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+# Loofah
+
+* https://github.com/flavorjones/loofah
+* http://rubydoc.info/github/flavorjones/loofah/master/frames
+* http://librelist.com/browser/loofah
+
+## Status
+
+|System|Status|
+|--|--|
+| Concourse | [![Concourse CI](https://ci.nokogiri.org/api/v1/teams/nokogiri-core/pipelines/loofah/jobs/ruby-2.5/badge)](https://ci.nokogiri.org/teams/nokogiri-core/pipelines/loofah?groups=master) |
+| Code Climate | [![Code Climate](https://codeclimate.com/github/flavorjones/loofah.svg)](https://codeclimate.com/github/flavorjones/loofah) |
+| Version Eye | [![Version Eye](https://www.versioneye.com/ruby/loofah/badge.png)](https://www.versioneye.com/ruby/loofah) |
+
+
+## Description
+
+Loofah is a general library for manipulating and transforming HTML/XML
+documents and fragments. It's built on top of Nokogiri and libxml2, so
+it's fast and has a nice API.
+
+Loofah excels at HTML sanitization (XSS prevention). It includes some
+nice HTML sanitizers, which are based on HTML5lib's whitelist, so it
+most likely won't make your codes less secure. (These statements have
+not been evaluated by Netexperts.)
+
+ActiveRecord extensions for sanitization are available in the
+[`loofah-activerecord` gem](https://github.com/flavorjones/loofah-activerecord).
+
+
+## Features
+
+* Easily write custom scrubbers for HTML/XML leveraging the sweetness of Nokogiri (and HTML5lib's whitelists).
+* Common HTML sanitizing tasks are built-in:
+  * _Strip_ unsafe tags, leaving behind only the inner text.
+  * _Prune_ unsafe tags and their subtrees, removing all traces that they ever existed.
+  * _Escape_ unsafe tags and their subtrees, leaving behind lots of <tt>&lt;</tt> and <tt>&gt;</tt> entities.
+  * _Whitewash_ the markup, removing all attributes and namespaced nodes.
+* Common HTML transformation tasks are built-in:
+  * Add the _nofollow_ attribute to all hyperlinks.
+* Format markup as plain text, with or without sensible whitespace handling around block elements.
+* Replace Rails's `strip_tags` and `sanitize` view helper methods.
+
+
+## Compare and Contrast
+
+Loofah is one of two known Ruby XSS/sanitization solutions that
+guarantees well-formed and valid markup (the other is Sanitize, which
+also uses Nokogiri).
+
+Loofah works on XML, XHTML and HTML documents.
+
+Also, it's pretty fast. Here is a benchmark comparing Loofah to other
+commonly-used libraries (ActionView, Sanitize, HTML5lib and HTMLfilter):
+
+* https://gist.github.com/170193
+
+Lastly, Loofah is extensible. It's super-easy to write your own custom
+scrubbers for whatever document manipulation you need. You don't like
+the built-in scrubbers? Build your own, like a boss.
+
+
+## The Basics
+
+Loofah wraps [Nokogiri](http://nokogiri.org) in a loving
+embrace. Nokogiri is an excellent HTML/XML parser. If you don't know
+how Nokogiri works, you might want to pause for a moment and go check
+it out. I'll wait.
+
+Loofah presents the following classes:
+
+* `Loofah::HTML::Document` and `Loofah::HTML::DocumentFragment`
+* `Loofah::XML::Document` and `Loofah::XML::DocumentFragment`
+* `Loofah::Scrubber`
+
+The documents and fragments are subclasses of the similar Nokogiri classes.
+
+The Scrubber represents the document manipulation, either by wrapping
+a block,
+
+``` ruby
+span2div = Loofah::Scrubber.new do |node|
+  node.name = "div" if node.name == "span"
+end
+```
+
+or by implementing a method.
+
+
+### Side Note: Fragments vs Documents
+
+Generally speaking, unless you expect to have a DOCTYPE and a single
+root node, you don't have a *document*, you have a *fragment*. For
+HTML, another rule of thumb is that *documents* have `html` and `body`
+tags, and *fragments* usually do not.
+
+HTML fragments should be parsed with Loofah.fragment. The result won't
+be wrapped in `html` or `body` tags, won't have a DOCTYPE declaration,
+`head` elements will be silently ignored, and multiple root nodes are
+allowed.
