wampy

WAMP RPC and Pub/Sub for stand alone clients and microservices

The WAMP protocol connects Clients via RPC or Pub/Sub over a Router.

A Client is some kind of application that calls or subscribes to another Client, else provides something for others to call or subscribe to. These are “Roles” that are performed by a Client, and they are referred to as Caller, Callee, Publisher and subscribe.

A Router is another type of application - a message broker - that is either a Broker or a Dealer, and highly likely to be Crossbar.io.

Whatever application you’re dealing with, WAMP refers to these as a Peer.

With wampy you can quickly and easily create Peers to implement these WAMP roles!

Quickstart: wampy from a Python console.

Before any messaging can happen you need a Router. This is a Peer that implements the Dealer or Broker roles, or both. Messages are then routed between Clients over an administritive domain called a “realm”.

For a quickstart I suggest that you use Crossbar.io and start it up on the default host and port with the default realm and roles. See the Crossbar.io docs for the instructions of this or alternatively run with wampy's testing setup pip install -r test_requirements.txt && crossbar start --config ./test/crossbar.config.json. By default, a Peer connects to this endpoint, but this is configurable on initialisation.

Then open a Python console.

In [1]: from wampy import Peer

In [2]: from wampy.entrypoints import rpc

In [3]: class BinaryNumberService(Peer):
            @rpc
            def get_binary_number(self, number):
                return bin(number)

In [4]: service = BinaryNumberService()

In [5]: service.start()

In [6]: service.session.id
Out[6]: 3941615218422338

If a Peer implements the Callee role, then just by starting the Peer you instruct it to register its RPC entrypoints with the Router.

In [7]]: from wampy.registry import get_registered_entrypoints

In [8]: get_registered_entrypoints()
Out[8]: {2010994119734585: (__main__.BinaryNumberService, 'get_binary_number')}

Any method of the Peer decorated with rpc will have been registered as publically availabile over the Router.

You can launch a client to call this entrypoint in this shell or in a new one – it really doesn't matter. You would need to explicitly pass host and port when not relying on the default values and you can also optionally give your Peer a name, which may help in your shell, app or your ELK stack.

In [9]: client = Peer(name="Binary Number Caller", host="localhost", port="8080")

In [10]: client.start()  # note that you can context-manage clients and avoid this step!

All clients know about the entrypoints made available by the DateService and with one you can call these over a RPC.

In [11]: client.rpc.get_binary_number(100)
Out [11]: u'0b1100100'

If you don’t context-manage your client, then you do have to explicitly call stop in order to gracefully disassociate yourself from the router, but also to tidy up the green threads and connections.

In [12]: client.stop()

You can also publish to and subscribe to topics. This is most fun when you open a second terminal!

In [1]: from wampy import Peer

In [2]: from wampy.entrypoints import subscribe

In [3]: class NewsReader(Peer):

            def __init__(self, *args, **kwargs):
                super(NewsReader, self).__init__(*args, **kwargs)
                self.messages = []

            @subscribe(topic="news")
            def handle_news(self, *args, **kwargs):
                headlines = kwargs['headlines']
                for headline in headlines:
                    self.messages.append(headline)

In [5]: reader = NewsReader()

In [6]: reader.start()

Because we're in a terminal you also need something to poll async for messages, such as...

In [7]: def listen_for_news(reader):
            import eventlet()
            while True:
                try:
                    message = reader.messages.pop()
                except IndexError:
                    eventlet.sleep()
                else:
                    print(message)

In [8]: listen_for_news(reader)

Jump back to the other terminal and publish some news!

In [13]: with cliient:
            client.publish(topic="news", headlines=[
                "wampy is great!",
                "probably best to use wampy in your next project!",
            ])

News will print out in your second terminal!

That’s about it so far.

exit()