Add a CLI argument validation utility

blueprint oslo-cliutils

In nova-manage and cinder-manage, we allow command arguments to be
passed as optional or positional arguments.

e.g.

  $> nova-manage floating create 10.0.0.1/28
  $> nova-manage floating create --ip_range 10.0.0.1/28

are equivalent.

Once nova-manage has collected those arguments, it calls the
appropriate command function with them as positional and keyword
arguments. If the user forgets to supply a required argument, they
merely get a TypeError with little useful information.

Improve the usability of these commands using a new utility function
to check that the required arguments have been supplied and raise a
useful exception if not.

Change-Id: If6e4a9f222a30472bbfbcd06859865bd4e37e139

1 files changed, 66 insertions, 0 deletions

diff --git a/openstack/common/cliutils.py b/openstack/common/cliutils.py
new file mode 100644
index 0000000..8f4dc44
--- /dev/null
+++ b/openstack/common/cliutils.py
@@ -0,0 +1,66 @@
+# vim: tabstop=4 shiftwidth=4 softtabstop=4
+
+# Copyright 2012 Red Hat, Inc.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+import inspect
+import string
+
+
+class MissingArgs(Exception):
+
+    def __init__(self, missing):
+        self.missing = missing
+
+    def __str__(self):
+        if len(self.missing) == 1:
+            return ("An argument is missing: %(missing)s" %
+                    dict(missing=self.missing[0]))
+        else:
+            return ("%(num)d arguments are missing: %(missing)s" %
+                    dict(num=len(self.missing),
+                         missing=string.join(self.missing, ', ')))
+
+
+def validate_args(fn, *args, **kwargs):
+    """Check that the supplied args are sufficient for calling a function.
+
+    >>> validate_args(lambda a: None)
+    Traceback (most recent call last):
+        ...
+    MissingArgs: An argument is missing: a
+    >>> validate_args(lambda a, b, c, d: None, 0, c=1)
+    Traceback (most recent call last):
+        ...
+    MissingArgs: 2 arguments are missing: b, d
+
+    :param fn: the function to check
+    :param arg: the positional arguments supplied
+    :param kwargs: the keyword arguments supplied
+    """
+    argspec = inspect.getargspec(fn)
+
+    num_defaults = len(argspec.defaults or [])
+    required_args = argspec.args[:len(argspec.args) - num_defaults]
+
+    def isbound(method):
+        return getattr(method, 'im_self', None) is not None
+
+    if isbound(fn):
+        required_args.pop(0)
+
+    missing = [arg for arg in required_args if arg not in kwargs]
+    missing = missing[len(args):]
+    if missing:
+        raise MissingArgs(missing)