+
+XML fragments should be parsed with Loofah.xml_fragment. The result
+won't have a DOCTYPE declaration, and multiple root nodes are allowed.
+
+HTML documents should be parsed with Loofah.document. The result will
+have a DOCTYPE declaration, along with `html`, `head` and `body` tags.
+
+XML documents should be parsed with Loofah.xml_document. The result
+will have a DOCTYPE declaration and a single root node.
+
+
+### Loofah::HTML::Document and Loofah::HTML::DocumentFragment
+
+These classes are subclasses of Nokogiri::HTML::Document and
+Nokogiri::HTML::DocumentFragment, so you get all the markup
+fixer-uppery and API goodness of Nokogiri.
+
+The module methods Loofah.document and Loofah.fragment will parse an
+HTML document and an HTML fragment, respectively.
+
+``` ruby
+Loofah.document(unsafe_html).is_a?(Nokogiri::HTML::Document)         # => true
+Loofah.fragment(unsafe_html).is_a?(Nokogiri::HTML::DocumentFragment) # => true
+```
+
+Loofah injects a `scrub!` method, which takes either a symbol (for
+built-in scrubbers) or a Loofah::Scrubber object (for custom
+scrubbers), and modifies the document in-place.
+
+Loofah overrides `to_s` to return HTML:
+
+``` ruby
+unsafe_html = "ohai! <div>div is safe</div> <script>but script is not</script>"
+
+doc = Loofah.fragment(unsafe_html).scrub!(:prune)
+doc.to_s    # => "ohai! <div>div is safe</div> "
+```
+
+and `text` to return plain text:
+
+``` ruby
+doc.text    # => "ohai! div is safe "
+```
+
+Also, `to_text` is available, which does the right thing with
+whitespace around block-level elements.
+
+``` ruby
+doc = Loofah.fragment("<h1>Title</h1><div>Content</div>")
+doc.text    # => "TitleContent"           # probably not what you want
+doc.to_text # => "\nTitle\n\nContent\n"   # better
+```
+
+### Loofah::XML::Document and Loofah::XML::DocumentFragment
+
+These classes are subclasses of Nokogiri::XML::Document and
+Nokogiri::XML::DocumentFragment, so you get all the markup
+fixer-uppery and API goodness of Nokogiri.
+
+The module methods Loofah.xml_document and Loofah.xml_fragment will
+parse an XML document and an XML fragment, respectively.
+
+``` ruby
+Loofah.xml_document(bad_xml).is_a?(Nokogiri::XML::Document)         # => true
+Loofah.xml_fragment(bad_xml).is_a?(Nokogiri::XML::DocumentFragment) # => true
+```
+
+### Nodes and NodeSets
+
+Nokogiri::XML::Node and Nokogiri::XML::NodeSet also get a `scrub!`
+method, which makes it easy to scrub subtrees.
+
+The following code will apply the `employee_scrubber` only to the
+`employee` nodes (and their subtrees) in the document:
+
+``` ruby
+Loofah.xml_document(bad_xml).xpath("//employee").scrub!(employee_scrubber)
+```
+
+And this code will only scrub the first `employee` node and its subtree:
+
+``` ruby
+Loofah.xml_document(bad_xml).at_xpath("//employee").scrub!(employee_scrubber)
+```
+
+### Loofah::Scrubber
+
+A Scrubber wraps up a block (or method) that is run on a document node:
+
+``` ruby
+# change all <span> tags to <div> tags
+span2div = Loofah::Scrubber.new do |node|
+  node.name = "div" if node.name == "span"
+end
+```
+
+This can then be run on a document:
+
+``` ruby
+Loofah.fragment("<span>foo</span><p>bar</p>").scrub!(span2div).to_s
+# => "<div>foo</div><p>bar</p>"
+```
+
+Scrubbers can be run on a document in either a top-down traversal (the
+default) or bottom-up. Top-down scrubbers can optionally return
+Scrubber::STOP to terminate the traversal of a subtree. Read below and
+in the Loofah::Scrubber class for more detailed usage.
