cleaning html

hi,

i am pretty sure i am reinventing the wheel here, but i could not find any
example how to remove unwanted html tags.

common suggestion is to use a whitelist, and that's exactly the problem.
Parser.HTML only processes known tags, but to use a whitelist, all the unknown
tags need to be removed.

consequently i wrote this:

string clean_html(string input, array(string)|void keeptags) 
{ 
    if (!keeptags) 
        keeptags = ({ "p", "li", "b", "i", "ol", "sup", "a", "strong", "em", "img", "blockquote" }); 
    mapping tags_found = ([ "tags":([]), "containers":([]) ]); 

    void collect_tags(object tag, string text) 
    { 
         if (tag->tag_name()[0]=='/') 
             tags_found->containers[tag->tag_name()[1..]] = ""; 
         else 
             tags_found->tags[tag->tag_name()] = ""; 
    }; 

    // record the name of every opening and closing tag
    // closing tags indicate containers

    Parser.HTML()->_set_tag_callback(collect_tags)->feed(input)->read(); 
 
    // because collect_tags is called for opening and closing tags separately,
    // the opening tags can't be distinguished between tags and containers,
    // but "tags" should only contain tags that are not containers

    tags_found->tags -= tags_found->containers; 
    tags_found->tags -= keeptags; 
    tags_found->containers -= keeptags; 

    // now we have a list of tags and containers that we want to clean out
    // couldn't find a way to reset _set_tag_callback, so use a new parser object instead.

    return Parser.HTML()->add_containers(tags_found->containers)->add_tags(tags_found->tags)->feed(input)->read();      

    // TODO: handle containers where we want to keep the content and only
    //       remove the tags themselves.
    //       handle unwanted tag-attributes
}

anyone got a better wheel?

greetings, martin.

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