sanitizer.py

"""Deprecated from html5lib 1.1.

See `here <https://github.com/html5lib/html5lib-python/issues/443>`_ for
information about its deprecation; `Bleach <https://github.com/mozilla/bleach>`_
is recommended as a replacement. Please let us know in the aforementioned issue
if Bleach is unsuitable for your needs.

"""

import re
import warnings
from xml.sax.saxutils import escape, unescape

from six.moves import urllib_parse as urlparse

from . import base
from ..constants import namespaces, prefixes

__all__ = ["Filter"]


_deprecation_msg = (
    "html5lib's sanitizer is deprecated; see " +
    "https://github.com/html5lib/html5lib-python/issues/443 and please let " +
    "us know if Bleach is unsuitable for your needs"
)

warnings.warn(_deprecation_msg, DeprecationWarning)

allowed_elements = frozenset((
    (namespaces['html'], 'a'),
    (namespaces['html'], 'abbr'),
    (namespaces['html'], 'acronym'),
    (namespaces['html'], 'address'),
    (namespaces['html'], 'area'),
    (namespaces['html'], 'article'),
    (namespaces['html'], 'aside'),
    (namespaces['html'], 'audio'),
    (namespaces['html'], 'b'),
    (namespaces['html'], 'big'),
    (namespaces['html'], 'blockquote'),
    (namespaces['html'], 'br'),
    (namespaces['html'], 'button'),
    (namespaces['html'], 'canvas'),
    (namespaces['html'], 'caption'),
    (namespaces['html'], 'center'),
    (namespaces['html'], 'cite'),
    (namespaces['html'], 'code'),
    (namespaces['html'], 'col'),
    (namespaces['html'], 'colgroup'),
    (namespaces['html'], 'command'),
    (namespaces['html'], 'datagrid'),
    (namespaces['html'], 'datalist'),
    (namespaces['html'], 'dd'),
    (namespaces['html'], 'del'),
    (namespaces['html'], 'details'),
    (namespaces['html'], 'dfn'),
    (namespaces['html'], 'dialog'),
    (namespaces['html'], 'dir'),
    (namespaces['html'], 'div'),
    (namespaces['html'], 'dl'),
    (namespaces['html'], 'dt'),
    (namespaces['html'], 'em'),
    (namespaces['html'], 'event-source'),
    (namespaces['html'], 'fieldset'),
    (namespaces['html'], 'figcaption'),
    (namespaces['html'], 'figure'),
    (namespaces['html'], 'footer'),
    (namespaces['html'], 'font'),
    (namespaces['html'], 'form'),
    (namespaces['html'], 'header'),
    (namespaces['html'], 'h1'),
    (namespaces['html'], 'h2'),
    (namespaces['html'], 'h3'),
    (namespaces['html'], 'h4'),
    (namespaces['html'], 'h5'),
    (namespaces['html'], 'h6'),
    (namespaces['html'], 'hr'),
    (namespaces['html'], 'i'),
    (namespaces['html'], 'img'),
    (namespaces['html'], 'input'),
    (namespaces['html'], 'ins'),
    (namespaces['html'], 'keygen'),
    (namespaces['html'], 'kbd'),
    (namespaces['html'], 'label'),
    (namespaces['html'], 'legend'),
    (namespaces['html'], 'li'),
    (namespaces['html'], 'm'),
    (namespaces['html'], 'map'),
    (namespaces['html'], 'menu'),
    (namespaces['html'], 'meter'),
    (namespaces['html'], 'multicol'),
    (namespaces['html'], 'nav'),
    (namespaces['html'], 'nextid'),
    (namespaces['html'], 'ol'),
    (namespaces['html'], 'output'),
    (namespaces['html'], 'optgroup'),
    (namespaces['html'], 'option'),
    (namespaces['html'], 'p'),
    (namespaces['html'], 'pre'),
    (namespaces['html'], 'progress'),
