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Define hosts' public suffix and registrable domain. #391

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Jun 7, 2018
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Define hosts' public suffix and registrable domain. #391

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Define hosts' public suffix and registrable domain.
mikewest May 25, 2018
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Expand Up @@ -272,6 +272,124 @@ for further processing.
U+0020 SPACE, U+0023 (#), U+0025 (%), U+002F (/), U+003A (:), U+003F (?), U+0040 (@), U+005B ([),
U+005C (\), or U+005D (]).

<p>A <a for=/>host</a>'s <dfn for=host export>public suffix</dfn> is the portion of a
<a for=/>host</a> which is included on the <cite>Public Suffix List</cite>. To obtain
<var>host</var>'s <a for=host>public suffix</a>, run these steps: [[!PSL]]

<ol>
<li><p>If <var>host</var> is not a <a>domain</a>, then return null.

<li><p>Return the <a for=host>public suffix</a> obtained by executing the
<a href="https://publicsuffix.org/list/">algorithm</a> defined by the Public Suffix List on
<var>host</var>. [[!PSL]].
</ol>

<p>A <a for=/>host</a>'s <dfn for=host export>registrable domain</dfn> is a <a>domain</a> formed by
the most specific public suffix, along with the domain label immediately preceeding it, if any. To
obtain <var>host</var>'s <a for=host>registrable domain</a>, run these steps:

<ol>
<li><p>If <var>host</var>'s <a for=host>public suffix</a> is null or <var>host</var>'s
<a for=host>public suffix</a> <a for=host>equals</a> <var>host</var>, then return null.

<li><p>Return the <a for=host>registrable domain</a> obtained by executing the
<a href="https://publicsuffix.org/list/">algorithm</a> defined by the Public Suffix List on
<var>host</var>. [[!PSL]]
</ol>

<div class=example id=example-host-psl>
<table>
<tr>
<th>Host input
<th>Public suffix
<th>Registrable domain
<tr>
<td><code>com</code>
<td><code>com</code>
<td><i>null</i>
<tr>
<td><code>example.com</code>
<td><code>com</code>
<td><code>example.com</code>
<tr>
<td><code>www.example.com</code>
<td><code>com</code>
<td><code>example.com</code>
<tr>
<td><code>sub.www.example.com</code>
<td><code>com</code>
<td><code>example.com</code>
<tr>
<td><code>EXAMPLE.COM</code>
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This is not a host, but input to the host parser.

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I think it's helpful to point out that no matter how folks spell the URL, it's going to be normalized. Perhaps shifting this table to include a URL rather than a host would make that point, especially for the punycode bits?

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I think it's fine to just list hosts, but we should label it "host input" or some such, to not confuse it with host as a concept, which is already parsed and normalized.

<td><code>com</code>
<td><code>example.com</code>
<tr>
<td><code>github.io</code>
<td><code>github.io</code>
<td><i>null</i>
<tr>
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Isn't this row duplicated? The previous one looks the same.

<td><code>whatwg.github.io</code>
<td><code>github.io</code>
<td><code>whatwg.github.io</code>
<tr>
<td><code>إختبار</code>
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Same as above. And also applies below.

<td><code>xn-kgbechtv</code>
<td><i>null</i>
<tr>
<td><code>example.إختبار</code>
<td><code>xn-kgbechtv</code>
<td><code>example.xn-kgbechtv</code>
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@sleevi sleevi Jun 4, 2018 •
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So one of the things is the PSL doesn't specify whether or not it returns U-Label or A-Label (that's left to the implementation). I'm curious the documentation here for the A-Label - is this an expectation of the contract?

That is, are you trying to show that either U-Label or A-Label can be returned regardless of U-Label or A-Label input, or are you trying to state that A-Labels should be the consistent return?

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Currently we don't rely on this anywhere (assuming it's consistent to be one or the other, is that at least required?), but A-label seems preferable as that'd be consistent with how the platform exposes URLs and origins overall.

I suspect this will only matter if we add an API, but it really depends on whether PSL dependencies keep getting added or not.

<tr>
<td><code>sub.example.إختبار</code>
<td><code>xn-kgbechtv</code>
<td><code>example.xn-kgbechtv</code>
</table>
</div>

<p>Two <a for=/>hosts</a>, <var>A</var> and <var>B</var> are said to be
<dfn for=host export>same site</dfn> with each other if either of the following statements are true:

<ul class=brief>
<li><p><var>A</var> <a for=host>equals</a> <var>B</var> and <var>A</var>'s
<a for=host>registrable domain</a> is non-null.

<li><p><var>A</var>'s <a for=host>registrable domain</a> is <var>B</var>'s
<a for=host>registrable domain</a> and is non-null.
</ul>

<div class=example id=example-same-site>
<p>Assuming that <code>suffix.example</code> is a <a for=host>public suffix</a> and that
<code>example.com</code> is not:

<ul>
<li><p><code>example.com</code>, <code>sub.example.com</code>, <code>other.example.com</code>,
<code>sub.sub.example.com</code>, and <code>sub.other.example.com</code> are all <a>same site</a>
with each other (and themselves), as their <a for=host>registrable domains</a> are
<code>example.com</code>.

<li><p><code>registrable.suffix.example</code>, <code>sub.registrable.suffix.example</code>,
<code>other.registrable.suffix.example</code>, <code>sub.sub.registrable.suffix.example</code>,
and <code>sub.other.registrable.suffix.example</code> are all <a>same site</a> with each other
(and themselves), as their <a for=host>registrable domains</a> are
<code>registrable.suffix.example</code>.

<li><p><code>example.com</code> and <code>registrable.suffix.example</code> are not
<a>same site</a> with each other, as their <a for=host>registrable domains</a> differ.

<li><p><code>suffix.example</code> is not <a>same site</a> with <code>suffix.example</code>, as
it is a <a for=host>public suffix</a>, and therefore has a null
<a for=host>registrable domain</a>.
</ul>
</div>

<p class=warning>Specifications should avoid depending on "<a for=host>public suffix</a>",
"<a for=host>registrable domain</a>", and "<a>same site</a>". The public suffix list will diverge
from client to client, and cannot be relied-upon to provide a hard security boundary. Specifications
which ignore this advice are encouraged to carefully consider whether URLs' schemes ought to be
incorporated into any decision made based upon whether or not two <a for=/>hosts</a> are
<a>same site</a>. HTML's <a>same origin-domain</a> concept is a reasonable example of this
consideration in practice.


<h3 id=idna>IDNA</h3>

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