Experimental RFC 7239 parser

forwarded_parser.py

import re
import types

_HTTP_QUOTED_STRING = r'"(?:[^\\"]|\\.)*"'
_HTTP_TOKEN = r"[!#\$%&'\*\+\-\.\^_`\|~0-9A-Za-z]+"
_PAIR = '{token}=(?:{token}|{quoted_string})'.format(
    token=_HTTP_TOKEN, quoted_string=_HTTP_QUOTED_STRING)
_LEXER_RE = re.compile('{pair}|.'.format(pair=_PAIR))


def parse_forwarded(field_values):
    all_elems = []
    for field_value in field_values:
        name = None
        elem = {}
        elems = [types.MappingProxyType(elem)]
        need_separator = False
        for match in _LEXER_RE.finditer(field_value):
            s = match.group(0)
            if len(s) > 1:                  # pair
                if need_separator:
                    break
                (name, value) = s.split('=', 1)
                if value[0] == '"':
                    value = re.sub(r'\\(.)', r'\1', value[1:-1])
                elem[name.lower()] = value
                need_separator = True
            elif s == ',':
                need_separator = False
                elem = {}
                elems.append(types.MappingProxyType(elem))
            elif s == ';':
                need_separator = False
            elif s != ' ' and s != '\t':
                break
        else:
            # Didn't ``break`` -- this `field_value` is correct
            all_elems.extend(elems)
    return all_elems


def test_parse_forwarded():
    assert parse_forwarded(['for=1.2.3.4']) == [{'for': '1.2.3.4'}]
    assert parse_forwarded(['for=1.2.3.4;,']) == [{'for': '1.2.3.4'}, {}]
    assert parse_forwarded(['for=1.2.3.4;by="', 'for=5.6.7.8']) == \
        [{'for': '5.6.7.8'}]
    assert parse_forwarded([
        r' For=1.2.3.4;By=_unknown;;Secret="Wow, \"secrets\"!";  ']
    ) == [{'for': '1.2.3.4', 'by': '_unknown', 'secret': 'Wow, "secrets"!'}]
    assert parse_forwarded([r'foo-bar="\"\"\\\\\a\b\c\"\\\\\""']) == \
        [{'foo-bar': r'""\\abc"\\"'}]
    assert parse_forwarded([r'foo-bar="\"\"\\\\\a\b\c\"\\\\""']) == []
    assert parse_forwarded([r'for=_1 by=_2']) == []
    assert parse_forwarded([r'for="_1"by="_2"']) == []
    assert parse_forwarded([r'for=_1/by=_2']) == []
    assert parse_forwarded([r'"for=1.2.3.4"']) == []
    assert parse_forwarded([r'xyzzy="' + '\\' * 10000 + '"']) == \
        [{'xyzzy': '\\' * 5000}]

if __name__ == '__main__':
    test_parse_forwarded()