path: root/oslo_messaging/rpc/client.py

# 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 six

from oslo.config import cfg
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 too high. It needs "
               "to be lower than 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


class _CallContext(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(_CallContext, 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 (not self.version_cap or
                utils.version_is_compatible(self.version_cap,
                                            self.target.version))

    def cast(self, ctxt, method, **kwargs):
        """Invoke a method and return immediately. See RPCClient.cast()."""
        msg = self._make_message(ctxt, method, kwargs)
        ctxt = self.serializer.serialize_context(ctxt)

        if self.version_cap:
            self._check_version_cap(msg.get('version'))
        try:
            self.transport._send(self.target, 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

        if self.version_cap:
            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)

    @classmethod
    def _prepare(cls, base,
                 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()."""
        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 = base.target(**kwargs)

        if timeout is cls._marker:
            timeout = base.timeout
        if retry is cls._marker:
            retry = base.retry
        if version_cap is cls._marker:
            version_cap = base.version_cap

        return _CallContext(base.transport, target,
                            base.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):
        """Prepare a method invocation context. See RPCClient.prepare()."""
        return self._prepare(self,
                             exchange, topic, namespace,
                             version, server, fanout,
                             timeout, version_cap, retry)


class RPCClient(object):

    """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='testtopic', 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='testtopic', 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")
    """

    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
        """
        self.conf = transport.conf
        self.conf.register_opts(_client_opts)

        self.transport = transport
        self.target = target
        self.timeout = timeout
        self.retry = retry
        self.version_cap = version_cap
        self.serializer = serializer or msg_serializer.NoOpSerializer()

        super(RPCClient, self).__init__()

    _marker = _CallContext._marker

    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.

        :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.

        :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()