HTML Sanitizer (removes unwanted tags)

[lhoward]

There have been many questions posted to Perlmonks recently asking about cleaning up HTML (either removing specific tags, or removing all tags except for a given few). Most people respond with one of two suggestions:

1. a regular expression - this has the problem that it may not work because of the way > and < may appear in the HTML
2. advice to check out <cpan://HTML::Parser> and use it as the basis for solving the problem

I've decided to delve in write some code that would serve as an example of how to properly filter out unwanted HTML tags from a document. I actually use <cpan://HTML::Filter> which is distributed with <cpan://HTML::Parser>. My code uses a hash of tags to keep; it could be easily adapted to work with a hash of tags to drop instead.

As always; any comments, criticism or advice on doing this better is appreciated.

package HTML::Sanitizer;
require HTML::Filter;
@ISA=qw(HTML::Filter);

my $data='';

my %keep=(
  a => 1,
  p => 1,
  img => 1
);

sub output{
  my $self=shift;
  my $d=$_[0];
  if($d=~/\<\s*\/?\s*(\w+)/){
    if(exists $keep{lc($1)}){
      $data.=$d;
    }
  }else{
    $data.=$d;
  }
}

my $p=HTML::Sanitizer->new();
$p->parse_file("index.html");

print $data;

[merlyn]

From a user interface standpoint, you might want to simplify the configurations section:

## BEGIN CONFIGURE
my @KEEP = qw(a p img br);
## END CONFIGURE
...
...
# just before the business loop:
my %keep; @keep{@KEEP} = ();
...
... "it's good" if exists $keep{$1}; # or whatever

That data structure requiring them to specify the whole hash is troublesome.

-- Randal L. Schwartz, Perl hacker

[ehdonhon]

Where does sub output() get invoked?

[lhoward]

Been too long since I wrote that code. In that code I am subclassing HTML::Filter into HTML::Sanitizer, replacing its output sub with the I wrote. I never explicitly call it.

There are slicker ways to solve this problem today, for instance the HTML::Sanitizer module that didn't even exist when I wrote this example.

L