    (namespaces['html'], 'q'),
    (namespaces['html'], 's'),
    (namespaces['html'], 'samp'),
    (namespaces['html'], 'section'),
    (namespaces['html'], 'select'),
    (namespaces['html'], 'small'),
    (namespaces['html'], 'sound'),
    (namespaces['html'], 'source'),
    (namespaces['html'], 'spacer'),
    (namespaces['html'], 'span'),
    (namespaces['html'], 'strike'),
    (namespaces['html'], 'strong'),
    (namespaces['html'], 'sub'),
    (namespaces['html'], 'summary'),
    (namespaces['html'], 'sup'),
    (namespaces['html'], 'table'),
    (namespaces['html'], 'tbody'),
    (namespaces['html'], 'td'),
    (namespaces['html'], 'textarea'),
    (namespaces['html'], 'time'),
    (namespaces['html'], 'tfoot'),
    (namespaces['html'], 'th'),
    (namespaces['html'], 'thead'),
    (namespaces['html'], 'tr'),
    (namespaces['html'], 'tt'),
    (namespaces['html'], 'u'),
    (namespaces['html'], 'ul'),
    (namespaces['html'], 'var'),
    (namespaces['html'], 'video'),
    (namespaces['html'], 'wbr'),
    (namespaces['mathml'], 'maction'),
    (namespaces['mathml'], 'math'),
    (namespaces['mathml'], 'merror'),
    (namespaces['mathml'], 'mfrac'),
    (namespaces['mathml'], 'mi'),
    (namespaces['mathml'], 'mmultiscripts'),
    (namespaces['mathml'], 'mn'),
    (namespaces['mathml'], 'mo'),
    (namespaces['mathml'], 'mover'),
    (namespaces['mathml'], 'mpadded'),
    (namespaces['mathml'], 'mphantom'),
    (namespaces['mathml'], 'mprescripts'),
    (namespaces['mathml'], 'mroot'),
    (namespaces['mathml'], 'mrow'),
    (namespaces['mathml'], 'mspace'),
    (namespaces['mathml'], 'msqrt'),
    (namespaces['mathml'], 'mstyle'),
    (namespaces['mathml'], 'msub'),
    (namespaces['mathml'], 'msubsup'),
    (namespaces['mathml'], 'msup'),
    (namespaces['mathml'], 'mtable'),
    (namespaces['mathml'], 'mtd'),
    (namespaces['mathml'], 'mtext'),
    (namespaces['mathml'], 'mtr'),
    (namespaces['mathml'], 'munder'),
    (namespaces['mathml'], 'munderover'),
    (namespaces['mathml'], 'none'),
    (namespaces['svg'], 'a'),
    (namespaces['svg'], 'animate'),
    (namespaces['svg'], 'animateColor'),
    (namespaces['svg'], 'animateMotion'),
    (namespaces['svg'], 'animateTransform'),
    (namespaces['svg'], 'clipPath'),
    (namespaces['svg'], 'circle'),
    (namespaces['svg'], 'defs'),
    (namespaces['svg'], 'desc'),
    (namespaces['svg'], 'ellipse'),
    (namespaces['svg'], 'font-face'),
    (namespaces['svg'], 'font-face-name'),
    (namespaces['svg'], 'font-face-src'),
    (namespaces['svg'], 'g'),
    (namespaces['svg'], 'glyph'),
    (namespaces['svg'], 'hkern'),
    (namespaces['svg'], 'linearGradient'),
    (namespaces['svg'], 'line'),
    (namespaces['svg'], 'marker'),
    (namespaces['svg'], 'metadata'),
    (namespaces['svg'], 'missing-glyph'),
    (namespaces['svg'], 'mpath'),
    (namespaces['svg'], 'path'),
    (namespaces['svg'], 'polygon'),
    (namespaces['svg'], 'polyline'),
    (namespaces['svg'], 'radialGradient'),
    (namespaces['svg'], 'rect'),
    (namespaces['svg'], 'set'),
    (namespaces['svg'], 'stop'),
    (namespaces['svg'], 'svg'),
    (namespaces['svg'], 'switch'),
    (namespaces['svg'], 'text'),
    (namespaces['svg'], 'title'),
    (namespaces['svg'], 'tspan'),
    (namespaces['svg'], 'use'),
))

