect flag</i>, a
<i>force same-origin flag</i>, and a <i>block cookies flag</i>, the following steps must be run:
<p class=note>The <i>block cookies flag</i> is obsolete now.
<!-- if invoked with the synchronous flag, make sure to release the storage mutex first -->
<!-- synchronous flag is only to be used in algorithms that are themselves asynchronous! Only
sync-XHR is allowed to make the mistake of screwing that up. :-P -->
<!-- the force same-origin flag is for use in places where we'll be moving to CORS one day; when
used, the algorithm must be invoked with a URL (not something else, like a POST request) whose
origin is the same as the /origin/, which must also be present, and the algorithm must not be
invoked with the manual redirect flag. -->
<ol>
<li><p>If there is a specific <i>override referrer source</i>, and it is a URL, then
let <var title>referrer</var> be the <i>override referrer source</i>.
<li>
<p>Otherwise, run these substeps:
<ol>
<li>
<p>Let <var title>document</var> be the appropriate <code>Document</code> as given by
the following list:
<dl class="switch">
<dt>If there is a specific <i>override referrer source</i>
<dd>The <i>override referrer source</i>.</dd>
<dt>When <span title=navigate>navigating</span>
<dd>The <span>active document</span> of the <span>source browsing context</span>.
<dt>When fetching resources for an element
<dd>The element's <span>node document</span>.
</dl>
<li><p>While <var title>document</var> is
<span>an <code>iframe</code> <code>srcdoc</code> document</span>, set
<var title>document</var> to
<var title>document</var>'s <span>browsing context</span>'s
<span>browsing context container</span>'s <code>Document</code> instead.
<li><p>If <var title>document</var>'s <span>origin</span> is not a scheme/host/port tuple,
then let <var title>referrer</var> be null.
<li><p>Otherwise, let <var title>referrer</var> be <span>the document's address</span> of <var title>document</var>.
<li><p>If <var title>referrer</var>'s <span title=concept-url-scheme>scheme</span> is
about/data/javascript, set <var title>referrer</var> to null.
</ol>
</li>
<li><p>If the <code>Document</code> with which any <span title=concept-task>tasks</span>
<span title="queue a task">queued</span> by this algorithm would be associated doesn't
have an associated <span>browsing context</span>, then terminate these steps.
<!--(redundant with 'at a time convenient...' below)
<li><p>Optionally, wait until the <code>Document</code> with which any <span
title="concept-task">tasks</span> <span title="queue a task">queued</span> by this algorithm
would be associated is <span title="active document">active</span>.</p></li>
-->
<li><p>Let <var title>req</var> be a new <span title=concept-request>request</span>.
<li><p>If this algorithm was invoked with "from an origin", set <var title>req</var>'s
<span title=concept-request-origin>origin</span> to <var title>origin</var>.
<li><p>Set <var title>req</var>'s <span title=concept-request-referrer>referrer</span> to
<var title>referrer</var>.
<li><p>Set <var title>req</var>'s <span title=concept-request-mode>mode</span> to
same-origin if the <i>force same-origin flag</i> is set, and to tainted cross-origin
otherwise.
<li><p>Set <var title>req</var>'s
<span title=concept-request-manual-redirect-flag>manual redirect flag</span> if
<i>manual redirect flag</i> is set.
<li><p>Set <var title>req</var>'s <span>synchronous flag</span> if
<i title>synchronous flag</i> is set.
<li><p><span title=concept-fetch>fetch</span> <var title>req</var>.
</ol>
<p>When the user agent is required to perform a
<dfn title=legacy-potentially-cors-enabled-fetch>potentially CORS-enabled fetch</dfn> of an
<var title>URL</var> with a mode <var title>mode</var> that is either
"No CORS", "Anonymous", or "Use Credentials", optionally using a <span>referrer source</span> <var title>referrer source</var>, with an <span>origin</span> <var title>origin</var>, and with a default origin behaviour
<var title>default</var> which is either "<i>taint</i>" or "<i>fail</i>", it must run these steps:
<ol>
<li><p>Let <var title>req</var> be a new <span title=concept-request>request</span>.
<li><p>Set <var title>req</var>'s
<span title=concept-request-origin>origin</span> to <var title>origin</var>.
<li>
<p>Set <var title>req</var>'s <span title=concept-request-mode>mode</span> to the value
corresponding to the first matching statement:
<dl class=switch>
<dt><var title>mode</var> is "No CORS" and <var title>default</var> is "<i>fail</i>"
<dd>same-origin
<dt><var title>mode</var> is "No CORS" and <var title>default</var> is "<i>taint</i>"
<dd>tainted cross-origin
<dt>Otherwise
<dd>CORS
</dl>
<li>
<p>If <var title>mode</var> is "Anonymous", set <var title>req</var>'s
<span title=concept-request-omit-credentials-mode>omit credentials mode</span> to
<i title>always</i>.
