# Source code for bleach.sanitizer

    from __future__ import unicode_literals

    from itertools import chain
    import re

    import six
    from six.moves.urllib.parse import urlparse
    from xml.sax.saxutils import unescape

    from bleach import html5lib_shim
    from bleach.utils import alphabetize_attributes, force_unicode

    #: List of allowed tags
    ALLOWED_TAGS = [
        'a',
        'abbr',
        'acronym',
        'b',
        'blockquote',
        'code',
        'em',
        'i',
        'li',
        'ol',
        'strong',
        'ul',
    ]

    #: Map of allowed attributes by tag
    ALLOWED_ATTRIBUTES = {
        'a': ['href', 'title'],
        'abbr': ['title'],
        'acronym': ['title'],
    }

    #: List of allowed styles
    ALLOWED_STYLES = []

    #: List of allowed protocols
    ALLOWED_PROTOCOLS = ['http', 'https', 'mailto']

    #: Invisible characters--0 to and including 31 except 9 (tab), 10 (lf), and 13 (cr)
    INVISIBLE_CHARACTERS = ''.join([chr(c) for c in chain(range(0, 9), range(11, 13), range(14, 32))])

    #: Regexp for characters that are invisible
    INVISIBLE_CHARACTERS_RE = re.compile(
        '[' + INVISIBLE_CHARACTERS + ']',
        re.UNICODE
    )

    #: String to replace invisible characters with. This can be a character, a
    #: string, or even a function that takes a Python re matchobj
    INVISIBLE_REPLACEMENT_CHAR = '?'

    class Cleaner(object):
        """Cleaner for cleaning HTML fragments of malicious content

        This cleaner is a security-focused function whose sole purpose is to remove
        malicious content from a string such that it can be displayed as content in
        a web page.

        To use::

            from bleach.sanitizer import Cleaner

            cleaner = Cleaner()

            for text in all_the_yucky_things:
                sanitized = cleaner.clean(text)

        .. Note::

           This cleaner is not designed to use to transform content to be used in
           non-web-page contexts.

        .. Warning::

           This cleaner is not thread-safe--the html parser has internal state.
           Create a separate cleaner per thread!

        """

        def __init__(self, tags=ALLOWED_TAGS, attributes=ALLOWED_ATTRIBUTES,
                     styles=ALLOWED_STYLES, protocols=ALLOWED_PROTOCOLS, strip=False,
                     strip_comments=True, filters=None):
            """Initializes a Cleaner

            :arg list tags: allowed list of tags; defaults to
                ``bleach.sanitizer.ALLOWED_TAGS``

            :arg dict attributes: allowed attributes; can be a callable, list or dict;
                defaults to ``bleach.sanitizer.ALLOWED_ATTRIBUTES``

            :arg list styles: allowed list of css styles; defaults to
                ``bleach.sanitizer.ALLOWED_STYLES``

            :arg list protocols: allowed list of protocols for links; defaults
                to ``bleach.sanitizer.ALLOWED_PROTOCOLS``

            :arg bool strip: whether or not to strip disallowed elements

            :arg bool strip_comments: whether or not to strip HTML comments

            :arg list filters: list of html5lib Filter classes to pass streamed content through

                .. seealso:: http://html5lib.readthedocs.io/en/latest/movingparts.html#filters

                .. Warning::

                   Using filters changes the output of ``bleach.Cleaner.clean``.
                   Make sure the way the filters change the output are secure.

            """
            self.tags = tags
            self.attributes = attributes
            self.styles = styles
            self.protocols = protocols
            self.strip = strip
            self.strip_comments = strip_comments
            self.filters = filters or []

            self.parser = html5lib_shim.BleachHTMLParser(
                tags=self.tags,
                strip=self.strip,
                consume_entities=False,
                namespaceHTMLElements=False
            )
            self.walker = html5lib_shim.getTreeWalker('etree')
            self.serializer = html5lib_shim.BleachHTMLSerializer(
                quote_attr_values='always',
                omit_optional_tags=False,
                escape_lt_in_attrs=True,

                # We want to leave entities as they are without escaping or
                # resolving or expanding
                resolve_entities=False,

