Html white list in c#

Question

Spent about 30 minutes or so on SO looking for a definitive solution to this problem.

This question seems to have been asked a lot of times but...

• Most solutions use regular expressions.
• There are a lot of posts saying that regular expresions should not be used to process html.
• There are lots of answers simply giving a link to the HTMLAgilityPack (on Codeplex) but no real examples of how to use this pack to meet the stated requirements.

So I am looking for the best solution to meet the following requirements.

• I want to provide an allowed list of HTML tags.
• Any tags not in the allowed list should be removed along with their attributes and contents.
• Any tags in the allowed list should be preserved with attributes and contents.
• The solution should cope with differnet localisations - it is possible users using languages and character sets other than those used in English will be used.
• [Added] The solution should handle text such as a forum post as opposed to a full html page - so tags such as b u i etc would be allowed but script div etc are not allowed and should be removed.

I am looking for a C# solution and if its best to use a RegEx then I am happy to do so. If there is an existing library that can do this I am also happy to use them. I would appreciate some example code where possible.

I am looking for a definitive and tried and tested method of solving this problem as opposed to extensive debate + closed posts etc :) :)

Thanks in advance.

Answer 1

You can use the Html Agility Pack for parsing the HTML. Then you can work with the elements the way you like and write it back to HTML again.