+
+Here's an XML example:
+
+``` ruby
+# remove all <employee> tags that have a "deceased" attribute set to true
+bring_out_your_dead = Loofah::Scrubber.new do |node|
+  if node.name == "employee" and node["deceased"] == "true"
+    node.remove
+    Loofah::Scrubber::STOP # don't bother with the rest of the subtree
+  end
+end
+Loofah.xml_document(File.read('plague.xml')).scrub!(bring_out_your_dead)
+```
+
+=== Built-In HTML Scrubbers
+
+Loofah comes with a set of sanitizing scrubbers that use HTML5lib's
+whitelist algorithm:
+
+``` ruby
+doc.scrub!(:strip)       # replaces unknown/unsafe tags with their inner text
+doc.scrub!(:prune)       #  removes unknown/unsafe tags and their children
+doc.scrub!(:escape)      #  escapes unknown/unsafe tags, like this: &lt;script&gt;
+doc.scrub!(:whitewash)   #  removes unknown/unsafe/namespaced tags and their children,
+                         #          and strips all node attributes
+```
+
+Loofah also comes with some common transformation tasks: 
+
+``` ruby
+doc.scrub!(:nofollow)    #     adds rel="nofollow" attribute to links
+doc.scrub!(:unprintable) #  removes unprintable characters from text nodes
+```
+
+See Loofah::Scrubbers for more details and example usage.
+
+
+### Chaining Scrubbers
+
+You can chain scrubbers:
+
+``` ruby
+Loofah.fragment("<span>hello</span> <script>alert('OHAI')</script>") \
+      .scrub!(:prune) \
+      .scrub!(span2div).to_s
+# => "<div>hello</div> "
+```
+
+### Shorthand
+
+The class methods Loofah.scrub_fragment and Loofah.scrub_document are
+shorthand.
+
+``` ruby
+Loofah.scrub_fragment(unsafe_html, :prune)
+Loofah.scrub_document(unsafe_html, :prune)
+Loofah.scrub_xml_fragment(bad_xml, custom_scrubber)
+Loofah.scrub_xml_document(bad_xml, custom_scrubber)
+```
+
+are the same thing as (and arguably semantically clearer than):
+
+``` ruby
+Loofah.fragment(unsafe_html).scrub!(:prune)
+Loofah.document(unsafe_html).scrub!(:prune)
+Loofah.xml_fragment(bad_xml).scrub!(custom_scrubber)
+Loofah.xml_document(bad_xml).scrub!(custom_scrubber)
+```
+
+
+### View Helpers
+
+Loofah has two "view helpers": Loofah::Helpers.sanitize and
+Loofah::Helpers.strip_tags, both of which are drop-in replacements for
+the Rails ActionView helpers of the same name.
+These are no longer required automatically. You must require `loofah/helpers`. 
+
+
+## Requirements
+
+* Nokogiri >= 1.5.9
+
+
+## Installation
+
+Unsurprisingly:
+
+* gem install loofah
+
+
+## Support
+
+The bug tracker is available here:
+
+* https://github.com/flavorjones/loofah/issues
+
+And the mailing list is on librelist:
+
+* loofah@librelist.com / http://librelist.com
+
+And the IRC channel is \#loofah on freenode.
+
+
+## Security
+
+Some tools may incorrectly report loofah is a potential security
+vulnerability. Loofah depends on Nokogiri, and it's possible to use
+Nokogiri in a dangerous way (by enabling its DTDLOAD option and
+disabling its NONET option).  This dangerous Nokogiri configuration,
+which is sometimes used by other components, can create an XML
+External Entity (XXE) vulnerability if the XML data is not trusted.
+However, loofah never enables this dangerous Nokogiri configuration;
+loofah never enables DTDLOAD, and it never disables NONET.
+
+
+## Related Links
+
+* Nokogiri: http://nokogiri.org
+* libxml2: http://xmlsoft.org
+* html5lib: https://code.google.com/p/html5lib
+
+
+## Authors
+
+* [Mike Dalessio](http://mike.daless.io) ([@flavorjones](https://twitter.com/flavorjones))
+* Bryan Helmkamp
+
+Featuring code contributed by:
+
+* Aaron Patterson
+* John Barnette
+* Josh Owens
+* Paul Dix
+* Luke Melia
+
+And a big shout-out to Corey Innis for the name, and feedback on the API.
+
+
+## Thank You
+
+The following people have generously donated via the Pledgie[http://pledgie.com] badge on the {Loofah github page}[https://github.com/flavorjones/loofah]:
+
+* Bill Harding
+
+
+## Historical Note
+
+This library was formerly known as Dryopteris, which was a very bad
+name that nobody could spell properly.
+
+
+## License
+
+Distributed under the MIT License. See `MIT-LICENSE.txt` for details.