gh-87112: Ensure that only ASCII digits are accepted as section number in MIME header parameter

[matthieucan]

With those changes, the MIME parameter parser discards parameters with an invalid section number that uses a non 0-9 digit such as super-script "²" or "𐩃" (Kharosthi number).

Before:

>>> import email.headerregistry
>>> reg = email.headerregistry.HeaderRegistry()
>>> reg('Content-Disposition', 'inline; foo*0=bar')
'inline; foo="bar"'
>>> reg('Content-Disposition', 'inline; foo*X=bar')
'inline;'
>>> reg('Content-Disposition', 'inline; foo*²=bar')
Traceback (most recent call last):
  File "<python-input-2>", line 1, in <module>
    reg('Content-Disposition', 'inline; foo*²=bar')
    ~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/matthieu/git/cpython/Lib/email/headerregistry.py", line 604, in __call__
    return self[name](name, value)
           ~~~~~~~~~~^^^^^^^^^^^^^
  File "/Users/matthieu/git/cpython/Lib/email/headerregistry.py", line 192, in __new__
    cls.parse(value, kwds)
    ~~~~~~~~~^^^^^^^^^^^^^
  File "/Users/matthieu/git/cpython/Lib/email/headerregistry.py", line 448, in parse
    kwds['parse_tree'] = parse_tree = cls.value_parser(value)
                                      ~~~~~~~~~~~~~~~~^^^^^^^
  File "/Users/matthieu/git/cpython/Lib/email/_header_value_parser.py", line 2736, in parse_content_disposition_header
    disp_header.append(parse_mime_parameters(value[1:]))
                       ~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^
  File "/Users/matthieu/git/cpython/Lib/email/_header_value_parser.py", line 2601, in parse_mime_parameters
    token, value = get_parameter(value)
                   ~~~~~~~~~~~~~^^^^^^^
  File "/Users/matthieu/git/cpython/Lib/email/_header_value_parser.py", line 2464, in get_parameter
    token, value = get_section(value)
                   ~~~~~~~~~~~^^^^^^^
  File "/Users/matthieu/git/cpython/Lib/email/_header_value_parser.py", line 2417, in get_section
    section.number = int(digits)
                     ~~~^^^^^^^^
ValueError: invalid literal for int() with base 10: '²'

After:

>>> import email.headerregistry
>>> reg = email.headerregistry.HeaderRegistry()
>>> reg('Content-Disposition', 'inline; foo*0=bar')
'inline; foo="bar"'
>>> reg('Content-Disposition', 'inline; foo*X=bar')
'inline;'
>>> reg('Content-Disposition', 'inline; foo*²=bar')
'inline;'

• Issue: email: ValueError in get_section when parsing header with non-ASCII digit #87112

[picnixz]

Suggested change

	while value and '0' <= value[0] <= '9':
	while value and ('0' <= value[0] <= '9'):

It will a bit clearer. Or you can still use a separate function to make it even cleareer. The bottleneck won't be the function call IMO.

[matthieucan]

I did that, but not the separate function. It was my understanding that @StanFromIreland was leaning towards not having an inner function

[StanFromIreland]

This is fine, I was against the function to check if it is in a dictionary.

[matthieucan]

Thank you! Just moved it to a separate function for extra-clarity