Indented banner raises ValueError and loses the whole config: is_banner_start and regex_banner disagree #907

Environment

• Python version: 3.12.13
• netutils version: 1.19.1

Expected Behavior

A line that is_banner_start() accepts should be parseable by regex_banner.

Observed Behavior

They disagree, and the whole config is lost rather than one line.

is_banner_start() matches the stripped line (line.lstrip().startswith(...)), while CiscoConfigParser.regex_banner requires banner at column 0:

^(banner\s+\S+|\s*vacant-message)\s+(?P<banner_delimiter>\^C|.)

An indented banner is therefore detected as a banner start, fails to resolve a delimiter, and the banner_end setter raises. The exception leaves __init__, so one such line makes the entire config unparseable.

Two hints that this is an oversight rather than intent: in that pattern the vacant-message alternative allows \s* and the banner one does not; and ASAConfigParser parses an indented banner, including the one shipped at tests/unit/mock/config/parser/base/cisco_asa/asa_nested_banner_sent.txt, while IOS, NX-OS and EOS raise on the same input.

Steps to Reproduce

1. pip install netutils==1.19.1

2. Run:

   from netutils.config.parser import IOSConfigParser
   IOSConfigParser("group-policy P attributes\n banner value hello\n")
   # ValueError: There was an error parsing your banner, the end of the banner could not be found
   

ASAConfigParser on that same input returns ['group-policy P attributes', ' banner value hello']. The sample is ASA syntax, chosen because netutils already ships a fixture for it; the point is that the two functions disagree, not that the line is valid IOS.

Possible fixes

Allow leading whitespace in regex_banner, or stop stripping in is_banner_start(). If the former, note the delimiter group . also matches the first character of a following word, so \^C|[^\w\s] may be wanted with it.

Happy to PR against develop.