251 lines
9.0 KiB
Python
251 lines
9.0 KiB
Python
|
|
# Copyright 2013 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.
|
|
|
|
"""
|
|
An RPC server exposes a number of endpoints, each of which contain a set of
|
|
methods which may be invoked remotely by clients over a given transport.
|
|
|
|
To create an RPC server, you supply a transport, target and a list of
|
|
endpoints.
|
|
|
|
A transport can be obtained simply by calling the get_transport() method::
|
|
|
|
transport = messaging.get_transport(conf)
|
|
|
|
which will load the appropriate transport driver according to the user's
|
|
messaging configuration. See get_transport() for more details.
|
|
|
|
The target supplied when creating an RPC server expresses the topic, server
|
|
name and - optionally - the exchange to listen on. See Target for more details
|
|
on these attributes.
|
|
|
|
Multiple RPC Servers may listen to the same topic (and exchange)
|
|
simultaineously. See RPCClient for details regarding how RPC requests are
|
|
distributed to the Servers in this case.
|
|
|
|
Each endpoint object may have a target attribute which may have namespace and
|
|
version fields set. By default, we use the 'null namespace' and version 1.0.
|
|
Incoming method calls will be dispatched to the first endpoint with the
|
|
requested method, a matching namespace and a compatible version number.
|
|
|
|
The first parameter to method invocations is always the request context
|
|
supplied by the client. The remaining parameters are the arguments supplied to
|
|
the method by the client. Endpoint methods may return a value. If so the RPC
|
|
Server will send the returned value back to the requesting client via the
|
|
transport.
|
|
|
|
The executor parameter controls how incoming messages will be received and
|
|
dispatched. By default, the most simple executor is used - the blocking
|
|
executor. This executor processes inbound RPC requests on the server's thread,
|
|
blocking it from processing additional requests until it finishes with the
|
|
current request. This includes time spent sending the reply message to the
|
|
transport if the method returns a result. Refer to the Executor documentation
|
|
for descriptions of the other types of executors.
|
|
|
|
*Note:* If the "eventlet" executor is used, the threading and time library need
|
|
to be monkeypatched.
|
|
|
|
The RPC reply operation is best-effort: the server will consider the message
|
|
containing the reply successfully sent once it is accepted by the messaging
|
|
transport. The server does not guarantee that the reply is processed by the
|
|
RPC client. If the send fails an error will be logged and the server will
|
|
continue to processing incoming RPC requests.
|
|
|
|
Parameters to the method invocation and values returned from the method are
|
|
python primitive types. However the actual encoding of the data in the message
|
|
may not be in primitive form (e.g. the message payload may be a dictionary
|
|
encoded as an ASCII string using JSON). A serializer object is used to convert
|
|
incoming encoded message data to primitive types. The serializer is also used
|
|
to convert the return value from primitive types to an encoding suitable for
|
|
the message payload.
|
|
|
|
RPC servers have start(), stop() and wait() methods to begin handling
|
|
requests, stop handling requests, and wait for all in-process requests to
|
|
complete after the Server has been stopped.
|
|
|
|
A simple example of an RPC server with multiple endpoints might be::
|
|
|
|
from oslo_config import cfg
|
|
import oslo_messaging
|
|
import time
|
|
|
|
class ServerControlEndpoint(object):
|
|
|
|
target = oslo_messaging.Target(namespace='control',
|
|
version='2.0')
|
|
|
|
def __init__(self, server):
|
|
self.server = server
|
|
|
|
def stop(self, ctx):
|
|
if self.server:
|
|
self.server.stop()
|
|
|
|
class TestEndpoint(object):
|
|
|
|
def test(self, ctx, arg):
|
|
return arg
|
|
|
|
transport = oslo_messaging.get_transport(cfg.CONF)
|
|
target = oslo_messaging.Target(topic='test', server='server1')
|
|
endpoints = [
|
|
ServerControlEndpoint(None),
|
|
TestEndpoint(),
|
|
]
|
|
server = oslo_messaging.get_rpc_server(transport, target, endpoints,
|
|
executor='blocking')
|
|
try:
|
|
server.start()
|
|
while True:
|
|
time.sleep(1)
|
|
except KeyboardInterrupt:
|
|
print("Stopping server")
|
|
|
|
server.stop()
|
|
server.wait()
|
|
|
|
"""
|
|
|
|
__all__ = [
|
|
'get_rpc_server',
|
|
'expected_exceptions',
|
|
'expose'
|
|
]
|
|
|
|
import logging
|
|
import sys
|
|
|
|
from oslo_messaging._i18n import _LE
|
|
from oslo_messaging.rpc import dispatcher as rpc_dispatcher
|
|
from oslo_messaging import server as msg_server
|
|
|
|
LOG = logging.getLogger(__name__)
|
|
|
|
|
|
class RPCServer(msg_server.MessageHandlingServer):
|
|
def __init__(self, transport, target, dispatcher, executor='blocking'):
|
|
super(RPCServer, self).__init__(transport, dispatcher, executor)
|
|
self._target = target
|
|
|
|
def _create_listener(self):
|
|
return self.transport._listen(self._target, 1, None)
|
|
|
|
def _process_incoming(self, incoming):
|
|
message = incoming[0]
|
|
try:
|
|
message.acknowledge()
|
|
except Exception:
|
|
LOG.exception(_LE("Can not acknowledge message. Skip processing"))
|
|
return
|
|
|
|
failure = None
|
|
try:
|
|
res = self.dispatcher.dispatch(message)
|
|
except rpc_dispatcher.ExpectedException as e:
|
|
failure = e.exc_info
|
|
LOG.debug(u'Expected exception during message handling (%s)', e)
|
|
except Exception:
