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Define the response Content-Type header parser
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Also known as "extract a MIME type" down right.

Tests: web-platform-tests/wpt#10525.

Helps with #814.

Fixes #529. Closes whatwg/mimesniff#30.
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@annevk
annevk committed Nov 9, 2018
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Expand Up @@ -317,6 +317,111 @@ specialized multimap. An ordered list of key-value pairs with potentially duplic
<li><p>Return the <a for="header">combined value</a> with <var>name</var> and <var>list</var>.
</ol>

<p>To
<dfn export for="header list" lt="get, decode, and split|getting, decoding, and splitting" id=concept-header-list-get-decode-split>get, decode, and split</dfn>
a <a for=header>name</a> <var>name</var> from <a for=/>header list</a> <var>list</var>, run these
steps:

<ol>
<li><p>Let <var>initialValue</var> be the result of <a for="header list">getting</a>
<var>name</var> from <var>list</var>.

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

<li><p>Let <var>input</var> be the result of <a>isomorphic decoding</a> <var>initialValue</var>.

<li><p>Let <var>position</var> be a <a for=string>position variable</a> for <var>input</var>,
initially pointing at the start of <var>input</var>.

<li><p>Let <var>values</var> be a <a for=/>list</a> of <a for=/>strings</p>, initially empty.

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

<li>
<p>While <var>position</var> is not past the end of <var>input</var>:

<ol>
<li>
<p>Let <var>temporaryValue</var> be the result of <a>collecting a sequence of code points</a>
that are not U+0022 (") or U+002C (,) from <var>input</var>, given <var>position</var>.

<p class=note><var>value</var> might be the empty string.

<li><p>If <var>value</var> is null, then set <var>value</var> to <var>temporaryValue</var>, and
append <var>temporaryValue</var> to <var>value</var> otherwise.

<li>
<p>If <var>position</var> is not past the end of <var>input</var>, then:

<ol>
<li>
<p>If the <a for=/>code point</a> at <var>position</var> within <var>input</var> is
U+0022 ("), then:

<ol>
<li><p>Append U+0022 (") to <var>value</var>.

<li><p>Append to <var>value</var> the result of <a>collecting a sequence of code points</a>
that are not U+0022 (") from <var>input</var>, given <var>position</var>.

<li>
<p>If <var>position</var> is not past the end of <var>input</var>, then:

<ol>
<li><p>Assert: the <a for=/>code point</p> at <var>position</var> within <var>input</var>
is U+0022 (").

<li><p>Advance <var>position</var> by 1.

<li><p>Append U+0022 (") to <var>value</var>.

<li><p><a for=iteration>Continue</a>.
</ol>
</ol>

<li>
<p>Otherwise:

<ol>
<li><p>Assert: the <a for=/>code point</p> at <var>position</var> within <var>input</var> is
U+002C (,).

<li><p>Advance <var>position</var> by 1.
</ol>
</ol>

<li><p>Remove all <a>HTTP tab or space</a> from the start and end of <var>value</var>.

<li><p><a for=list>Append</a> <var>value</var> to <var>values</var>.

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

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

<div class=example id=example-header-list-get-decode-split>
<p>This is how <a>get, decode, and split</a> functions in practice:

<table>
<tr>
<th>Input
<th>Output
<tr>
<td>`<code>nosniff,</code>`
<td>"<code>nosniff</code>" and the empty string
<tr>
<td>`<code>text/html;", x/x</code>`
<td>"<code>text/html;", x/x</code>"
<tr>
<td>`<code>x/x;test="hi",y/y</code>`
<td>"<code>x/x;test="hi"</code>" and "<code>y/y</code>"
<tr>
<td>`<code>x / x,,,1</code>`
<td>"<code>x / x</code>", the empty string, the empty string, and "<code>1</code>"
</table>
</div>

<p>To <dfn export for="header list" id=concept-header-list-append>append</dfn> a
<a for=header>name</a>/<a for=header>value</a> <var>name</var>/<var>value</var> pair to a
<a for=/>header list</a> <var>list</var>, run these steps:
Expand Down Expand Up @@ -683,12 +788,49 @@ run these steps:
from a <a for=/>header list</a> <var>headers</var>, run these steps:

<ol>
<li><p>Let <var>mimeType</var> be the result of <a>extracting header list values</a> given
`<code>Content-Type</code>` and <var>headers</var>.
<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>If <var>mimeType</var> is null or failure, then return the empty byte sequence.
<li><p>Let <var>values</var> be the result of
<a for="header list">getting, decoding, and spliting</a> `<code>Content-Type</code>` from
<var>headers</var>.

<li><p>Return <var>mimeType</var>, <a lt="byte-lowercase">byte-lowercased</a>.
<li>
<p><a for=/>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>'s <a for="MIME type">essence</a> is <var>essence</var>:

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

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

<hr>
Expand Down Expand Up @@ -2525,20 +2667,13 @@ response <a for=/>header</a> can be used to require checking of a <a for=/>respo
steps:

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

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

<li><p>Let <var>stringValue</var> be the <a>isomorphic decode</a> of <var>value</var>.

<li><p>Let <var>tokens</var> be the result of
<a lt="strictly split a string">strictly splitting</a> <var>stringValue</var> on U+002C (,).

<li><p>Let <var>firstToken</var> be the result of removing all <a>HTTP tab or space</a> from the
start and end of <var>tokens</var>[0].
<li><p>If <var>values</var> is null, then return false.

<li><p>If <var>firstToken</var> is an <a>ASCII case-insensitive</a> match for
<li><p>If <var>values</var>[0] is an <a>ASCII case-insensitive</a> match for
"<code>nosniff</code>", then return true.

<li><p>Return false.
Expand Down

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