<!-- XXX unset by default? -->
<!-- nullify Origin / Referer too? -->
<li class=XXX><p>Determine <var title>req</var>'s
<span title=concept-request-referrer>referrer</span> as per <span title=concept-fetch>fetch</span>.
<li><p><span title=concept-fetch>fetch</span> <var title>req</var>.
</ol>
<h2>Conformance</h2>
<p>All diagrams, examples, and notes in this specification are
non-normative, as are all sections explicitly marked non-normative.
Everything else in this specification is normative.
<p>The key words "MUST", "MUST NOT", "REQUIRED", <!--"SHALL", "SHALL
NOT",--> "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"OPTIONAL" in the normative parts of this specification are to be
interpreted as described in RFC2119. For readability, these words do
not appear in all uppercase letters in this specification.
<span data-anolis-ref>RFC2119</span>
<h2>Terminology</h2>
<p>This specification uses terminology from the Encoding and URL Standards.
<span data-anolis-ref>ENCODING</span>
<span data-anolis-ref>URL</span>
<p>A <dfn>byte string</dfn> is a <span data-anolis-spec=encoding>byte</span> sequence
written down as a <span data-anolis-spec=encoding>string</span>. To avoid confusion with
an actual string quotation marks are omitted.
<p class=example>"<code title>true</code>" is a
<span data-anolis-spec=encoding>string</span>, while <code title>true</code> is a
<span>byte string</span>.
<p>A <dfn>case-insensitive byte string</dfn> is a <span>byte string</span> that when
compared considers bytes in the range 0x41 to 0x5A to be a match for their corresponding
byte in the range 0x61 to 0x7A.
<p class=example>The
<span title="case-insensitive byte string">case-insensitive byte strings</span>
<code title>Content-Type</code> and <code title>content-TYPE</code> are equal.
<h3>HTTP</h3>
<p>While <span title=concept-fetch>fetching</span> encompasses more than just HTTP, it
borrows a number of concepts from HTTP and applies these to resources obtained via other
means (e.g. via <code title>data</code> URL).
<p>A <dfn title=concept-method>method</dfn> is a <span>byte string</span>.
<p>A <dfn title=concept-header>header</dfn> consists of a
<dfn title=concept-header-name>name</dfn> and <dfn title=concept-header-value>value</dfn>.
A <span title=concept-header-name>name</span> is a
<span>case-insensitive byte string</span> and a
<span title=concept-header-value>value</span> is a <span>byte string</span>.
<p>A <dfn>simple method</dfn> is a <span title=concept-method>method</span> that is
<code title>GET</code>, <code title>HEAD</code>, or <code title>POST</code>.
<p>A <dfn>simple header</dfn> is a <span title=concept-header>header</span> whose
<span title=concept-header-name>name</span> is <code title>Accept</code>,
<code title>Accept-Language</code>, or <code title>Content-Language</code>, or whose
<span title=concept-header-name>name</span> is <code title>Content-Type</code> and
<span title=concept-header-value>value</span>, <span class=XXX>once parsed,</span> is
<code title>application/x-www-form-urlencoded</code>,
<code title>multipart/form-data</code>,
or <code title>text/plain</code>.
<p class=XXX>What we never resolved in the old specification was whether only certain
parameters should be allowed and how exactly the MIME type parsing would work. Hopefully
<a href=http://mimesniff.spec.whatwg.org/#parse-a-mime-type>parsing MIME types</a> will
solve this.
<!-- example if people ask: "Content-Type: text/plain;" -->
<h3>Requests</h3>
<p>The input to <span title=concept-fetch>fetch</span> is a
<dfn title=concept-request>request</dfn>.
<p>A <span title=concept-request>request</span> has an associated
<dfn title=concept-request-method>method</dfn>. Unless stated otherwise a
<span title=concept-request>request</span>'s
<span title=concept-request-method>method</span> is <code title>GET</code>.
<p>A <span title=concept-request>request</span> has an associated
<dfn title=concept-request-url>url</dfn> (a
<span data-anolis-spec=url title=concept-parsed-url>parsed URL</span>).
<p>A <span title=concept-request>request</span> has associated
<dfn title=concept-request-author-headers>author headers</dfn> and
<dfn title=concept-request-headers>headers</dfn>. Unless stated otherwise
<span title=concept-request>request</span>'s
<span title=concept-request-author-headers>author headers</span>
and <span title=concept-request-headers>headers</span> are empty lists of
<span title=concept-header>headers</span>.
<p>A <span title=concept-request>request</span> has an associated
<dfn title=concept-request-origin>origin</dfn>, and
<dfn>force <code title>Origin</code> header flag</dfn>. Unless stated otherwise a
<span title=concept-request>request</span>'s
<span title=concept-request-origin>origin</span> is null and its
<span>force <code title>Origin</code> header flag</span> is unset.
