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Added support for link rel=compression-dictionary #11620

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6069214
Added support for link rel=compression-dictionary
pmeenan Sep 3, 2025
b188167
Fixed CORS mode processing and http link processing
pmeenan Sep 4, 2025
552c472
Fixed No CORS
pmeenan Sep 4, 2025
7e2c161
Fixed link header processing
pmeenan Sep 4, 2025
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Original file line number Diff line number Diff line change
Expand Up @@ -15557,6 +15557,7 @@ interface <dfn interface>HTMLLinkElement</dfn> : <span>HTMLElement</span> {
the processing model, and are supported by the user agent. The possible <span
data-x="concept-supported-tokens">supported tokens</span> are
<code data-x="rel-alternate">alternate</code>,
<code data-x="rel-compression-dictionary">compression-dictionary</code>,
<code data-x="rel-dns-prefetch">dns-prefetch</code>,
<code data-x="rel-expect">expect</code>,
<code data-x="rel-icon">icon</code>,
Expand Down Expand Up @@ -26186,6 +26187,7 @@ document.body.appendChild(wbr);</code></pre>

<p>Keywords that are <dfn>body-ok</dfn> affect whether <code>link</code> elements are
<span>allowed in the body</span>. The <span>body-ok</span> keywords are
<code data-x="rel-compression-dictionary">compression-dictionary</code>,
<code data-x="rel-dns-prefetch">dns-prefetch</code>,
<code data-x="rel-modulepreload">modulepreload</code>,
<code data-x="rel-pingback">pingback</code>,
Expand Down Expand Up @@ -26251,6 +26253,17 @@ document.body.appendChild(wbr);</code></pre>
<td>Gives the permalink for the nearest ancestor section.</td>
</tr>

<tr>
<td><code data-x="rel-compression-dictionary">compression-dictionary</code></td>
<td><span data-x="external resource link">External Resource</span></td>
<td colspan="2"><em>not allowed</em></td>
<td class="yes"> Yes </td>
<td class="yes"> Yes </td>
<td>Specifies that the user agent should preemptively <span data-x="concept-fetch">fetch</span> and cache the
target resource as it is likely to be useful as a compression dictionary for future
<span data-x="concept-fetch">fetches</span>. <ref>RFC9842</ref></td>
</tr>

<tr>
<td><code data-x="rel-dns-prefetch">dns-prefetch</code></td>
<td><span data-x="external resource link">External Resource</span></td>
Expand Down Expand Up @@ -26672,6 +26685,93 @@ document.body.appendChild(wbr);</code></pre>
Link Relation</cite>. <ref>RFC6596</ref></p>


<h5>Link type "<dfn attr-value for="link/rel"><code
data-x="rel-compression-dictionary">compression-dictionary</code></dfn>"</h5>

<p>The <code data-x="rel-compression-dictionary">compression-dictionary</code> keyword may be used
with <code>link</code> elements. This keyword creates an <span data-x="external resource link">external
resource link</span>. This keyword is <span>body-ok</span>.</p>

<p>The <code data-x="rel-compression-dictionary">compression-dictionary</code> keyword indicates
that preemptively <span data-x="concept-fetch">fetching</span> and caching the specified resource
or same-site document is likely to be beneficial, as it is highly likely that the user will
be able to this resource as a compression dictionary for future
<span data-x="concept-fetch">fetches</span>. <ref>RFC9842</ref></p>

<p>There is no default type for resources given by the
<code data-x="rel-compression-dictionary">compression-dictionary</code> keyword.</p>

<p>The appropriate times to <span data-x="fetch and process the linked resource">fetch and
process</span> this type of link are:</p>

<ul>
<li><p>When the <span>external resource link</span> is created on a <code>link</code> element
that is already <span>browsing-context connected</span>.</p></li>

<li><p>When the <span>external resource link</span>'s <code>link</code> element <span>becomes
browsing-context connected</span>.</p></li>

<li><p>When the <code data-x="attr-link-href">href</code> attribute of the <code>link</code>
element of an <span>external resource link</span> that is already <span>browsing-context
connected</span> is changed.</p></li>

<li><p>When the <code data-x="attr-link-crossorigin">crossorigin</code> attribute of the
<code>link</code> element of an <span data-x="external resource link">external resource
link</span> that is already <span>browsing-context connected</span> is set, changed, or
removed.</p></li>
</ul>

