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# cython: language_level=3str
"""A cleanup tool for HTML.
Removes unwanted tags and content. See the `Cleaner` class for
details.
"""
import copy
import re
from urllib.parse import urlsplit, unquote_plus
from lxml import etree
from lxml.html import defs
from lxml.html import fromstring, XHTML_NAMESPACE
from lxml.html import xhtml_to_html, _transform_result
__all__ = ['clean_html', 'clean', 'Cleaner', 'autolink', 'autolink_html',
'word_break', 'word_break_html']
# Look at http://code.sixapart.com/trac/livejournal/browser/trunk/cgi-bin/cleanhtml.pl
# Particularly the CSS cleaning; most of the tag cleaning is integrated now
# I have multiple kinds of schemes searched; but should schemes be
# whitelisted instead?
# max height?
# remove images? Also in CSS? background attribute?
# Some way to whitelist object, iframe, etc (e.g., if you want to
# allow *just* embedded YouTube movies)
# Log what was deleted and why?
# style="behavior: ..." might be bad in IE?
# Should we have something for just <meta http-equiv>? That's the worst of the
# metas.
# UTF-7 detections? Example:
# <HEAD><META HTTP-EQUIV="CONTENT-TYPE" CONTENT="text/html; charset=UTF-7"> </HEAD>+ADw-SCRIPT+AD4-alert('XSS');+ADw-/SCRIPT+AD4-
# you don't always have to have the charset set, if the page has no charset
# and there's UTF7-like code in it.
# Look at these tests: http://htmlpurifier.org/live/smoketests/xssAttacks.php
# This is an IE-specific construct you can have in a stylesheet to
# run some Javascript:
_replace_css_javascript = re.compile(
r'expression\s*\(.*?\)', re.S|re.I).sub
# Do I have to worry about @\nimport?
_replace_css_import = re.compile(
r'@\s*import', re.I).sub
_looks_like_tag_content = re.compile(
r'</?[a-zA-Z]+|\son[a-zA-Z]+\s*=',
(re.ASCII)).search
# All kinds of schemes besides just javascript: that can cause
# execution:
_find_image_dataurls = re.compile(
r'data:image/(.+);base64,', re.I).findall
_possibly_malicious_schemes = re.compile(
r'(javascript|jscript|livescript|vbscript|data|about|mocha):',
re.I).findall
# SVG images can contain script content
_is_unsafe_image_type = re.compile(r"(xml|svg)", re.I).search
def _has_javascript_scheme(s):
safe_image_urls = 0
for image_type in _find_image_dataurls(s):
if _is_unsafe_image_type(image_type):
return True
safe_image_urls += 1
return len(_possibly_malicious_schemes(s)) > safe_image_urls
_substitute_whitespace = re.compile(r'[\s\x00-\x08\x0B\x0C\x0E-\x19]+').sub
# FIXME: check against: http://msdn2.microsoft.com/en-us/library/ms537512.aspx
_conditional_comment_re = re.compile(
r'\[if[\s\n\r]+.*?][\s\n\r]*>', re.I|re.S)
_find_styled_elements = etree.XPath(
"descendant-or-self::*[@style]")
_find_external_links = etree.XPath(
("descendant-or-self::a [normalize-space(@href) and substring(normalize-space(@href),1,1) != '#'] |"
"descendant-or-self::x:a[normalize-space(@href) and substring(normalize-space(@href),1,1) != '#']"),
namespaces={'x':XHTML_NAMESPACE})
class Cleaner:
"""
Instances cleans the document of each of the possible offending
elements. The cleaning is controlled by attributes; you can
override attributes in a subclass, or set them in the constructor.
``scripts``:
Removes any ``<script>`` tags.
``javascript``:
Removes any Javascript, like an ``onclick`` attribute. Also removes stylesheets
as they could contain Javascript.
``comments``:
Removes any comments.
``style``:
Removes any style tags.
``inline_style``
Removes any style attributes. Defaults to the value of the ``style`` option.
``links``:
Removes any ``<link>`` tags
``meta``:
Removes any ``<meta>`` tags
``page_structure``:
Structural parts of a page: ``<head>``, ``<html>``, ``<title>``.
``processing_instructions``:
Removes any processing instructions.
``embedded``:
Removes any embedded objects (flash, iframes)
``frames``:
Removes any frame-related tags
``forms``:
Removes any form tags
``annoying_tags``:
Tags that aren't *wrong*, but are annoying. ``<blink>`` and ``<marquee>``
``remove_tags``:
A list of tags to remove. Only the tags will be removed,
their content will get pulled up into the parent tag.
