Re: [whatwg/fetch] Editorial: clarify how to get MIME type for request and response (PR #1657)

@annevk commented on this pull request.



>  <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>.
+<dfn id=concept-body-mime-type for=Body>MIME type</dfn> algorithm which returns the result of
+<a for=Body>get the MIME type</a> with <a>this</a>.

I think we should remove this, no? Callers can use "get the MIME type" directly.

> @@ -7168,6 +7168,24 @@ returns failure or a <a for=/>MIME type</a>.
 
 <hr>
 
+<div algorithm>
+<p>To <dfn id=concept-body-get-mime-type for=Body>get the MIME type</dfn>, given an object, <var>requestOrResponse</var>, including the
+{{Body}} interface mixin, run these steps:

Either

> given an object that includes Body _objectThatIncludesBody_:

or

> given a Request or Response object _requestOrResponse_:

The latter is probably best as the algorithm will have to branch on them as well.

> @@ -7168,6 +7168,24 @@ returns failure or a <a for=/>MIME type</a>.
 
 <hr>
 
+<div algorithm>
+<p>To <dfn id=concept-body-get-mime-type for=Body>get the MIME type</dfn>, given an object, <var>requestOrResponse</var>, including the
+{{Body}} interface mixin, run these steps:
+
+<ol>
+ <li><p>If <var>requestOrResponse</var>'s has an associated <a for=Headers>header list</a>,

This needs to be something like:

> 1. Let _headers_ be null.
> 2. If _requestOrResponse_ is a Request object, then set _headers_ to _requestOrResponse_'s request's header list.
> 3. Otherwise, set _headers_ to _requestOrResponse_'s response's header list.
> 4. [Do something with _headers_.]

> +<p>A {{Request}} object's <a for=Body>MIME type</a> is to <a for=Body>get the MIME type</a> with
+<a>this</a>.

We should be able to remove this completely. Same for the equivalent on Response.

> + <li><p>Let <var>bodyWithType</var> be the result of <a for=BodyInit>extracting</a> <a>this</a>'s
+ <a for=Body>body</a>.
+ <li><p>Return <var>bodyWithType</var>'s <a for="body with type">type</a>.

This shouldn't be needed. This already happens as part of constructing a Request or Response, no?

>  </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>:
+
+<ol>
+<li><p>Let <var>mimeType</var> be the result of <a for=Body>get the MIME type</a> with <a>this</a>.
+<li>
+  <p>Switch on <var>mimeType</var>'s <a for="MIME type">essence</a> and run the corresponding
+  steps:

It looks like the text here was wrong before as MIME type can be null. So we probably need to pull the "Otherwise" branch forward and deal with that here.

I guess it's fair if you want to leave that as a follow-up as you didn't introduce it.

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