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Add a speculative flag to Request as well as related processing #881

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Add a speculative flag to Request as well as related processing #881

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Add a speculative flag to Reqeust, and related processing
yoavweiss Mar 19, 2019
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yoavweiss Mar 19, 2019
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Add somewhat fuzzy language about aborts
yoavweiss Mar 21, 2019
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yoavweiss Mar 21, 2019
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yoavweiss Mar 21, 2019
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36 changes: 32 additions & 4 deletions fetch.bs
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Original file line number Diff line number Diff line change
Expand Up @@ -1077,6 +1077,9 @@ explicitly set <a for=/>request</a>'s
<p id=keep-alive-flag>A <a for=/>request</a> has an associated
<dfn for=request export>keepalive flag</dfn>. Unless stated otherwise it is unset.

<p id=speculative-flag>A <a for=/>request</a> has an associated
<dfn for=request export>speculative flag</dfn>. Unless stated otherwise it is unset.
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Probably this should be a boolean, as I think we're leaning more towards explicit booleans as opposed to "flags"s these days?


<p class="note no-backref">This can be used to allow the request to outlive the
<a>environment settings object</a>, e.g.,
<code>navigator.sendBeacon</code> and the HTML <code>img</code> element set this flag. Requests with
Expand Down Expand Up @@ -1947,8 +1950,8 @@ functionality.
<p>When a <a for=fetch>fetch group</a> is
<dfn export for="fetch group" id=concept-fetch-group-terminate>terminated</dfn>,
for each associated <a for="fetch group">fetch record</a> whose
<a for="fetch record">request</a>'s <a>done flag</a> or
<a>keepalive flag</a> is unset,
<a for="fetch record">request</a>'s <a>done flag</a>,
<a>keepalive flag</a>, and <a>speculative flag</a> are all unset,
<a lt=terminated for=fetch>terminate</a> the
<a for="fetch group">fetch record</a>'s
<a for="fetch record">fetch</a>.
Expand Down Expand Up @@ -3101,6 +3104,11 @@ the request.
<a for=request>origin</a> to <var>request</var>'s
<a for=request>client</a>'s <a for="environment settings object">origin</a>.

<li><p>If a <var>request</var>'s <a for=request>speculative flag</a> is set, then the user agent
may <a for=fetch lt=terminated>terminate</a> the <a for=/>fetch</a> and return an <a>aborted
network error</a>, in cases where it's reasonable to believe it will result in better user
experience.

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@annevk I wasn't sure what to write here, so started by writing something. It feels a bit fuzzy to be part of the processing model, so advice on making it better would be appreciated

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How concrete is it in the implementation?

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Currently I'm not aware of implementations that do that at the moment. When discussing whatwg/html#4115 @youennf wanted to give UAs the concrete possibility to do so, while staying conformant.

<li>
<p>If <var>request</var>'s <a for=request>header list</a>
<a for="header list">does not contain</a> `<code>Accept</code>`, then:
Expand Down Expand Up @@ -3138,8 +3146,9 @@ the request.

<li>
<p>If <var>request</var>'s <a for=request>priority</a> is null, then use <var>request</var>'s
<a for=request>initiator</a> and <a for=request>destination</a> appropriately in setting
<var>request</var>'s <a for=request>priority</a> to a user-agent-defined object.
<a for=request>initiator</a>, <a for=request>destination</a>, and <a for=request>speculative
flag</a> appropriately in setting <var>request</var>'s <a for=request>priority</a> to a
user-agent-defined object.

<p class=note>The user-agent-defined object could encompass stream weight and dependency
for HTTP/2, and equivalent information used to prioritize dispatch and processing of
Expand Down Expand Up @@ -4072,6 +4081,12 @@ Range Requests</cite>. [[HTTP-RANGE]] However, this is not widely supported by b

<p>is true, and unset otherwise.

<li><p>If <var>httpRequest</var>'s <a for=request>speculative flag</a> is set,
<a for="header list">append</a>
`<code>Sec-Purpose</code>`/`<code>prefetch</code>` to
<var>httpRequest</var>'s
<a for=request>header list</a>.

<li><p>Let <var>contentLengthValue</var> be null.

<li><p>If <var>httpRequest</var>'s <a for=request>body</a> is null and
Expand Down Expand Up @@ -5628,6 +5643,7 @@ interface Request {
readonly attribute RequestRedirect redirect;
readonly attribute DOMString integrity;
readonly attribute boolean keepalive;
readonly attribute boolean speculative;
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This would only result in setting the header? You'd still get the response and such?

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Yeah, that's the current intention. Even though prefetch is destined for the next navigation, the current renderer can still get the response (e.g. onload fires for it).

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Well, but this adds it to fetch() as a new feature. Was that intended? Or should this only be accessible via <link>?

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I thought it'd be needed to make those headers survive SWs (although that may vary based on where #880 ends up)

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But this would also allow creation. Surviving SW should happen based on copying private state I think.

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^That sounds right to me. This is similar to the idea that priority is a concept that gets preserved here but is never exposed to the Fetch API.

readonly attribute boolean isReloadNavigation;
readonly attribute boolean isHistoryNavigation;
readonly attribute AbortSignal signal;
Expand Down Expand Up @@ -5787,6 +5803,11 @@ initially a new {{AbortSignal}} object.
<dd>Returns a boolean indicating whether or not <var>request</var> can outlive the global in which
it was created.

<dt><code><var>request</var> . <a attribute for=Request>speculative</a></code>
<dd>Returns a boolean indicating whether or not <var>request</var> is a speculative fetch, which
means it could be ignored by the user agent, have low priority, and can outlive the global in which
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it was created.

<dt><code><var>request</var> . <a attribute for=Request>isReloadNavigation</a></code>
<dd>Returns a boolean indicating whether or not <var>request</var> is for a reload navigation.

Expand Down Expand Up @@ -5918,6 +5939,9 @@ constructor must run these steps:
<dt><a>keepalive flag</a>
<dd><var>request</var>'s <a>keepalive flag</a>.

<dt><a>speculative flag</a>
<dd><var>request</var>'s <a>speculative flag</a>.

<dt><a for=request>reload-navigation flag</a>
<dd><var>request</var>'s <a for=request>reload-navigation flag</a>.

Expand Down Expand Up @@ -6210,6 +6234,10 @@ must return the <a>context object</a>'s <a for=Request>request</a>'s
must return true if the <a>context object</a>'s <a for=Request>request</a>'s <a>keepalive flag</a>
is set, and false otherwise.

<p>The <dfn attribute for=Request><code>speculative</code></dfn> attribute's getter, when invoked,
must return true if the <a>context object</a>'s <a for=Request>request</a>'s <a>speculative flag</a>
is set, and false otherwise.

<p>The <dfn attribute for=Request><code>isReloadNavigation</code></dfn> attribute's getter, when
invoked, must return true if the <a>context object</a>'s <a for=Request>request</a>'s
<a for=request>reload-navigation flag</a> is set, and false otherwise.
Expand Down