``kill_tags``:
A list of tags to kill. Killing also removes the tag's content,
i.e. the whole subtree, not just the tag itself.
``allow_tags``:
A list of tags to include (default include all).
``remove_unknown_tags``:
Remove any tags that aren't standard parts of HTML.
``safe_attrs_only``:
If true, only include 'safe' attributes (specifically the list
from the feedparser HTML sanitisation web site).
``safe_attrs``:
A set of attribute names to override the default list of attributes
considered 'safe' (when safe_attrs_only=True).
``add_nofollow``:
If true, then any <a> tags will have ``rel="nofollow"`` added to them.
``host_whitelist``:
A list or set of hosts that you can use for embedded content
(for content like ``<object>``, ``<link rel="stylesheet">``, etc).
You can also implement/override the method
``allow_embedded_url(el, url)`` or ``allow_element(el)`` to
implement more complex rules for what can be embedded.
Anything that passes this test will be shown, regardless of
the value of (for instance) ``embedded``.
Note that this parameter might not work as intended if you do not
make the links absolute before doing the cleaning.
Note that you may also need to set ``whitelist_tags``.
``whitelist_tags``:
A set of tags that can be included with ``host_whitelist``.
The default is ``iframe`` and ``embed``; you may wish to
include other tags like ``script``, or you may want to
implement ``allow_embedded_url`` for more control. Set to None to
include all tags.
This modifies the document *in place*.
"""
scripts = True
javascript = True
comments = True
style = False
inline_style = None
links = True
meta = True
page_structure = True
processing_instructions = True
embedded = True
frames = True
forms = True
annoying_tags = True
remove_tags = ()
allow_tags = ()
kill_tags = ()
remove_unknown_tags = True
safe_attrs_only = True
safe_attrs = defs.safe_attrs
add_nofollow = False
host_whitelist = ()
whitelist_tags = {'iframe', 'embed'}
def __init__(self, **kw):
not_an_attribute = object()
for name, value in kw.items():
default = getattr(self, name, not_an_attribute)
if default is None or default is True or default is False:
pass
elif isinstance(default, (frozenset, set, tuple, list)):
# Catch common error of passing ('host') instead of a tuple.
if isinstance(value, str):
raise TypeError(
f"Expected a collection, got str: {name}={value!r}")
else:
raise TypeError(
f"Unknown parameter: {name}={value!r}")
setattr(self, name, value)
if self.inline_style is None and 'inline_style' not in kw:
self.inline_style = self.style
if kw.get("allow_tags"):
if kw.get("remove_unknown_tags"):
raise ValueError("It does not make sense to pass in both "
"allow_tags and remove_unknown_tags")
self.remove_unknown_tags = False
self.host_whitelist = frozenset(self.host_whitelist) if self.host_whitelist else ()
# Used to lookup the primary URL for a given tag that is up for
# removal:
_tag_link_attrs = dict(
script='src',
link='href',
# From: http://java.sun.com/j2se/1.4.2/docs/guide/misc/applet.html
# From what I can tell, both attributes can contain a link:
applet=['code', 'object'],
iframe='src',
embed='src',
layer='src',
# FIXME: there doesn't really seem like a general way to figure out what
# links an <object> tag uses; links often go in <param> tags with values
# that we don't really know. You'd have to have knowledge about specific
# kinds of plugins (probably keyed off classid), and match against those.
##object=?,
# FIXME: not looking at the action currently, because it is more complex
# than than -- if you keep the form, you should keep the form controls.
##form='action',
a='href',
)
def __call__(self, doc):
"""
Cleans the document.
"""
try:
getroot = doc.getroot
except AttributeError:
pass # Element instance
else:
doc = getroot() # ElementTree instance, instead of an element
# convert XHTML to HTML
xhtml_to_html(doc)
# Normalize a case that IE treats <image> like <img>, and that
# can confuse either this step or later steps.
for el in doc.iter('image'):
el.tag = 'img'
if not self.comments:
# Of course, if we were going to kill comments anyway, we don't
# need to worry about this
self.kill_conditional_comments(doc)
kill_tags = set(self.kill_tags or ())
remove_tags = set(self.remove_tags or ())
allow_tags = set(self.allow_tags or ())
if self.scripts:
kill_tags.add('script')
if self.safe_attrs_only:
safe_attrs = set(self.safe_attrs)
for el in doc.iter(etree.Element):
attrib = el.attrib
for aname in attrib.keys():
if aname not in safe_attrs:
del attrib[aname]
if self.javascript:
if not (self.safe_attrs_only and
self.safe_attrs == defs.safe_attrs):
# safe_attrs handles events attributes itself
for el in doc.iter(etree.Element):
attrib = el.attrib
for aname in attrib.keys():
if aname.startswith('on'):
del attrib[aname]
doc.rewrite_links(self._remove_javascript_link,
resolve_base_href=False)
