# Copyright 2010 United States Government as represented by the # Administrator of the National Aeronautics and Space Administration. # All Rights Reserved. # 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. __all__ = [ 'ClientSendError', 'RPCClient', 'RPCVersionCapError', 'RemoteError', ] import abc from oslo_config import cfg import six from oslo_messaging._drivers import base as driver_base from oslo_messaging import _utils as utils from oslo_messaging import exceptions from oslo_messaging import serializer as msg_serializer _client_opts = [ cfg.IntOpt('rpc_response_timeout', default=60, help='Seconds to wait for a response from a call.'), ] class RemoteError(exceptions.MessagingException): """Signifies that a remote endpoint method has raised an exception. Contains a string representation of the type of the original exception, the value of the original exception, and the traceback. These are sent to the parent as a joined string so printing the exception contains all of the relevant info. """ def __init__(self, exc_type=None, value=None, traceback=None): self.exc_type = exc_type self.value = value self.traceback = traceback msg = ("Remote error: %(exc_type)s %(value)s\n%(traceback)s." % dict(exc_type=self.exc_type, value=self.value, traceback=self.traceback)) super(RemoteError, self).__init__(msg) class RPCVersionCapError(exceptions.MessagingException): def __init__(self, version, version_cap): self.version = version self.version_cap = version_cap msg = ("Requested message version, %(version)s is incompatible. It " "needs to be equal in major version and less than or equal " "in minor version as the specified version cap " "%(version_cap)s." % dict(version=self.version, version_cap=self.version_cap)) super(RPCVersionCapError, self).__init__(msg) class ClientSendError(exceptions.MessagingException): """Raised if we failed to send a message to a target.""" def __init__(self, target, ex): msg = 'Failed to send to target "%s": %s' % (target, ex) super(ClientSendError, self).__init__(msg) self.target = target self.ex = ex @six.add_metaclass(abc.ABCMeta) class _BaseCallContext(object): _marker = object() def __init__(self, transport, target, serializer, timeout=None, version_cap=None, retry=None): self.conf = transport.conf self.transport = transport self.target = target self.serializer = serializer self.timeout = timeout self.retry = retry self.version_cap = version_cap super(_BaseCallContext, self).__init__() def _make_message(self, ctxt, method, args): msg = dict(method=method) msg['args'] = dict() for argname, arg in six.iteritems(args): msg['args'][argname] = self.serializer.serialize_entity(ctxt, arg) if self.target.namespace is not None: msg['namespace'] = self.target.namespace if self.target.version is not None: msg['version'] = self.target.version return msg def _check_version_cap(self, version): if not utils.version_is_compatible(self.version_cap, version): raise RPCVersionCapError(version=version, version_cap=self.version_cap) def can_send_version(self, version=_marker): """Check to see if a version is compatible with the version cap.""" version = self.target.version if version is self._marker else version return utils.version_is_compatible(self.version_cap, version) @classmethod def _check_version(cls, version): if version is not cls._marker: # quick sanity check to make sure parsable version numbers are used try: utils.version_is_compatible(version, version) except (IndexError, ValueError): raise exceptions.MessagingException( "Version must contain a major and minor integer. Got %s" % version) def cast(self, ctxt, method, **kwargs): """Invoke a method and return immediately. See RPCClient.cast().""" msg = self._make_message(ctxt, method, kwargs) msg_ctxt = self.serializer.serialize_context(ctxt) self._check_version_cap(msg.get('version')) try: self.transport._send(self.target, msg_ctxt, msg, retry=self.retry) except driver_base.TransportDriverError as ex: raise ClientSendError(self.target, ex) def call(self, ctxt, method, **kwargs): """Invoke a method and wait for a reply. See RPCClient.call().""" if self.target.fanout: raise exceptions.InvalidTarget('A call cannot be used with fanout', self.target) msg = self._make_message(ctxt, method, kwargs) msg_ctxt = self.serializer.serialize_context(ctxt) timeout = self.timeout if self.timeout is None: timeout = self.conf.rpc_response_timeout self._check_version_cap(msg.get('version')) try: result = self.transport._send(self.target, msg_ctxt, msg, wait_for_reply=True, timeout=timeout, retry=self.retry) except driver_base.TransportDriverError as ex: raise ClientSendError(self.target, ex) return self.serializer.deserialize_entity(ctxt, result) @abc.abstractmethod def prepare(self, exchange=_marker, topic=_marker, namespace=_marker, version=_marker, server=_marker, fanout=_marker, timeout=_marker, version_cap=_marker, retry=_marker): """Prepare a method invocation context. See RPCClient.prepare().""" class _CallContext(_BaseCallContext): _marker = _BaseCallContext._marker @classmethod def _prepare(cls, call_context, exchange=_marker, topic=_marker, namespace=_marker, version=_marker, server=_marker, fanout=_marker, timeout=_marker, version_cap=_marker, retry=_marker): cls._check_version(version) kwargs = dict( exchange=exchange, topic=topic, namespace=namespace, version=version, server=server, fanout=fanout) kwargs = dict([(k, v) for k, v in kwargs.items() if v is not cls._marker]) target = call_context.target(**kwargs) if timeout is cls._marker: timeout = call_context.timeout if version_cap is cls._marker: version_cap = call_context.version_cap if retry is cls._marker: retry = call_context.retry return _CallContext(call_context.transport, target, call_context.serializer, timeout, version_cap, retry) def prepare(self, exchange=_marker, topic=_marker, namespace=_marker, version=_marker, server=_marker, fanout=_marker, timeout=_marker, version_cap=_marker, retry=_marker): return _CallContext._prepare(self, exchange, topic, namespace, version, server, fanout, timeout, version_cap, retry) class RPCClient(_BaseCallContext): """A class for invoking methods on remote servers. The RPCClient class is responsible for sending method invocations to remote servers via a messaging transport. A default target is supplied to the RPCClient constructor, but target attributes can be overridden for individual method invocations using the prepare() method. A method invocation consists of a request context dictionary, a method name and a dictionary of arguments. A cast() invocation just sends the request and returns immediately. A call() invocation waits for the server to send a return value. This class is intended to be used by wrapping it in another class which provides methods on the subclass to perform the remote invocation using call() or cast():: class TestClient(object): def __init__(self, transport): target = messaging.Target(topic='test', version='2.0') self._client = messaging.RPCClient(transport, target) def test(self, ctxt, arg): return self._client.call(ctxt, 'test', arg=arg) An example of using the prepare() method to override some attributes of the default target:: def test(self, ctxt, arg): cctxt = self._client.prepare(version='2.5') return cctxt.call(ctxt, 'test', arg=arg) RPCClient have a number of other properties - for example, timeout and version_cap - which may make sense to override for some method invocations, so they too can be passed to prepare():: def test(self, ctxt, arg): cctxt = self._client.prepare(timeout=10) return cctxt.call(ctxt, 'test', arg=arg) However, this class can be used directly without wrapping it another class. For example:: transport = messaging.get_transport(cfg.CONF) target = messaging.Target(topic='test', version='2.0') client = messaging.RPCClient(transport, target) client.call(ctxt, 'test', arg=arg) but this is probably only useful in limited circumstances as a wrapper class will usually help to make the code much more obvious. By default, cast() and call() will block until the message is successfully sent. However, the retry parameter can be used to have message sending fail with a MessageDeliveryFailure after the given number of retries. For example:: client = messaging.RPCClient(transport, target, retry=None) client.call(ctxt, 'sync') try: client.prepare(retry=0).cast(ctxt, 'ping') except messaging.MessageDeliveryFailure: LOG.error("Failed to send ping message") """ _marker = _BaseCallContext._marker def __init__(self, transport, target, timeout=None, version_cap=None, serializer=None, retry=None): """Construct an RPC client. :param transport: a messaging transport handle :type transport: Transport :param target: the default target for invocations :type target: Target :param timeout: an optional default timeout (in seconds) for call()s :type timeout: int or float :param version_cap: raise a RPCVersionCapError version exceeds this cap :type version_cap: str :param serializer: an optional entity serializer :type serializer: Serializer :param retry: an optional default connection retries configuration None or -1 means to retry forever 0 means no retry N means N retries :type retry: int """ if serializer is None: serializer = msg_serializer.NoOpSerializer() super(RPCClient, self).