                # Bleach has its own sanitizer, so don't use the html5lib one
                sanitize=False,

                # Bleach sanitizer alphabetizes already, so don't use the html5lib one
                alphabetical_attributes=False,
            )

        def clean(self, text):
            """Cleans text and returns sanitized result as unicode

            :arg str text: text to be cleaned

            :returns: sanitized text as unicode

            :raises TypeError: if ``text`` is not a text type

            """
            if not isinstance(text, six.string_types):
                message = "argument cannot be of '{name}' type, must be of text type".format(
                    name=text.__class__.__name__)
                raise TypeError(message)

            if not text:
                return u''

            text = force_unicode(text)

            dom = self.parser.parseFragment(text)
            filtered = BleachSanitizerFilter(
                source=self.walker(dom),

                # Bleach-sanitizer-specific things
                attributes=self.attributes,
                strip_disallowed_elements=self.strip,
                strip_html_comments=self.strip_comments,

                # html5lib-sanitizer things
                allowed_elements=self.tags,
                allowed_css_properties=self.styles,
                allowed_protocols=self.protocols,
                allowed_svg_properties=[],
            )

            # Apply any filters after the BleachSanitizerFilter
            for filter_class in self.filters:
                filtered = filter_class(source=filtered)

            return self.serializer.render(filtered)

    def attribute_filter_factory(attributes):
        """Generates attribute filter function for the given attributes value

        The attributes value can take one of several shapes. This returns a filter
        function appropriate to the attributes value. One nice thing about this is
        that there's less if/then shenanigans in the ``allow_token`` method.

        """
        if callable(attributes):
            return attributes

        if isinstance(attributes, dict):
            def _attr_filter(tag, attr, value):
                if tag in attributes:
                    attr_val = attributes[tag]
                    if callable(attr_val):
                        return attr_val(tag, attr, value)

                    if attr in attr_val:
                        return True

                if '*' in attributes:
                    attr_val = attributes['*']
                    if callable(attr_val):
                        return attr_val(tag, attr, value)

                    return attr in attr_val

                return False

            return _attr_filter

        if isinstance(attributes, list):
            def _attr_filter(tag, attr, value):
                return attr in attributes

            return _attr_filter

        raise ValueError('attributes needs to be a callable, a list or a dict')

    class BleachSanitizerFilter(html5lib_shim.SanitizerFilter):
        """html5lib Filter that sanitizes text

        This filter can be used anywhere html5lib filters can be used.

        """
        def __init__(self, source, attributes=ALLOWED_ATTRIBUTES,
                     strip_disallowed_elements=False, strip_html_comments=True,
                     **kwargs):
            """Creates a BleachSanitizerFilter instance

            :arg Treewalker source: stream

            :arg list tags: allowed list of tags; defaults to
                ``bleach.sanitizer.ALLOWED_TAGS``

            :arg dict attributes: allowed attributes; can be a callable, list or dict;
                defaults to ``bleach.sanitizer.ALLOWED_ATTRIBUTES``

            :arg list styles: allowed list of css styles; defaults to
                ``bleach.sanitizer.ALLOWED_STYLES``

            :arg list protocols: allowed list of protocols for links; defaults
                to ``bleach.sanitizer.ALLOWED_PROTOCOLS``

            :arg bool strip_disallowed_elements: whether or not to strip disallowed
                elements

            :arg bool strip_html_comments: whether or not to strip HTML comments

            """
            self.attr_filter = attribute_filter_factory(attributes)
            self.strip_disallowed_elements = strip_disallowed_elements
            self.strip_html_comments = strip_html_comments

            return super(BleachSanitizerFilter, self).__init__(source, **kwargs)

        def sanitize_stream(self, token_iterator):
            for token in token_iterator:
                ret = self.sanitize_token(token)

                if not ret:
                    continue

                if isinstance(ret, list):
                    for subtoken in ret:
                        yield subtoken
                else:
                    yield ret

        def merge_characters(self, token_iterator):
            """Merge consecutive Characters tokens in a stream"""
            characters_buffer = []

            for token in token_iterator:
                if characters_buffer:
                    if token['type'] == 'Characters':
                        characters_buffer.append(token)
                        continue
                    else:
                        # Merge all the characters tokens together into one and then
                        # operate on it.
                        new_token = {
                            'data': ''.join([char_token['data'] for char_token in characters_buffer]),
                            'type': 'Characters'
                        }
                        characters_buffer = []
                        yield new_token

                elif token['type'] == 'Characters':
                    characters_buffer.append(token)
                    continue

                yield token

            new_token = {
                'data': ''.join([char_token['data'] for char_token in characters_buffer]),
                'type': 'Characters'
            }
            yield new_token

        def __iter__(self):
            return self.merge_characters(self.sanitize_stream(html5lib_shim.Filter.__iter__(self)))

        def sanitize_token(self, token):
            """Sanitize a token either by HTML-encoding or dropping.

