Do not treat an indented banner as the start of a banner

changes/907.fixed

@@ -0,0 +1 @@
+Fixed an indented banner aborting the parse of an entire config. `is_banner_start` matched the stripped line while the banner patterns anchor at the start of it, and where the two disagreed the resulting `ValueError` left `__init__`. Affected the Cisco IOS, NX-OS, IOS-XR and Arista EOS parsers.

netutils/config/parser.py

@@ -580,6 +580,14 @@ def is_banner_one_line(config_line: str) -> bool:
     def is_banner_start(self, line: str) -> bool:
         """Determine if the line starts a banner config."""
         state = super(CiscoConfigParser, self).is_banner_start(line)
+        if state and not self.regex_banner.match(line):
+            # The inherited check matches the stripped line, while regex_banner
+            # anchors `banner` at the start of it. Where the two disagree the
+            # line cannot yield a delimiter, and setting banner_end below would
+            # raise out of __init__ and lose the whole config. Treat it as an
+            # ordinary line instead, which is what ASAConfigParser already does
+            # by not stripping in its own is_banner_start.
+            return False
         if state:
             self.banner_end = line
         return state
@@ -728,6 +736,17 @@ class EOSConfigParser(BaseSpaceConfigParser):
 
     banner_end = "EOF"
 
+    def is_banner_start(self, line: str) -> bool:
+        """Determine if the line starts a banner config.
+
+        Deliberately does not strip the line. The inherited check does, so an
+        indented `banner` was taken for the start of a banner, and the search
+        for the "EOF" terminator then ran to the end of the config and raised
+        out of __init__, losing everything. ASAConfigParser does the same thing
+        for the same reason.
+        """
+        return any(line.startswith(banner_start) for banner_start in self.banner_start)
+
     def _build_banner(self, config_line: str) -> t.Optional[str]:
         """Handle banner config lines.
 

tests/unit/test_parser.py

@@ -70,6 +70,39 @@ def test_incorrect_banner_ios():
         compliance.parser_map["cisco_ios"](banner_cfg).config_lines  # pylint: disable=expression-not-assigned
 
 
+def test_indented_banner_is_not_a_banner_start():
+    """An indented banner must not abort the parse of the whole config.
+
+    is_banner_start matched the stripped line while the banner patterns anchor
+    at the start of it. Where the two disagreed the line could not yield a
+    delimiter, and the resulting ValueError left __init__, so one such line lost
+    the entire config. ASAConfigParser already avoided this by not stripping.
+    """
+    cfg = "group-policy P attributes\n banner value hello\n"
+    for network_os in ("cisco_ios", "cisco_nxos", "cisco_asa", "arista_eos", "cisco_iosxr"):
+        config_lines = compliance.parser_map[network_os](cfg).config_lines
+        assert [line.config_line for line in config_lines] == [
+            "group-policy P attributes",
+            " banner value hello",
+        ], network_os
+
+
+@pytest.mark.parametrize(
+    ("network_os", "banner"),
+    [
+        ("cisco_ios", "banner motd ^C\nhello\n^C\n"),
+        ("cisco_nxos", "banner motd ^C\nhello\n^C\n"),
+        ("arista_eos", "banner motd EOF\nhello\nEOF\n"),
+    ],
+)
+def test_top_level_banner_still_folds(network_os, banner):
+    """The guard above must not stop a real, unindented banner being folded."""
+    config_lines = compliance.parser_map[network_os](banner + "hostname r1\n").config_lines
+    assert config_lines[0].config_line.startswith("banner motd")
+    assert "hello" in config_lines[1].config_line
+    assert config_lines[-1].config_line == "hostname r1"
+
+
 def test_duplicate_line():
     logging = (
         "!\n"