Re: [whatwg/fetch] Define data: URLs (#579)

TimothyGu commented on this pull request.



> @@ -5630,6 +5621,81 @@ if the script checks that the URL has the right hostname.
 
 
 
+<h2 id=data-urls><code>data:</code> URLs</h2>
+
+<p>For an informative description of <code>data:</code> URLs see RFC 2397. This section replaces its
+normative processing requirements. [[!RFC2397]]

Informative link instead of normative?

> +
+ <li>
+  <p>If <var>mimeType</var> contains an <a>ASCII case-insensitive</a> match for
+  "<code>;base64;</code>" or ends with an <a>ASCII case-insensitive</a> match for
+  "<code>;base64</code>", then:
+
+  <ol>
+   <li><p>Set <var>body</var> to the <span class=XXX>web base64 decoding</span> of <var>body</var>.
+   <!-- web base64 currently takes string input (see window.atob, which defines it for now). I guess
+        we can convert body to a string first by straightforward mapping, but maybe it would make
+        more sense if web base64 decoding operated on bytes? Or was polymorphic? -->
+
+   <li><p>If <var>body</var> is failure, then return failure.
+
+   <li><p>Remove the code point sequence that is an <a>ASCII case-insensitive</a> match for
+   "<code>;base64</code>" from <var>mimeType</var>.

Or `;base64;`

> +  "<code>;base64</code>", then:
+
+  <ol>
+   <li><p>Set <var>body</var> to the <span class=XXX>web base64 decoding</span> of <var>body</var>.
+   <!-- web base64 currently takes string input (see window.atob, which defines it for now). I guess
+        we can convert body to a string first by straightforward mapping, but maybe it would make
+        more sense if web base64 decoding operated on bytes? Or was polymorphic? -->
+
+   <li><p>If <var>body</var> is failure, then return failure.
+
+   <li><p>Remove the code point sequence that is an <a>ASCII case-insensitive</a> match for
+   "<code>;base64</code>" from <var>mimeType</var>.
+  </ol>
+
+ <li><p>If <var>mimeType</var> starts with an <a>ASCII case-insensitive</a> match for
+ "<code>charset;</code>", then prepend "<code>text/plain</code>" to <var>mimeType</var>.

`;charset`?

The "starts with" part would also break URLs like `data:;myownprop=abc;charset=UTF-8,%E4%B8%AD%E6%96%87` and `data:;myownprop=abc,stuff`. The latter is technically invalid according to the RFC but works in Chrome and Firefox.

> +   <li><p>Remove the code point sequence that is an <a>ASCII case-insensitive</a> match for
+   "<code>;base64</code>" from <var>mimeType</var>.
+  </ol>
+
+ <li><p>If <var>mimeType</var> starts with an <a>ASCII case-insensitive</a> match for
+ "<code>charset;</code>", then prepend "<code>text/plain</code>" to <var>mimeType</var>.
+
+ <li><p>If <var>mimeType</var> is the empty string or is not a
+ <span class=XXX>valid MIME type</span>, then set <var>mimeType</var> to
+ "<code>text/plain;charset=US-ASCII</code>".
+
+ <li><p>Set <var>mimeTypeBytes</var> to <var>mimeType</var> with each code point mapped to a byte of
+ equal value.
+ <!-- See above about a dedicated function. -->
+
+ <li><p>Return <var>mimeTypeBytes</var> and <var>body</var>.

Why not return *mimeType* instead?

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