            Unlike sanitizer.Filter, allowed_attributes can be a dict of {'tag':
            ['attribute', 'pairs'], 'tag': callable}.

            Here callable is a function with two arguments of attribute name and
            value. It should return true of false.

            Also gives the option to strip tags instead of encoding.

            :arg dict token: token to sanitize

            :returns: token or list of tokens

            """
            token_type = token['type']
            if token_type in ['StartTag', 'EndTag', 'EmptyTag']:
                if token['name'] in self.allowed_elements:
                    return self.allow_token(token)

                elif self.strip_disallowed_elements:
                    return None

                else:
                    if 'data' in token:
                        # Alphabetize the attributes before calling .disallowed_token()
                        # so that the resulting string is stable
                        token['data'] = alphabetize_attributes(token['data'])
                    return self.disallowed_token(token)

            elif token_type == 'Comment':
                if not self.strip_html_comments:
                    return token
                else:
                    return None

            elif token_type == 'Characters':
                return self.sanitize_characters(token)

            else:
                return token

        def sanitize_characters(self, token):
            """Handles Characters tokens

            Our overridden tokenizer doesn't do anything with entities. However,
            that means that the serializer will convert all ``&`` in Characters
            tokens to ``&amp;``.

            Since we don't want that, we extract entities here and convert them to
            Entity tokens so the serializer will let them be.

            :arg token: the Characters token to work on

            :returns: a list of tokens

            """
            data = token.get('data', '')

            if not data:
                return token

            data = INVISIBLE_CHARACTERS_RE.sub(INVISIBLE_REPLACEMENT_CHAR, data)
            token['data'] = data

            # If there isn't a & in the data, we can return now
            if '&' not in data:
                return token

            new_tokens = []

            # For each possible entity that starts with a "&", we try to extract an
            # actual entity and re-tokenize accordingly
            for part in html5lib_shim.next_possible_entity(data):
                if not part:
                    continue

                if part.startswith('&'):
                    entity = html5lib_shim.match_entity(part)
                    if entity is not None:
                        if entity == 'amp':
                            # LinkifyFilter can't match urls across token boundaries
                            # which is problematic with &amp; since that shows up in
                            # querystrings all the time. This special-cases &amp;
                            # and converts it to a & and sticks it in as a
                            # Characters token. It'll get merged with surrounding
                            # tokens in the BleachSanitizerfilter.__iter__ and
                            # escaped in the serializer.
                            new_tokens.append({'type': 'Characters', 'data': '&'})
                        else:
                            new_tokens.append({'type': 'Entity', 'name': entity})

                        # Length of the entity plus 2--one for & at the beginning
                        # and and one for ; at the end
                        remainder = part[len(entity) + 2:]
                        if remainder:
                            new_tokens.append({'type': 'Characters', 'data': remainder})
                        continue

                new_tokens.append({'type': 'Characters', 'data': part})

            return new_tokens

        def sanitize_uri_value(self, value, allowed_protocols):
            """Checks a uri value to see if it's allowed

            :arg value: the uri value to sanitize
            :arg allowed_protocols: list of allowed protocols

            :returns: allowed value or None

            """
            # NOTE(willkg): This transforms the value into one that's easier to
            # match and verify, but shouldn't get returned since it's vastly
            # different than the original value.