allowed_attributes = frozenset((
    # HTML attributes
    (None, 'abbr'),
    (None, 'accept'),
    (None, 'accept-charset'),
    (None, 'accesskey'),
    (None, 'action'),
    (None, 'align'),
    (None, 'alt'),
    (None, 'autocomplete'),
    (None, 'autofocus'),
    (None, 'axis'),
    (None, 'background'),
    (None, 'balance'),
    (None, 'bgcolor'),
    (None, 'bgproperties'),
    (None, 'border'),
    (None, 'bordercolor'),
    (None, 'bordercolordark'),
    (None, 'bordercolorlight'),
    (None, 'bottompadding'),
    (None, 'cellpadding'),
    (None, 'cellspacing'),
    (None, 'ch'),
    (None, 'challenge'),
    (None, 'char'),
    (None, 'charoff'),
    (None, 'choff'),
    (None, 'charset'),
    (None, 'checked'),
    (None, 'cite'),
    (None, 'class'),
    (None, 'clear'),
    (None, 'color'),
    (None, 'cols'),
    (None, 'colspan'),
    (None, 'compact'),
    (None, 'contenteditable'),
    (None, 'controls'),
    (None, 'coords'),
    (None, 'data'),
    (None, 'datafld'),
    (None, 'datapagesize'),
    (None, 'datasrc'),
    (None, 'datetime'),
    (None, 'default'),
    (None, 'delay'),
    (None, 'dir'),
    (None, 'disabled'),
    (None, 'draggable'),
    (None, 'dynsrc'),
    (None, 'enctype'),
    (None, 'end'),
    (None, 'face'),
    (None, 'for'),
    (None, 'form'),
    (None, 'frame'),
    (None, 'galleryimg'),
    (None, 'gutter'),
    (None, 'headers'),
    (None, 'height'),
    (None, 'hidefocus'),
    (None, 'hidden'),
    (None, 'high'),
    (None, 'href'),
    (None, 'hreflang'),
    (None, 'hspace'),
    (None, 'icon'),
    (None, 'id'),
    (None, 'inputmode'),
    (None, 'ismap'),
    (None, 'keytype'),
    (None, 'label'),
    (None, 'leftspacing'),
    (None, 'lang'),
    (None, 'list'),
    (None, 'longdesc'),
    (None, 'loop'),
    (None, 'loopcount'),
    (None, 'loopend'),
    (None, 'loopstart'),
    (None, 'low'),
    (None, 'lowsrc'),
    (None, 'max'),
    (None, 'maxlength'),
    (None, 'media'),
    (None, 'method'),
    (None, 'min'),
    (None, 'multiple'),
    (None, 'name'),
    (None, 'nohref'),
    (None, 'noshade'),
    (None, 'nowrap'),
    (None, 'open'),
    (None, 'optimum'),
    (None, 'pattern'),
    (None, 'ping'),
    (None, 'point-size'),
    (None, 'poster'),
    (None, 'pqg'),
    (None, 'preload'),
    (None, 'prompt'),
    (None, 'radiogroup'),
    (None, 'readonly'),
    (None, 'rel'),
    (None, 'repeat-max'),
    (None, 'repeat-min'),
    (None, 'replace'),
    (None, 'required'),
    (None, 'rev'),
    (None, 'rightspacing'),
    (None, 'rows'),
    (None, 'rowspan'),
    (None, 'rules'),
    (None, 'scope'),
    (None, 'selected'),
    (None, 'shape'),
    (None, 'size'),
    (None, 'span'),
    (None, 'src'),
    (None, 'start'),
    (None, 'step'),
    (None, 'style'),
    (None, 'summary'),
    (None, 'suppress'),
    (None, 'tabindex'),
    (None, 'target'),
    (None, 'template'),
    (None, 'title'),
    (None, 'toppadding'),
    (None, 'type'),
    (None, 'unselectable'),
    (None, 'usemap'),
    (None, 'urn'),
    (None, 'valign'),
    (None, 'value'),
    (None, 'variable'),
    (None, 'volume'),
    (None, 'vspace'),
    (None, 'vrml'),
    (None, 'width'),
    (None, 'wrap'),
    (namespaces['xml'], 'lang'),
    # MathML attributes
    (None, 'actiontype'),
    (None, 'align'),
    (None, 'columnalign'),
    (None, 'columnalign'),
    (None, 'columnalign'),
    (None, 'columnlines'),
    (None, 'columnspacing'),
    (None, 'columnspan'),
    (None, 'depth'),
    (None, 'display'),
    (None, 'displaystyle'),
    (None, 'equalcolumns'),
    (None, 'equalrows'),
    (None, 'fence'),
    (None, 'fontstyle'),
    (None, 'fontweight'),
    (None, 'frame'),
    (None, 'height'),
    (None, 'linethickness'),
    (None, 'lspace'),
    (None, 'mathbackground'),
    (None, 'mathcolor'),
    (None, 'mathvariant'),
    (None, 'mathvariant'),
    (None, 'maxsize'),
    (None, 'minsize'),
    (None, 'other'),
