[V3 RPC] Add basic RPC functionality (#1017)

* Add basic RPC functionality

* Add load/unload/reload rpc commands

* Reorganize without rpc_ready event

* Remove rpc ready event

* Removed bot reference from rpc module

* Close RPC server cleanly

* refactor bot

* Refactor a bit and make RPC server initialization based on a cli flag

* Fix version resolver

* standardize version getters

* Pick a new port number

redbot/core/rpc.py

@@ -0,0 +1,82 @@
+from typing import NewType, TYPE_CHECKING
+
+import asyncio
+
+from aiohttp.web import Application
+from aiohttp_json_rpc import JsonRpc
+
+import logging
+
+if TYPE_CHECKING:
+    from .bot import Red
+
+log = logging.getLogger('red.rpc')
+JsonSerializable = NewType('JsonSerializable', dict)
+
+_rpc = JsonRpc(logger=log)
+
+_rpc_server = None  # type: asyncio.AbstractServer
+
+
+async def initialize(bot: "Red"):
+    global _rpc_server
+
+    app = Application(loop=bot.loop)
+    app.router.add_route('*', '/rpc', _rpc)
+
+    handler = app.make_handler()
+
+    _rpc_server = await bot.loop.create_server(handler, '127.0.0.1', 6133)
+
+    log.debug('Created RPC _rpc_server listener.')
+
+
+def add_topic(topic_name: str):
+    """
+    Adds a topic for clients to listen to.
+
+    :param topic_name:
+    """
+    _rpc.add_topics(topic_name)
+
+
+def notify(topic_name: str, data: JsonSerializable):
+    """
+    Publishes a notification for the given topic name to all listening clients.
+
+    data MUST be json serializable.
+
+    note::
+
+        This method will fail silently.
+
+    :param topic_name:
+    :param data:
+    """
+    _rpc.notify(topic_name, data)
+
+
+def add_method(prefix, method):
+    """
+    Makes a method available to RPC clients. The name given to clients will be as
+    follows::
+
+        "{}__{}".format(prefix, method.__name__)
+
+    note::
+
+        This method will fail silently.
+
+    :param prefix:
+    :param method:
+        MUST BE A COROUTINE OR OBJECT.
+    :return:
+    """
+    _rpc.add_methods(
+        ('', method),
+        prefix=prefix
+    )
+
+
+def clean_up():
+    _rpc_server.close()