__init__( transport, target, serializer, timeout, version_cap, retry ) self.conf.register_opts(_client_opts) def prepare(self, exchange=_marker, topic=_marker, namespace=_marker, version=_marker, server=_marker, fanout=_marker, timeout=_marker, version_cap=_marker, retry=_marker): """Prepare a method invocation context. Use this method to override client properties for an individual method invocation. For example:: def test(self, ctxt, arg): cctxt = self.prepare(version='2.5') return cctxt.call(ctxt, 'test', arg=arg) :param exchange: see Target.exchange :type exchange: str :param topic: see Target.topic :type topic: str :param namespace: see Target.namespace :type namespace: str :param version: requirement the server must support, see Target.version :type version: str :param server: send to a specific server, see Target.server :type server: str :param fanout: send to all servers on topic, see Target.fanout :type fanout: bool :param timeout: an optional default timeout (in seconds) for call()s :type timeout: int or float :param version_cap: raise a RPCVersionCapError version exceeds this cap :type version_cap: str :param retry: an optional connection retries configuration None or -1 means to retry forever 0 means no retry N means N retries :type retry: int """ return _CallContext._prepare(self, exchange, topic, namespace, version, server, fanout, timeout, version_cap, retry) def cast(self, ctxt, method, **kwargs): """Invoke a method and return immediately. Method arguments must either be primitive types or types supported by the client's serializer (if any). Similarly, the request context must be a dict unless the client's serializer supports serializing another type. Note: cast does not ensure that the remote method will be executed on each destination. But it does ensure that the method will be not executed twice on a destination (e.g. 'at-most-once' execution). Note: there are no ordering guarantees across successive casts, even among casts to the same destination. Therefore methods may be executed in an order different from the order in which they are cast. :param ctxt: a request context dict :type ctxt: dict :param method: the method name :type method: str :param kwargs: a dict of method arguments :type kwargs: dict :raises: MessageDeliveryFailure """ self.prepare().cast(ctxt, method, **kwargs) def call(self, ctxt, method, **kwargs): """Invoke a method and wait for a reply. Method arguments must either be primitive types or types supported by the client's serializer (if any). Similarly, the request context must be a dict unless the client's serializer supports serializing another type. The semantics of how any errors raised by the remote RPC endpoint method are handled are quite subtle. Firstly, if the remote exception is contained in one of the modules listed in the allow_remote_exmods messaging.get_transport() parameter, then it this exception will be re-raised by call(). However, such locally re-raised remote exceptions are distinguishable from the same exception type raised locally because re-raised remote exceptions are modified such that their class name ends with the '_Remote' suffix so you may do:: if ex.__class__.__name__.endswith('_Remote'): # Some special case for locally re-raised remote exceptions Secondly, if a remote exception is not from a module listed in the allowed_remote_exmods list, then a messaging.RemoteError exception is raised with all details of the remote exception. Note: call is done 'at-most-once'. In case of we can't known if the call have been done correctly, because we didn't get the response on time, MessagingTimeout exception is raised. The real reason can vary, transport failure, worker doesn't answer in time or crash, ... :param ctxt: a request context dict :type ctxt: dict :param method: the method name :type method: str :param kwargs: a dict of method arguments :type kwargs: dict :raises: MessagingTimeout, RemoteError, MessageDeliveryFailure """ return self.prepare().call(ctxt, method, **kwargs) def can_send_version(self, version=_marker): """Check to see if a version is compatible with the version cap.""" return self.prepare(version=version).can_send_version()