<p>A <span title=concept-request>request</span> has an associated
<dfn title=concept-request-referrer>referrer</dfn>. Unless stated otherwise it is null.
<p>A <span title=concept-request>request</span> has an associated
<dfn title=concept-request-body>body</dfn>. Unless stated otherwise a
<span title=concept-request>request</span>'s <span title=concept-request-body>body</span>
is null.
<p>A <span title=concept-request>request</span> has an associated
<dfn>synchronous flag</dfn>. Unless stated otherwise a
<span title=concept-request>request</span>'s <span>synchronous flag</span> is unset.
<p>A <span title=concept-request>request</span> has an associated
<dfn title=concept-request-mode>mode</dfn>, which is one of <i title>same-origin</i>,
<i title>tainted cross-origin</i>, and <i title>CORS</i>. Unless stated otherwise,
<span title=concept-request>request</span>'s <span title=concept-request-mode>mode</span>
is <i title>tainted cross-origin</i>.
<p>A <span title=concept-request>request</span> has an associated
<dfn>force preflight flag</dfn>. Unless stated otherwise, it is unset and only relevant
when <span title=concept-request>request</span>'s
<span title=concept-request-mode>mode</span> is <i title>CORS</i>.
<p>A <span title=concept-request>request</span> has an associated
<dfn title=concept-request-omit-credentials-mode>omit credentials mode</dfn>, which is
one of <i title>always</i>, <i title>CORS</i>, and <i title>never</i>.
<p class=XXX>I think we want the default to become <i title>always</i>, but currently it
is <i title>never</i>.
<p>A a<span title=concept-request>request</span> has an associated
<dfn title=concept-request-use-url-credentials-flag>use URL credentials flag</dfn>.
Unless stated otherwise, it is unset.
<p>A <span title=concept-request>request</span> has an associated
<dfn title=concept-request-manual-redirect-flag>manual redirect flag</dfn>. Unless stated
otherwise, it is unset.
<p>A <span title=concept-request>request</span> has an associated
<dfn title=concept-request-redirect-count>redirect count</dfn>.
Unless stated otherwise a <span title=concept-request>request</span>'s
<span title=concept-request-redirect-count>redirect count</span> is zero.
<h3>Responses</h3>
<p>The result of <span title=concept-fetch>fetch</span> is a
<dfn title=concept-response>response</dfn>. A <span title=concept-response>response</span>
is build incrementally over time. All its fields are not necessarily available straight
away.
<p>A <span title=concept-response>response</span> has an associated
<dfn title=concept-response-type>type</dfn> which is one of <i title>default</i>,
<i title>redirect</i>, and <i title>error</i>. Unless stated otherwise, it is
<i title>default</i>.
<p>A <span title=concept-response>response</span> has an associated
<dfn title=concept-response-status>status</dfn>,
<dfn title=concept-response-status-message>status message</dfn>,
<dfn title=concept-response-location>location</dfn>,
<dfn title=concept-response-headers>headers</dfn>, and a
<dfn title=concept-response-body>body</dfn>.
<p>A <span title=concept-response>response</span> is either <dfn>CORS-same-origin</dfn> or
<dfn>CORS-cross-origin</dfn>. Unless otherwise indicated a
<span title=concept-response>response</span> is <span>CORS-same-origin</span>.
<p class=note>When introducing new APIs, unless there is a very good reason, only use
<span title=concept-response>responses</span> that are <span>CORS-same-origin</span> and
treat others as <span title=concept-network-error>network errors</span>. This distinction
is used today e.g. to allow <span title=concept-response>responses</span> from a different
<span>origin</span> not <span title=concept-fetch>fetched</span> using
<span title=concept-request>request</span>'s <span title=concept-request-mode>mode</span>
<i title>CORS</i> to still be displayed using the HTML <code title>img</code> element, but
not have their <span title=concept-response-body>body</span> extracted using the HTML
<code title>canvas</code> element.
<hr>
<p>Unless stated otherwise, a <span title=concept-response>response</span>'s
<span title=concept-response-status>status</span> is <code title>200</code>,
<span title=concept-response-status-message>status message</span> is <code title>OK</code>,
<span title=concept-response-location>location</span> is null,
<span title=concept-response-headers>headers</span> is an empty list, and
<span title=concept-response-body>body</span> is null,
<p>A <span title=concept-response>response</span> whose
<span title=concept-response-type>type</span> is <i title>error</i> is known as a
<dfn title=concept-network-error>network error</dfn>.
<p>A <span title=concept-network-error>network error</span>'s
<span title=concept-response-status>status</span> is <code title>0</code>,
<span title=concept-response-status-message>status message</span> is the empty <span>byte string</span>,
<span title=concept-response-location>location</span> is null,
<span title=concept-response-headers>headers</span> is an empty list, and
<span title=concept-response-body>body</span> is null,
<p>A <span title=concept-response>response</span> whose
<span title=concept-response-type>type</span> is <i title>redirect</i> is known as a
<dfn title=concept-redirect>redirect</dfn>.