# If we're deleting style then we don't have to remove JS links
# from styles, otherwise...
if not self.inline_style:
for el in _find_styled_elements(doc):
old = el.get('style')
new = _replace_css_javascript('', old)
new = _replace_css_import('', new)
if self._has_sneaky_javascript(new):
# Something tricky is going on...
del el.attrib['style']
elif new != old:
el.set('style', new)
if not self.style:
for el in list(doc.iter('style')):
if el.get('type', '').lower().strip() == 'text/javascript':
el.drop_tree()
continue
old = el.text or ''
new = _replace_css_javascript('', old)
# The imported CSS can do anything; we just can't allow:
new = _replace_css_import('', new)
if self._has_sneaky_javascript(new):
# Something tricky is going on...
el.text = '/* deleted */'
elif new != old:
el.text = new
if self.comments:
kill_tags.add(etree.Comment)
if self.processing_instructions:
kill_tags.add(etree.ProcessingInstruction)
if self.style:
kill_tags.add('style')
if self.inline_style:
etree.strip_attributes(doc, 'style')
if self.links:
kill_tags.add('link')
elif self.style or self.javascript:
# We must get rid of included stylesheets if Javascript is not
# allowed, as you can put Javascript in them
for el in list(doc.iter('link')):
if 'stylesheet' in el.get('rel', '').lower():
# Note this kills alternate stylesheets as well
if not self.allow_element(el):
el.drop_tree()
if self.meta:
kill_tags.add('meta')
if self.page_structure:
remove_tags.update(('head', 'html', 'title'))
if self.embedded:
# FIXME: is <layer> really embedded?
# We should get rid of any <param> tags not inside <applet>;
# These are not really valid anyway.
for el in list(doc.iter('param')):
parent = el.getparent()
while parent is not None and parent.tag not in ('applet', 'object'):
parent = parent.getparent()
if parent is None:
el.drop_tree()
kill_tags.update(('applet',))
# The alternate contents that are in an iframe are a good fallback:
remove_tags.update(('iframe', 'embed', 'layer', 'object', 'param'))
if self.frames:
# FIXME: ideally we should look at the frame links, but
# generally frames don't mix properly with an HTML
# fragment anyway.
kill_tags.update(defs.frame_tags)
if self.forms:
remove_tags.add('form')
kill_tags.update(('button', 'input', 'select', 'textarea'))
if self.annoying_tags:
remove_tags.update(('blink', 'marquee'))
_remove = []
_kill = []
for el in doc.iter():
if el.tag in kill_tags:
if self.allow_element(el):
continue
_kill.append(el)
elif el.tag in remove_tags:
if self.allow_element(el):
continue
_remove.append(el)
if _remove and _remove[0] == doc:
# We have to drop the parent-most tag, which we can't
# do. Instead we'll rewrite it:
el = _remove.pop(0)
el.tag = 'div'
el.attrib.clear()
elif _kill and _kill[0] == doc:
# We have to drop the parent-most element, which we can't
# do. Instead we'll clear it:
el = _kill.pop(0)
if el.tag != 'html':
el.tag = 'div'
el.clear()
_kill.reverse() # start with innermost tags
for el in _kill:
el.drop_tree()
for el in _remove:
el.drop_tag()
if self.remove_unknown_tags:
if allow_tags:
raise ValueError(
"It does not make sense to pass in both allow_tags and remove_unknown_tags")
allow_tags = set(defs.tags)
if allow_tags:
# make sure we do not remove comments/PIs if users want them (which is rare enough)
if not self.comments:
allow_tags.add(etree.Comment)
if not self.processing_instructions:
allow_tags.add(etree.ProcessingInstruction)
bad = []
for el in doc.iter():
if el.tag not in allow_tags:
bad.append(el)
if bad:
if bad[0] is doc:
el = bad.pop(0)
el.tag = 'div'
el.attrib.clear()
for el in bad:
el.drop_tag()
if self.add_nofollow:
for el in _find_external_links(doc):
if not self.allow_follow(el):
rel = el.get('rel')
if rel:
if ('nofollow' in rel
and ' nofollow ' in (' %s ' % rel)):
continue
rel = '%s nofollow' % rel
else:
rel = 'nofollow'
el.set('rel', rel)
def allow_follow(self, anchor):
"""
Override to suppress rel="nofollow" on some anchors.
