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Introduce get the MIME type for Request/Response
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Body's MIME type concept was a bit unclear to folks, so replace it with a more explicit algorithm.

This also fixes a "failure-pointer" dereference issue in the formData() method as Body's MIME type could be failure. Get the MIME type returns null or a MIME type as that is better for Blob objects going forward.

And while we're here also clarify the return value of extract a MIME type and correct one caller that thought it would return null rather than failure.

Co-authored-by: Anne van Kesteren <annevk@annevk.nl>
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@CYBAI @annevk
CYBAI and annevk authored Jun 2, 2023
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151 changes: 85 additions & 66 deletions fetch.bs
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Expand Up @@ -3747,7 +3747,8 @@ defined here as the model defined in HTTP is not compatible with web content. [[
<div algorithm>
<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:
from a <a for=/>header list</a> <var>headers</var>, run these steps. They return failure or a
<a for=/>MIME type</a>.

<ol>
<li><p>Let <var>charset</var> be null.
Expand Down Expand Up @@ -4773,7 +4774,7 @@ steps:
<a for="header list">extracting a MIME type</a> from <var>response</var>'s
<a for=response>header list</a>.

<li><p>If <var>mimeType</var> is non-null, then set <var>bodyInfo</var>'s
<li><p>If <var>mimeType</var> is not failure, then set <var>bodyInfo</var>'s
<a for="response body info">content type</a> to the result of
<a>minimizing a supported MIME type</a> given <var>mimeType</var>.
</ol>
Expand Down Expand Up @@ -7138,10 +7139,6 @@ HTML, will likely not be exposed here. Rather, an HTML parser API might accept a
due course.
<!-- https://lists.w3.org/Archives/Public/public-whatwg-archive/2014Jun/thread.html#msg72 -->

<p>Objects including the {{Body}} interface mixin need to define an associated
<dfn id=concept-body-mime-type for=Body>MIME type</dfn> algorithm which takes no arguments and
returns failure or a <a for=/>MIME type</a>.

<p>Objects including the {{Body}} interface mixin have an associated
<dfn id=concept-body-body for=Body>body</dfn> (null or a <a for=/>body</a>).

Expand Down Expand Up @@ -7177,6 +7174,28 @@ returns failure or a <a for=/>MIME type</a>.

<hr>

<div algorithm>
<p>To <dfn id=concept-body-mime-type for=Body>get the MIME type</dfn>, given a {{Request}} or
{{Response}} object <var>requestOrResponse</var>:

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

<li><p>If <var>requestOrResponse</var> is a {{Request}} object, then set <var>headers</var> to
<var>requestOrResponse</var>'s <a for=Request>request</a>'s <a for=request>header list</a>.

<li><p>Otherwise, set <var>headers</var> to <var>requestOrResponse</var>'s
<a for=Response>response</a>'s <a for=response>header list</a>.

<li><p>Let <var>mimeType</var> be the result of <a for="header list">extracting a MIME type</a>
from <var>headers</var>.

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

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

<div algorithm>
<p>The <dfn attribute for=Body><code>body</code></dfn> getter steps are to return null if
<a>this</a>'s <a for=Body>body</a> is null; otherwise <a>this</a>'s <a for=Body>body</a>'s
Expand Down Expand Up @@ -7233,69 +7252,76 @@ of running <a for=Body>consume body</a> with <a>this</a> and the following step
<p>The <dfn method for=Body><code>blob()</code></dfn> method steps are to return the result
of running <a for=Body>consume body</a> with <a>this</a> and the following step given a
<a for=/>byte sequence</a> <var>bytes</var>: return a {{Blob}} whose contents are <var>bytes</var>
and whose {{Blob/type}} attribute is <a>this</a>'s <a for=Body>MIME type</a>.
and whose {{Blob/type}} attribute is the result of <a for=Body>get the MIME type</a> with
<a>this</a>.
<!-- This is wrong. It should really set an underlying concept to this. -->
</div>

<div algorithm>
<p>The <dfn method for=Body><code>formData()</code></dfn> method steps are to return the result of
running <a for=Body>consume body</a> with <a>this</a> and the following step given a
<a for=/>byte sequence</a> <var>bytes</var>: switch on <a>this</a>'s <a for=Body>MIME type</a>'s
<a for="MIME type">essence</a> and run the corresponding steps:
<a for=/>byte sequence</a> <var>bytes</var>:

<dl class=switch>
<dt>"<code>multipart/form-data</code>",
<dd>
<ol>
<li>
<p>Parse <var>bytes</var>, using the value of the `<code>boundary</code>` parameter from
<a>this</a>'s <a for=Body>MIME type</a>, per the rules set forth in
<cite>Returning Values from Forms: multipart/form-data</cite>. [[!RFC7578]]</p>

<p>Each part whose `<code>Content-Disposition</code>` header contains a `<code>filename</code>`
parameter must be parsed into an <a for="entry list">entry</a> whose value is a {{File}} object
whose contents are the contents of the part. The {{File/name}} attribute of the {{File}} object
must have the value of the `<code>filename</code>` parameter of the part. The {{Blob/type}}
attribute of the {{File}} object must have the value of the `<code>Content-Type</code>` header
of the part if the part has such header, and `<code>text/plain</code>` (the default defined by
[[!RFC7578]] section 4.4) otherwise.</p>

<p>Each part whose `<code>Content-Disposition</code>` header does not contain a
`<code>filename</code>` parameter must be parsed into an <a for="entry list">entry</a> whose
value is the <a lt="UTF-8 decode without BOM">UTF-8 decoded without BOM</a> content of the part.
<span class=note>This is done regardless of the presence or the value of a
`<code>Content-Type</code>` header and regardless of the presence or the value of a
`<code>charset</code>` parameter.</span></p>

<p class=note>A part whose `<code>Content-Disposition</code>` header contains a
`<code>name</code>` parameter whose value is `<code>_charset_</code>` is parsed like any other
part. It does not change the encoding.</p>
</li>

<li><p>If that fails for some reason, then <a>throw</a> a {{TypeError}}.