    (None, 'reversed'),
    (None, 'rowalign'),
    (None, 'rowalign'),
    (None, 'rowalign'),
    (None, 'rowlines'),
    (None, 'rowspacing'),
    (None, 'rowspan'),
    (None, 'rspace'),
    (None, 'scriptlevel'),
    (None, 'selection'),
    (None, 'separator'),
    (None, 'start'),
    (None, 'stretchy'),
    (None, 'width'),
    (None, 'width'),
    (namespaces['xlink'], 'href'),
    (namespaces['xlink'], 'show'),
    (namespaces['xlink'], 'type'),
    # SVG attributes
    (None, 'accent-height'),
    (None, 'accumulate'),
    (None, 'additive'),
    (None, 'alphabetic'),
    (None, 'arabic-form'),
    (None, 'ascent'),
    (None, 'attributeName'),
    (None, 'attributeType'),
    (None, 'baseProfile'),
    (None, 'bbox'),
    (None, 'begin'),
    (None, 'by'),
    (None, 'calcMode'),
    (None, 'cap-height'),
    (None, 'class'),
    (None, 'clip-path'),
    (None, 'color'),
    (None, 'color-rendering'),
    (None, 'content'),
    (None, 'cx'),
    (None, 'cy'),
    (None, 'd'),
    (None, 'dx'),
    (None, 'dy'),
    (None, 'descent'),
    (None, 'display'),
    (None, 'dur'),
    (None, 'end'),
    (None, 'fill'),
    (None, 'fill-opacity'),
    (None, 'fill-rule'),
    (None, 'font-family'),
    (None, 'font-size'),
    (None, 'font-stretch'),
    (None, 'font-style'),
    (None, 'font-variant'),
    (None, 'font-weight'),
    (None, 'from'),
    (None, 'fx'),
    (None, 'fy'),
    (None, 'g1'),
    (None, 'g2'),
    (None, 'glyph-name'),
    (None, 'gradientUnits'),
    (None, 'hanging'),
    (None, 'height'),
    (None, 'horiz-adv-x'),
    (None, 'horiz-origin-x'),
    (None, 'id'),
    (None, 'ideographic'),
    (None, 'k'),
    (None, 'keyPoints'),
    (None, 'keySplines'),
    (None, 'keyTimes'),
    (None, 'lang'),
    (None, 'marker-end'),
    (None, 'marker-mid'),
    (None, 'marker-start'),
    (None, 'markerHeight'),
    (None, 'markerUnits'),
    (None, 'markerWidth'),
    (None, 'mathematical'),
    (None, 'max'),
    (None, 'min'),
    (None, 'name'),
    (None, 'offset'),
    (None, 'opacity'),
    (None, 'orient'),
    (None, 'origin'),
    (None, 'overline-position'),
    (None, 'overline-thickness'),
    (None, 'panose-1'),
    (None, 'path'),
    (None, 'pathLength'),
    (None, 'points'),
    (None, 'preserveAspectRatio'),
    (None, 'r'),
    (None, 'refX'),
    (None, 'refY'),
    (None, 'repeatCount'),
    (None, 'repeatDur'),
    (None, 'requiredExtensions'),
    (None, 'requiredFeatures'),
    (None, 'restart'),
    (None, 'rotate'),
    (None, 'rx'),
    (None, 'ry'),
    (None, 'slope'),
    (None, 'stemh'),
    (None, 'stemv'),
    (None, 'stop-color'),
    (None, 'stop-opacity'),
    (None, 'strikethrough-position'),
    (None, 'strikethrough-thickness'),
    (None, 'stroke'),
    (None, 'stroke-dasharray'),
    (None, 'stroke-dashoffset'),
    (None, 'stroke-linecap'),
    (None, 'stroke-linejoin'),
    (None, 'stroke-miterlimit'),
    (None, 'stroke-opacity'),
    (None, 'stroke-width'),
    (None, 'systemLanguage'),
    (None, 'target'),
    (None, 'text-anchor'),
    (None, 'to'),
    (None, 'transform'),
    (None, 'type'),
    (None, 'u1'),
    (None, 'u2'),
    (None, 'underline-position'),
    (None, 'underline-thickness'),
    (None, 'unicode'),
    (None, 'unicode-range'),
    (None, 'units-per-em'),
    (None, 'values'),
    (None, 'version'),
    (None, 'viewBox'),
    (None, 'visibility'),
    (None, 'width'),
    (None, 'widths'),
    (None, 'x'),
    (None, 'x-height'),
    (None, 'x1'),
    (None, 'x2'),
    (namespaces['xlink'], 'actuate'),
    (namespaces['xlink'], 'arcrole'),
    (namespaces['xlink'], 'href'),
    (namespaces['xlink'], 'role'),
    (namespaces['xlink'], 'show'),
    (namespaces['xlink'], 'title'),
    (namespaces['xlink'], 'type'),
    (namespaces['xml'], 'base'),
    (namespaces['xml'], 'lang'),
    (namespaces['xml'], 'space'),
    (None, 'y'),
    (None, 'y1'),
    (None, 'y2'),
    (None, 'zoomAndPan'),
))

