Add option to escape non-whitelisted elements instead of stripping them

[rgrove]

Feature request from Ævar Arnfjörð Bjarmason:

My use case is that I'm calling Sanitize like this:

def clean(html)
  return Sanitize.clean(html, :elements => ['a'],
                   :attributes => {'a' => ['href']},
                   :protocols => {'a' => {'href' => ['http', 'https']}})
end

And this is the output I really want:

clean("<b>") ==> &lt;b&gt;
clean("<b><a href=\"http://example.com\">example</a>") ==> &lt;b&gt;<a href="http://example.com">example</a>

Instead Sanitize will comptetely strip the unacceptable HTML tag.

We should implement a setting to make the stripping optional.

[rgrove]

Turns out this is likely to be quite a bit more complicated to implement than I originally thought, unless we escape the tag and all of its contents, regardless of whether the contents include legal tags.

This is going to take some more thought.

[cluesque]

+1 .. my example is simpler:

clean("a < b") ==> "a &lt; b"

[rgrove]

Added an :escape_only config setting. If set to true, Sanitize will escape non-whitelisted elements and their contents instead of removing them. Closed by 5bbd6d3

Not a perfect solution, but it's the best that can be done without adding unwarranted complexity.

[iangreenleaf]

Looks like this feature was removed in 122c29f. How come?

[rgrove]

Basically for the reason described above. Escaping an element means you must also escape all its children, even if some of them would otherwise be whitelisted. In many cases, double-escaping can result as well. So far I haven't found a solution I'm happy with, and I'd rather have no feature than a buggy feature.