<h2><dfn>CORS protocol</dfn></h2>
<p>To prevent leaking data from resources behind a firewall (intranets), the platform has
a <span>CORS protocol</span> layered on top of HTTP. It allows resources to declare they
can be shared with resources residing on a different <span>origin</span>.
<p>This section explains the <span>CORS protocol</span> as it pertains to servers.
Requirements for user agents are integrated in the <span title=concept-fetch>fetch</span>
algorithm.
<p class=XXX>
<h2>Fetching</h2>
<p>To perform a <dfn title=concept-fetch>fetch</dfn> using <var title>request</var>,
optionally with a <i title>CORS flag</i>, run these steps:
<p class=note>The <i title>CORS flag</i> within the <span title=concept-fetch>fetch</span>
algorithm is used for handling <span title=concept-redirect>redirects</span>. When using
<span title=concept-fetch>fetch</span> externally only the <var title>request</var>
parameter should be passed.
<ol>
<li><p>Let <var title>url</var> be <var title>request</var>'s
<span title=concept-request-url>url</span>.
<li><p>Let <var title>origin</var> be <var title>request</var>'s
<span title=concept-request-origin>origin</span>.
<li><p>If <var title>request</var>'s <span>synchronous flag</span> is unset and
<span title=concept-fetch>fetch</span> is not invoked recursively, run the remaining steps asynchronously.
<li>
<p>Let <var title>response</var> be the value corresponding to the first matching
statement:
<dl class=switch>
<dt><var title>url</var>'s <span>origin</span> is <var title>origin</var> and the <i title>CORS flag</i> is unset
<dt><var title>url</var>'s <span data-anolis-spec=url title=concept-url-scheme>scheme</span>
is one of "<code title>about</code>", "<code title>blob</code>", and "<code title>data</code>",
and <Var title>request</var>'s <span title=concept-request-redirect-count>redirect count</span> is zero
<dd><p>The result of performing a <span title=concept-basic-fetch>basic fetch</span> using <var title>request</var>.
<dt><var title>request</var>'s <span title=concept-request-mode>mode</span> is
"same-origin"
<dd><p>A <span title=concept-network-error>network error</span>.
<dt><var title>request</var>'s <span title=concept-request-mode>mode</span> is
"tainted cross-origin"
<dd>
<p>The result of performing a <span title=concept-basic-fetch>basic fetch</span> using
<var title>request</var>, marked <span>CORS-cross-origin</span>.
<!-- file URLs end up here as they are not same-origin typically. -->
<dt><var title>url</var>'s <span title=concept-url-scheme>scheme</span> is not one of
"<code title>http</code>" and "<code title>https</code>"
<dd><p>A <span title=concept-network-error>network error</span>.
<dt><var title>request</var>'s <span>force preflight flag</span> is set
<dt><var title>request</var>'s <span title=concept-request-method>method</span> is not
a <span>simple method</span>
<dt>A <span title=concept-header>header</span> in <var title>request</var>'s
<span title=concept-author-headers>author headers</span> is not a <span>simple header</span>
<dd><p>The result of performing a <span>CORS fetch with preflight</span> using <var title>request</span>.
<dt>Otherwise
<dd><p>The result of performing a <span title=concept-basic-fetch>basic fetch</span> using
<var title>request</var> with the <i title>CORS flag</i> set.
</dl>
<li><p>If <span title=concept-fetch>fetch</span> is invoked recursively, return <var title>response</var>.
<li><p>If <var title>request</var>'s <span>synchronous flag</span> is set, wait for
<var title>response</var> to have been fully transmitted and then return it.
<li><p>Keep <span>queueing</span> <span>tasks</span> on the
<span>networking task source</span> until the <var title>response</var> has been fully
transmitted. If no transmission is taking place, <span>queue</span> at least one
<span>task</span>.
</ol>
<h3>Basic fetch</h3>
<p>To perform a <dfn title=concept-basic-fetch>basic fetch</dfn> using <var title>request</var>, with an optional
<i title>CORS flag</i> and <i title>HTTP authentication flag</i>, switch on <var title>request</var>'s
<span title=concept-request-url>url</span>'s
<span data-anolis-spec=url title=concept-url-scheme>scheme</span> and run the associated
steps:
<dl class=switch>
<dt>"<code title>about</code>"
<dd>
<p>If <var title>request</var>'s <span title=concept-request-url>url</span>'s
<span data-anolis-spec=url title=concept-url-scheme-data>scheme data</span> is
"<code title>blank</code>", return a <span title=concept-response>response</span> whose
<span title=concept-response-headers>headers</span> consist of a single
<span title=concept-header>header</span> whose
<span title=concept-header-name>name</span> is <code title>Content-Type</code> and
<span title=concept-header-value>value</span> is
"<code title>text/html;charset=utf-8</code>", and
<span title=concept-response-body>body</span> is the empty string.
