How to safely HTML encode content which may already be HTML encoded?

Question

I need to HTML encode some text which may or may not already be HTML encoded (perhaps only partially). Is the following safe? Are there any characters/encodings that could cause unexpected behaviour?

HttpUtility.HtmlEncode(HttpUtility.HtmlDecode(text))

Thanks

Answer 1

Your logic " HttpUtility.HtmlEncode(HttpUtility.HtmlDecode(text)) " is safe. There is a standard for HTML characters encoding. Take a look.

Answer 2

There is no built-in functionality. But I would use:

 return 
     HttpUtility.HtmlDecode(text)!=text ? text : HttpUtility.HtmlEncode(text);