Source code for oslo_messaging.target

# 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.


class Target(object):

    """Identifies the destination of messages.

    A Target encapsulates all the information to identify where a message
    should be sent or what messages a server is listening for.

    Different subsets of the information encapsulated in a Target object is
    relevant to various aspects of the API:

      an RPC Server's target:
        topic and server is required; exchange is optional
      an RPC endpoint's target:
        namespace and version is optional
      an RPC client sending a message:
        topic is required, all other attributes optional
      a Notification Server's target:
        topic is required, exchange is optional; all other attributes ignored
      a Notifier's target:
        topic is required, exchange is optional; all other attributes ignored

    Its attributes are:

    :param exchange: A scope for topics. Leave unspecified to default to the
      control_exchange configuration option.
    :type exchange: str
    :param topic: A name which identifies the set of interfaces exposed by a
      server. Multiple servers may listen on a topic and messages will be
      dispatched to one of the servers selected in a best-effort round-robin
      fashion (unless fanout is ``True``).
    :type topic: str
    :param namespace: Identifies a particular RPC interface (i.e. set of
      methods) exposed by a server. The default interface has no namespace
      identifier and is referred to as the null namespace.
    :type namespace: str
    :param version: RPC interfaces have a major.minor version number associated
      with them. A minor number increment indicates a backwards compatible
      change and an incompatible change is indicated by a major number bump.
      Servers may implement multiple major versions and clients may require
      indicate that their message requires a particular minimum minor version.
    :type version: str
    :param server: RPC Clients can request that a message be directed to a
      specific server, rather than just one of a pool of servers listening on
      the topic.
    :type server: str
    :param fanout: Clients may request that a copy of the message be delivered
      to all servers listening on a topic by setting fanout to ``True``, rather
      than just one of them.
    :type fanout: bool
    :param legacy_namespaces: A server always accepts messages specified via
      the 'namespace' parameter, and may also accept messages defined via
      this parameter. This option should be used to switch namespaces safely
      during rolling upgrades.
    :type legacy_namespaces: list of strings
    """

    def __init__(self, exchange=None, topic=None, namespace=None,
                 version=None, server=None, fanout=None,
                 legacy_namespaces=None):
        self.exchange = exchange
        self.topic = topic
        self.namespace = namespace
        self.version = version
        self.server = server
        self.fanout = fanout
        self.accepted_namespaces = [namespace] + (legacy_namespaces or [])

    def __call__(self, **kwargs):
        for a in ('exchange', 'topic', 'namespace',
                  'version', 'server', 'fanout'):
            kwargs.setdefault(a, getattr(self, a))
        return Target(**kwargs)

    def __eq__(self, other):
        return vars(self) == vars(other)

    def __ne__(self, other):
        return not self == other

    def __repr__(self):
        attrs = []
        for a in ['exchange', 'topic', 'namespace',
                  'version', 'server', 'fanout']:
            v = getattr(self, a)
            if v:
                attrs.append((a, v))
        values = ', '.join(['%s=%s' % i for i in attrs])
        return '<Target ' + values + '>'

    def __hash__(self):
        return id(self)