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# 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.
import abc
import logging
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
from oslo_messaging import transport as msg_transport
__all__ = [
'ClientSendError',
'RPCClient',
'RPCVersionCapError',
'RemoteError',
]
LOG = logging.getLogger(__name__)
_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,
call_monitor_timeout=None, transport_options=None):
self.conf = transport.conf
self.transport = transport
self.target = target
self.serializer = serializer
self.timeout = timeout
self.call_monitor_timeout = call_monitor_timeout
self.retry = retry
self.version_cap = version_cap
self.transport_options = transport_options
super(_BaseCallContext, self).__init__()
def _make_message(self, ctxt, method, args):
msg = dict(method=method)
msg['args'] = dict()
for argname, arg in args.items():
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,
transport_options=self.transport_options)
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
cm_timeout = self.call_monitor_timeout
self._check_version_cap(msg.get('version'))
try:
result = \
self.transport._send(self.target, msg_ctxt, msg,
wait_for_reply=True, timeout=timeout,
call_monitor_timeout=cm_timeout,
retry=self.retry,
transport_options=self.transport_options)
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,
call_monitor_timeout=_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,
call_monitor_timeout=_marker, transport_options=_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
if call_monitor_timeout is cls._marker:
call_monitor_timeout = call_context.call_monitor_timeout
if transport_options is cls._marker:
transport_options = call_context.transport_options
return _CallContext(call_context.transport, target,
call_context.serializer,
timeout, version_cap, retry,
call_monitor_timeout, transport_options)
def prepare(self, exchange=_marker, topic=_marker, namespace=_marker,
version=_marker, server=_marker, fanout=_marker,
timeout=_marker, version_cap=_marker, retry=_marker,
call_monitor_timeout=_marker):
return _CallContext._prepare(self,
exchange, topic, namespace,
version, server, fanout,
timeout, version_cap, retry,
call_monitor_timeout)
class RPCClient(_BaseCallContext):
"""A class for invoking methods on remote RPC servers.
The RPCClient class is responsible for sending method invocations to and
receiving return values from remote RPC servers via a messaging transport.
Two RPC patterns are supported: RPC calls and RPC casts.
An RPC cast is used when an RPC method does *not* return a value to
the caller. An RPC call is used when a return value is expected from the
method. For further information see the cast() and call() methods.
The default target used for all subsequent calls and casts is supplied to
the RPCClient constructor. The client uses the target to control how the
RPC request is delivered to a server. If only the target's topic (and
optionally exchange) are set, then the RPC can be serviced by any server
that is listening to that topic (and exchange). If multiple servers are
listening on that topic/exchange, then one server is picked using a
best-effort round-robin algorithm. Alternatively, the client can set the
Target's ``server`` attribute to the name of a specific server to send the
RPC request to one particular server. In the case of RPC cast, the RPC
request can be broadcast to all servers listening to the Target's
topic/exchange by setting the Target's ``fanout`` property to ``True``.
While the default target is set on construction, 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.
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_rpc_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.
If the connection to the messaging service is not active when an RPC
request is made the client will block waiting for the connection to
complete. If the connection fails to complete, the client will try to
re-establish that connection. By default this will continue indefinitely
until the connection completes. However, the retry parameter can be used to
have the RPC request 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,
call_monitor_timeout=None, transport_options=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 is attempted.
N means attempt at most N retries.
:type retry: int
:param call_monitor_timeout: an optional timeout (in seconds) for
active call heartbeating. If specified,
requires the server to heartbeat
long-running calls at this interval
(less than the overall timeout
parameter).
:type call_monitor_timeout: int
"""
if serializer is None:
serializer = msg_serializer.NoOpSerializer()
if not isinstance(transport, msg_transport.RPCTransport):
LOG.warning("Using notification transport for RPC. Please use "
"get_rpc_transport to obtain an RPC transport "
"instance.")
super(RPCClient, self).__init__(
transport, target, serializer, timeout, version_cap, retry,
call_monitor_timeout, transport_options
)
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,
call_monitor_timeout=_marker, transport_options=_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 is attempted.
N means attempt at most N retries.
:type retry: int
:param transport_options: additional parameters to configure the driver
for example to send parameters as "mandatory"
flag in RabbitMQ
:type transport_options: dictionary
:param call_monitor_timeout: an optional timeout (in seconds) for
active call heartbeating. If specified,
requires the server to heartbeat
long-running calls at this interval
(less than the overall timeout
parameter).
:type call_monitor_timeout: int
"""
return _CallContext._prepare(self,
exchange, topic, namespace,
version, server, fanout,
timeout, version_cap, retry,
call_monitor_timeout, transport_options)
def cast(self, ctxt, method, **kwargs):
"""Invoke a method without blocking for a return value.
The cast() method is used to invoke an RPC method that does not return
a value. cast() RPC requests may be broadcast to all Servers listening
on a given topic by setting the fanout Target property to ``True``.
The cast() operation is best-effort: cast() will block the
calling thread until the RPC request method is accepted by the
messaging transport, but cast() does *not* verify that the RPC method
has been invoked by the server. cast() does guarantee that the
method will be not executed twice on a destination (e.g. 'at-most-once'
execution).
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.
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.
: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 if the messaging transport fails to
accept the request.
"""
self.prepare().cast(ctxt, method, **kwargs)
def call(self, ctxt, method, **kwargs):
"""Invoke a method and wait for a reply.
The call() method is used to invoke RPC methods that return a
value. Since only a single return value is permitted it is not possible
to call() to a fanout target.
call() will block the calling thread until the messaging transport
provides the return value, a timeout occurs, or a non-recoverable error
occurs.
call() guarantees that the RPC request is done 'at-most-once' which
ensures that the call will never be duplicated. However if the call
should fail or time out before the return value arrives then there are
no guarantees whether or not the method was invoked.
Since call() blocks until completion of the RPC method, call()s from
the same thread are guaranteed to be processed in-order.
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_rpc_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.
: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()
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