A ReDoS proof email address validation

email_validator.py

from re import match

def validateEmail(email):
  valid = 'abcdefghijklmnopqrstuvwxyz1234567890!#$%&\'*+-/=?^_`{}|~'
  if not email:
    return False
  email = email.lower()
  if email.startswith('"'):
    i = 1
    while i < min(64, len(email)):
      if email[i] in (valid + '()<>[]:;@,. '):
        i += 1
        continue
      if email[i] == '\\':
        if email[i+1:] and email[i+1] in (valid + '()<>[]:;@,.\\" '):
          i += 2
          continue
        return False
      if email[i] == '"':
        break
      return False
    if i == 64:
      i -= 1
    if not (email[i+1:] and email[i+1] == '@'):
      return False
    return validateDomain(email[i+2:])
  i = 0
  while i < min(64, len(email)):
    if email[i] in valid:
      i += 1
      continue
    if email[i] == '.':
      if i == 0 or not email[i+1:] or email[i+1] in '.@':
        return False
      i += 1
      continue
    if email[i] == '@':
      if i == 0:
        return False
      i -= 1
      break
    return False
  if i == 64:
    i -= 1
  if not (email[i+1:] and email[i+1] == '@'):
    return False
  return validateDomain(email[i+2:])

def validateDomain(domain):
  fqdn = r"^(?:(?:[a-z0-9]{1,2}|[a-z0-9][a-z0-9-]{,61}[a-z0-9])\.)*(?:[a-z0-9]{1,2}|[a-z0-9][a-z0-9-]{,61}?[a-z0-9])$"
  addr4 = r"(?:(?:[01]?[0-9]{1,2}|2(?:[0-4]?[0-9]|5[0-5]))\.){3}(?:[01]?[0-9]{1,2}|2(?:[0-4]?[0-9]|5[0-5]))$"
  if not domain or domain[255:]:
    return False
  if not domain.startswith('['):
    return not match(addr4, domain) and bool(match(fqdn, domain))
  if not domain.endswith(']'):
    return False
  domain = domain[1:-1]
  if match(f"^{addr4}", domain):
    return domain != '0.0.0.0'
  if domain.endswith('::'):
    return False
  v4_flg = False
  try:
    _, last = domain.rsplit(':', 1)
  except:
    return False
  if match(addr4, last):
    if domain == '0.0.0.0':
      return False
    domain = domain.replace(last, '0:0')
    v4_flg = True
  if '::' in domain:
    oc = 8 - domain.count(':')
    if oc < 1:
      return False
    domain = domain.replace('::', f":{'0:' * oc}")
    if domain.startswith(':'):
      domain = f'0{domain}'
    if domain.endswith(':'):
      domain = f'{domain}0'
  elems = domain.split(':')
  if len(elems) != 8:
    return False
  res = 0
  for i, a in enumerate(elems):
    if a[4:]:
      return False
    try:
      res += int(a, 16) << ((7 - i) * 16)
    except Exception as e:
      return False
  return res != 0 and (not v4_flg or res >> 32 == 0xffff)

