and to the # existing allowlisted elements. Sanitize.fragment(html, Sanitize::Config.merge(Sanitize::Config::BASIC, :elements => Sanitize::Config::BASIC[:elements] + ['div', 'table'], :remove_contents => true )) ``` The example above adds the `

` and `

` elements to a copy of the existing list of elements in `Sanitize::Config::BASIC`. If you instead want to completely overwrite the elements array with your own, you can omit the `+` operation: ```ruby # Overwrite :elements instead of creating a copy with new entries. Sanitize.fragment(html, Sanitize::Config.merge(Sanitize::Config::BASIC, :elements => ['div', 'table'], :remove_contents => true )) ``` ### Config Settings #### :add_attributes (Hash) Attributes to add to specific elements. If the attribute already exists, it will be replaced with the value specified here. Specify all element names and attributes in lowercase. ```ruby :add_attributes => { 'a' => {'rel' => 'nofollow'} } ``` #### :allow_comments (boolean) Whether or not to allow HTML comments. Allowing comments is strongly discouraged, since IE allows script execution within conditional comments. The default value is `false`. #### :allow_doctype (boolean) Whether or not to allow well-formed HTML doctype declarations such as "" when sanitizing a document. This setting is ignored when sanitizing fragments. The default value is `false`. #### :attributes (Hash) Attributes to allow on specific elements. Specify all element names and attributes in lowercase. ```ruby :attributes => { 'a' => ['href', 'title'], 'blockquote' => ['cite'], 'img' => ['alt', 'src', 'title'] } ``` If you'd like to allow certain attributes on all elements, use the symbol `:all` instead of an element name. ```ruby # Allow the class attribute on all elements. :attributes => { :all => ['class'], 'a' => ['href', 'title'] } ``` To allow arbitrary HTML5 `data-*` attributes, use the symbol `:data` in place of an attribute name. ```ruby # Allow arbitrary HTML5 data-* attributes on

elements. :attributes => { 'div' => [:data] } ``` #### :css (Hash) Hash of the following CSS config settings to be used when sanitizing CSS (either standalone or embedded in HTML). ##### :css => :allow_comments (boolean) Whether or not to allow CSS comments. The default value is `false`. ##### :css => :allow_hacks (boolean) Whether or not to allow browser compatibility hacks such as the IE `*` and `_` hacks. These are generally harmless, but technically result in invalid CSS. The default is `false`. ##### :css => :at_rules (Array or Set) Names of CSS [at-rules][at-rules] to allow that may not have associated blocks, such as `import` or `charset`. Names should be specified in lowercase. [at-rules]:https://developer.mozilla.org/en-US/docs/Web/CSS/At-rule ##### :css => :at_rules_with_properties (Array or Set) Names of CSS [at-rules][at-rules] to allow that may have associated blocks containing CSS properties. At-rules like `font-face` and `page` fall into this category. Names should be specified in lowercase. ##### :css => :at_rules_with_styles (Array or Set) Names of CSS [at-rules][at-rules] to allow that may have associated blocks containing style rules. At-rules like `media` and `keyframes` fall into this category. Names should be specified in lowercase. ##### :css => :import_url_validator This is a `Proc` (or other callable object) that will be called and passed the URL specified for any `@import` [at-rules][at-rules]. You can use this to limit what can be imported, for example something like the following to limit `@import` to Google Fonts URLs: ```ruby Proc.new { |url| url.start_with?("https://fonts.googleapis.com") } ``` ##### :css => :properties (Array or Set) List of CSS property names to allow. Names should be specified in lowercase. ##### :css => :protocols (Array or Set) URL protocols to allow in CSS URLs. Should be specified in lowercase. If you'd like to allow the use of relative URLs which don't have a protocol, include the symbol `:relative` in the protocol array. #### :elements (Array or Set) Array of HTML element names to allow. Specify all names in lowercase. Any elements not in this array will be removed. ```ruby :elements => %w[ a abbr b blockquote br cite code dd dfn dl dt em i kbd li mark ol p pre q s samp small strike strong sub sup time u ul var ] ``` **Warning:** Sanitize cannot fully sanitize the contents of `

` or ` `
elements, since these elements don't follow the same parsing rules as the rest
of HTML. If you add `math` or `svg` to the allowlist, you must assume that any
content inside them will be allowed, even if that content would otherwise be
removed by Sanitize.

#### :parser_options (Hash)

[Parsing options](https://github.com/rubys/nokogumbo/tree/v2.0.1#parsing-options) supplied to `nokogumbo`.

```ruby
:parser_options => {
  max_errors: -1,
  max_tree_depth: -1
}
```

#### :protocols (Hash)

URL protocols to allow in specific attributes. If an attribute is listed here
and contains a protocol other than those specified (or if it contains no
protocol at all), it will be removed.

```ruby
:protocols => {
  'a'   => {'href' => ['ftp', 'http', 'https', 'mailto']},
  'img' => {'src'  => ['http', 'https']}
}
```

If you'd like to allow the use of relative URLs which don't have a protocol,
include the symbol `:relative` in the protocol array:

```ruby
:protocols => {
  'a' => {'href' => ['http', 'https', :relative]}
}
```

#### :remove_contents (boolean or Array or Set)

If this is `true`, Sanitize will remove the contents of any non-allowlisted
elements in addition to the elements themselves. By default, Sanitize leaves the
safe parts of an element's contents behind when the element is removed.

