wampy 1.1.0

WAMP RPC and Pub/Sub for python interactive shells, scripts, apps and microservices

wampy

[whomp-ee]

For a background as to what WAMP is, please see here.

This is a Python implementation of WAMP using Gevent, but you can also configure wampy to use eventlet, if that is how your application does async. Wampy is is a light-weight alternative to autobahn.

With wampy, you can quickly and easily create your own WAMP clients, whether this is in a web app, a microservice, a script or just in a Python shell. You can integrate wampy into your existing applications without having to re-write or re-design anything.

wampy tries to provide an intuitive API for your WAMP messaging.

See ReadTheDocs for more detailed documentation, but the README here is detailed enough to get going.

wampy features

• Remote Procedure Calls over websockets
• Publish and Subscribe over websockets
• Open Source and Open Thoughts - see internals and then the entire WIKI
• Use wampy as a microservice/app, or in your Flask or nameko apps, or in scripts.... or just in a Python shell!
• Client Authentication (Ticket and WCA)
• Transport Layer Security
• CLI for easy and rapid development
• Pytest fixtures to use when testing your projects, including a Crossbar.io fixture that tears down between each test
• nameko integration with namekowwamp
• Flask integration with flaskwwamp
• Compatible with gevent, eventlet and asyncio
• Alpha features (see below)

QuickStart - Connect and Go!

If you've already got access to a running Router which has other Peers connected, then stay here. If not, jump to the next section. If you're still here...

pip install wampy

...and then open a Python shell.

The example here assumes a Peer connected to a Router on localhost, port 8080, that has registered a remote procedure called get_foobar, and you want to call that procedure.

from wampy.peers import Client

with Client() as client:
    response = client.rpc.get_foobar()

# do something with the response here

The same example here, but the Router is on a remote host.

from wampy.peers import Client

with Client(url="ws://example.com:8080") as client:
    response = client.rpc.get_foobar()

# do something with the response here

The WAMP Session is "context managed", meaning it begins as you enter, and ends as you exit the scope of the client instance.

See ReadTheDocs for much more detail on this.

Running and Calling a wampy Application

Before any messaging can happen you need a Router. Messages are then routed between Clients over an administrative domain on the Router called a Realm.

For the quickest of starts I suggest that you use Crossbar.io and start it up on the default host and port, and with the default realm and roles. See the Crossbar.io docs for the instructions on this or alternatively run with wampy's testing setup.

Note, if you already have Crossbar installed and running you do not need these steps, because the dev requirements also include Crossbar.

$ make dev-install

$ crossbar start --config ./wampy/testing/configs/crossbar.json

wampy RPC

Now open your preferred text editor and we'll write a few lines of Python constructing a simple WAMP service that takes a decimal number and returns the binary representation of it - wowzers!

from wampy.peers.clients import Client
from wampy.roles import callee

class BinaryNumberService(Client):

    @callee
    def get_binary_number(self, number):
        return bin(number)

Save this module somewhere on your Python path and we'll use a wampy command line interface tool to start the service.

$ wampy run path.to.your.module.including.module_name:BinaryNumberService

For example, running one of the wampy example applications against the Router suggested previously:

$ wampy run docs.examples.services:DateService --config ./wampy/testing/configs/crossbar.json

Actually - no need to panic! The BinaryNumberService example already exists in the wampy examples so put that text editor away if you like. Just execute from the command line:

$ wampy run docs.examples.services:BinaryNumberService --config ./wampy/testing/configs/crossbar.json

Now, open a Python console in a new terminal, allowing the BinaryNumberService to run uninterupted in your original terminal (but once you're done with it Ctrl-C is required).

In [1]: from wampy.peers.clients import Client

In [2]: with Client(url="ws://localhost:8080") as client:
            result = client.rpc.get_binary_number(number=100)

In [3]: result
Out[3]: u'0b1100100'

wampy RPC for Crossbar.io

The RPC pattern above was inspired by the nameko project, but this pattern may not feel intuitive for those familiar with Crossbar.io, the primary Router used by wampy.

For this reason there also exists the CallProxy object which implements the call API by more loosely wrapping wampy's Call Message. In this pattern, applications and their endpoints are identified by dot delimented strings rather than a single API name, e.g.

"com.example.endpoint"

Just like the rpc API, the call API is directly available on every wampy client. Lets look at the two examples side by side.

>>> client.rpc.get_foo_bar(eggs, foo=bar, spam=ham)
>>> client.call("get_foo_bar", eggs, foo=bar, spam=ham)

Noted these are very similar and achieve the same, but the intention here is for the call API to behave more like a classic Crossbar.io application and the rpc to be used in namekowwamp.

The call API however does allow calls of the form...

>>> client.call("com.myapp.foo.bar", eggs, foo=bar, spam=ham) 

...which you will not be able to do with the rpc API.

