"""
This module implements a VERY limited parser that finds tags in
the head of HTML or XHTML documents and parses out their attributes
according to the OpenID spec. It is a liberal parser, but it requires
these things from the data in order to work:
- There must be an open tag
- There must be an open
tag inside of the tag
- Only s that are found inside of the tag are parsed
(this is by design)
- The parser follows the OpenID specification in resolving the
attributes of the link tags. This means that the attributes DO NOT
get resolved as they would by an XML or HTML parser. In particular,
only certain entities get replaced, and href attributes do not get
resolved relative to a base URL.
From http://openid.net/specs.bml#linkrel:
- The openid.server URL MUST be an absolute URL. OpenID consumers
MUST NOT attempt to resolve relative URLs.
- The openid.server URL MUST NOT include entities other than &,
<, >, and ".
The parser ignores SGML comments and . Both kinds of
quoting are allowed for attributes.
The parser deals with invalid markup in these ways:
- Tag names are not case-sensitive
- The tag is accepted even when it is not at the top level
- The tag is accepted even when it is not a direct child of
the tag, but a tag must be an ancestor of the
tag
- tags are accepted even when they are not direct children of
the tag, but a tag must be an ancestor of the
tag
- If there is no closing tag for an open or tag, the
remainder of the document is viewed as being inside of the tag. If
there is no closing tag for a tag, the link tag is treated
as a short tag. Exceptions to this rule are that closes
and or closes
- Attributes of the tag are not required to be quoted.
- In the case of duplicated attribute names, the attribute coming
last in the tag will be the value returned.
- Any text that does not parse as an attribute within a link tag will
be ignored. (e.g. will ignore
pumpkin)
- If there are more than one or tag, the parser only
looks inside of the first one.
- The contents of
''', flags)
tag_expr = r'''
# Starts with the tag name at a word boundary, where the tag name is
# not a namespace
<%(tag_name)s\b(?!:)
# All of the stuff up to a ">", hopefully attributes.
(?P[^>]*?)
(?: # Match a short tag
/>
| # Match a full tag
>
(?P.*?)
# Closed by
(?: # One of the specified close tags
?%(closers)s\s*>
# End of the string
| \Z
)
)
'''
def tagMatcher(tag_name, *close_tags):
if close_tags:
options = '|'.join((tag_name,) + close_tags)
closers = '(?:%s)' % (options,)
else:
closers = tag_name
expr = tag_expr % locals()
return re.compile(expr, flags)
# Must contain at least an open html and an open head tag
html_find = tagMatcher('html')
head_find = tagMatcher('head', 'body')
link_find = re.compile(r'\w+)=
# Then either a quoted or unquoted attribute
(?:
# Match everything that\'s between matching quote marks
(?P["\'])(?P.*?)(?P=qopen)
|
# If the value is not quoted, match up to whitespace
(?P(?:[^\s<>/]|/(?!>))+)
)
|
(?P[<>])
''', flags)
# Entity replacement:
replacements = {
'amp':'&',
'lt':'<',
'gt':'>',
'quot':'"',
}
ent_replace = re.compile(r'&(%s);' % '|'.join(replacements.keys()))
def replaceEnt(mo):
"Replace the entities that are specified by OpenID"
return replacements.get(mo.group(1), mo.group())
def parseLinkAttrs(html):
"""Find all link tags in a string representing a HTML document and
return a list of their attributes.
@param html: the text to parse
@type html: str or unicode
@return: A list of dictionaries of attributes, one for each link tag
@rtype: [[(type(html), type(html))]]
"""
stripped = removed_re.sub('', html)
html_mo = html_find.search(stripped)
if html_mo is None or html_mo.start('contents') == -1:
return []
start, end = html_mo.span('contents')
head_mo = head_find.search(stripped, start, end)
if head_mo is None or head_mo.start('contents') == -1:
return []
start, end = head_mo.span('contents')
link_mos = link_find.finditer(stripped, head_mo.start(), head_mo.end())
matches = []
for link_mo in link_mos:
start = link_mo.start() + 5
link_attrs = {}
for attr_mo in attr_find.finditer(stripped, start):
if attr_mo.lastgroup == 'end_link':
break
# Either q_val or unq_val must be present, but not both
# unq_val is a True (non-empty) value if it is present
attr_name, q_val, unq_val = attr_mo.group(
'attr_name', 'q_val', 'unq_val')
attr_val = ent_replace.sub(replaceEnt, unq_val or q_val)
link_attrs[attr_name] = attr_val
matches.append(link_attrs)
return matches
def relMatches(rel_attr, target_rel):
"""Does this target_rel appear in the rel_str?"""
# XXX: TESTME
rels = rel_attr.strip().split()
for rel in rels:
rel = rel.lower()
if rel == target_rel:
return 1
return 0
def linkHasRel(link_attrs, target_rel):
"""Does this link have target_rel as a relationship?"""
# XXX: TESTME
rel_attr = link_attrs.get('rel')
return rel_attr and relMatches(rel_attr, target_rel)
def findLinksRel(link_attrs_list, target_rel):
"""Filter the list of link attributes on whether it has target_rel
as a relationship."""
# XXX: TESTME
matchesTarget = lambda attrs: linkHasRel(attrs, target_rel)
return filter(matchesTarget, link_attrs_list)
def findFirstHref(link_attrs_list, target_rel):
"""Return the value of the href attribute for the first link tag
in the list that has target_rel as a relationship."""
# XXX: TESTME
matches = findLinksRel(link_attrs_list, target_rel)
if not matches:
return None
first = matches[0]
return first.get('href')