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Define the Content-Type header parser #831

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merged 17 commits into from Nov 27, 2018
Merged

Define the Content-Type header parser #831

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a28d42c
Define the response Content-Type header parser
annevk Nov 9, 2018
d9164cd
correct some omissions
annevk Nov 12, 2018
ec0a86a
move content-type parsing to its own section and add some context
annevk Nov 12, 2018
e622e48
use result of extracting a MIME type correctly within Fetch
annevk Nov 12, 2018
5f7cd8f
address feedback
annevk Nov 13, 2018
45a4d41
oh bs
annevk Nov 13, 2018
e9e8dbc
(ignoring parameters) be gone
annevk Nov 13, 2018
c789062
do quoted strings properly
annevk Nov 14, 2018
3eb6d14
oops
annevk Nov 14, 2018
392d618
remove the need for temporaryValue and clarify how special charset is
annevk Nov 19, 2018
3185710
nest less (not a 100% sure this is better)
annevk Nov 21, 2018
2386726
address remaining feedback
annevk Nov 21, 2018
2d5d2a9
domenic asking for examples revealed a bug to me
annevk Nov 21, 2018
ccc6f14
give collecting an HTTP quoted string an extract-value flag to simpli…
annevk Nov 21, 2018
0670924
add CORS example
annevk Nov 21, 2018
c1f48b3
personal nit
annevk Nov 21, 2018
eed035b
final commit?
annevk Nov 22, 2018
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113 changes: 65 additions & 48 deletions fetch.bs
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Expand Up @@ -584,6 +584,9 @@ each other by 0x2C 0x20, in order.
"<code>text/plain</code>", then return false.
</ol>

<p class=warning>This intentionally does not use <a>extract a MIME type</a> as it is rather
forgiving and servers are not expected to implement it.
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<dt>`<code><a href=http://httpwg.org/http-extensions/client-hints.html#dpr>DPR</a></code>`
<dt>`<code><a href=http://httpwg.org/http-extensions/client-hints.html#downlink>Downlink</a></code>`
<dt>`<code><a href=http://httpwg.org/http-extensions/client-hints.html#save-data>Save-Data</a></code>`
Expand Down Expand Up @@ -798,54 +801,6 @@ run these steps:
<li><p>Return <var>values</var>.
</ol>

<p>To
<dfn export for="header list" lt="extract a MIME type|extracting a MIME type" id=concept-header-extract-mime-type>extract a MIME type</dfn>
from a <a for=/>header list</a> <var>headers</var>, run these steps:

<ol>
<li><p>Let <var>charset</var> be null.

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

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

<li><p>Let <var>values</var> be the result of
<a for="header list">getting, decoding, and splitting</a> `<code>Content-Type</code>` from
<var>headers</var>.

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

<li>
<p><a for=list>For each</a> <var>value</var> of <var>values</var>:

<ol>
<li><p>Set <var>mimeType</var> to the result of <a lt="parse a MIME type">parsing</a>
<var>value</var>.

<li>
<p>If <var>mimeType</var> is not failure and <var>mimeType</var>'s
<a for="MIME type">essence</a> is not "<code>*/*</code>" or <var>essence</var>, then:

<ol>
<li><p>Set <var>charset</var> to null.

<li><p>If <var>mimeType</var>'s <a for="MIME type">parameters</a>["<code>charset</code>"]
<a for=map>exists</a>, then set <var>charset</var> to <var>mimeType</var>'s
<a for="MIME type">parameters</a>["<code>charset</code>"].

<li><p>Set <var>essence</var> to <var>mimeType</var>'s <a for="MIME type">essence</a>.
</ol>

<li><p>Otherwise, if <var>mimeType</var> is not failure, <var>mimeType</var>'s
<a for="MIME type">essence</a> is <var>essence</var>, <var>mimeType</var>'s
<a for="MIME type">parameters</a>["<code>charset</code>"] does not <a for=map>exist</a>, and
<var>charset</var> is non-null, set <var>mimeType</var>'s
<a for="MIME type">parameters</a>["<code>charset</code>"] to <var>charset</var>.
</ol>

<li><p>Return <var>mimeType</var>.
</ol>

<hr>

<p>A <dfn id=default-user-agent-value export>default `<code>User-Agent</code>` value</dfn> is a
Expand Down Expand Up @@ -2668,6 +2623,68 @@ consideration for the security consequences. New exceptions can be proposed by
<a href=https://github.com/whatwg/fetch/issues/new>filing an issue</a>.


<h3 id=content-type-header>`<code>Content-Type</code>` header</h3>

<p>The `<code>Content-Type</code>` header is largely defined in HTTP. Its processing model is
defined here as the ABNF defined in HTTP is not compatible with web content. [[HTTP]]

<p>To
<dfn export for="header list" lt="extract a MIME type|extracting a MIME type" id=concept-header-extract-mime-type>extract a MIME type</dfn>
from a <a for=/>header list</a> <var>headers</var>, run these steps:

<ol>
<li><p>Let <var>charset</var> be null.

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

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

<li><p>Let <var>values</var> be the result of
<a for="header list">getting, decoding, and splitting</a> `<code>Content-Type</code>` from
<var>headers</var>.

<li><p>If <var>values</var> is null, then return failure.
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<li>
<p><a for=list>For each</a> <var>value</var> of <var>values</var>:

<ol>
<li><p>Set <var>mimeType</var> to the result of <a lt="parse a MIME type">parsing</a>
<var>value</var>.
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<li>
<p>If <var>mimeType</var> is not failure and <var>mimeType</var>'s
<a for="MIME type">essence</a> is not "<code>*/*</code>" or <var>essence</var>, then:
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<ol>
<li><p>Set <var>charset</var> to null.

<li><p>If <var>mimeType</var>'s <a for="MIME type">parameters</a>["<code>charset</code>"]
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<a for=map>exists</a>, then set <var>charset</var> to <var>mimeType</var>'s
<a for="MIME type">parameters</a>["<code>charset</code>"].

<li><p>Set <var>essence</var> to <var>mimeType</var>'s <a for="MIME type">essence</a>.
</ol>

<li><p>Otherwise, if <var>mimeType</var> is not failure, <var>mimeType</var>'s
<a for="MIME type">essence</a> is <var>essence</var>, <var>mimeType</var>'s
<a for="MIME type">parameters</a>["<code>charset</code>"] does not <a for=map>exist</a>, and
<var>charset</var> is non-null, set <var>mimeType</var>'s
<a for="MIME type">parameters</a>["<code>charset</code>"] to <var>charset</var>.
</ol>

<li><p>Return <var>mimeType</var>.
</ol>
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<p class=warning>Treat <a>extract a MIME type</a> returning failure or anything but the needed
<a>MIME type</a>'s <a for="MIME type">essence</a> as a fatal error. Existing web platform features
not following this has been a major source of security vulnerabilities over the years.

<p class=note>A <a>MIME type</a>'s <a for="MIME type">parameters</a> are typically ignored and this
practice has not been a problem.



<h3 id=x-content-type-options-header>`<code>X-Content-Type-Options</code>` header</h3>

<p>The
Expand Down