mirror of
https://github.com/vichan-devel/vichan.git
synced 2024-12-04 20:08:02 +01:00
149 lines
6.0 KiB
HTML
149 lines
6.0 KiB
HTML
<?xml version="1.0" encoding="UTF-8"?>
|
|
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
|
|
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
|
|
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"><head>
|
|
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
|
|
<meta name="description" content="Explains various methods for allowing IDs in documents safely in HTML Purifier." />
|
|
<link rel="stylesheet" type="text/css" href="./style.css" />
|
|
|
|
<title>IDs - HTML Purifier</title>
|
|
|
|
</head><body>
|
|
|
|
<h1 class="subtitled">IDs</h1>
|
|
<div class="subtitle">What they are, why you should(n't) wear them, and how to deal with it</div>
|
|
|
|
<div id="filing">Filed under End-User</div>
|
|
<div id="index">Return to the <a href="index.html">index</a>.</div>
|
|
<div id="home"><a href="http://htmlpurifier.org/">HTML Purifier</a> End-User Documentation</div>
|
|
|
|
<p>Prior to HTML Purifier 1.2.0, this library blithely accepted user input that
|
|
looked like this:</p>
|
|
|
|
<pre><a id="fragment">Anchor</a></pre>
|
|
|
|
<p>...presenting an attractive vector for those that would destroy standards
|
|
compliance: simply set the ID to one that is already used elsewhere in the
|
|
document and voila: validation breaks. There was a half-hearted attempt to
|
|
prevent this by allowing users to blacklist IDs, but I suspect that no one
|
|
really bothered, and thus, with the release of 1.2.0, IDs are now <em>removed</em>
|
|
by default.</p>
|
|
|
|
<p>IDs, however, are quite useful functionality to have, so if users start
|
|
complaining about broken anchors you'll probably want to turn them back on
|
|
with %Attr.EnableID. But before you go mucking around with the config
|
|
object, it's probably worth to take some precautions to keep your page
|
|
validating. Why?</p>
|
|
|
|
<ol>
|
|
<li>Standards-compliant pages are good</li>
|
|
<li>Duplicated IDs interfere with anchors. If there are two id="foobar"s in a
|
|
document, which spot does a browser presented with the fragment #foobar go
|
|
to? Most browsers opt for the first appearing ID, making it impossible
|
|
to references the second section. Similarly, duplicated IDs can hijack
|
|
client-side scripting that relies on the IDs of elements.</li>
|
|
</ol>
|
|
|
|
<p>You have (currently) four ways of dealing with the problem.</p>
|
|
|
|
|
|
|
|
<h2 class="subtitled">Blacklisting IDs</h2>
|
|
<div class="subsubtitle">Good for pages with single content source and stable templates</div>
|
|
|
|
<p>Keeping in terms with the
|
|
<acronym title="Keep It Simple, Stupid">KISS</acronym> principle, let us
|
|
deal with the most obvious solution: preventing users from using any IDs that
|
|
appear elsewhere on the document. The method is simple:</p>
|
|
|
|
<pre>$config->set('Attr.EnableID', true);
|
|
$config->set('Attr.IDBlacklist' array(
|
|
'list', 'of', 'attribute', 'values', 'that', 'are', 'forbidden'
|
|
));</pre>
|
|
|
|
<p>That being said, there are some notable drawbacks. First of all, you have to
|
|
know precisely which IDs are being used by the HTML surrounding the user code.
|
|
This is easier said than done: quite often the page designer and the system
|
|
coder work separately, so the designer has to constantly be talking with the
|
|
coder whenever he decides to add a new anchor. Miss one and you open yourself
|
|
to possible standards-compliance issues.</p>
|
|
|
|
<p>Furthermore, this position becomes untenable when a single web page must hold
|
|
multiple portions of user-submitted content. Since there's obviously no way
|
|
to find out before-hand what IDs users will use, the blacklist is helpless.
|
|
And since HTML Purifier validates each segment separately, perhaps doing
|
|
so at different times, it would be extremely difficult to dynamically update
|
|
the blacklist in between runs.</p>
|
|
|
|
<p>Finally, simply destroying the ID is extremely un-userfriendly behavior: after
|
|
all, they might have simply specified a duplicate ID by accident.</p>
|
|
|
|
<p>Thus, we get to our second method.</p>
|
|
|
|
|
|
|
|
<h2 class="subtitled">Namespacing IDs</h2>
|
|
<div class="subsubtitle">Lazy developer's way, but needs user education</div>
|
|
|
|
<p>This method, too, is quite simple: add a prefix to all user IDs. With this
|
|
code:</p>
|
|
|
|
<pre>$config->set('Attr.EnableID', true);
|
|
$config->set('Attr.IDPrefix', 'user_');</pre>
|
|
|
|
<p>...this:</p>
|
|
|
|
<pre><a id="foobar">Anchor!</a></pre>
|
|
|
|
<p>...turns into:</p>
|
|
|
|
<pre><a id="user_foobar">Anchor!</a></pre>
|
|
|
|
<p>As long as you don't have any IDs that start with user_, collisions are
|
|
guaranteed not to happen. The drawback is obvious: if a user submits
|
|
id="foobar", they probably expect to be able to reference their page with
|
|
#foobar. You'll have to tell them, "No, that doesn't work, you have to add
|
|
user_ to the beginning."</p>
|
|
|
|
<p>And yes, things get hairier. Even with a nice prefix, we still have done
|
|
nothing about multiple HTML Purifier outputs on one page. Thus, we have
|
|
a second configuration value to piggy-back off of: %Attr.IDPrefixLocal:</p>
|
|
|
|
<pre>$config->set('Attr.IDPrefixLocal', 'comment' . $id . '_');</pre>
|
|
|
|
<p>This new attributes does nothing but append on to regular IDPrefix, but is
|
|
special in that it is volatile: it's value is determined at run-time and
|
|
cannot possibly be cordoned into, say, a .ini config file. As for what to
|
|
put into the directive, is up to you, but I would recommend the ID number
|
|
the text has been assigned in the database. Whatever you pick, however, it
|
|
has to be unique and stable for the text you are validating. Note, however,
|
|
that we require that %Attr.IDPrefix be set before you use this directive.</p>
|
|
|
|
<p>And also remember: the user has to know what this prefix is too!</p>
|
|
|
|
|
|
|
|
<h2>Abstinence</h2>
|
|
|
|
<p>You may not want to bother. That's okay too, just don't enable IDs.</p>
|
|
|
|
<p>Personally, I would take this road whenever user-submitted content would be
|
|
possibly be shown together on one page. Why a blog comment would need to use
|
|
anchors is beyond me.</p>
|
|
|
|
|
|
|
|
<h2>Denial</h2>
|
|
|
|
<p>To revert back to pre-1.2.0 behavior, simply:</p>
|
|
|
|
<pre>$config->set('Attr.EnableID', true);</pre>
|
|
|
|
<p>Don't come crying to me when your page mysteriously stops validating, though.</p>
|
|
|
|
</body>
|
|
</html>
|
|
|
|
<!-- vim: et sw=4 sts=4
|
|
-->
|