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Add support for compression dictionary transport #1854

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1d64408
Added compression-dictionary destination
pmeenan Aug 25, 2025
cd5a16d
Added processing of the use-as-dictionary response header
pmeenan Aug 25, 2025
7d86734
Added support for dictionary matching
pmeenan Aug 25, 2025
606c33f
Added "dcb" and "dcz" decoding
pmeenan Aug 25, 2025
bb72fc2
Fixed build errors
pmeenan Aug 26, 2025
8bc5398
Switched compression dictionary reference to use the (pending) RFC nu…
pmeenan Sep 3, 2025
defe29f
Add no-cors dictionary support with Cross-Origin-Resource-Policy opt-in
pmeenan Nov 13, 2025
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153 changes: 150 additions & 3 deletions fetch.bs
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Original file line number Diff line number Diff line change
Expand Up @@ -81,6 +81,9 @@ urlPrefix:https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-layered-cooki
"HTTP-CACHING": {
"aliasOf": "RFC9111"
},
"HTTP-COMPRESSION-DICTIONARIES": {
"aliasOf": "RFC9842"
},
Comment on lines +84 to +86
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@annevk annevk Nov 18, 2025

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We can just reference the RFC number directly. No need for an alias.

"HTTP1": {
"aliasOf": "RFC9112"
},
Expand Down Expand Up @@ -1798,6 +1801,7 @@ is "<code>all</code>" or "<code>none</code>". Unless stated otherwise it is "<co
<p>A <a for=/>request</a> has an associated
<dfn export for=request id=concept-request-initiator>initiator</dfn>, which is
the empty string,
"<code>compression-dictionary</code>",
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@annevk annevk Nov 18, 2025

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Why do we need a distinct initiator if we also have a distinct destination?

"<code>download</code>",
"<code>imageset</code>",
"<code>manifest</code>",
Expand All @@ -1812,6 +1816,7 @@ device to assist defining CSP and Mixed Content. It is not exposed to JavaScript
<p>A <dfn export>destination type</dfn> is one of:
the empty string,
"<code>audio</code>",
"<code>compression-dictionary</code>",
"<code>audioworklet</code>",
"<code>document</code>",
"<code>embed</code>",
Expand Down Expand Up @@ -1956,6 +1961,11 @@ not always relevant and might require different behavior.
<td>"<code>video</code>"
<td><code>media-src</code>
<td>HTML's <code>&lt;video></code> element
<tr>
<td>"<code>compression-dictionary</code>"
<td>"<code>compression-dictionary</code>"
<td><code>default-src</code>
<td>HTML's <code>&lt;link rel=compression-dictionary&gt;</code>
<tr>
<td>"<code>download</code>"
<td>""
Expand Down Expand Up @@ -3267,6 +3277,22 @@ or an <a>implementation-defined</a> value.
</div>


<h3 id=compression-dictionary-cache-partitions>Compression-dictionary cache partitions</h3>

<div algorithm>
<p>To <dfn>determine the compression-dictionary cache partition</dfn>, given a <a for=/>request</a> <var>request</var>:

<ol>
<li><p>Let <var>key</var> be the result of <a for=request>determining the network partition key</a>
given <var>request</var>.

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

<li><p>Return the unique compression-dictionary cache associated with <var>key</var>. [[!HTTP-COMPRESSION-DICTIONARIES]]
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Are there PRs against Storage and Clear-Site-Data about clearing this cache? It would be good if those were linked from the commit message.

</ol>
</div>


<h3 id=port-blocking>Port blocking</h3>

<p class=note>New protocols can avoid the need for blocking ports by negotiating the protocol
Expand Down Expand Up @@ -6235,8 +6261,9 @@ run these steps:
<li><p>If <var>httpRequest</var>'s <a for=request>cache mode</a> is
"<code>only-if-cached</code>", then return a <a>network error</a>.

<li><p>Let <var>forwardResponse</var> be the result of running <a>HTTP-network fetch</a> given
<var>httpFetchParams</var>, <var>includeCredentials</var>, and <var>isNewConnectionFetch</var>.
<li><p>Let <var>forwardResponse</var> be the result of running
<a>HTTP-network compression-dictionary fetch</a> given <var>httpFetchParams</var>,
<var>includeCredentials</var>, and <var>isNewConnectionFetch</var>.

<li><p>If <var>httpRequest</var>'s <a for=request>method</a> is <a>unsafe</a> and
<var>forwardResponse</var>'s <a for=response>status</a> is in the range 200 to 399, inclusive,
Expand Down Expand Up @@ -6385,12 +6412,131 @@ run these steps:
<li><p>If <var>isAuthenticationFetch</var> is true, then create an <a>authentication entry</a> for
<var>request</var> and the given realm.

