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[3.14] gh-135661: Fix parsing start and end tags in HTMLParser according to the HTML5 standard (GH-135930) #136255

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Jul 3, 2025
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[3.14] gh-135661: Fix parsing start and end tags in HTMLParser according to the HTML5 standard (GH-135930) #136255

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gh-135661: Fix parsing start and end tags in HTMLParser according to … 
…the HTML5 standard (GH-135930)

* Whitespaces no longer accepted between `</` and the tag name.
  E.g. `</ script>` does not end the script section.

* Vertical tabulation (`\v`) and non-ASCII whitespaces no longer recognized
  as whitespaces. The only whitespaces are `\t\n\r\f `.

* Null character (U+0000) no longer ends the tag name.

* Attributes and slashes after the tag name in end tags are now ignored,
  instead of terminating after the first `>` in quoted attribute value.
  E.g. `</script/foo=">"/>`.

* Multiple slashes and whitespaces between the last attribute and closing `>`
  are now ignored in both start and end tags. E.g. `<a foo=bar/ //>`.

* Multiple `=` between attribute name and value are no longer collapsed.
  E.g. `<a foo==bar>` produces attribute "foo" with value "=bar".

* Whitespaces between the `=` separator and attribute name or value are no
  longer ignored. E.g. `<a foo =bar>` produces two attributes "foo" and
  "=bar", both with value None; `<a foo= bar>` produces two attributes:
  "foo" with value "" and "bar" with value None.

* Fix Sphinx errors.

* Apply suggestions from code review

Co-authored-by: Ezio Melotti <ezio.melotti@gmail.com>

* Address review comments.

* Move to Security.

---------
(cherry picked from commit 0243f97)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
Co-authored-by: Ezio Melotti <ezio.melotti@gmail.com>
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@serhiy-storchaka @ezio-melotti @miss-islington
2 people authored and miss-islington committed Jul 3, 2025
commit 87302042e2f455d02b93242feead5484a19cc11c
143 changes: 69 additions & 74 deletions Lib/html/parser.py
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Original file line number Diff line number Diff line change
Expand Up @@ -31,15 +31,43 @@
piclose = re.compile('>')
commentclose = re.compile(r'--\s*>')
# Note:
# 1) if you change tagfind/attrfind remember to update locatestarttagend too;
# 2) if you change tagfind/attrfind and/or locatestarttagend the parser will
# 1) if you change tagfind/attrfind remember to update locatetagend too;
# 2) if you change tagfind/attrfind and/or locatetagend the parser will
# explode, so don't do it.
# see http://www.w3.org/TR/html5/tokenization.html#tag-open-state
# and http://www.w3.org/TR/html5/tokenization.html#tag-name-state
tagfind_tolerant = re.compile(r'([a-zA-Z][^\t\n\r\f />\x00]*)(?:\s|/(?!>))*')
attrfind_tolerant = re.compile(
r'((?<=[\'"\s/])[^\s/>][^\s/=>]*)(\s*=+\s*'
r'(\'[^\']*\'|"[^"]*"|(?![\'"])[^>\s]*))?(?:\s|/(?!>))*')
# see the HTML5 specs section "13.2.5.6 Tag open state",
# "13.2.5.8 Tag name state" and "13.2.5.33 Attribute name state".
# https://html.spec.whatwg.org/multipage/parsing.html#tag-open-state
# https://html.spec.whatwg.org/multipage/parsing.html#tag-name-state
# https://html.spec.whatwg.org/multipage/parsing.html#attribute-name-state
tagfind_tolerant = re.compile(r'([a-zA-Z][^\t\n\r\f />]*)(?:[\t\n\r\f ]|/(?!>))*')
attrfind_tolerant = re.compile(r"""
(
(?<=['"\t\n\r\f /])[^\t\n\r\f />][^\t\n\r\f /=>]* # attribute name
)
(= # value indicator
('[^']*' # LITA-enclosed value
|"[^"]*" # LIT-enclosed value
|(?!['"])[^>\t\n\r\f ]* # bare value
)
)?
(?:[\t\n\r\f ]|/(?!>))* # possibly followed by a space
""", re.VERBOSE)
locatetagend = re.compile(r"""
[a-zA-Z][^\t\n\r\f />]* # tag name
[\t\n\r\f /]* # optional whitespace before attribute name
(?:(?<=['"\t\n\r\f /])[^\t\n\r\f />][^\t\n\r\f /=>]* # attribute name
(?:= # value indicator
(?:'[^']*' # LITA-enclosed value
|"[^"]*" # LIT-enclosed value
|(?!['"])[^>\t\n\r\f ]* # bare value
)
)?
[\t\n\r\f /]* # possibly followed by a space
)*
>?
""", re.VERBOSE)
# The following variables are not used, but are temporarily left for
# backward compatibility.
locatestarttagend_tolerant = re.compile(r"""
<[a-zA-Z][^\t\n\r\f />\x00]* # tag name
(?:[\s/]* # optional whitespace before attribute name
Expand All @@ -56,8 +84,6 @@
\s* # trailing whitespace
""", re.VERBOSE)
endendtag = re.compile('>')
# the HTML 5 spec, section 8.1.2.2, doesn't allow spaces between
# </ and the tag name, so maybe this should be fixed
endtagfind = re.compile(r'</\s*([a-zA-Z][-.a-zA-Z0-9:_]*)\s*>')