attr_val_is_uri = frozenset((
    (None, 'href'),
    (None, 'src'),
    (None, 'cite'),
    (None, 'action'),
    (None, 'longdesc'),
    (None, 'poster'),
    (None, 'background'),
    (None, 'datasrc'),
    (None, 'dynsrc'),
    (None, 'lowsrc'),
    (None, 'ping'),
    (namespaces['xlink'], 'href'),
    (namespaces['xml'], 'base'),
))

svg_attr_val_allows_ref = frozenset((
    (None, 'clip-path'),
    (None, 'color-profile'),
    (None, 'cursor'),
    (None, 'fill'),
    (None, 'filter'),
    (None, 'marker'),
    (None, 'marker-start'),
    (None, 'marker-mid'),
    (None, 'marker-end'),
    (None, 'mask'),
    (None, 'stroke'),
))

svg_allow_local_href = frozenset((
    (None, 'altGlyph'),
    (None, 'animate'),
    (None, 'animateColor'),
    (None, 'animateMotion'),
    (None, 'animateTransform'),
    (None, 'cursor'),
    (None, 'feImage'),
    (None, 'filter'),
    (None, 'linearGradient'),
    (None, 'pattern'),
    (None, 'radialGradient'),
    (None, 'textpath'),
    (None, 'tref'),
    (None, 'set'),
    (None, 'use')
))

allowed_css_properties = frozenset((
    'azimuth',
    'background-color',
    'border-bottom-color',
    'border-collapse',
    'border-color',
    'border-left-color',
    'border-right-color',
    'border-top-color',
    'clear',
    'color',
    'cursor',
    'direction',
    'display',
    'elevation',
    'float',
    'font',
    'font-family',
    'font-size',
    'font-style',
    'font-variant',
    'font-weight',
    'height',
    'letter-spacing',
    'line-height',
    'max-height',
    'min-height',
    'max-width',
    'min-width',
    'overflow',
    'pause',
    'pause-after',
    'pause-before',
    'pitch',
    'pitch-range',
    'richness',
    'speak',
    'speak-header',
    'speak-numeral',
    'speak-punctuation',
    'speech-rate',
    'stress',
    'text-align',
    'text-decoration',
    'text-indent',
    'unicode-bidi',
    'vertical-align',
    'voice-family',
    'volume',
    'white-space',
    'width',
))

allowed_css_keywords = frozenset((
    'auto',
    'aqua',
    'black',
    'block',
    'blue',
    'bold',
    'both',
    'bottom',
    'brown',
    'center',
    'collapse',
    'dashed',
    'dotted',
    'fuchsia',
    'gray',
    'green',
    '!important',
    'italic',
    'left',
    'lime',
    'maroon',
    'medium',
    'none',
    'navy',
    'normal',
    'nowrap',
    'olive',
    'pointer',
    'purple',
    'red',
    'right',
    'solid',
    'silver',
    'teal',
    'top',
    'transparent',
    'underline',
    'white',
    'yellow',
))

allowed_svg_properties = frozenset((
    'fill',
    'fill-opacity',
    'fill-rule',
    'stroke',
    'stroke-width',
    'stroke-linecap',
    'stroke-linejoin',
    'stroke-opacity',
))

allowed_protocols = frozenset((
    'ed2k',
    'ftp',
    'http',
    'https',
    'irc',
    'mailto',
    'news',
    'gopher',
    'nntp',
    'telnet',
    'webcal',
    'xmpp',
    'callto',
    'feed',
    'urn',
    'aim',
    'rsync',
    'tag',
    'ssh',
    'sftp',
    'rtsp',
    'afs',
    'data',
))

