Expose an entry point to list all config options

Register a oslo.messaging entry point in the oslo.config.opts namespace
which, when called, returns a list of the configuration options which
may be registered by the library at runtime.

The idea here is that the sample config file generator can query this
and include the returned options in the sample config file of any
applications which use the library.

Some sample code for fetching available options:

  import pkg_resources

  for ep in pkg_resources.iter_entry_points('oslo.config.opts'):
      if ep.name == "oslo.messaging":
          list_opts = ep.load()
          for g, opts in list_opts():
              opts.sort(key=lambda x: x.name)
              print "[%s]" % g
              for o in opts:
                  print "%s = %s" % (o.name, o.default)
              print

Related-Bug: #1241566
Change-Id: Ic28351258652d2ea38974e2f4d1aa6b1d3dd7192

doc/source/index.rst

@@ -17,6 +17,7 @@ Contents
    notifier
    serializer
    exceptions
+   opts
    conffixture
 
 Release Notes

oslo/messaging/opts.py

@@ -0,0 +1,75 @@
+
+# Copyright 2014 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.
+
+__all__ = [
+    'list_opts'
+]
+
+import copy
+import itertools
+
+from oslo.messaging._drivers import amqp
+from oslo.messaging._drivers import common as drivers_common
+from oslo.messaging._drivers import impl_qpid
+from oslo.messaging._drivers import impl_rabbit
+from oslo.messaging._drivers import impl_zmq
+from oslo.messaging._drivers import matchmaker
+from oslo.messaging._drivers import matchmaker_redis
+from oslo.messaging._drivers import matchmaker_ring
+from oslo.messaging._executors import impl_eventlet
+from oslo.messaging.notify import notifier
+from oslo.messaging.rpc import client
+from oslo.messaging import transport
+
+_global_opt_lists = [
+    amqp.amqp_opts,
+    drivers_common._exception_opts,
+    impl_qpid.qpid_opts,
+    impl_rabbit.rabbit_opts,
+    impl_zmq.zmq_opts,
+    matchmaker.matchmaker_opts,
+    matchmaker_redis.matchmaker_redis_opts,
+    impl_eventlet._eventlet_opts,
+    notifier._notifier_opts,
+    client._client_opts,
+    transport._transport_opts
+]
+
+_opts = [
+    (None, list(itertools.chain(*_global_opt_lists))),
+    ('matchmaker_ring', matchmaker_ring.matchmaker_opts),
+]
+
+
+def list_opts():
+    """Return a list of oslo.config options available in the library.
+
+    The returned list includes all oslo.config options which may be registered
+    at runtime by the library.
+
+    Each element of the list is a tuple. The first element is the name of the
+    group under which the list of elements in the second element will be
+    registered. A group name of None corresponds to the [DEFAULT] group in
+    config files.
+
+    This function is also discoverable via the 'oslo.messaging' entry point
+    under the 'oslo.config.opts' namespace.
+
+    The purpose of this is to allow tools like the Oslo sample config file
+    generator to discover the options exposed to users by this library.
+
+    :returns: a list of (group_name, opts) tuples
+    """
+    return [(g, copy.deepcopy(o)) for g, o in _opts]

setup.cfg

@@ -49,6 +49,9 @@ oslo.messaging.notify.drivers =
     test = oslo.messaging.notify._impl_test:TestDriver
     noop = oslo.messaging.notify._impl_noop:NoOpDriver
 
+oslo.config.opts =
+    oslo.messaging = oslo.messaging.opts:list_opts
+
 [build_sphinx]
 source-dir = doc/source
 build-dir = doc/build

tests/test_opts.py

@@ -0,0 +1,47 @@
+
+# Copyright 2014 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 pkg_resources
+
+from oslo.messaging import opts
+from tests import utils as test_utils
+
+
+class OptsTestCase(test_utils.BaseTestCase):
+
+    def _test_list_opts(self, result):
+        self.assertEqual(2, len(result))
+
+        groups = [g for (g, l) in result]
+        self.assertIn(None, groups)
+        self.assertIn('matchmaker_ring', groups)
+
+        opt_names = [o.name for (g, l) in result for o in l]
+        self.assertIn('rpc_backend', opt_names)
+        self.assertIn('allowed_rpc_exception_modules', opt_names)
+
+    def test_list_opts(self):
+        self._test_list_opts(opts.list_opts())
+
+    def test_entry_point(self):
+        result = None
+        for ep in pkg_resources.iter_entry_points('oslo.config.opts'):
+            if ep.name == "oslo.messaging":
+                list_fn = ep.load()
+                result = list_fn()
+                break
+
+        self.assertIsNotNone(result)
+        self._test_list_opts(result)