Add load_from_options_getter to plugin loading

Loading from getter function was introduced into keystoneclient as a way
to enable OCC and auth_token middleware to define more unusual loading
mechanisms.

It was skipped in the move to keystoneauth. This adds it back.

Closes-Bug: #1514339
Change-Id: I1d464917e0ddec8e13f9395ad75db6ccc53cb813

keystoneauth1/loading/base.py

@@ -123,3 +123,26 @@ class BaseLoader(object):
             raise exceptions.MissingRequiredOptions(missing_required)
 
         return self.plugin_class(**kwargs)
+
+    def load_from_options_getter(self, getter, **kwargs):
+        """Load a plugin from a getter function that returns appropriate values
+
+        To handle cases other than the provided CONF and CLI loading you can
+        specify a custom loader function that will be queried for the option
+        value.
+        The getter is a function that takes a
+        :py:class:`keystoneauth1.loading.Opt` and returns a value to load with.
+
+        :param getter: A function that returns a value for the given opt.
+        :type getter: callable
+
+        :returns: An authentication Plugin.
+        :rtype: :py:class:`keystoneauth1.plugin.BaseAuthPlugin`
+        """
+        for opt in self.get_options():
+            val = getter(opt)
+            if val is not None:
+                val = opt.type(val)
+            kwargs.setdefault(opt.dest, val)
+
+        return self.load_from_options(**kwargs)

keystoneauth1/loading/cli.py

@@ -97,12 +97,7 @@ def load_from_argparse_arguments(namespace, **kwargs):
     else:
         plugin = base.get_plugin_loader(namespace.os_auth_type)
 
-    plugin_opts = plugin.get_options()
+    def _getter(opt):
+        return getattr(namespace, 'os_%s' % opt.dest)
 
-    for opt in plugin_opts:
-        val = getattr(namespace, 'os_%s' % opt.dest)
-        if val is not None:
-            val = opt.type(val)
-        kwargs.setdefault(opt.dest, val)
-
-    return plugin.load_from_options(**kwargs)
+    return plugin.load_from_options_getter(_getter)

keystoneauth1/loading/conf.py

@@ -129,10 +129,7 @@ def load_from_conf_options(conf, group, **kwargs):
 
     conf.register_opts(oslo_opts, group=group)
 
-    for opt in plugin_opts:
-        val = conf[group][opt.dest]
-        if val is not None:
-            val = opt.type(val)
-        kwargs.setdefault(opt.dest, val)
+    def _getter(opt):
+        return conf[group][opt.dest]
 
-    return plugin.load_from_options(**kwargs)
+    return plugin.load_from_options_getter(_getter, **kwargs)

keystoneauth1/tests/unit/loading/test_loading.py

@@ -50,3 +50,30 @@ class LoadingTests(utils.TestCase):
 
         for l in loaders.values():
             self.assertIsInstance(l, loading.BaseLoader)
+
+    def test_loading_getter(self):
+
+        called_opts = []
+
+        vals = {'a-int': 44,
+                'a-bool': False,
+                'a-float': 99.99,
+                'a-str': 'value'}
+
+        val = uuid.uuid4().hex
+
+        def _getter(opt):
+            called_opts.append(opt.name)
+            # return str because oslo.config should convert them back
+            return str(vals[opt.name])
+
+        p = utils.MockLoader().load_from_options_getter(_getter, other=val)
+
+        self.assertEqual(set(vals), set(called_opts))
+
+        for k, v in vals.items():
+            # replace - to _ because it's the dest used to create kwargs
+            self.assertEqual(v, p[k.replace('-', '_')])
+
+        # check that additional kwargs get passed through
+        self.assertEqual(val, p['other'])