allowed_content_types = frozenset((
    'image/png',
    'image/jpeg',
    'image/gif',
    'image/webp',
    'image/bmp',
    'text/plain',
))


data_content_type = re.compile(r'''
                                ^
                                # Match a content type <application>/<type>
                                (?P<content_type>[-a-zA-Z0-9.]+/[-a-zA-Z0-9.]+)
                                # Match any character set and encoding
                                (?:(?:;charset=(?:[-a-zA-Z0-9]+)(?:;(?:base64))?)
                                  |(?:;(?:base64))?(?:;charset=(?:[-a-zA-Z0-9]+))?)
                                # Assume the rest is data
                                ,.*
                                $
                                ''',
                               re.VERBOSE)


class Filter(base.Filter):
    """Sanitizes token stream of XHTML+MathML+SVG and of inline style attributes"""
    def __init__(self,
                 source,
                 allowed_elements=allowed_elements,
                 allowed_attributes=allowed_attributes,
                 allowed_css_properties=allowed_css_properties,
                 allowed_css_keywords=allowed_css_keywords,
                 allowed_svg_properties=allowed_svg_properties,
                 allowed_protocols=allowed_protocols,
                 allowed_content_types=allowed_content_types,
                 attr_val_is_uri=attr_val_is_uri,
                 svg_attr_val_allows_ref=svg_attr_val_allows_ref,
                 svg_allow_local_href=svg_allow_local_href):
        """Creates a Filter

        :arg allowed_elements: set of elements to allow--everything else will
            be escaped

        :arg allowed_attributes: set of attributes to allow in
            elements--everything else will be stripped

        :arg allowed_css_properties: set of CSS properties to allow--everything
            else will be stripped

        :arg allowed_css_keywords: set of CSS keywords to allow--everything
            else will be stripped

        :arg allowed_svg_properties: set of SVG properties to allow--everything
            else will be removed

        :arg allowed_protocols: set of allowed protocols for URIs

        :arg allowed_content_types: set of allowed content types for ``data`` URIs.

        :arg attr_val_is_uri: set of attributes that have URI values--values
            that have a scheme not listed in ``allowed_protocols`` are removed

        :arg svg_attr_val_allows_ref: set of SVG attributes that can have
            references

        :arg svg_allow_local_href: set of SVG elements that can have local
            hrefs--these are removed

        """
        super(Filter, self).__init__(source)

        warnings.warn(_deprecation_msg, DeprecationWarning)

        self.allowed_elements = allowed_elements
        self.allowed_attributes = allowed_attributes
        self.allowed_css_properties = allowed_css_properties
        self.allowed_css_keywords = allowed_css_keywords
        self.allowed_svg_properties = allowed_svg_properties
        self.allowed_protocols = allowed_protocols
        self.allowed_content_types = allowed_content_types
        self.attr_val_is_uri = attr_val_is_uri
        self.svg_attr_val_allows_ref = svg_attr_val_allows_ref
        self.svg_allow_local_href = svg_allow_local_href

    def __iter__(self):
        for token in base.Filter.__iter__(self):
            token = self.sanitize_token(token)
            if token:
                yield token

    # Sanitize the +html+, escaping all elements not in ALLOWED_ELEMENTS, and
    # stripping out all attributes not in ALLOWED_ATTRIBUTES. Style attributes
    # are parsed, and a restricted set, specified by ALLOWED_CSS_PROPERTIES and
    # ALLOWED_CSS_KEYWORDS, are allowed through. attributes in ATTR_VAL_IS_URI
    # are scanned, and only URI schemes specified in ALLOWED_PROTOCOLS are
    # allowed.
    #
    #   sanitize_html('<script> do_nasty_stuff() </script>')
    #    => &lt;script> do_nasty_stuff() &lt;/script>
    #   sanitize_html('<a href="javascript: sucker();">Click here for $100</a>')
    #    => <a>Click here for $100</a>
    def sanitize_token(self, token):

        # accommodate filters which use token_type differently
        token_type = token["type"]
        if token_type in ("StartTag", "EndTag", "EmptyTag"):
            name = token["name"]
            namespace = token["namespace"]
            if ((namespace, name) in self.allowed_elements or
                (namespace is None and
                 (namespaces["html"], name) in self.allowed_elements)):
                return self.allowed_token(token)
            else:
                return self.disallowed_token(token)
        elif token_type == "Comment":
            pass
        else:
            return token

    def allowed_token(self, token):
        if "data" in token:
            attrs = token["data"]
            attr_names = set(attrs.keys())