"""
return False
def allow_element(self, el):
"""
Decide whether an element is configured to be accepted or rejected.
:param el: an element.
:return: true to accept the element or false to reject/discard it.
"""
if el.tag not in self._tag_link_attrs:
return False
attr = self._tag_link_attrs[el.tag]
if isinstance(attr, (list, tuple)):
for one_attr in attr:
url = el.get(one_attr)
if not url:
return False
if not self.allow_embedded_url(el, url):
return False
return True
else:
url = el.get(attr)
if not url:
return False
return self.allow_embedded_url(el, url)
def allow_embedded_url(self, el, url):
"""
Decide whether a URL that was found in an element's attributes or text
if configured to be accepted or rejected.
:param el: an element.
:param url: a URL found on the element.
:return: true to accept the URL and false to reject it.
"""
if self.whitelist_tags is not None and el.tag not in self.whitelist_tags:
return False
parts = urlsplit(url)
if parts.scheme not in ('http', 'https'):
return False
if parts.hostname in self.host_whitelist:
return True
return False
def kill_conditional_comments(self, doc):
"""
IE conditional comments basically embed HTML that the parser
doesn't normally see. We can't allow anything like that, so
we'll kill any comments that could be conditional.
"""
has_conditional_comment = _conditional_comment_re.search
self._kill_elements(
doc, lambda el: has_conditional_comment(el.text),
etree.Comment)
def _kill_elements(self, doc, condition, iterate=None):
bad = []
for el in doc.iter(iterate):
if condition(el):
bad.append(el)
for el in bad:
el.drop_tree()
def _remove_javascript_link(self, link):
# links like "j a v a s c r i p t:" might be interpreted in IE
new = _substitute_whitespace('', unquote_plus(link))
if _has_javascript_scheme(new):
# FIXME: should this be None to delete?
return ''
return link
_substitute_comments = re.compile(r'/\*.*?\*/', re.S).sub
def _has_sneaky_javascript(self, style):
"""
Depending on the browser, stuff like ``e x p r e s s i o n(...)``
can get interpreted, or ``expre/* stuff */ssion(...)``. This
checks for attempt to do stuff like this.
Typically the response will be to kill the entire style; if you
have just a bit of Javascript in the style another rule will catch
that and remove only the Javascript from the style; this catches
more sneaky attempts.
"""
style = self._substitute_comments('', style)
style = style.replace('\\', '')
style = _substitute_whitespace('', style)
style = style.lower()
if _has_javascript_scheme(style):
return True
if 'expression(' in style:
return True
if '@import' in style:
return True
if '</noscript' in style:
# e.g. '<noscript><style><a title="</noscript><img src=x onerror=alert(1)>">'
return True
if _looks_like_tag_content(style):
# e.g. '<math><style><img src=x onerror=alert(1)></style></math>'
return True
return False
def clean_html(self, html):
result_type = type(html)
if isinstance(html, (str, bytes)):
doc = fromstring(html)
else:
doc = copy.deepcopy(html)
self(doc)
return _transform_result(result_type, doc)
clean = Cleaner()
clean_html = clean.clean_html
############################################################
## Autolinking
############################################################
_link_regexes = [
re.compile(r'(?P<body>https?://(?P<host>[a-z0-9._-]+)(?:/[/\-_.,a-z0-9%&?;=~]*)?(?:\([/\-_.,a-z0-9%&?;=~]*\))?)', re.I),
# This is conservative, but autolinking can be a bit conservative:
re.compile(r'mailto:(?P<body>[a-z0-9._-]+@(?P<host>[a-z0-9_.-]+[a-z]))', re.I),
]
_avoid_elements = ['textarea', 'pre', 'code', 'head', 'select', 'a']
_avoid_hosts = [
re.compile(r'^localhost', re.I),
re.compile(r'\bexample\.(?:com|org|net)$', re.I),
re.compile(r'^127\.0\.0\.1$'),
]
_avoid_classes = ['nolink']
def autolink(el, link_regexes=_link_regexes,
avoid_elements=_avoid_elements,
avoid_hosts=_avoid_hosts,
avoid_classes=_avoid_classes):
"""
Turn any URLs into links.
It will search for links identified by the given regular
expressions (by default mailto and http(s) links).
It won't link text in an element in avoid_elements, or an element
with a class in avoid_classes. It won't link to anything with a
host that matches one of the regular expressions in avoid_hosts
(default localhost and 127.0.0.1).
If you pass in an element, the element's tail will not be
substituted, only the contents of the element.
