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Add Async Stale While Revalidate Handling
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Add definitions around fresh, stale-while-revalidate and stale responses.

Define a new flag that allows no-cache mode to not append Cache-Control
header. This allows stale while revalidate to use this mode and not to
force revalidation of upstream caches.

Fixes whatwg#852
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@dtapuska
dtapuska committed Mar 12, 2019
1 parent 265974f commit 99c3b37
Showing 1 changed file with 79 additions and 30 deletions.
109 changes: 79 additions & 30 deletions fetch.bs
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Expand Up @@ -41,6 +41,9 @@ url:https://tools.ietf.org/html/rfc7234#section-1.2.1;text:delta-seconds;type:df
"REFERRER": {
"aliasOf": "referrer-policy"
},
"STALE-WHILE-REVALIDATE": {
"aliasOf": "RFC5861"
},
"SW": {
"aliasOf": "service-workers"
},
Expand Down Expand Up @@ -1404,10 +1407,14 @@ Unless stated otherwise, it is unset.
<div class="note no-backref">
<dl>
<dt>"<code>default</code>"
<dd><a for=/>Fetch</a> will inspect the HTTP cache on the way to the network.
If there is a fresh response it will be used. If there is a stale response a conditional request
will be created, and a normal request otherwise. It then updates the HTTP cache with the response.
[[!HTTP]] [[!HTTP-SEMANTICS]] [[!HTTP-COND]] [[!HTTP-CACHING]] [[!HTTP-AUTH]]
<dd><a for=/>Fetch</a> will inspect the HTTP cache on the way to the network. If the HTTP cache
contains a matching <a>fresh response</a> it will be returned. If the HTTP cache contains a
matching <a>stale-while-revalidate response</a> it will be returned, and a conditional network
fetch will be made to update the entry in the HTTP cache. If the HTTP cache contains a matching
<a>stale response</a>, a conditional network fetch will be returned to update the entry in
the HTTP cache. Otherwise, a non-conditional network fetch will be returned to update the entry
in the HTTP cache.
[[!HTTP]] [[!HTTP-SEMANTICS]] [[!HTTP-COND]] [[!HTTP-CACHING]] [[!HTTP-AUTH]] [[!STALE-WHILE-REVALIDATE]]

<dt>"<code>no-store</code>"
<dd>Fetch behaves as if there is no HTTP cache at all.
Expand Down Expand Up @@ -1521,6 +1528,10 @@ Unless stated otherwise, it is zero.
which is "<code>basic</code>", "<code>cors</code>", or "<code>opaque</code>".
Unless stated otherwise, it is "<code>basic</code>".

<p>A <a for=/>request</a> has an associated
<dfn export for=request id=no-cache-prevent-cache-control>prevent no-cache cache-control header modification flag</dfn>.
Unless stated otherwise, it is unset.

<p>A <a for=/>request</a> has an associated <dfn export for=request id=done-flag>done flag</dfn>.
Unless stated otherwise, it is unset.

Expand Down Expand Up @@ -1896,6 +1907,17 @@ is a <a>filtered response</a> whose
<li><p>Return <var>newResponse</var>.
</ol>

<p>A <dfn export id=concept-fresh-response>fresh response</dfn> is a <a for=/>response</a> whose
age is within its <a href=https://tools.ietf.org/html/rfc7234#section-4.2.1>freshness lifetime</a>.

<p>A <dfn export id=concept-stale-while-revalidate-response>stale-while-revalidate response</dfn> is a
<a for=/>response</a> that is not a <a>fresh response</a>, and its current age is within
the <a href=https://tools.ietf.org/html/rfc5861#section-3>stale-while-revalidate lifetime</a>.

<p>A <dfn export id=concept-stale-response>stale response</dfn> is
a <a for=/>response</a> is a response that is not a <a>fresh response</a> or a
<a>stale-while-revalidate response</a>.


<h4 id=miscellaneous>Miscellaneous</h4>

Expand Down Expand Up @@ -4151,10 +4173,11 @@ Range Requests</cite>. [[HTTP-RANGE]] However, this is not widely supported by b
`<code>If-Range</code>`, then set <var>httpRequest</var>'s
<a for=request>cache mode</a> to "<code>no-store</code>".

<li><p>If <var>httpRequest</var>'s <a for=request>cache mode</a> is "<code>no-cache</code>" and
<var>httpRequest</var>'s <a for=request>header list</a> <a for="header list">does not contain</a>
`<code>Cache-Control</code>`, then <a for="header list">append</a>
`<code>Cache-Control</code>`/`<code>max-age=0</code>` to
<li><p>If <var>httpRequest</var>'s <a for=request>cache mode</a> is "<code>no-cache</code>",
<var>httpRequest</var>'s <a for=request>prevent no-cache cache-control header modification flag</a>
is unset, and <var>httpRequest</var>'s <a for=request>header list</a>
<a for="header list">does not contain</a> `<code>Cache-Control</code>`, then
<a for="header list">append</a> `<code>Cache-Control</code>`/`<code>max-age=0</code>` to
<var>httpRequest</var>'s <a for=request>header list</a>.

