Fix the bug of "openstack console log show"

The behaviors are inconsistent while different
negative line numbers specified.

Change-Id: I2573f3e789f5603c896758971830ffc0b94c5e2b
Closes-Bug: #1512263

openstackclient/common/parseractions.py

@@ -65,3 +65,18 @@ class RangeAction(argparse.Action):
             # Too many values
             msg = "Invalid range, too many values"
             raise argparse.ArgumentError(self, msg)
+
+
+class NonNegativeAction(argparse.Action):
+    """A custom action to check whether the value is non-negative or not
+
+    Ensures the value is >= 0.
+    """
+
+    def __call__(self, parser, namespace, values, option_string=None):
+        try:
+            assert(int(values) >= 0)
+            setattr(namespace, self.dest, values)
+        except Exception:
+            msg = "%s expected a non-negative integer" % (str(option_string))
+            raise argparse.ArgumentTypeError(self, msg)

openstackclient/tests/common/test_parseractions.py

@@ -102,3 +102,58 @@ class TestKeyValueAction(utils.TestCase):
         expect = {'green': '100%'}
         self.assertDictEqual(expect, actual)
         self.assertEqual(None, failhere)
+
+
+class TestNonNegativeAction(utils.TestCase):
+    def test_negative_values(self):
+        parser = argparse.ArgumentParser()
+
+        # Set up our typical usage
+        parser.add_argument(
+            '--foo',
+            metavar='<foo>',
+            type=int,
+            action=parseractions.NonNegativeAction,
+        )
+
+        self.assertRaises(
+            argparse.ArgumentTypeError,
+            parser.parse_args,
+            "--foo -1".split()
+        )
+
+    def test_zero_values(self):
+        parser = argparse.ArgumentParser()
+
+        # Set up our typical usage
+        parser.add_argument(
+            '--foo',
+            metavar='<foo>',
+            type=int,
+            action=parseractions.NonNegativeAction,
+        )
+
+        results = parser.parse_args(
+            '--foo 0'.split()
+        )
+
+        actual = getattr(results, 'foo', None)
+        self.assertEqual(actual, 0)
+
+    def test_positive_values(self):
+        parser = argparse.ArgumentParser()
+
+        # Set up our typical usage
+        parser.add_argument(
+            '--foo',
+            metavar='<foo>',
+            type=int,
+            action=parseractions.NonNegativeAction,
+        )
+
+        results = parser.parse_args(
+            '--foo 1'.split()
+        )
+
+        actual = getattr(results, 'foo', None)
+        self.assertEqual(actual, 1)