If this is an Array or Set of element names, then only the contents of the
specified elements (when filtered) will be removed, and the contents of all
other filtered elements will be left behind.

The default value is `%w[iframe math noembed noframes noscript plaintext script style svg xmp]`.

#### :transformers (Array or callable)

Custom HTML transformer or array of custom transformers. See the Transformers
section below for details.

#### :whitespace_elements (Hash)

Hash of element names which, when removed, should have their contents surrounded
by whitespace to preserve readability.

Each element name is a key pointing to another Hash, which provides the specific
whitespace that should be inserted `:before` and `:after` the removed element's
position. The `:after` value will only be inserted if the removed element has
children, in which case it will be inserted after those children.

```ruby
:whitespace_elements => {
  'br'  => { :before => "\n", :after => "" },
  'div' => { :before => "\n", :after => "\n" },
  'p'   => { :before => "\n", :after => "\n" }
}
```

The default elements with whitespace added before and after are:

```
address article aside blockquote br dd div dl dt
footer h1 h2 h3 h4 h5 h6 header hgroup hr li nav
ol p pre section ul

```

## Transformers

Transformers allow you to filter and modify HTML nodes using your own custom
logic, on top of (or instead of) Sanitize's core filter. A transformer is any
object that responds to `call()` (such as a lambda or proc).

To use one or more transformers, pass them to the `:transformers` config
setting. You may pass a single transformer or an array of transformers.

```ruby
Sanitize.fragment(html, :transformers => [
  transformer_one,
  transformer_two
])
```

### Input

Each transformer's `call()` method will be called once for each node in the HTML
(including elements, text nodes, comments, etc.), and will receive as an
argument a Hash that contains the following items:

  * **:config** - The current Sanitize configuration Hash.

  * **:is_allowlisted** - `true` if the current node has been allowlisted by a
    previous transformer, `false` otherwise. It's generally bad form to remove
    a node that a previous transformer has allowlisted.

  * **:node** - A `Nokogiri::XML::Node` object representing an HTML node. The
    node may be an element, a text node, a comment, a CDATA node, or a document
    fragment. Use Nokogiri's inspection methods (`element?`, `text?`, etc.) to
    selectively ignore node types you aren't interested in.

  * **:node_allowlist** - Set of `Nokogiri::XML::Node` objects in the current
    document that have been allowlisted by previous transformers, if any. It's
    generally bad form to remove a node that a previous transformer has
    allowlisted.

  * **:node_name** - The name of the current HTML node, always lowercase (e.g.
    "div" or "span"). For non-element nodes, the name will be something like
    "text", "comment", "#cdata-section", "#document-fragment", etc.

### Output

A transformer doesn't have to return anything, but may optionally return a Hash,
which may contain the following items:

  * **:node_allowlist** -  Array or Set of specific `Nokogiri::XML::Node`
    objects to add to the document's allowlist, bypassing the current Sanitize
    config. These specific nodes and all their attributes will be allowlisted,
    but their children will not be.

If a transformer returns anything other than a Hash, the return value will be
ignored.

### Processing

Each transformer has full access to the `Nokogiri::XML::Node` that's passed into
it and to the rest of the document via the node's `document()` method. Any
changes made to the current node or to the document will be reflected instantly
in the document and passed on to subsequently called transformers and to
Sanitize itself. A transformer may even call Sanitize internally to perform
custom sanitization if needed.

Nodes are passed into transformers in the order in which they're traversed.
Sanitize performs top-down traversal, meaning that nodes are traversed in the
same order you'd read them in the HTML, starting at the top node, then its first
child, and so on.

```ruby
html = %[

foo

bar

] transformer = lambda do |env| puts env[:node_name] if env[:node].element? end # Prints "header", "span", "strong", "p", "footer". Sanitize.fragment(html, :transformers => transformer) ``` Transformers have a tremendous amount of power, including the power to completely bypass Sanitize's built-in filtering. Be careful! Your safety is in your own hands. ### Example: Transformer to allow image URLs by domain The following example demonstrates how to remove image elements unless they use a relative URL or are hosted on a specific domain. It assumes that the `` element and its `src` attribute are already allowlisted. ```ruby require 'uri' image_allowlist_transformer = lambda do |env| # Ignore everything except elements. return unless env[:node_name] == 'img' node = env[:node] image_uri = URI.parse(node['src']) # Only allow relative URLs or URLs with the example.com domain. The # image_uri.host.nil? check ensures that protocol-relative URLs like # "//evil.com/foo.jpg". unless image_uri.host == 'example.com' || (image_uri.host.nil? && image_uri.relative?) node.unlink # `Nokogiri::XML::Node#unlink` removes a node from the document end end ``` ### Example: Transformer to allow YouTube video embeds The following example demonstrates how to create a transformer that will safely allow valid YouTube video embeds without having to allow other kinds of embedded content, which would be the case if you tried to do this by just allowing all ` ] Sanitize.fragment(html, :transformers => youtube_transformer) # => '' ``` License ------- Copyright (c) 2015 Ryan Grove (ryan@wonko.com) Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.