            # Remove forbidden attributes
            for to_remove in (attr_names - self.allowed_attributes):
                del token["data"][to_remove]
                attr_names.remove(to_remove)

            # Remove attributes with disallowed URL values
            for attr in (attr_names & self.attr_val_is_uri):
                assert attr in attrs
                # I don't have a clue where this regexp comes from or why it matches those
                # characters, nor why we call unescape. I just know it's always been here.
                # Should you be worried by this comment in a sanitizer? Yes. On the other hand, all
                # this will do is remove *more* than it otherwise would.
                val_unescaped = re.sub("[`\x00-\x20\x7f-\xa0\\s]+", '',
                                       unescape(attrs[attr])).lower()
                # remove replacement characters from unescaped characters
                val_unescaped = val_unescaped.replace("\ufffd", "")
                try:
                    uri = urlparse.urlparse(val_unescaped)
                except ValueError:
                    uri = None
                    del attrs[attr]
                if uri and uri.scheme:
                    if uri.scheme not in self.allowed_protocols:
                        del attrs[attr]
                    if uri.scheme == 'data':
                        m = data_content_type.match(uri.path)
                        if not m:
                            del attrs[attr]
                        elif m.group('content_type') not in self.allowed_content_types:
                            del attrs[attr]

            for attr in self.svg_attr_val_allows_ref:
                if attr in attrs:
                    attrs[attr] = re.sub(r'url\s*\(\s*[^#\s][^)]+?\)',
                                         ' ',
                                         unescape(attrs[attr]))
            if (token["name"] in self.svg_allow_local_href and
                (namespaces['xlink'], 'href') in attrs and re.search(r'^\s*[^#\s].*',
                                                                     attrs[(namespaces['xlink'], 'href')])):
                del attrs[(namespaces['xlink'], 'href')]
            if (None, 'style') in attrs:
                attrs[(None, 'style')] = self.sanitize_css(attrs[(None, 'style')])
            token["data"] = attrs
        return token

    def disallowed_token(self, token):
        token_type = token["type"]
        if token_type == "EndTag":
            token["data"] = "</%s>" % token["name"]
        elif token["data"]:
            assert token_type in ("StartTag", "EmptyTag")
            attrs = []
            for (ns, name), v in token["data"].items():
                attrs.append(' %s="%s"' % (name if ns is None else "%s:%s" % (prefixes[ns], name), escape(v)))
            token["data"] = "<%s%s>" % (token["name"], ''.join(attrs))
        else:
            token["data"] = "<%s>" % token["name"]
        if token.get("selfClosing"):
            token["data"] = token["data"][:-1] + "/>"

        token["type"] = "Characters"

        del token["name"]
        return token

    def sanitize_css(self, style):
        # disallow urls
        style = re.compile(r'url\s*\(\s*[^\s)]+?\s*\)\s*').sub(' ', style)

        # gauntlet
        if not re.match(r"""^([:,;#%.\sa-zA-Z0-9!]|\w-\w|'[\s\w]+'|"[\s\w]+"|\([\d,\s]+\))*$""", style):
            return ''
        if not re.match(r"^\s*([-\w]+\s*:[^:;]*(;\s*|$))*$", style):
            return ''

        clean = []
        for prop, value in re.findall(r"([-\w]+)\s*:\s*([^:;]*)", style):
            if not value:
                continue
            if prop.lower() in self.allowed_css_properties:
                clean.append(prop + ': ' + value + ';')
            elif prop.split('-')[0].lower() in ['background', 'border', 'margin',
                                                'padding']:
                for keyword in value.split():
                    if keyword not in self.allowed_css_keywords and \
                            not re.match(r"^(#[0-9a-fA-F]+|rgb\(\d+%?,\d*%?,?\d*%?\)?|\d{0,2}\.?\d{0,2}(cm|em|ex|in|mm|pc|pt|px|%|,|\))?)$", keyword):  # noqa
                        break
                else:
                    clean.append(prop + ': ' + value + ';')
            elif prop.lower() in self.allowed_svg_properties:
                clean.append(prop + ': ' + value + ';')

        return ' '.join(clean)