"""How to escape &'s in URLs.
Please read about `Ampersands (&'s) in URLs`_.
The short answer is, if you have a URL with more than one parameter, you should
wrap it with ``$htmlent`` when you embed it in HTML if you want to pass DTD
validation. If you don't care, then it really won't matter. What follows is
an explanation of why I can't make it any easier on you.
1. You must escape &'s in URLs in order to pass DTD validation. Per the
spec, a browser could look at ``http://a.com/?a=b©=2`` and interpret
the ``©=`` as part of value of the ``a`` variable instead of a new
variable named ``copy;`` because ``©`` is an HTML entity.
2. To handle #1, Aquarium use to escape the &'s in every URL automatically.
3. However, #2 broke redirects if you redirected to a URL with more than
one parameter. I so rarely did this, that I didn't know about the bug for
a good year.
4. To fix the bug in #3, we came up with a scheme to always escape &'s but deal
with the redirect case specially. Now imagine if you create a HTML link
whose URL has a parameter named referrer that is set to your current URL,
which itself happens to have two parameters. When the user clicks on the
link, Aquarium now has a GET parameter named referrer that is a URL. The
programmer can use that URL directly in HTML (in which case the &'s must be
escaped) or he might redirect to it (in which case the &'s must not be
escaped). The programmer is never going to remember whether the URL is
already escaped (per #3, it already is) and whether he needs to escape it
for a link or unescape it for a redirect. His brain would core dump.
When it comes to escaping things, a good general rule is to escape things at
the last possible moment. By violating this rule, bad things were happening.
5. We could force engineers to wrap every URL in HTML with htmlent, but that
would suck. Too much existing code doesn't.
6. Browsers are smart, and most of the time, if you don't escape the &'s, the
browser won't get confused. In fact, you can't generate a URL like
``http://a.com/?a=b©=2`` with Aquarium anyway, because the ; will
get urlencoded to ``%3B``. Hence, it's not possible to get Aquarium to
generate a URL that would confuse the browser. Programmers who are worried
about passing DTD validation and have a URL with more than one parameter
will just have to use ``$htmlent``. That's better than forcing every
programmer to think about the problem every time he generates a URL since,
practically speaking, the warning is pedantic.
.. _Ampersands (&'s) in URLs:
http://www.htmlhelp.com/tools/validator/problems.html#amp
"""
__docformat__ = "restructuredtext"
# Created: Tue Mar 14 18:25:45 PST 2006
# Author: Shannon -jj Behrens, Brandon Golm, Eric Huss
# Email: jjinux@users.sourceforge.net
#
# Copyright (c) Shannon -jj Behrens. All rights reserved.
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