netcmd: add optparse validators and Range validator

Add the ability to the add validators to optparse Option fields.

The Option class was already subclassed in `netcmd/__init__.py` so
adding some functionality to this was relatively easy.

Added the ability to add Validator classes to a field so that this can
be used for anything else in the future, but for now there is a Range
validator required by upcoming auto silo commands.

Signed-off-by: Rob van der Linde <rob@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Joseph Sutton <josephsutton@catalyst.net.nz>

python/samba/netcmd/__init__.py

@@ -26,10 +26,38 @@ import sys
 import traceback
 import textwrap
 
+from .validators import ValidationError
+
 
 class Option(SambaOption):
+    ATTRS = SambaOption.ATTRS + ["validators"]
     SUPPRESS_HELP = optparse.SUPPRESS_HELP
 
+    def run_validators(self, opt, value):
+        """Runs the list of validators on the current option.
+
+        If the validator raises ValidationError, turn that into CommandError
+        which gives nicer output.
+        """
+        validators = getattr(self, "validators") or []
+
+        for validator in validators:
+            try:
+                validator(opt, value)
+            except ValidationError as e:
+                raise CommandError(e)
+
+    def convert_value(self, opt, value):
+        """Override convert_value to run validators just after.
+
+        This can also be done in process() but there we would have to
+        replace the entire method.
+        """
+        value = super().convert_value(opt, value)
+        self.run_validators(opt, value)
+        return value
+
+
 # This help formatter does text wrapping and preserves newlines
 
 

python/samba/netcmd/validators.py

@@ -0,0 +1,77 @@
+# Unix SMB/CIFS implementation.
+#
+# validators
+#
+# Copyright (C) Catalyst.Net Ltd. 2023
+#
+# Written by Rob van der Linde <rob@catalyst.net.nz>
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+
+from abc import ABCMeta, abstractmethod
+
+
+class ValidationError(Exception):
+    pass
+
+
+class Validator(metaclass=ABCMeta):
+
+    @abstractmethod
+    def __call__(self, field, value):
+        pass
+
+
+class Range(Validator):
+    """Checks if the value is within range min ... max."""
+
+    def __init__(self, min=None, max=None):
+        if min is None and max is None:
+            raise ValueError("Range without a min and max doesn't make sense.")
+
+        self.min = min
+        self.max = max
+
+    def __call__(self, field, value):
+        """Check if value is within the range min ... max.
+
+        It is possible to omit min, or omit max, in which case a more
+        tailored error message is returned.
+        """
+        if self.min is not None and self.max is None:
+            if value < self.min:
+                raise ValidationError(f"{field} must be at least {self.min}")
+
+        elif self.min is None and self.max is not None:
+            if value > self.max:
+                raise ValidationError(
+                    f"{field} cannot be greater than {self.max}")
+
+        elif self.min is not None and self.max is not None:
+            if value < self.min or value > self.max:
+                raise ValidationError(
+                    f"{field} must be between {self.min} and {self.max}")
+
+
+class OneOf(Validator):
+    """Checks if the value is in a list of possible choices."""
+
+    def __init__(self, choices):
+        self.choices = sorted(choices)
+
+    def __call__(self, field, value):
+        if value not in self.choices:
+            allowed_choices = ", ".join(self.choices)
+            raise ValidationError(f"{field} must be one of: {allowed_choices}")