# Character reference processing logic specific to attribute values
Expand Down Expand Up @@ -141,7 +167,8 @@ def get_starttag_text(self):

def set_cdata_mode(self, elem):
self.cdata_elem = elem.lower()
self.interesting = re.compile(r'</\s*%s\s*>' % self.cdata_elem, re.I)
self.interesting = re.compile(r'</%s(?=[\t\n\r\f />])' % self.cdata_elem,
re.IGNORECASE|re.ASCII)

def clear_cdata_mode(self):
self.interesting = interesting_normal
Expand All @@ -166,7 +193,7 @@ def goahead(self, end):
# & near the end and see if it's followed by a space or ;.
amppos = rawdata.rfind('&', max(i, n-34))
if (amppos >= 0 and
not re.compile(r'[\s;]').search(rawdata, amppos)):
not re.compile(r'[\t\n\r\f ;]').search(rawdata, amppos)):
break # wait till we get all the text
j = n
else:
Expand Down Expand Up @@ -310,7 +337,7 @@ def parse_html_declaration(self, i):
return self.parse_bogus_comment(i)

# Internal -- parse bogus comment, return length or -1 if not terminated
# see http://www.w3.org/TR/html5/tokenization.html#bogus-comment-state
# see https://html.spec.whatwg.org/multipage/parsing.html#bogus-comment-state
def parse_bogus_comment(self, i, report=1):
rawdata = self.rawdata
assert rawdata[i:i+2] in ('<!', '</'), ('unexpected call to '
Expand All @@ -336,6 +363,8 @@ def parse_pi(self, i):

# Internal -- handle starttag, return end or -1 if not terminated
def parse_starttag(self, i):
# See the HTML5 specs section "13.2.5.8 Tag name state"
# https://html.spec.whatwg.org/multipage/parsing.html#tag-name-state
self.__starttag_text = None
endpos = self.check_for_whole_start_tag(i)
if endpos < 0:
Expand Down Expand Up @@ -381,76 +410,42 @@ def parse_starttag(self, i):
# or -1 if incomplete.
def check_for_whole_start_tag(self, i):
rawdata = self.rawdata
m = locatestarttagend_tolerant.match(rawdata, i)
if m:
j = m.end()
next = rawdata[j:j+1]
if next == ">":
return j + 1
if next == "/":
if rawdata.startswith("/>", j):
return j + 2
if rawdata.startswith("/", j):
# buffer boundary
return -1
# else bogus input
if j > i:
return j
else:
return i + 1
if next == "":
# end of input
return -1
if next in ("abcdefghijklmnopqrstuvwxyz=/"
"ABCDEFGHIJKLMNOPQRSTUVWXYZ"):
# end of input in or before attribute value, or we have the
# '/' from a '/>' ending
return -1
if j > i:
return j
else:
return i + 1
raise AssertionError("we should not get here!")
match = locatetagend.match(rawdata, i+1)
assert match
j = match.end()
if rawdata[j-1] != ">":
return -1
return j

# Internal -- parse endtag, return end or -1 if incomplete
def parse_endtag(self, i):
# See the HTML5 specs section "13.2.5.7 End tag open state"
# https://html.spec.whatwg.org/multipage/parsing.html#end-tag-open-state
rawdata = self.rawdata
assert rawdata[i:i+2] == "</", "unexpected call to parse_endtag"
match = endendtag.search(rawdata, i+1) # >
if not match:
if rawdata.find('>', i+2) < 0: # fast check
return -1
gtpos = match.end()
match = endtagfind.match(rawdata, i) # </ + tag + >
if not match:
if self.cdata_elem is not None:
self.handle_data(rawdata[i:gtpos])
return gtpos
# find the name: w3.org/TR/html5/tokenization.html#tag-name-state
namematch = tagfind_tolerant.match(rawdata, i+2)
if not namematch:
# w3.org/TR/html5/tokenization.html#end-tag-open-state
if rawdata[i:i+3] == '</>':
return i+3
else:
return self.parse_bogus_comment(i)
tagname = namematch.group(1).lower()
# consume and ignore other stuff between the name and the >
# Note: this is not 100% correct, since we might have things like
# </tag attr=">">, but looking for > after the name should cover
# most of the cases and is much simpler
gtpos = rawdata.find('>', namematch.end())
self.handle_endtag(tagname)
return gtpos+1
if not endtagopen.match(rawdata, i): # </ + letter
if rawdata[i+2:i+3] == '>': # </> is ignored
# "missing-end-tag-name" parser error
return i+3
else:
return self.parse_bogus_comment(i)

elem = match.group(1).lower() # script or style
if self.cdata_elem is not None:
if elem != self.cdata_elem:
self.handle_data(rawdata[i:gtpos])
return gtpos
match = locatetagend.match(rawdata, i+2)
assert match
j = match.end()
if rawdata[j-1] != ">":
return -1

self.handle_endtag(elem)
# find the name: "13.2.5.8 Tag name state"
# https://html.spec.whatwg.org/multipage/parsing.html#tag-name-state
match = tagfind_tolerant.match(rawdata, i+2)
assert match
tag = match.group(1).lower()
self.handle_endtag(tag)
self.clear_cdata_mode()
return gtpos
return j

# Overridable -- finish processing of start+end tag: <tag.../>
def handle_startendtag(self, tag, attrs):
Expand Down
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