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Sanitize.js

Sanitize.js is a whitelist-based HTML sanitizer. Given a list of acceptable elements and attributes, Sanitize.js will remove all unacceptable HTML from a DOM node.

Using a simple configuration syntax, you can tell Sanitize to allow certain elements, certain attributes within those elements, and even certain URL protocols within attributes that contain URLs. Any HTML elements or attributes that you don't explicitly allow will be removed.

Because it's working directly with the DOM tree, rather than a bunch of fragile regular expressions, Sanitize.js has no trouble dealing with malformed or maliciously-formed HTML, and will always output valid HTML or XHTML.

Sanitize.js heavily inspired by the Ruby Sanitize library (http://github.com/rgrove/sanitize). It tries to port it as faithful as possible.

Author: Gabriel Birke (mailto:gabriel@lebenplusplus.de)
Version: 1.0
Copyright: Copyright (c) 2010 Gabriel Birke. All rights reserved.
License: MIT License (http://opensource.org/licenses/mit-license.php)
Website: http://github.com/gbirke/Sanitize.js

Usage

If you don't specify any configuration options, Sanitize will use its strictest settings by default, which means it will strip all HTML and leave only text behind.
HTML:

<p id="para1"><b><a href="http://foo.com/">foo</a></b><img src="http://foo.com/bar.jpg" /></p>

JavaScript:

var p = document.getElementById('para1');
var s = new Sanitize();
alert(s.clean_node(p)); // => 'foo'

The original node won't be changed, what you get back is a document fragment with the sanitized child nodes (and their complete contents) of the original DOM node.

Configuration

In addition to the ultra-safe default settings that leave just the plain text behind, Sanitize comes with three other built-in modes. The modes reside in separate JavaScript files that must loaded additionally to the sanitize.js file.

Sanitize.Config.RESTRICTED

Allows only very simple inline formatting markup. No links, images, or block elements.

var s = new Sanitize(Sanitize.Config.RESTRICTED);
alert(s.clean_node(p)); // => '<b>foo</b>'

Sanitize.Config.BASIC

Allows a variety of markup including formatting tags, links, and lists. Images and tables are not allowed, links are limited to FTP, HTTP, HTTPS, and mailto protocols, and a rel="nofollow" attribute is added to all links to mitigate SEO spam.

var s = new Sanitize(Sanitize.Config.BASIC);
alert(s.clean_node(p));
// => '<b><a href="http://foo.com/" rel="nofollow">foo</a></b>'

Sanitize.Config.RELAXED

Allows an even wider variety of markup than BASIC, including images and tables. Links are still limited to FTP, HTTP, HTTPS, and mailto protocols, while images are limited to HTTP and HTTPS. In this mode, rel="nofollow" is not added to links.

var s = new Sanitize(Sanitize.Config.RELAXED);
alert(s.clean_node(p));
// => '<b><a href="http://foo.com/">foo</a></b><img src="http://foo.com/bar.jpg" />'

Configuration object parameters

If the built-in modes don't meet your needs, you can easily specify a custom configuration:

var s = new Sanitize({ 
    elements:   ['a', 'span'],
    attributes: { 
        a: ['href', 'title'], 
        span: ['class'] 
    },
    protocols:  { 
        a: { href: ['http', 'https', 'mailto'] }
    }
});
s.clean_node(p);

add_attributes (Object)

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.

add_attributes: {
    a: {'rel': 'nofollow'}
}

attributes (Object)

Attributes to allow for specific elements. Specify all element names and attributes in lowercase.

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.

attributes: {
    '__ALL__': ['class'],
    a: ['href', 'title']
}

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.

dom (DOM document)

An object that implements a DOM document interface. It is mainly used to create new element, attribute and document fragment nodes.

If you are using Sanitize in the browser, this will default to the global document variable. If you are using it on the server side, you must provide your own DOM implementation.

elements (Array)

Array of element names to allow. Specify all names in lowercase.

elements: [
    'a', 'b', 'blockquote', 'br', 'cite', 'code', 'dd', 'dl', 'dt', 'em',
    'i', 'li', 'ol', 'p', 'pre', 'q', 'small', 'strike', 'strong', 'sub',
    'sup', 'u', 'ul'
]

protocols (Object)

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.

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 variable Sanitize.RELATIVE in the protocol array:

protocols: {
    a: { href: ['http', 'https', Sanitize.RELATIVE]}
}

Note however, that the HTML parser of Internet Explorer automatically converts relative URLs into absolute URLs with http protocol.

remove_contents (boolean or Array)

If set to true, Sanitize will remove the contents of any non-whitelisted 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 set to an Array 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 false.

transformers (Array)

See below.

Transformers

Transformers allow you to filter and alter nodes using your own custom logic, on top of (or instead of) Sanitize's core filter. A transformer is a function that returns either null or an Object containing certain optional response values.

To use one or more transformers, pass them to the transformers config setting:

var s = new Sanitize({ transformers: [transformer_one, transformer_two]});

Input

Each registered transformer function will be called once for each element node in the HTML, and will receive as an argument an environment Object that contains the following items:

allowed_elements : Object with whitelisted element names as keys, to facilitate fast lookups of whitelisted elements.

config : The current Sanitize configuration Hash.

dom : A DOM document object.

node A DOM node object representing an HTML element.

node_name : The name of the current HTML node, always lowercase (e.g. "div" or "span").

whitelist_nodes : Array of DOM nodes that have already been whitelisted by previous transformers, if any.

Processing

Each transformer has full access to the DOM node that's passed into it and to the rest of the document via the node's DOM methods method. Any changes will be 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.

Transformers have a tremendous amount of power, including the power to completely bypass Sanitize's built-in filtering. Be careful!

Output

A transformer may return either null or an Object. A return value of null indicates that the transformer does not wish to act on the current node in any way. A returned Object may contain the following items, all of which are optional:

attr_whitelist : Array of attribute names to add to the whitelist for the current node, in addition to any whitelisted attributes already defined in the current config.

node : DOM node object that should replace the current node. All subsequent transformers and Sanitize itself will receive this new node.

whitelist : If true, the current node (and only the current node) will be whitelisted, regardless of the current Sanitize config.

whitelist_nodes : Array of specific DOM node objects to whitelist, anywhere in the document, regardless of the current Sanitize config.

Known Bugs and Limitations

  • The style attribute is always dropped on Internet Explorer 5-7.
  • Internet Explorer always converts relative URL values to absolute URLs.

Contributors

The following lovely people have contributed to Sanitize in the form of patches or ideas that later became code:

License

Copyright (c) 2010 Gabriel Birke gabriel@lebenplusplus.de

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.