<li>
<p>If <var>response</var>'s <a for=response>header list</a>
<a for="header list">contains</a> `<code>Use-As-Dictionary</code>`, then:
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Suggested change
<a for="header list">contains</a> `<code>Use-As-Dictionary</code>`, then:
<a for="header list">contains</a> `<code>Use-As-Dictionary</code>`:

<!-- This is defined in [[!HTTP-COMPRESSION-DICTIONARIES]] -->

<ol>
<li><p>Let <var>dictionaryValue</var> be the result of
<a for="header list">getting a structured field value</a> given `<code>Use-As-Dictionary</code>`,
"<code>dictionary</code>", and <var>response</var>'s <a for=response>header list</a>.

<li><p>If <var>dictionaryValue</var> is null or <var>dictionaryValue</var>["<code>match</code>"]
does not <a for=map>exist</a>, then return <var>response</var>.

<li><p>Let <var>pattern</var> be the result of creating a URL pattern from
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"creating a URL pattern" needs some kind of link to a definition.

<var>dictionaryValue</var>["<code>match</code>"] and <var>request</var>'s
<a for=request>current URL</a>.

<li><p>If <var>pattern</var> is failure or <var>pattern</var> has regexp groups, then return
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"has regexp groups" needs a definition.

<var>response</var>.

<li><p>Let <var>compressionDictionaryCache</var> be the result of
<a>determining the compression-dictionary cache partition</a> given <var>request</var>.

<li><p>If <var>compressionDictionaryCache</var> is null, then return <var>response</var>.
Comment on lines +6435 to +6438
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@annevk annevk Nov 18, 2025

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Maybe we should do this before creating a URL pattern. This seems less expensive.


<li><p>Let <var>corpPolicy</var> be the result of <a for="header list">getting</a>
`<a http-header><code>Cross-Origin-Resource-Policy</code></a>` from <var>response</var>'s
<a for=response>header list</a>.

<li><p>If <var>request</var>'s <a for=request>response tainting</a> is "<code>opaque</code>" and
<var>corpPolicy</var> is not `<code>cross-origin</code>`, then return <var>response</var>.
Comment on lines +6440 to +6445
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@annevk annevk Nov 18, 2025

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This isn't good enough. We want corpPolicy to be a good value across redirects. We should have tests for that as well.


<li><p>Let <var>expirationTime</var> be the time at which the <var>response</var> becomes stale.
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This needs more links to definitions.


<li><p>If <var>expirationTime</var> is not in the future, then return <var>response</var>.

<li><p>Store <var>response</var> in <var>compressionDictionaryCache</var> with its associated
<var>dictionaryValue</var> and <var>expirationTime</var>.
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@annevk annevk Nov 18, 2025

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Shouldn't we also store pattern somewhere?

</ol>

<li><p>Return <var>response</var>. <span class=note>Typically <var>response</var>'s
<a for=response>body</a>'s <a for=body>stream</a> is still being enqueued to after
returning.</span>
</ol>
</div>

<h3 id=http-network-compression-dictionary-fetch>HTTP-network compression-dictionary fetch</h3>

<div algorithm>
<p>To <dfn id=concept-http-network-compression-dictionary-fetch>HTTP-network compression-dictionary fetch</dfn>,
given a <a for=/>fetch params</a> <var>fetchParams</var>, an optional boolean
<var>includeCredentials</var> (default false), and an optional boolean <var>forceNewConnection</var>
(default false), run these steps:

<ol>
<li><p>Let <var>request</var> be <var>fetchParams</var>'s <a for="fetch params">request</a>.

<li><p>If <var>request</var>'s <a for=request>mode</a> is "<code>no-cors</code>", then return the
result of running <a>HTTP-network fetch</a> given <var>fetchParams</var>,
<var>includeCredentials</var>, and <var>forceNewConnection</var>.

<li><p>If the user agent is configured to block cookies for <var>request</var>, then return the
result of running <a>HTTP-network fetch</a> given <var>fetchParams</var>,
<var>includeCredentials</var>, and <var>forceNewConnection</var>.
Comment on lines +6476 to +6478
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@annevk annevk Nov 18, 2025

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I don't understand this. The dictionary is partitioned so how is it different from the HTTP cache?


<li><p>Let <var>compressionDictionaryCache</var> be the result of
<a>determining the compression-dictionary cache partition</a> given <var>request</var>.

<li><p>If <var>compressionDictionaryCache</var> is null, then return the result of running
<a>HTTP-network fetch</a> given <var>fetchParams</var>, <var>includeCredentials</var>, and
<var>forceNewConnection</var>.

