NAME
HTML::Restrict - Strip unwanted HTML tags and attributes
VERSION
version 1.0.3
SYNOPSIS
This module uses *HTML::Parser* to strip HTML from text in a restrictive
manner. By default all HTML is restricted. You may alter the default
behaviour by supplying your own tag rules.
use HTML::Restrict;
my $hr = HTML::Restrict->new();
# use default rules to start with (strip away all HTML)
my $processed = $hr->process(' <b>i am bold</b> ');
# $processed now equals: 'i am bold'
# Now, a less restrictive example:
use HTML::Restrict;
my $hr = HTML::Restrict->new();
$hr->set_rules({
b => [],
img => [qw( src alt / )]
});
my $html = q[<body><b>hello</b> <img src="pic.jpg" alt="me" id="test" /></body>];
my $processed = $hr->process( $html );
# $processed now equals: <b>hello</b> <img src="pic.jpg" alt="me" />
CONSTRUCTOR AND STARTUP
new()
Creates and returns a new HTML::Restrict object.
my $hr = HTML::Restrict->new()
HTML::Restrict doesn't require any params to be passed to new. If your
goal is to remove all HTML from text, then no further setup is required.
Just pass your text to the process() method and you're done:
my $plain_text = $hr->process( $html );
If you need to set up specific rules, have a look at the params which
HTML::Restrict recognizes:
* "rules => \%rules"
Rules should be passed as a HASHREF of allowed tags. Each hash value
should represent the allowed attributes for the listed tag. For
example, if you want to allow a fair amount of HTML, you can try
something like this:
my %rules = (
a => [qw( href target )],
b => [],
caption => [],
center => [],
em => [],
i => [],
img => [qw( alt border height width src style )],
li => [],
ol => [],
p => [qw(style)],
span => [qw(style)],
strong => [],
sub => [],
sup => [],
table => [qw( style border cellspacing cellpadding align )],
tbody => [],
td => [],
tr => [],
u => [],
ul => [],
);
my $hr = HTML::Restrict->new( rules => \%rules )
Or, to allow only bolded text:
my $hr = HTML::Restrict->new( rules => { b => [] } );
Allow bolded text, images and some (but not all) image attributes:
my %rules = (
b => [ ],
img => [qw( src alt width height border / )
);
my $hr = HTML::Restrict->new( rules => \%rules );
Since *HTML::Parser* treats a closing slash as an attribute, you'll
need to add "/" to your list of allowed attributes if you'd like
your tags to retain closing slashes. For example:
my $hr = HTML::Restrict->new( rules =>{ hr => [] } );
$hr->process( "<hr />"); # returns: <hr>
my $hr = HTML::Restrict->new( rules =>{ hr => [qw( / )] } );
$hr->process( "<hr />"); # returns: <hr />
HTML::Restrict strips away any tags and attributes which are not
explicitly allowed. It also rebuilds your explicitly allowed tags
and places their attributes in the order in which they appear in
your rules.
So, if you define the following rules:
my %rules = (
...
img => [qw( src alt title width height id / )]
...
);
then your image tags will all be built like this:
<img src=".." alt="..." title="..." width="..." height="..." id=".." />
This gives you greater consistency in your tag layout. If you don't
care about element order you don't need to pay any attention to
this, but you should be aware that your elements are being
reconstructed rather than just stripped down.
* "trim => [0|1]"
By default all leading and trailing spaces will be removed when text
is processed. Set this value to 0 in order to disable this
behaviour.
* "uri_schemes => [undef, 'http', 'https', 'irc', ... ]"
As of version 1.0.3, URI scheme checking is performed on all href
and src tag attributes. The following schemes are allowed out of the
box. No action is required on your part:
[ undef, 'http', 'https' ]
(undef represents relative URIs). These restrictions have been put
in place to prevent XSS in the form of:
<a href="javascript:alert(document.cookie)">click for cookie!</a>
See URI for more detailed info on scheme parsing. If, for example,
you wanted to filter out every scheme barring SSL, you would do it
like this:
uri_schemes => ['https']
This feature is new in 1.0.3. Previous to this, there was no schema
checking at all. Moving forward, you'll need to whitelist explicitly
all URI schemas which are not supported by default. This is in
keeping with the whitelisting behaviour of this module and is also
the safest possible approach. Keep in mind that changes to
uri_schemes are not additive, so you'll need to include the defaults
in any changes you make, should you wish to keep them:
# defaults + irc
uri_schemes => [ 'undef', 'http', 'https', 'irc' ]
SUBROUTINES/METHODS
process( $html )
This is the method which does the real work. It parses your data,
removes any tags and attributes which are not specifically allowed and
returns the resulting text. Requires and returns a SCALAR.
get_rules
An accessor method, which returns a HASHREF of allowed tags and their
allowed attributes. Returns an empty HASHREF by default, since the
default behaviour is to disallow all HTML.
get_uri_schemes
Accessor method which returns an ARRAYREF of allowed URI schemes.
set_rules( \%rules )
Sets the rules which will be used to process your data. By default all
HTML tags are off limits. Use this method to define the HTML elements
and corresponding attributes you'd like to use.
If you only need to set rules once, you might want to pass them to the
new() method when constructing the object, but you may also set your
rules using set_rules(). If you want to apply different rules to
different data without creating a new object each time, set_rules() will
handle changing the object's behaviour for you.
Please note that set_rules is a mutator method, so your changes are not
cumulative. The last rules passed to the set_rules method are the rules
which will be applied to your data when it is processed.
For example:
# create object which allows only a and img tags
my $hr = HTML::Restrict->new( rules => { a => [ ...], img => [ ... ] } );
# return to defaults (no HTML allowed)
$hr->set_rules({});
set_uri_schemes
Override existing URI schemes:
$hr->set_uri_schemes([ 'http', 'https', undef, 'ftp' ]);
trim( 0|1 )
By default all leading and trailing spaces will be removed when text is
processed. Set this value to 0 in order to disable this behaviour.
For example, to allow leading and trailing whitespace:
$hr->trim( 0 );
my $trimmed = $hr->process(' <b>i am bold</b> ');
# $trimmed now equals: ' i am bold '
MOTIVATION
There are already several modules on the CPAN which accomplish much of
the same thing, but after doing a lot of poking around, I was unable to
find a solution with a simple setup which I was happy with.
The most common use case might be stripping HTML from user submitted
data completely or allowing just a few tags and attributes to be
displayed. With the exception of URI scheme checking, this module
doesn't do any validation on the actual content of the tags or
attributes. If this is a requirement, you can either mess with the
parser object, post-process the text yourself or have a look at one of
the more feature-rich modules in the SEE ALSO section below.
My aim here is to keep things easy and, hopefully, cover a lot of the
less complex use cases with just a few lines of code and some brief
documentation. The idea is to be up and running quickly.
SEE ALSO
HTML::TagFilter, HTML::Defang, HTML::Declaw, HTML::StripScripts,
HTML::Detoxifier, HTML::Sanitizer, HTML::Scrubber
ACKNOWLEDGEMENTS
Thanks to Raybec Communications <http://www.raybec.com> for funding my
work on this module and for releasing it to the world.
Thanks also to the following for patches and bug reports:
Mark Jubenville (ioncache)
Duncan Forsyth
Rick Moore
Arthur Axel 'fREW' Schmidt
AUTHOR
Olaf Alders <olaf@wundercounter.com>
COPYRIGHT AND LICENSE
This software is copyright (c) 2012 by Olaf Alders.
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.