<!-- introduce about:unicorn -->
<p>Otherwise, return a <span title=concept-network-error>network error</span>.
<dt>"<code title>blob</code>"
<dd>
<p class=XXX>It has been argued this should be handled outside of
<span title=concept-fetch>fetching</span>.
<dt>"<code title>data</code>"
<dd>
<p>If <var title>request</var>'s <span title=concept-request-method>method</span> is
<code title>GET</code> and
<a href="http://simonsapin.github.com/data-urls/">obtaining a resource</a> from
<var title>request</var>'s <span title=concept-request-url>url</span> does not return
failure, return a <span title=concept-response>response</span> whose
<span title=concept-response-headers>headers</span> consist of a single
<span title=concept-header>header</span> whose
<span title=concept-header-name>name</span> is <code title>Content-Type</code> and
<span title=concept-header-value>value</span> is the MIME type and parameters returned
from <a href="http://simonsapin.github.com/data-urls/">obtaining a resource</a>, and
<span title=concept-response-body>body</span> is the data returned from
<a href="http://simonsapin.github.com/data-urls/">obtaining a resource</a>.
<!-- XXX "obtaining a resource" needs a better reference -->
<p>Otherwise, return a <span title=concept-network-error>network error</span>.
<dt>"<code title>file</code>"
<dd>
<p>For now, unfortunate as it is, <code>file</code>
<span data-anolis-spec=url title=concept-url>URLs</span> are left as an exercise for the
reader.
<p>When in doubt, return a <span title=concept-network-error>network error</span>.
<dt>"<code title>ftp</code>"
<dd>
<p>Follow the requirements from FTP to retrieve a resource.
<p class=XXX>Map the result to <span title=concept-response>response</span>.
<dt>"<code title>http</code>"
<dt>"<code title>https</code>"
<dd>
<p>Set up an HTTP request following the requirements from HTTP and TLS as appropriate,
with these additional constraints:
<ol>
<li>
<p>If <var title>request</var>'s
<span title=concept-request-referrer>referrer</span> is not null, include a
<code title>Referer</code> <span title=concept-header>header</span>
whose <span title=concept-header-value>value</span> is <var title>request</var>'s
<span title=concept-request-referrer>referrer</span>.
<p class=note>User agents are encouraged to provide the end user with options to
always exclude <code title>Referer</code> <span title=concept-header>headers </span>
or have it expose less sensitive information.
<li>
<p>If <var title>request</var>'s <span>force <code>Origin</code> header flag</span> is
set, include an <code title>Origin</code> <span title=concept-header>header</span>
whose <span title=concept-header-value>value</span> is <var title>request</var>'s
<span title=concept-request-origin>origin</span>,
<span class=XXX>serialized to bytes</span>.
<li>
<p>Include all of <var title>request</var>'s
<span title=concept-request-headers>headers</span> and let them replace any
<span title=concept-header>headers</span> with the same
<span title=concept-header-name>name</span> already present in the HTTP request.
<li>
<p>Include all of <var title>request</var>'s
<span title=concept-request-author-headers>author headers</span> as long as their
<span title=concept-header-name>name</span> is <em>not</em> present in the
HTTP request.
<li>
<p>If <var title>request</var>'s
<span title=concept-request-omit-credentials-mode>omit credentials mode</span> is
<i title>always</i> or <var title>request</var>'s
<span title=concept-request-omit-credentials-mode>omit credentials mode</span> is
<i title>CORS</i> and the <i title>CORS flag</i> is unset, run these substeps:
<ol>
<li><p>Include <code title>Cookie</code> headers associated with
<var title>request</var>'s <span title=concept-request-url>url</span>.
<span data-anolis-ref>COOKIES</span>
<!-- http://wiki.whatwg.org/wiki/HTTP_Authentication -->
<li><p>If there's an <b title>authentication entry</b> for <var title>request</var>'s
<span title=concept-request-url>url</span> and either
<var title>request</var>'s <span title=concept-request-use-url-credentials-flag>use URL credentials flag</span> is unset or
<var title>request</var>'s <span title=concept-request-url>url</span>
does not include credentials, include the <code>Authorization</code> header from the
<b title>authentication entry</b>.
<!-- XXX need to define "includes credentials" in URL as username != "" and password != null??
need to define the cache concept -->
<li><p>Otherwise, if <var title>request</var>'s <span title=concept-request-url>url</span>
includes credentials, and the <i title>HTTP authentication flag</i> is set, include an
<code>Authorization</code> header using those credentials.
<!-- XXX ... -->
</ol>
<li>
<p>If there's a <b title>proxy authentication entry</b>, use it as appropriate.
