From ee0e546150ab74e7936a315865f8d4d436a1a9a0 Mon Sep 17 00:00:00 2001
From: Mark McLoughlin <markmc@redhat.com>
Date: Mon, 10 Jun 2013 10:34:52 +0100
Subject: [PATCH] Some error handling improvements

---
 openstack/common/messaging/__init__.py        |  8 +++-
 .../common/messaging/_drivers/impl_fake.py    |  4 +-
 openstack/common/messaging/exceptions.py      | 11 +++++-
 openstack/common/messaging/transport.py       | 37 ++++++++++++++++---
 4 files changed, 49 insertions(+), 11 deletions(-)

diff --git a/openstack/common/messaging/__init__.py b/openstack/common/messaging/__init__.py
index 89d1ba3ee..9bc5b0d1c 100644
--- a/openstack/common/messaging/__init__.py
+++ b/openstack/common/messaging/__init__.py
@@ -13,10 +13,14 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-from .exceptions import MessagingException
-from .exceptions import MessagingTimeout
 from .rpc.client import RPCClient
 from .rpc.server import BlockingRPCServer
 from .serializer import Serializer
 from .target import Target
 from .transport import get_transport
+
+from .exceptions import MessagingException
+from .exceptions import MessagingTimeout
+
+from .transport import DriverLoadFailure
+from .transport import InvalidTransportURL
diff --git a/openstack/common/messaging/_drivers/impl_fake.py b/openstack/common/messaging/_drivers/impl_fake.py
index 92ebc02e3..a4e4236e5 100644
--- a/openstack/common/messaging/_drivers/impl_fake.py
+++ b/openstack/common/messaging/_drivers/impl_fake.py
@@ -20,7 +20,7 @@ import Queue
 import time
 
 from openstack.common.gettextutils import _
-from openstack.common.messaging import exceptions
+from openstack.common import messaging
 from openstack.common.messaging._drivers import base
 from openstack.common.messaging import _utils as utils
 
@@ -119,7 +119,7 @@ class FakeDriver(base.BaseDriver):
                 break
 
             if timeout and (time.time() - start_time > timeout):
-                raise exceptions.MessagingTimeout(
+                raise messaging.MessagingTimeout(
                     _('No listeners found for topic %s') % target.topic)
 
             time.sleep(.05)
diff --git a/openstack/common/messaging/exceptions.py b/openstack/common/messaging/exceptions.py
index c9fb5575e..54b123a07 100644
--- a/openstack/common/messaging/exceptions.py
+++ b/openstack/common/messaging/exceptions.py
@@ -13,9 +13,16 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+
 class MessagingException(Exception):
-    pass
+    """Base class for exceptions."""
+
+    def __init__(self, msg=None):
+        self.msg = msg
+
+    def __str__(self):
+        return self.msg
 
 
 class MessagingTimeout(MessagingException):
-    pass
+    """Raised if message sending times out."""
diff --git a/openstack/common/messaging/transport.py b/openstack/common/messaging/transport.py
index dbd4cdafb..195774bd4 100644
--- a/openstack/common/messaging/transport.py
+++ b/openstack/common/messaging/transport.py
@@ -21,6 +21,9 @@ import urlparse
 from oslo.config import cfg
 from stevedore import driver
 
+from openstack.common.messaging import exceptions
+
+
 _transport_opts = [
     cfg.StrOpt('transport_url',
                default=None,
@@ -75,6 +78,24 @@ class Transport(object):
         return self._driver.listen(target)
 
 
+class InvalidTransportURL(exceptions.MessagingException):
+    """Raised if transport URL is invalid."""
+
+    def __init__(self, url, msg):
+        super(InvalidTransportURL, self).__init__(msg)
+        self.url = url
+
+
+class DriverLoadFailure(exceptions.MessagingException):
+    """Raised if a transport driver can't be loaded."""
+
+    def __init__(self, driver, ex):
+        msg = 'Failed to load transport driver "%s": %s' % (driver, ex)
+        super(DriverLoadFailure, self).__init__(msg)
+        self.driver = driver
+        self.ex = ex
+
+
 def get_transport(conf, url=None):
     """A factory method for Transport objects.
 
@@ -102,6 +123,8 @@ def get_transport(conf, url=None):
     url = url or conf.transport_url
     if url is not None:
         rpc_backend = urlparse.urlparse(url).scheme
+        if not rpc_backend:
+            raise InvalidTransportURL(url, 'No scheme specified in "%s"' % url)
     else:
         rpc_backend = conf.rpc_backend
 
@@ -109,9 +132,13 @@ def get_transport(conf, url=None):
     if url is not None:
         kwargs['url'] = url
 
-    mgr = driver.DriverManager('openstack.common.messaging.drivers',
-                               rpc_backend,
-                               invoke_on_load=True,
-                               invoke_args=[conf],
-                               invoke_kwds=kwargs)
+    try:
+        mgr = driver.DriverManager('openstack.common.messaging.drivers',
+                                   rpc_backend,
+                                   invoke_on_load=True,
+                                   invoke_args=[conf],
+                                   invoke_kwds=kwargs)
+    except RuntimeError as ex:
+        raise DriverLoadFailure(rpc_backend, ex)
+
     return Transport(mgr.driver)