51c9b47c33
In oslo.messaging design phase, it was planned to introduce executor specific RPCServer types though they were never implemented. References to those types sneaked into docstrings from the original design document. Since we're not going to implement those types now, docstrings should be updated accordingly. Change-Id: Ic4017bb8f89d47115bb7dc59483e81d26c76212b
148 lines
5.4 KiB
Python
148 lines
5.4 KiB
Python
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# Copyright 2013 Red Hat, Inc.
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#
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# Licensed under the Apache License, Version 2.0 (the "License"); you may
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# not use this file except in compliance with the License. You may obtain
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# a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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# License for the specific language governing permissions and limitations
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# under the License.
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"""
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An RPC server exposes a number of endpoints, each of which contain a set of
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methods which may be invoked remotely by clients over a given transport.
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To create an RPC server, you supply a transport, target and a list of
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endpoints.
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A transport can be obtained simply by calling the get_transport() method::
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transport = messaging.get_transport(conf)
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which will load the appropriate transport driver according to the user's
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messaging configuration configuration. See get_transport() for more details.
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The target supplied when creating an RPC server expresses the topic, server
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name and - optionally - the exchange to listen on. See Target for more details
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on these attributes.
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Each endpoint object may have a target attribute which may have namespace and
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version fields set. By default, we use the 'null namespace' and version 1.0.
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Incoming method calls will be dispatched to the first endpoint with the
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requested method, a matching namespace and a compatible version number.
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RPC servers have start(), stop() and wait() messages to begin handling
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requests, stop handling requests and wait for all in-process requests to
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complete.
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A simple example of an RPC server with multiple endpoints might be::
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from oslo.config import cfg
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from oslo import messaging
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class ServerControlEndpoint(object):
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target = messaging.Target(namespace='control',
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version='2.0')
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def __init__(self, server):
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self.server = server
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def stop(self, ctx):
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self.server.stop()
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class TestEndpoint(object):
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def test(self, ctx, arg):
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return arg
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transport = messaging.get_transport(cfg.CONF)
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target = messaging.Target(topic='test', server='server1')
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endpoints = [
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ServerControlEndpoint(self),
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TestEndpoint(),
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]
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server = messaging.get_rpc_server(transport, target, endpoints,
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executor='eventlet')
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server.start()
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server.wait()
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Clients can invoke methods on the server by sending the request to a topic and
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it gets sent to one of the servers listening on the topic, or by sending the
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request to a specific server listening on the topic, or by sending the request
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to all servers listening on the topic (known as fanout). These modes are chosen
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via the server and fanout attributes on Target but the mode used is transparent
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to the server.
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The first parameter to method invocations is always the request context
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supplied by the client.
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Parameters to the method invocation are primitive types and so must be the
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return values from the methods. By supplying a serializer object, a server can
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deserialize a request context and arguments from - and serialize return values
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to - primitive types.
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"""
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__all__ = [
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'get_rpc_server',
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'expected_exceptions',
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]
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from oslo.messaging.rpc import dispatcher as rpc_dispatcher
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from oslo.messaging import server as msg_server
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def get_rpc_server(transport, target, endpoints,
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executor='blocking', serializer=None):
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"""Construct an RPC server.
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The executor parameter controls how incoming messages will be received and
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dispatched. By default, the most simple executor is used - the blocking
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executor.
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:param transport: the messaging transport
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:type transport: Transport
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:param target: the exchange, topic and server to listen on
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:type target: Target
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:param endpoints: a list of endpoint objects
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:type endpoints: list
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:param executor: name of a message executor - e.g. 'eventlet', 'blocking'
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:type executor: str
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:param serializer: an optional entity serializer
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:type serializer: Serializer
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"""
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dispatcher = rpc_dispatcher.RPCDispatcher(target, endpoints, serializer)
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return msg_server.MessageHandlingServer(transport, dispatcher, executor)
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def expected_exceptions(*exceptions):
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"""Decorator for RPC endpoint methods that raise expected exceptions.
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Marking an endpoint method with this decorator allows the declaration
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of expected exceptions that the RPC server should not consider fatal,
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and not log as if they were generated in a real error scenario.
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Note that this will cause listed exceptions to be wrapped in an
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ExpectedException, which is used internally by the RPC sever. The RPC
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client will see the original exception type.
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"""
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def outer(func):
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def inner(*args, **kwargs):
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try:
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return func(*args, **kwargs)
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# Take advantage of the fact that we can catch
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# multiple exception types using a tuple of
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# exception classes, with subclass detection
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# for free. Any exception that is not in or
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# derived from the args passed to us will be
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# ignored and thrown as normal.
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except exceptions:
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raise rpc_dispatcher.ExpectedException()
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return inner
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return outer
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