<span data-anolis-ref>HTTP</span>
<p class=note>This intentionally does not depend on <var title>request</var>'s
<span title=concept-request-omit-credentials-mode>omit credentials mode</span>.
</ol>
<p>If the HTTP request is terminated before all headers from the resource are obtained,
return a <span title=concept-network-error>network error</span>.
<p>Otherwise, when the headers from the resource are obtained, let
<var title>response</var> be a new <span title=concept-response>response</span> and set
its fields appropriately. <span class=XXX>Need to spell this out. Whenever we do not
include <code>Cookie</code> headers we also need to ignore <code>Set-Cookie</code>
headers in the response.</span>
<p>If the <i title>CORS flag</i> is set and a <span>CORS check</span> for
<var title>request</var> and <var title>response</var> returns failure, return a
<span title=concept-network-error>network error</span>.
<p>If <var title>response</var>'s <span title=concept-response-status>status</span> is
301, 302, 303, 307, or 308, run these steps:
<ol>
<li><p>If <var title>response</var>'s
<span title=concept-response-headers>headers</span> do not contain a
<span title=concept-header>header</span> whose
<span title=concept-header-name>name</span> is <code title>Location</code>, return
<var title>response</var>.
<li><p>If <var title>response</var>'s
<span title=concept-response-headers>headers</span> contain more than one
<span title=concept-header>header</span> whose
<span title=concept-header-name>name</span> is <code title>Location</code>, return a
<span title=concept-network-error>network error</span>.
<!-- only Gecko does this; if removed add "first" below -->
<li><p>Let <var title>location</var> be the
<span title=concept-header-value>value</span> of the
<span title=concept-header>header</span> whose
<span title=concept-header-name>name</span> is <code title>Location</code> within
<var title>response</var>'s <span title=concept-response-headers>headers</span>.
<li><p>Let <var title>parsed location</var> be the result of
<span data-anolis-spec=url title=concept-url-parser>parsing</span>
<var title>location</var> with <var title>request</var>'s
<span title=concept-request-url>url</span>.
<li><p>If <var title>parsed location</var> is failure, return a
<span title=concept-network-error>network error</span>.
<li><p>If <var title>request</var>'s
<span title=concept-request-redirect-count>redirect count</span> is twenty, return a
<span title=concept-network-error>network error</span>.
<li><p>Increase <var title>request</var>'s
<span title=concept-request-redirect-count>redirect count</span> by one.
<li><p>Set <var title>response</var>'s <span title=concept-response-type>type</span> to
<i title>redirect</i>.
<li><p>Set <var title>response</var>'s
<span title=concept-response-location>location</span> to
<var title>parsed location</var>.
<li>
<p>If <var title>request</var>'s
<span title=concept-request-manual-redirect-flag>manual redirect flag</span> is unset,
run these substeps:
<ol>
<li><p>If <var title>response</var>'s
<span title=concept-response-location>location</span>'s <span>origin</span> is not
<var title>request</var>'s <span title=concept-request-url>url</span>'s
<span>origin</span>, set <var title>request</var>'s
<span title=concept-request-origin>origin</span> to a globally unique identifier.
<li><p>If the <i title>CORS flag</i> is set and <var title>response</var>'s
<span title=concept-response-location>location</span>'s
<span data-anolis-spec=url title=concept-url-username>username</span> or
<span data-anolis-spec=url title=concept-url-password>password</span> is non-null,
return a <span title=concept-network-error>network error</span>.
<li><p>Set <var title>request</var>'s <span title=concept-request-url>url</span> to
<var title>response</var>'s <span title=concept-response-location>location</span>.
<li><p>Return the result of performing a <span title=concept-fetch>fetch</span> using
<var title>request</var>, with the <i title>CORS flag</i> set if set.
</ol>
</ol>
<p>Otherwise, if
<var title>response</var>'s <span title=concept-response-status>status</span> is 401,
run these steps:
<ol>
<li><p>If the <i title>CORS flag</i> is set, return <var title>response</var>.
<li class=XXX><p>Needs testing: multiple <code>WWW-Authenticate</code> headers,
missing, parsing issues.
<li>
<p>If <var title>request</var>'s
<span title=concept-request-use-url-credentials-flag>use URL credentials flag</span>
is unset, or the <i title>HTTP authentication flag</i> is set, run these substeps:
<ol>
<li><p>Prompt the end user for a username and password.
<li><p>Set <var title>request</var>'s <span title=concept-request-url>url</span>'s
<span data-anolis-spec=url title=concept-url-username>username</span> and
<span data-anolis-spec=url title=concept-url-password>password</span> to the given
values.
<!-- XXX sanitization? -->
</ol>
<li><p>Return the result of performing a <span title=concept-basic-fetch>basic fetch</span> using
<var title>request</var>, with the <i title>HTTP authentication flag</i> set.