|
|
# current sys.exc_info() content can be overriden
|
|
# by another exception raised by a log handler during
|
|
# LOG.exception(). So keep a copy and delete it later.
|
|
failure = sys.exc_info()
|
|
LOG.exception(_LE('Exception during message handling'))
|
|
|
|
try:
|
|
if failure is None:
|
|
message.reply(res)
|
|
else:
|
|
message.reply(failure=failure)
|
|
except Exception:
|
|
LOG.exception(_LE("Can not send reply for message"))
|
|
finally:
|
|
# NOTE(dhellmann): Remove circular object reference
|
|
# between the current stack frame and the traceback in
|
|
# exc_info.
|
|
del failure
|
|
|
|
|
|
def get_rpc_server(transport, target, endpoints,
|
|
executor='blocking', serializer=None, access_policy=None):
|
|
"""Construct an RPC server.
|
|
|
|
:param transport: the messaging transport
|
|
:type transport: Transport
|
|
:param target: the exchange, topic and server to listen on
|
|
:type target: Target
|
|
:param endpoints: a list of endpoint objects
|
|
:type endpoints: list
|
|
:param executor: name of a message executor - for example
|
|
'eventlet', 'blocking'
|
|
:type executor: str
|
|
:param serializer: an optional entity serializer
|
|
:type serializer: Serializer
|
|
:param access_policy: an optional access policy.
|
|
Defaults to LegacyRPCAccessPolicy
|
|
:type access_policy: RPCAccessPolicyBase
|
|
"""
|
|
dispatcher = rpc_dispatcher.RPCDispatcher(endpoints, serializer,
|
|
access_policy)
|
|
return RPCServer(transport, target, dispatcher, executor)
|
|
|
|
|
|
def expected_exceptions(*exceptions):
|
|
"""Decorator for RPC endpoint methods that raise expected exceptions.
|
|
|
|
Marking an endpoint method with this decorator allows the declaration
|
|
of expected exceptions that the RPC server should not consider fatal,
|
|
and not log as if they were generated in a real error scenario.
|
|
|
|
Note that this will cause listed exceptions to be wrapped in an
|
|
ExpectedException, which is used internally by the RPC sever. The RPC
|
|
client will see the original exception type.
|
|
"""
|
|
def outer(func):
|
|
def inner(*args, **kwargs):
|
|
try:
|
|
return func(*args, **kwargs)
|
|
# Take advantage of the fact that we can catch
|
|
# multiple exception types using a tuple of
|
|
# exception classes, with subclass detection
|
|
# for free. Any exception that is not in or
|
|
# derived from the args passed to us will be
|
|
# ignored and thrown as normal.
|
|
except exceptions:
|
|
raise rpc_dispatcher.ExpectedException()
|
|
return inner
|
|
return outer
|
|
|
|
|
|
def expose(func):
|
|
"""Decorator for RPC endpoint methods that are exposed to the RPC client.
|
|
|
|
If the dispatcher's access_policy is set to ExplicitRPCAccessPolicy then
|
|
endpoint methods need to be explicitly exposed.::
|
|
|
|
# foo() cannot be invoked by an RPC client
|
|
def foo(self):
|
|
pass
|
|
|
|
# bar() can be invoked by an RPC client
|
|
@rpc.expose
|
|
def bar(self):
|
|
pass
|
|
|
|
"""
|
|
|
|
func.exposed = True
|
|
|
|
return func
|