            # Convert all character entities in the value
            new_value = html5lib_shim.convert_entities(value)

            # Nix backtick, space characters, and control characters
            new_value = re.sub(
                r"[`\000-\040\177-\240\s]+",
                '',
                new_value
            )

            # Remove REPLACEMENT characters
            new_value = new_value.replace('\ufffd', '')

            # Lowercase it--this breaks the value, but makes it easier to match
            # against
            new_value = new_value.lower()

            try:
                # Drop attributes with uri values that have protocols that aren't
                # allowed
                parsed = urlparse(new_value)
            except ValueError:
                # URI is impossible to parse, therefore it's not allowed
                return None

            if parsed.scheme:
                # If urlparse found a scheme, check that
                if parsed.scheme in allowed_protocols:
                    return value

            else:
                # Allow uris that are just an anchor
                if new_value.startswith('#'):
                    return value

                # Handle protocols that urlparse doesn't recognize like "myprotocol"
                if ':' in new_value and new_value.split(':')[0] in allowed_protocols:
                    return value

                # If there's no protocol/scheme specified, then assume it's "http"
                # and see if that's allowed
                if 'http' in allowed_protocols:
                    return value

            return None

        def allow_token(self, token):
            """Handles the case where we're allowing the tag"""
            if 'data' in token:
                # Loop through all the attributes and drop the ones that are not
                # allowed, are unsafe or break other rules. Additionally, fix
                # attribute values that need fixing.
                #
                # At the end of this loop, we have the final set of attributes
                # we're keeping.
                attrs = {}
                for namespaced_name, val in token['data'].items():
                    namespace, name = namespaced_name

                    # Drop attributes that are not explicitly allowed
                    #
                    # NOTE(willkg): We pass in the attribute name--not a namespaced
                    # name.
                    if not self.attr_filter(token['name'], name, val):
                        continue

                    # Drop attributes with uri values that use a disallowed protocol
                    # Sanitize attributes with uri values
                    if namespaced_name in self.attr_val_is_uri:
                        new_value = self.sanitize_uri_value(val, self.allowed_protocols)
                        if new_value is None:
                            continue
                        val = new_value

                    # Drop values in svg attrs with non-local IRIs
                    if namespaced_name in self.svg_attr_val_allows_ref:
                        new_val = re.sub(r'url\s*\(\s*[^#\s][^)]+?\)',
                                         ' ',
                                         unescape(val))
                        new_val = new_val.strip()
                        if not new_val:
                            continue

                        else:
                            # Replace the val with the unescaped version because
                            # it's a iri
                            val = new_val

                    # Drop href and xlink:href attr for svg elements with non-local IRIs
                    if (None, token['name']) in self.svg_allow_local_href:
                        if namespaced_name in [
                                (None, 'href'), (html5lib_shim.namespaces['xlink'], 'href')
                        ]:
                            if re.search(r'^\s*[^#\s]', val):
                                continue

                    # If it's a style attribute, sanitize it
                    if namespaced_name == (None, u'style'):
                        val = self.sanitize_css(val)

                    # At this point, we want to keep the attribute, so add it in
                    attrs[namespaced_name] = val

                token['data'] = alphabetize_attributes(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():
                    # If we end up with a namespace, but no name, switch them so we
                    # have a valid name to use.
                    if ns and not name:
                        ns, name = name, ns

                    # Figure out namespaced name if the namespace is appropriate
                    # and exists; if the ns isn't in prefixes, then drop it.
                    if ns is None or ns not in html5lib_shim.prefixes:
                        namespaced_name = name
                    else:
                        namespaced_name = '%s:%s' % (html5lib_shim.prefixes[ns], name)

                    attrs.append(' %s="%s"' % (
                        namespaced_name,
                        # NOTE(willkg): HTMLSerializer escapes attribute values
                        # already, so if we do it here (like HTMLSerializer does),
                        # then we end up double-escaping.
                        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):
            """Sanitizes css in style tags"""
            # Convert entities in the style so that it can be parsed as CSS
            style = html5lib_shim.convert_entities(style)

            # Drop any url values before we do anything else
            style = re.compile(r'url\s*\(\s*[^\s)]+?\s*\)\s*').sub(' ', style)

            # The gauntlet of sanitization

            # Validate the css in the style tag and if it's not valid, then drop
            # the whole thing.
            parts = style.split(';')
            gauntlet = re.compile(
                r"""^([-/:,#%.'"\sa-zA-Z0-9!]|\w-\w|'[\s\w]+'\s*|"[\s\w]+"|\([\d,%\.\s]+\))*$"""
            )

            for part in parts:
                if not gauntlet.match(part):
                    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.lower() in self.allowed_svg_properties:
                    clean.append(prop + ': ' + value + ';')

            return ' '.join(clean)