</ol>
<p>Otherwise, if
<var title>response</var>'s <span title=concept-response-status>status</span> is 407,
run these steps:
<ol>
<li class=XXX><p>Needs testing: multiple <code>Proxy-Authenticate</code> headers,
missing, parsing issues.
<li>
<p>Prompt the end user as appropriate and store the result as appropriate as a
<b title>proxy authentication entry</b>.
<span data-anolis-ref>HTTP</span>
<p class=note>Remaining details surrounding proxy authentication are defined by HTTP.
<li><p>Return the result of performing <span title=concept-basic-fetch>basic fetch</span> using
<var title>request</var>.
</ol>
<p>If the <i title>HTTP authentication flag</i> is set, create an <b title>authentication entry</b> for
<var title>request</var>'s <span title=concept-request-url>url</span> and the given
realm. <span data-anolis-ref>HTTPAUTH</span>
<p>Return <var title>response</var>.
<dt>Otherwise
<dd><p>Return a <span title=concept-network-error>network error</span>.
</dl>
<h3>CORS fetch with preflight</h3>
<p>To perform a <dfn>CORS fetch with preflight</dfn> using <var title>request</var>, run
these steps:
<ol>
<li>
<p>If
<ul>
<li>there is no <span>method cache match</span> for
<var title>request</var>'s <span title=concept-request-method>method</span> using
<var title>request</var>, and
<li>either <var title>request</var>'s <span title=concept-request-method>method</span>
is a not <span>simple method</span> or <var title>request</var>'s
<span>force preflight flag</span> is set, and
<li>there is at least one <span title=concept-header>header</span>
<span title=concept-header-name>name</span> in <var title>request</var>'s
<span title=concept-request-author-headers>author headers</span> for which there is no
<span>header name cache match</span> using <var title>request</var> and for which the
<span title=concept-header>header</span> is not a <span>simple header</span>
</ul>
<p>then run these substeps:
<ol>
<li><p>Let <var title>response</var> be a <span>CORS preflight fetch</span> using
<var title>request</var>.
<li><p>If <var title>response</var> is a <span title=concept-network-error>network error</span>, return
<var title>response</var>.
</ol>
<li><p>Set <var title>request</var>'s
<span title=concept-request-manual-redirect-flag>manual redirect flag</span>.
<li><p>Let <var title>response</var> be a <span title=concept-basic-fetch>basic fetch</span> using
<var title>request</var> with the <i title>CORS flag</i> set.
<li><p>If <var title>response</var> is a <span title=concept-redirect>redirect</span>, set its
<span title=concept-response-type>type</span> to <i title>error</i>.
<li><p>If <var title>response</var> is a <span title=concept-network-error>network error</span>,
<span title=cache-clear>clear</span> using <var title>request</var>.
<li><p>Return <var title>response</var>.
</ol>
<h3>CORS preflight fetch</h3>
<p>To perform a <dfn>CORS preflight fetch</dfn> using <var title>request</var>, run these
steps:
<ol>
<li><p>Let <var title>preflight</var> be a new <span title=concept-request>request</span>.
<li><p>Set <var title>preflight</var>'s <span title=concept-request-url>url</span> to
<var title>request</var>'s <span title=concept-request-url>url</span>.
<li><p>Set <var title>preflight</var>'s <span title=concept-request-origin>origin</span> to
<var title>request</var>'s <span title=concept-request-origin>origin</span>.
<li><p>Set <var title>preflight</var>'s <span title=concept-request-referrer>referrer</span> to
<var title>request</var>'s <span title=concept-request-referrer>referrer</span>.
<li><p>Set <var title>preflight</var>'s <span title=concept-request-method>method</span> to
<code title>OPTIONS</code>.
<li><p>Append a <span title=concept-header>header</span>
<span title=concept-header-name>named</span>
<code title>Access-Control-Request-Method</code> with
<span title=concept-header-value>value</span> <var title>request</var>'s
<span title=concept-request-method>method</span> to <var title>preflight</var>'s
<span title=concept-request-headers>headers</span>.
<li><p>Let <var title>headers</var> be the <span title=concept-header-name>names</span>
of <var title>request</var>'s
<span title=concept-request-author-headers>author headers</span>, sorted
lexicographically and <span class=XXX>byte lowercased</span>.
<li><p>Let <var title>header value</var> be the items in <var title>headers</var>
separated from each other by 0x2C 0x20.
<li><p>Append a <span title=concept-header>header</span>
<span title=concept-header-name>named</span>
<code title>Access-Control-Request-Headers</code> with
<span title=concept-header-value>value</span> <var title>header value</var> to
<var title>preflight</var>'s <span title=concept-request-headers>headers</span>.
<li><p>Set <var title>preflight</var>'s
<span title=concept-request-manual-redirect-flag>manual redirect flag</span>.
