netmiko: Huawei special_login_handler is not logging in successfully

The reason for Huawei telnet trouble netmiko.exceptions.ReadException: Unable to successfully split output based on pattern is that pattern (]\s*$|>\s*$|(Change now|Please choose 'YES' or 'NO').+) contains nested group (nested parentheses). To fix this issue, changes of source code needed.

Details:

1. In this string: https://github.com/ktbyers/netmiko/blob/f3b5da244e6ce1e5fd7bd89fd36b090e854828b4/netmiko/huawei/huawei.py#L132 combined_pattern created - i mean this pattern (]\s*$|>\s*$|(Change now|Please choose 'YES' or 'NO').+)
2. Then created combined_pattern passes to read_until_pattern method here https://github.com/ktbyers/netmiko/blob/f3b5da244e6ce1e5fd7bd89fd36b090e854828b4/netmiko/huawei/huawei.py#L155
3. Bad thing happend here: https://github.com/ktbyers/netmiko/blob/f3b5da244e6ce1e5fd7bd89fd36b090e854828b4/netmiko/base_connection.py#L636 After splitting, we got result list of length = 4, and this is the reason for ReadException here: https://github.com/ktbyers/netmiko/blob/f3b5da244e6ce1e5fd7bd89fd36b090e854828b4/netmiko/base_connection.py#L645
4. And the reason of len(result) = 4 is that combined_pattern has nested parentheses here:

(]\s*$|>\s*$|(Change now|Please choose 'YES' or 'NO').+)
             ^                                      ^

@Toxic-Waste- you can try to edit file /home/<snip>/.local/lib/python3.10/site-packages/netmiko/huawei/huawei.py on line 131 change this:

password_change_prompt = r"(Change now|Please choose 'YES' or 'NO').+"

to this:

password_change_prompt = r"Change now|Please choose 'YES' or 'NO'"

But you must understand that:

• it is not good to change package’s code directly like that
• it can cause unexpected error in another place
• this is just a dirty quick fix that worked for my case

@ktbyers I can try to analize side effects of proposed changes and craft Pull Request if you like. But if you think that PR is redundant, please let me know. Thanks!

@ktbyers Yes, i see.

import re
from netmiko import ConnectHandler
host = input('Input Dest host: ')

device = {
    'device_type': 'huawei_telnet',
    'ip':   host,
    'username': 'login',
    'password': 'pass',
    'port' : 23,
    'verbose': True,
    'session_log': f'{host}.log'
}

net_connect = ConnectHandler(**device)

pip3 list | grep netmiko
netmiko                      4.1.0

I can confirm the issue using Netmiko 4.0.0 (latest pip release together with Python 3.10.4) using device_type = 'huawei'.

With the Netmiko 3.4.0 release everything works fine. Also, it doesn’t seem to make any difference whether the password change prompt is displayed or not (see both tracebacks below).

netmiko.exceptions.ReadException: Unable to successfully split output based on pattern:
pattern=((Change now|Please choose))|([\]>]\s*$)
output='\nWarning: The password will expire in 11 days.\nThe password needs to be changed. Change now? [Y/N]: '
results=['\nWarning: The password will expire in 11 days.\nThe password needs to be changed. ', 'Change now', 'Change now', None, '? [Y/N]: ']

netmiko.exceptions.ReadException: Unable to successfully split output based on pattern:
pattern=((Change now|Please choose))|([\]>]\s*$)
output='\nInfo: Current mode: Monitor (automatically making switching decisions).\nWarning: The intelligent upgrade function is disabled. Log in to the web platform and enable this function.\n  -----------------------------------------------------------------------------     \n  User last login information:     [...]      \n  -----------------------------------------------------------------------------\n<AC6508>'
results=['\nInfo: Current mode: Monitor (automatically making switching decisions).\nWarning: The intelligent upgrade function is disabled. Log in to the web platform and enable this function.\n  -----------------------------------------------------------------------------     \n  User last login information:     [...]    \n  -----------------------------------------------------------------------------\n<AC6508', None, None, '>', '']

After spending some time investigating the issue I found out that the pattern matching logic in read_until_pattern expects the pattern to split exactly in 3 parts (using re.split), see base_connection.py#L579 for reference. Seems this change was introduced during some fundamental changes to the channel reading logic in in https://github.com/ktbyers/netmiko/commit/793100dcfd76d3eb5089ba4cd27c99e3c3c0f886.

I have proposed a fix and documented some more info in #2719.