Better error handling in server.start()

Transport drivers can raise transport driver specific exceptions
in listen(). Catch such exceptions and wrap them in a ServerListenError
which callers to start() can explicitly handle.

openstack/common/messaging/__init__.py

@@ -47,6 +47,7 @@ RPCVersionCapError = client.RPCVersionCapError
 
 MessagingServerError = server.MessagingServerError
 ExecutorLoadFailure = server.ExecutorLoadFailure
+ServerListenError = server.ServerListenError
 
 RPCDispatcherError = rpc_dispatcher.RPCDispatcherError
 NoSuchMethod = rpc_dispatcher.NoSuchMethod

openstack/common/messaging/_drivers/base.py

@@ -15,6 +15,12 @@
 
 import abc
 
+from openstack.common.messaging import exceptions
+
+
+class TransportDriverError(exceptions.MessagingException):
+    """Base class for transport driver specific exceptions."""
+
 
 class IncomingMessage(object):
 

openstack/common/messaging/_drivers/impl_fake.py

@@ -24,15 +24,13 @@ from openstack.common.messaging._drivers import base
 from openstack.common.messaging import _utils as utils
 
 
-class InvalidTarget(ValueError):
+class InvalidTarget(base.TransportDriverError, ValueError):
 
     def __init__(self, msg, target):
-        self.msg = msg
+        msg = msg + ":" + str(target)
+        super(InvalidTarget, self).__init__(msg)
         self.target = target
 
-    def __str__(self):
-        return self.msg + ":" + str(self.target)
-
 
 class FakeIncomingMessage(base.IncomingMessage):
 

openstack/common/messaging/server.py

@@ -19,6 +19,7 @@
 from stevedore import driver
 
 from openstack.common import log as logging
+from openstack.common.messaging._drivers import base as driver_base
 from openstack.common.messaging import exceptions
 
 _LOG = logging.getLogger(__name__)
@@ -38,6 +39,16 @@ class ExecutorLoadFailure(MessagingServerError):
         self.ex = ex
 
 
+class ServerListenError(MessagingServerError):
+    """Raised if we failed to listen on a target."""
+
+    def __init__(self, target, ex):
+        msg = 'Failed to listen on target "%s": %s' % (target, ex)
+        super(ServerListenError, self).__init__(msg)
+        self.target = target
+        self.ex = ex
+
+
 class MessageHandlingServer(object):
     """Server for handling messages.
 
@@ -101,7 +112,12 @@ class MessageHandlingServer(object):
         """
         if self._executor is not None:
             return
-        listener = self.transport._listen(self.target)
+
+        try:
+            listener = self.transport._listen(self.target)
+        except driver_base.TransportDriverError as ex:
+            raise ServerListenError(self.target, ex)
+
         self._executor = self._executor_cls(self.conf, listener,
                                             self.dispatcher)
         self._executor.start()