<li><p>Let <var title>response</var> be the result of performing a
<span title=concept-basic-fetch>basic fetch</span> using <var title>preflight</var> with the <i title>CORS flag</i>
set.
<li>
<p>If <var title>response</var>'s <span title=concept-response-status>status</span> is
in the range 200 to 299, run these substeps:
<!-- CORS said 200 here but nobody implemented that:
http://lists.w3.org/Archives/Public/public-webappsec/2013Feb/0078.html -->
<ol>
<li><p>Let <var title>methods</var> be the result of
<span title=concept-header-parse>parsing</span> all <var title>response</var>'s
<span title=concept-response-headers>headers</span>'
<span title=concept-header-name>named</span> <code>Access-Control-Allow-Methods</code>.
<li><p>Let <var title>header names</var> be the result of
<span title=concept-header-parse>parsing</span> all <var title>response</var>'s
<span title=concept-response-headers>headers</span>'
<span title=concept-header-name>named</span> <code>Access-Control-Allow-Headers</code>.
<li><p>If either <var title>methods</var> or <var title>header names</var> is failure,
return a <span title=concept-network-error>network error</span>.
<li>
<p>If <var title>methods</var> is empty <var title>request</var>'s
<span>force preflight flag</span> is set, append <var title>request</var>'s
<span title=concept-request-method>method</span> to <var title>methods</var>.
<p class=note>This ensures that a <span>CORS preflight fetch</span> that happened
solely because of <var title>request</var>'s <span>force preflight flag</span> is too.
<li><p>If <var title>request</var>'s <span title=concept-request-method>method</span>
is not in <var title>methods</var> and is not a <span>simple method</span>, return
failure.
<li><p>If one of <var title>request</var>'s
<span title=concept-request-headers>headers</span>'
<span title=concept-header-name>names</span> is not in <var title>header names</var> or
its corresponding <span title=concept-header>header</span> is not a
<span>simple header</span>, return a <span title=concept-network-error>network error</span>.
<li><p>Let <var title>max-age</var> be the result of
<span title=concept-header-parse>parsing</span> all <var title>response</var>'s
<span title=concept-response-headers>headers</span>'
<span title=concept-header-name>named</span> <code>Access-Control-Max-Age</code>.
<li><p>If <var title>max-age</var> is failure, set <var title>max-age</var> to zero.
<li><p>If <var title>max-age</var> is greater than an imposed limit on
<span title=cache-max-age>max-age</span>, set <var title>max-age</var> to the imposed
limit.
<li><p>If the user agent does not provide for a cache, return
<var title>response</var>.
<li><p>For each method in <var title>methods</var> for which there is a
<span>method cache match</span> using <var title>request</var>, set matching entry's
<span title="cache-max-age">max-age</span> to <var title>max-age</var>.
<li>
<p>For each <var title>method</var> in <var title>methods</var> for which there is
<em>no</em> <span>method cache match</span> using <var title>request</var>, create a
new entry in the <span>CORS preflight cache</span> as follows:
<dl>
<dt><span title=cache-origin>origin</span>
<dd><var title>request</var>'s <span title=concept-request-origin>origin</span>
<dt><span title=cache-url>url</span>
<dd><var title>request</var>'s <span title=concept-request-url>url</span>
<dt><span title=cache-max-age>max-age</span>
<dd><var title>max-age</var>
<dt><span title="cache-credentials">credentials</span>
<dd>False if <var title>request</var>'s
<span title=concept-request-omit-credentials-mode>omit credentials mode</span> is not
<i title>never</i>, and true otherwise
<dt><span title="cache-method">method</span></dt>
<dd><var title>method</var>
</dl>
<li><p>For each header name in <var title>header names</var> for which there is a
<span>header name cache match</span> using <var title>request</var>, set
matching entry's <span title=cache-max-age>max-age</span> to <var title>max-age</var>.
<li>
<p>For each <var title>header name</var> in <var title>header names</var> for which
there is <em>no</em> <span>header name cache match</span> using
<var title>request</var>, create a new entry in the <span>CORS preflight cache</span>
as follows:
<dl>
<dt><span title=cache-origin>origin</span>
<dd><var title>request</var>'s <span title=concept-request-origin>origin</span>
<dt><span title=cache-url>url</span>
<dd><var title>request</var>'s <span title=concept-request-url>url</span>
<dt><span title=cache-max-age>max-age</span>
<dd><var title>max-age</var>
<dt><span title=cache-credentials>credentials</span>
<dd>False if <var title>request</var>'s
<span title=concept-request-omit-credentials-mode>omit credentials mode</span> is not
<i title>never</i>, and true otherwise
<dt><span title=cache-header-name>header name</span></dt>
<dd><var title>header name</var>
</dl>
<li><p>Return <var title>response</var>.
</ol>
<li><p>Otherwise, return a <span title=concept-network-error>network error</span>.
</ol>