<li><p>Let <var>bestMatch</var> be the result of finding the best matching dictionary in
<var>compressionDictionaryCache</var> for <var>request</var> as defined in
[[!HTTP-COMPRESSION-DICTIONARIES]].

<li><p>If <var>bestMatch</var> is null, then return the result of running <a>HTTP-network fetch</a>
given <var>fetchParams</var>, <var>includeCredentials</var>, and <var>forceNewConnection</var>.

<li><p>Add the `<code>Available-Dictionary</code>` and `<code>Dictionary-ID</code>`
(if applicable) headers to <var>request</var> using <var>bestMatch</var> as defined in
[[!HTTP-COMPRESSION-DICTIONARIES]].

<li><p><a for="header list">Combine</a> (`<code>Accept-Encoding</code>`, `<code>dcb</code>`)
in <var>request</var>'s <a for=request>header list</a>.

<li><p><a for="header list">Combine</a> (`<code>Accept-Encoding</code>`, `<code>dcz</code>`)
in <var>request</var>'s <a for=request>header list</a>.
Comment on lines +6498 to +6502
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@annevk annevk Nov 18, 2025

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Are we doing this even if web developers set these headers? That seems rather sketchy.


<li><p>Let <var>response</var> be the result of running <a>HTTP-network fetch</a> given
<var>fetchParams</var>, <var>includeCredentials</var>, and <var>forceNewConnection</var>.

<li><p>Let <var>codings</var> be the result of <a>extracting header list values</a> given
`<code>Content-Encoding</code>` and <var>response</var>'s <a for=response>header list</a>.

<li><p>If <var>codings</var> is null or does not contain `<code>dcb</code>` or `<code>dcz</code>`,
then return <var>response</var>.

<li><p>Let <var>corpPolicy</var> be the result of <a for="header list">getting</a>
`<a http-header><code>Cross-Origin-Resource-Policy</code></a>` from <var>response</var>'s
<a for=response>header list</a>.

<li><p>If <var>response</var>'s <a for=response>type</a> is "<code>opaque</code>" and
<var>corpPolicy</var> is not `<code>cross-origin</code>`, then return a
<a>network error</a>.

<li><p>Let <var>availableDictionaryHash</var> be the result of
<a>getting a structured field value</a> given `<code>Available-Dictionary</code>`,
"<code>bytestring</code>", and <var>request</var>'s <a for=request>header list</a>.

<li><p>Let <var>newBody</var> be a new <a for=/>body</a> whose <a for=body>stream</a> is the
result of transforming <var>response</var>'s <a for=response>body</a>'s <a for=body>stream</a>
with an algorithm that verifies that the dictionary hash in the stream matches
<var>availableDictionaryHash</var> and decodes the rest of the stream with the applicable
algorithm as defined in [[!HTTP-COMPRESSION-DICTIONARIES]]. If verification or decoding fails,
the transformed stream must error.

<li><p>Set <var>response</var>'s <a for=response>body</a> to <var>newBody</var>.

<li><p><a>Delete</a> `<code>Content-Encoding</code>` from <var>response</var>'s
<a for=response>header list</a>.

<li><p>Return <var>response</var>.
</ol>
</div>

<h3 id=http-network-fetch>HTTP-network fetch</h3>

Expand Down Expand Up @@ -6458,6 +6604,7 @@ optional boolean <var>forceNewConnection</var> (default false), run these steps:

<ul>
<li><p>Follow the relevant requirements from HTTP. [[!HTTP]] [[!HTTP-CACHING]]
[[!HTTP-COMPRESSION-DICTIONARIES]]

<li>
<p>If <var>request</var>'s <a for=request>body</a> is non-null, and <var>request</var>'s
Expand Down Expand Up @@ -8314,7 +8461,7 @@ dictionary RequestInit {
any window; // can only be set to null
};

enum RequestDestination { "", "audio", "audioworklet", "document", "embed", "font", "frame", "iframe", "image", "json", "manifest", "object", "paintworklet", "report", "script", "sharedworker", "style", "track", "video", "worker", "xslt" };
enum RequestDestination { "", "audio", "audioworklet", "compression-dictionary", "document", "embed", "font", "frame", "iframe", "image", "json", "manifest", "object", "paintworklet", "report", "script", "sharedworker", "style", "track", "video", "worker", "xslt" };
enum RequestMode { "navigate", "same-origin", "no-cors", "cors" };
enum RequestCredentials { "omit", "same-origin", "include" };
enum RequestCache { "default", "no-store", "reload", "no-cache", "force-cache", "only-if-cached" };
Expand Down