Use an HTML5 compliant parser that interprets HTML as a browser would to parse
the Markdown result and then sanitize based on the result.
Escape unrecognized and disallowed HTML in the result.
Currently works with a hard coded whitelist of safe HTML tags and attributes.
If autolink encounters a link which already has an escaped html entity,
it would escape the ampersand again, producing things like these:
& --> &
" --> "
This commit solves that by first looking for all entity-looking things
in the link and copying those ranges verbatim, only considering the rest
of the string for escaping.
Doesn't seem to have considerable performance impact.
The mailto: links are processed the old way.
When the source Markdown contains an anchor tag with URL as link text
(i.e. <a href=...>http://foo.bar</a>), autolink converts that link text
into another anchor tag, which is nonsense. Detect this situation with
regexp and early exit autolink processing.
This drops the naive approach at <script> tag stripping and resorts to
full sanitization of html. The general idea (and the regexps) is grabbed
from Stack Exchange's PageDown JavaScript Markdown processor[1]. Like in
PageDown, it's implemented as a separate pass over resulting html.
Includes a metric ton (but not all) of test cases from here[2]. Several
are commented out since they don't pass yet.
Stronger (but still incomplete) fix for #11.
[1] http://code.google.com/p/pagedown/wiki/PageDown
[2] https://www.owasp.org/index.php/XSS_Filter_Evasion_Cheat_Sheet