"""
if el.tag in avoid_elements:
return
class_name = el.get('class')
if class_name:
class_name = class_name.split()
for match_class in avoid_classes:
if match_class in class_name:
return
for child in list(el):
autolink(child, link_regexes=link_regexes,
avoid_elements=avoid_elements,
avoid_hosts=avoid_hosts,
avoid_classes=avoid_classes)
if child.tail:
text, tail_children = _link_text(
child.tail, link_regexes, avoid_hosts, factory=el.makeelement)
if tail_children:
child.tail = text
index = el.index(child)
el[index+1:index+1] = tail_children
if el.text:
text, pre_children = _link_text(
el.text, link_regexes, avoid_hosts, factory=el.makeelement)
if pre_children:
el.text = text
el[:0] = pre_children
def _link_text(text, link_regexes, avoid_hosts, factory):
leading_text = ''
links = []
last_pos = 0
while 1:
best_match, best_pos = None, None
for regex in link_regexes:
regex_pos = last_pos
while 1:
match = regex.search(text, pos=regex_pos)
if match is None:
break
host = match.group('host')
for host_regex in avoid_hosts:
if host_regex.search(host):
regex_pos = match.end()
break
else:
break
if match is None:
continue
if best_pos is None or match.start() < best_pos:
best_match = match
best_pos = match.start()
if best_match is None:
# No more matches
if links:
assert not links[-1].tail
links[-1].tail = text
else:
assert not leading_text
leading_text = text
break
link = best_match.group(0)
end = best_match.end()
if link.endswith('.') or link.endswith(','):
# These punctuation marks shouldn't end a link
end -= 1
link = link[:-1]
prev_text = text[:best_match.start()]
if links:
assert not links[-1].tail
links[-1].tail = prev_text
else:
assert not leading_text
leading_text = prev_text
anchor = factory('a')
anchor.set('href', link)
body = best_match.group('body')
if not body:
body = link
if body.endswith('.') or body.endswith(','):
body = body[:-1]
anchor.text = body
links.append(anchor)
text = text[end:]
return leading_text, links
def autolink_html(html, *args, **kw):
result_type = type(html)
if isinstance(html, (str, bytes)):
doc = fromstring(html)
else:
doc = copy.deepcopy(html)
autolink(doc, *args, **kw)
return _transform_result(result_type, doc)
autolink_html.__doc__ = autolink.__doc__
############################################################
## Word wrapping
############################################################
_avoid_word_break_elements = ['pre', 'textarea', 'code']
_avoid_word_break_classes = ['nobreak']
def word_break(el, max_width=40,
avoid_elements=_avoid_word_break_elements,
avoid_classes=_avoid_word_break_classes,
break_character=chr(0x200b)):
"""
Breaks any long words found in the body of the text (not attributes).
Doesn't effect any of the tags in avoid_elements, by default
``<textarea>`` and ``<pre>``
Breaks words by inserting ​, which is a unicode character
for Zero Width Space character. This generally takes up no space
in rendering, but does copy as a space, and in monospace contexts
usually takes up space.
See http://www.cs.tut.fi/~jkorpela/html/nobr.html for a discussion
"""
# Character suggestion of ​ comes from:
# http://www.cs.tut.fi/~jkorpela/html/nobr.html
if el.tag in _avoid_word_break_elements:
return
class_name = el.get('class')
if class_name:
dont_break = False
class_name = class_name.split()
for avoid in avoid_classes:
if avoid in class_name:
dont_break = True
break
if dont_break:
return
if el.text:
el.text = _break_text(el.text, max_width, break_character)
for child in el:
word_break(child, max_width=max_width,
avoid_elements=avoid_elements,
avoid_classes=avoid_classes,
break_character=break_character)
if child.tail:
child.tail = _break_text(child.tail, max_width, break_character)
def word_break_html(html, *args, **kw):
result_type = type(html)
doc = fromstring(html)
word_break(doc, *args, **kw)
return _transform_result(result_type, doc)
def _break_text(text, max_width, break_character):
words = text.split()
for word in words:
if len(word) > max_width:
replacement = _insert_break(word, max_width, break_character)
text = text.replace(word, replacement)
return text
_break_prefer_re = re.compile(r'[^a-z]', re.I)
def _insert_break(word, width, break_character):
orig_word = word
result = ''
while len(word) > width:
start = word[:width]
breaks = list(_break_prefer_re.finditer(start))
if breaks:
last_break = breaks[-1]
# Only walk back up to 10 characters to find a nice break:
if last_break.end() > width-10:
# FIXME: should the break character be at the end of the
# chunk, or the beginning of the next chunk?
start = word[:last_break.end()]
result += start + break_character
word = word[len(start):]
result += word
return result