<li><p>Return a new {{FormData}} object, appending each <a for="entry list">entry</a>, resulting
from the parsing operation, to its <a for=FormData>entry list</a>.
</ol>
<ol>
<li><p>Let <var>mimeType</var> be the result of <a for=Body>get the MIME type</a> with <a>this</a>.

<p class=XXX>The above is a rough approximation of what is needed for
`<code>multipart/form-data</code>`, a more detailed parsing specification is to be
written. Volunteers welcome.
<li>
<p>If <var>mimeType</var> is non-null, then switch on <var>mimeType</var>'s
<a for="MIME type">essence</a> and run the corresponding steps:

<dt>"<code>application/x-www-form-urlencoded</code>",
<dd>
<ol>
<li><p>Let <var>entries</var> be the result of <a lt="urlencoded parser">parsing</a>
<var>bytes</var>.
<dl class=switch>
<dt>"<code>multipart/form-data</code>"
<dd>
<ol>
<li>
<p>Parse <var>bytes</var>, using the value of the `<code>boundary</code>` parameter from
<var>mimeType</var>, per the rules set forth in
<cite>Returning Values from Forms: multipart/form-data</cite>. [[!RFC7578]]

<p>Each part whose `<code>Content-Disposition</code>` header contains a
`<code>filename</code>` parameter must be parsed into an <a for="entry list">entry</a> whose
value is a {{File}} object whose contents are the contents of the part. The {{File/name}}
attribute of the {{File}} object must have the value of the `<code>filename</code>` parameter
of the part. The {{Blob/type}} attribute of the {{File}} object must have the value of the
`<code>Content-Type</code>` header of the part if the part has such header, and
`<code>text/plain</code>` (the default defined by [[!RFC7578]] section 4.4) otherwise.

<p>Each part whose `<code>Content-Disposition</code>` header does not contain a
`<code>filename</code>` parameter must be parsed into an <a for="entry list">entry</a> whose
value is the <a lt="UTF-8 decode without BOM">UTF-8 decoded without BOM</a> content of the
part. <span class=note>This is done regardless of the presence or the value of a
`<code>Content-Type</code>` header and regardless of the presence or the value of a
`<code>charset</code>` parameter.</span>

<p class=note>A part whose `<code>Content-Disposition</code>` header contains a
`<code>name</code>` parameter whose value is `<code>_charset_</code>` is parsed like any other
part. It does not change the encoding.

<li><p>If that fails for some reason, then <a>throw</a> a {{TypeError}}.

<li><p>Return a new {{FormData}} object, appending each <a for="entry list">entry</a>,
resulting from the parsing operation, to its <a for=FormData>entry list</a>.
</ol>

<li><p>If <var>entries</var> is failure, then <a>throw</a> a {{TypeError}}.
<p class=XXX>The above is a rough approximation of what is needed for
`<code>multipart/form-data</code>`, a more detailed parsing specification is to be written.
Volunteers welcome.

<li><p>Return a new {{FormData}} object whose <a for=FormData>entry list</a> is
<var>entries</var>.
</ol>
<dt>"<code>application/x-www-form-urlencoded</code>"
<dd>
<ol>
<li><p>Let <var>entries</var> be the result of <a lt="urlencoded parser">parsing</a>
<var>bytes</var>.

<dt>Otherwise
<dd><p><a>Throw</a> a {{TypeError}}.
</dl>
<li><p>If <var>entries</var> is failure, then <a>throw</a> a {{TypeError}}.

<li><p>Return a new {{FormData}} object whose <a for=FormData>entry list</a> is
<var>entries</var>.
</ol>
</dl>

<li><p><a>Throw</a> a {{TypeError}}.
</ol>
</div>

<div algorithm>
Expand Down Expand Up @@ -7387,10 +7413,6 @@ omitted from <a enum><code>RequestMode</code></a> as it cannot be used nor obser
<p>A {{Request}} object has an associated <dfn for=Request>signal</dfn> (null or an {{AbortSignal}}
object), initially null.

<p>A {{Request}} object's <a for=Body>MIME type</a> is to return the result of
<a for="header list">extracting a MIME type</a> from its <a for=Request>request</a>'s
<a for=request>header list</a>.

<p>A {{Request}} object's <a for=Body>body</a> is its
<a for=Request>request</a>'s
<a for=request>body</a>.
Expand Down Expand Up @@ -8078,10 +8100,6 @@ enum ResponseType { "basic", "cors", "default", "error", "opaque", "opaqueredire
<p>A {{Response}} object also has an associated <dfn for=Response export>headers</dfn> (null or a
{{Headers}} object), initially null.

<p>A {{Response}} object's <a for=Body>MIME type</a> is to return the result of
<a for="header list">extracting a MIME type</a> from its <a for=Response>response</a>'s
<a for=response>header list</a>.

<p>A {{Response}} object's <a for=Body>body</a> is its
<a for=Response>response</a>'s <a for=response>body</a>.

Expand Down Expand Up @@ -8978,6 +8996,7 @@ Brad Porter,
Bryan Smith,
Caitlin Potter,
Cameron McCormack,
白丞祐 (Cheng-You Bai)<!-- CYBAI; GitHub -->,
Chirag S Kumar<!-- fictionistique; GitHub -->,
Chris Needham,
Chris Rebert,
Expand Down

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