<p>The <span>fetch and process the linked resource</span> steps for this type of linked resource,
given a <code>link</code> element <var>el</var>, are to <span
data-x="create link options from element">create link options</span> from <var>el</var> and
to <span>load a compression dictionary</span> given the result and <var>el</var>.</p>

<p>The <span>process a link header</span> step for this type of linked resource given a <span
data-x="link processing options">link processing options</span> <var>options</var> are to
<span>load a compression dictionary</span> given <var>options</var>.</p>

<p>To <dfn>load a compression dictionary</dfn> given a <span>link processing options</span>
<var>options</var> and optional <code>link</code> element <var>el</var>:</p>

<ol>
<li><p>If <var>options</var>'s <span data-x="link options crossorigin">crossorigin</span>
is <span data-x="attr-crossorigin-none">No CORS</span>, set <var>options</var>'s
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Related to #11619 (comment): this step will never execute, as per https://html.spec.whatwg.org/#cors-settings-attribute the attribute always has a state.

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Thanks. I changed it to check to see if crossorigin was "No CORS" and change it to Anonymous. Another way to word it that matches the original text would be to reference the original creation of "el", something like If, when the element is created, the crossorigin attribute is not set...

<span data-x="link options crossorigin">crossorigin</span> to
<span data-x="attr-crossorigin-anonymous">Anonymous</span>.</p></li>

<li><p>Set <var>options</var>'s <span data-x="link options destination">destination</span> to
the empty string.</p></li>

<li><p>Let <var>request</var> be the result of <span data-x="create a link request">creating a
link request</span> given <var>options</var>.</p></li>

<li><p>If <var>request</var> is null, then return.</p></li>

<li><p>Set <var>request</var>'s <span data-x="concept-request-initiator">initiator</span> to
"<code data-x="">compression-dictionary</code>".</p></li>

<li>
<p>Let <var>processCompressionDictionaryResponse</var> be the following steps given a <span
data-x="concept-response">response</span> <var>response</var> and null, failure, or a
<span>byte sequence</span> <var>bytesOrNull</var>:</p>

<ol>
<li><p>If <var>response</var> is a <span>network error</span> and <var>el</var> is set, <span
data-x="concept-event-fire">fire an event</span> named <code
data-x="event-error">error</code> at <var>el</var>.</p></li>

<li><p>Otherwise, if <var>el</var> is set, <span data-x="concept-event-fire">fire an event</span>
named <code data-x="event-load">load</code> at <var>el</var>.</p></li>
</ol>
</li>

<li><p>The user agent should <span data-x="concept-fetch">fetch</span> <var>request</var>, with
<i data-x="processResponseConsumeBody">processResponseConsumeBody</i> set to
<var>processCompressionDictionaryResponse</var>. User agents may delay the fetching of
<var>request</var> to prioritize other requests that are necessary for the current document.</p></li>
</ol>

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Double-checking that this is intended? https://datatracker.ietf.org/doc/draft-ietf-httpbis-compression-dictionary/ seems to imply the Link: header should work, but this mandates that in browsers it do nothing.

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Thanks. Mistake from mirroring the prefetch behavior. Should be fixed now. The flow feels a bit weird since I merged the header and link element processing steps but need to not fire the load/error in the header side of things (made el optional to the processing). Happy for suggestions on ways to make it cleaner.

Presumably we could also treat it more like preconnect and fire-and-forget without load/error events.

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I think the intended pattern is supposed to be like what preload does. I believe you could make that work, but I haven't double-checked...


<h5>Link type "<dfn attr-value for="link/rel"><code
data-x="rel-dns-prefetch">dns-prefetch</code></dfn>"</h5>

Expand Down Expand Up @@ -147865,6 +147965,9 @@ INSERT INTERFACES HERE
<dt id="refsRFC8297">[RFC8297]</dt>
<dd><cite><a href="https://httpwg.org/specs/rfc8297.html">An HTTP Status Code for Indicating Hints</a></cite>, K. Oku. IETF.</dd>

<dt id="refsRFC9842">[RFC9842]</dt>
<dd><cite><a href="https://www.rfc-editor.org/rfc/rfc9842">Compression Dictionary Transport</a></cite>, P. Meenan, Y. Weiss. IETF.</dd>

<dt id="refsSCREENORIENTATION">[SCREENORIENTATION]</dt>
<dd><cite><a href="https://w3c.github.io/screen-orientation/">Screen Orientation</a></cite>, M. Cáceres. W3C.</dd>

Expand Down