Publishing and Subscribing is equally as simple

To demonstrate, first of all you need a Subscriber. You can either create one yourself in a Python module (as a subclass of a wampy Client) or use the example Client already for you in docs.examples.services.

Here we use the said example service, but all a Subscriber is is a wampy Client with a method decorated by subscribe. Take a look and see for yourself in the examples.

Let's start up that example service.

$ wampy run docs.examples.services:SubscribingService --config ./wampy/testing/configs/crossbar.json

Now we have a service running that subscribes to the topic "foo".

In another terminal, with a wampy virtualenv, you can create a Publisher - which is no different to any other wampy Client.

In [1]: from wampy.peers import Client

In [2]: with Client() as client:
            result = client.publish(topic="foo", message="spam")

Hopefully you'll see any message you send printed to the screen where the example service is running. You'll also see the meta data that wampy chooses to send.

Please note. wampy believes in explicit kwargs and not bare args, so you can only publish keyword arguments. Bare arguments don't tell readers enough about the call, so even though WAMP supports them, wampy does not.

It doesn't matter what the kwargs are they will be published, but you might find a call like this is not supported by subscribers of other WAMP implementations (sorry) e.g.

In [1]: from wampy.peers import Client

In [2]: with Client() as client:
            client.publish(
                topic="foo",
                ham="spam",
                birds={'foo_bird': 1, 'bar_bird': 2},
                message="hello world",
            )

Notice topic is always first, followed by kwargs. Happy to explore how implementations like autobahn can be supported here.

See ReadTheDocs for more detailed documentation.

Have Fun With Wampy

You can simply import a wampy client into a Python shell and start creating WAMP apps. Open a few shells and start clients running! Or start an example app and open a shell and start calling it. Don't forget to start Crossbar first though!

$ make install

$ crossbar start --config ./wampy/testing/configs/crossbar.json

Extensions

Wampy is a "simple" WAMP client and so it can easily be integrated with other frameworks. The current extensions are:

• Flask-WAMP
• nameko-wamp

Extensions for other Python Frameworks are encouraged!

Async Networking

The default backend for async networking is gevent, but you can switch this to eventlet if that is what your applications already use.

$ export WAMPY_ASYNC_NAME=eventlet

Swapping back is easy.

$ export WAMPY_ASYNC_NAME=gevent

Gevent is officially supported but eventlet no longer is, sorry. There were issues with Eventlet and Python 3.7 that I cannot currently work around.

Async.io would require a complete re-write, and if you're already using the standard library and want to use wampy that is not a problem - just roll with the default gevent - as the two event loops can run side by side.

Why does wampy support both eventlet and gevent? Because wampy is not a framework like Flask or nameko, and wampy tries to make as few assumptions about the process it is running in as possible. Wampy is intended to be integrated into existing Python apps as an easy way to send and receive WAMP messages, and if your app is already committed to a paritcular async architecture, then wampy may not be usable unless he can switch between them freely. And do remember: both options are compatible with the core asyncio library, so don't be put off if your app uses this.

Alpha Features

WebSocket Client -> Server Pings

Disabled by default, but by setting the environment variable DEFAULT_HEARTBEAT_SECONDS you can tell wampy to start Pinging the Router/Broker, i.e. Crossbar.

$ export DEFAULT_HEARTBEAT_SECONDS=5

There is also HEARTBEAT_TIMEOUT_SECONDS (defaults to 2 seconds) which on missed will incrmeent a missed Pong counter. That's it for now; WIP.

WAMP Call TimeOuts

WAMP advacned protocol describes an RPC timeout which wampy implements but Crossbar as yet does not. See https://github.com/crossbario/crossbar/issues/299. wampy does pass your preferred value to the Router/Broker in the Call Message, but the actual timeout is implemented by wampy, simply cutting the request off at the head. Sadly this does mean the server still may return a value for you and your app will have to handle this. We send the Cancel Message too, but there are issues here as well: Work In Progress.

Running the tests

$ pip install --editable .[dev]
$ py.test ./test -v

Build the docs

$ pip install -r rtd_requirements.txt
$ sphinx-build -E -b html ./docs/ ./docs/_build/

If you like this project, then Thank You, and you're welcome to get involved.

Contributing

Firstly. thank you everyone who does. And everyone is welcome to. And thanks for reading the CONTRIBUTING guidelines. And for adding yourselves to the CONTRIBUTORS list on your PR - you should! Many thanks. It's also great to hear how everyone uses wampy, so please do share how with me on your PR in comments.

Then, please read about the internals.

Finally.... get coding!!

Thanks!

TroubleShooting

Crossbar.io is used by the test runner and has many dependencies.

Mac OS

snappy/snappymodule.cc:31:10: fatal error: 'snappy-c.h' file not found #include <snappy-c.h>

Fix by brew install snappy