IMAP4.login_plain() does not reject NUL in a memoryview credential #159631

Bug description:

IMAP4.login_plain() raises ValueError for a user name or password that contains NUL, but not when the value is a memoryview or another bytes-like object other than bytes and bytearray. The NUL is then sent in the PLAIN message as an extra field separator.

import imaplib

class IMAP4(imaplib.IMAP4):
    def __init__(self):
        pass
    def authenticate(self, mechanism, authobject):
        print(authobject(b''))

IMAP4().login_plain(memoryview(b'user\0admin'), b'password')

Output:

b'\x00user\x00admin\x00password'

Expected: ValueError: NUL is not allowed in user name or password, as with login_plain(b'user\0admin', b'password').

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-159631: Reject NUL in memoryview credentials in IMAP4.login_plain() #159633