<li>
Expand Down Expand Up @@ -4283,32 +4306,57 @@ Range Requests</cite>. [[HTTP-RANGE]] However, this is not widely supported by b

<!-- cache hit -->
<ol>
<li><p>If <var>storedResponse</var> requires validation (i.e., it is not fresh), then set the
<var>revalidatingFlag</var>.

<li>
<p>If the <var>revalidatingFlag</var> is set and <var>httpRequest</var>'s
<a for=request>cache mode</a> is neither "<code>force-cache</code>" nor
"<code>only-if-cached</code>", then:

<p>If <a for=request>cache mode</a> is "<code>default</code>" and
<var>storedResponse</var> is a <a>stale-while-revalidate response</a>, then:
<ol>
<li><p>If <var>storedResponse</var>'s <a for=response>header list</a>
<a for="header list">contains</a> `<code>ETag</code>`, then <a for="header list">append</a>
`<code>If-None-Match</code>` with its value to <var>httpRequest</var>'s
<a for=request>header list</a>.

<li><p>If <var>storedResponse</var>'s <a for=response>header list</a>
<a for="header list">contains</a> `<code>Last-Modified</code>`, then
<a for="header list">append</a> `<code>If-Modified-Since</code>` with its value to
<var>httpRequest</var>'s <a for=request>header list</a>.
</ol>
<li><p>Set <var>response</var> to <var>storedResponse</var>.
<li><p>Set <var>response</var>'s <a for=response>cache state</a> to "<code>local</code>".
<li><p>Let <var>revalidateRequest</var> be a <a for=request>clone</a> of <var>request</var>.
<li><p>Set <var>revalidateRequest</var>'s <a for=request>cache mode</a> set to
"<code>no-cache</code>".
<li><p>Set <var>revalidateRequest</var>'s <a for=request>prevent no-cache cache-control header modification flag</a>.
<li><p>Set <var>revalidateRequest</var>'s <a for=request>service-workers mode</a> set to
"<code>none</code>".
<li>
<p><a>In parallel</a> perform <a for=main>main fetch</a> using <var>revalidateRequest</var>.

<p class=note>See also the
"<a href=https://tools.ietf.org/html/rfc7234#section-4.3.4>Sending a Validation Request</a>"
chapter of <cite>HTTP Caching</cite> [[!HTTP-CACHING]].
<p class=note>Note the parallel fetch is only meant to update the state of the HTTP cache
and the response will be unused until another cache access. The stale response will be used
as the response to current request. The parallel fetch will be issued in the context of
the browsing context so if it is destroyed the request will be aborted.

</ol>
<li>
<p>Otherwise:
<ol>
<li><p>If <var>storedResponse</var> is a <a>stale response</a>, then set the
<var>revalidatingFlag</var>.

<li><p>Otherwise, set <var>response</var> to <var>storedResponse</var> and set
<var>response</var>'s <a for=response>cache state</a> to "<code>local</code>".
<li>
<p>If the <var>revalidatingFlag</var> is set and <var>httpRequest</var>'s
<a for=request>cache mode</a> is neither "<code>force-cache</code>" nor
"<code>only-if-cached</code>", then:

<ol>
<li><p>If <var>storedResponse</var>'s <a for=response>header list</a>
<a for="header list">contains</a> `<code>ETag</code>`, then <a for="header list">append</a>
`<code>If-None-Match</code>` with its value to <var>httpRequest</var>'s
<a for=request>header list</a>.

<li><p>If <var>storedResponse</var>'s <a for=response>header list</a>
<a for="header list">contains</a> `<code>Last-Modified</code>`, then
<a for="header list">append</a> `<code>If-Modified-Since</code>` with its value to
<var>httpRequest</var>'s <a for=request>header list</a>.
</ol>

<p class=note>See also the
"<a href=https://tools.ietf.org/html/rfc7234#section-4.3.4>Sending a Validation Request</a>"
chapter of <cite>HTTP Caching</cite> [[!HTTP-CACHING]].

<li><p>Otherwise, set <var>response</var> to <var>storedResponse</var> and set
<var>response</var>'s <a for=response>cache state</a> to "<code>local</code>".
</ol>
</ol>
</ol>
</ol>
Expand Down Expand Up @@ -7028,6 +7076,7 @@ Clement Pellerin,
Collin Jackson,
Daniel Robertson,
Daniel Veditz,
Dave Tapuska,
David Benjamin,
David Håsäther,
David Orchard,
Expand Down

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