if __name__ == "__main__":
  import unittest
  valid_emails = [
    '[email protected]',
    '[email protected]',
    '[email protected]',
    '[email protected]',
    '[email protected]',
    '[email protected]',
    '[email protected]',
    '-email@domain',
    '[email protected]',
    "abc.#%&'/=~`*+?{}^$-|@ghi.com",
    '[email protected]',
    '[email protected]',
    'user+mailbox/[email protected]',
    'customer/[email protected]',
    "!#$%&'*+-/=?^_`.{|}[email protected]",
    '!def!xyz%[email protected]',
    '"e#$$%&@>mail"@domain.com',
    '"em,ail"@localhost',
    '"Abc@def"@example.com',
    '"Fred\\ Bloggs"@example.com',
    '"Joe.\\\\Blow"@example.com',
    '"Joe.\\"Blow"@example.com',
    '".dot_kara_hazimaru"@example.com',
    '"I.likeyou."@example.com',
    '"I..love...you"@example.com',
    '[email protected]',
    '[email protected]',
    'email@localhost',
    'a@a',
    '[email protected]',
    '[email protected]',
    '[email protected]',
    '[email protected]',
    '[email protected]',
    'email@[123.123.123.123]',
    'a@[255.255.255.255]',
    'a@[001.002.003.004]',
    'a@[2001:0db8:bd05:01d2:288a:1fc0:0001:10ee]',
    'a@[2001:db8:20:3:1000:100:20:3]',
    'a@[2001:db8::1234:0:0:9abc]',
    'a@[2001:db8::9abc]',
    'a@[::1]', 'ea@[::ffff:255.255.255.255]',
    'a@abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ01234567890.com',
    'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789+/@example.com',
    '"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ01234567+/"@example.com',
    'abcdefhghijklmnopqrstuvwxyzABC@aaaaaaaa01.aaaaaaaa02.aaaaaaaa03.aaaaaaaa04.aaaaaaaa05.aaaaaaaa06.aaaaaaaa07.aaaaaaaa08.aaaaaaaa09.aaaaaaaa10.aaaaaaaa11.aaaaaaaa12.aaaaaaaa13.aaaaaaaa14.aaaaaaaa15.aaaaaaaa16.aaaaaaaa17.aaaaaaaa18.aaaaaaaa19.aaaaaaaa20.aaaaaaaa21.aaaaaaaa22.aaaaaaaa23',
    'abcdefhghijklmnopqrstuvwxyzABCD@aaaaaaaa01.aaaaaaaa02.aaaaaaaa03.aaaaaaaa04.aaaaaaaa05.aaaaaaaa06.aaaaaaaa07.aaaaaaaa08.aaaaaaaa09.aaaaaaaa10.aaaaaaaa11.aaaaaaaa12.aaaaaaaa13.aaaaaaaa14.aaaaaaaa15.aaaaaaaa16.aaaaaaaa17.aaaaaaaa18.aaaaaaaa19.aaaaaaaa20.aaaaaaaa21.aaaaaaaa22.aaaaaaaa23.zz',
    '"abcdefhghijklmnopqrstuvwxyzABC"@aaaaaaaa01.aaaaaaaa02.aaaaaaaa03.aaaaaaaa04.aaaaaaaa05.aaaaaaaa06.aaaaaaaa07.aaaaaaaa08.aaaaaaaa09.aaaaaaaa10.aaaaaaaa11.aaaaaaaa12.aaaaaaaa13.aaaaaaaa14.aaaaaaaa15.aaaaaaaa16.aaaaaaaa17.aaaaaaaa18.aaaaaaaa19.aaaaaaaa20.com',
    '"abcdefhghijklmnopqrstuvwxyzABCD"@aaaaaaaa01.aaaaaaaa02.aaaaaaaa03.aaaaaaaa04.aaaaaaaa05.aaaaaaaa06.aaaaaaaa07.aaaaaaaa08.aaaaaaaa09.aaaaaaaa10.aaaaaaaa11.aaaaaaaa12.aaaaaaaa13.aaaaaaaa14.aaaaaaaa15.aaaaaaaa16.aaaaaaaa17.aaaaaaaa18.aaaaaaaa19.aaaaaaaa20.com'
  ]
  invalid_emails = [
    '[email protected]',
    '[email protected]',
    '[email protected]',
    '[email protected]',
    '[email protected]',
    "abc.def@#%&'/=~`*+?{}^$-|.com",
    'ab<[email protected]',
    'abc.de<[email protected]',
    '[email protected]',
    '[email protected]',
    '[email protected]',
    'あいうえお@domain.com',
    '[email protected]',
    '[email protected]',
    '[email protected]',
    "abc.def@ghi.#%&'/=~`*+?{}^$-|",
    'abc.def@gh<i.com',
    '[email protected]<m',
    '[email protected]',
    '[email protected]',
    '[email protected]',
    '[email protected]',
    'a@[::ffff:0:255.255.255.255]',
    'email@[111.222.333.44444]',
    'a@[0.0.0.0]',
    'a@[255.255.255.256]',
    'a@[example.com]',
    'a@[example.com:hoge]',
    'a@[fuga:xxxxxxx]',
    'a@[2001:0db8:bd05:01d2:288a::1fc0:0001:10ee]',
    'a@[2001:0db8:bd05:01d2:288a:1fc0:0001:10ee:11fe]',
    'a@[::]',
    'a@[0::0]',
    'a@[1::]',
    'a@[1:2:3:4:5:6:7::]',
    'a@[::255.255.255.255]',
    'a@[2001:db8:3:4::192.0.2.33]',
    'a@[64:ff9b::192.0.2.33]',
    'a@abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ012345678901.com',
    'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789+/[email protected]',
    '"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ01234567+/a"@example.com',
    'abcdefhghijklmnopqrstuvwxyzABCD@aaaaaaaa01.aaaaaaaa02.aaaaaaaa03.aaaaaaaa04.aaaaaaaa05.aaaaaaaa06.aaaaaaaa07.aaaaaaaa08.aaaaaaaa09.aaaaaaaa10.aaaaaaaa11.aaaaaaaa12.aaaaaaaa13.aaaaaaaa14.aaaaaaaa15.aaaaaaaa16.aaaaaaaa17.aaaaaaaa18.aaaaaaaa19.aaaaaaaa20.aaaaaaaa21.aaaaaaaa22.aaaaaaaa23.zzz',
    'plainaddress',
    '@domain.com',
    'Joe Smith <[email protected]>',
    'email.domain.com',
    'email@[email protected]',
    '[email protected] (Joe Smith)',
    'email@ example',
    '"foo"."bar"@example.com'
  ]
  class ValidatorTest(unittest.TestCase):
    for e in valid_emails:
      locals()[f'test_valid: {e}'] = (lambda e: lambda self: self.assertTrue(validateEmail(e)))(e)
    for e in invalid_emails:
      locals()[f'test_invalid: {e}'] = (lambda e: lambda self: self.assertFalse(validateEmail(e)))(e)
    del e
  unittest.main()

timeit.py

from time import time
from email_validator import validateEmail

for n in range(5, 12):
  s = "username@host" + ".abcde" * n + "."
  start = time()
  validateEmail(s)
  print(f'{len(s)}:', f'{time() - start}secs')