Setting up a SOAP server with minimum fuss

I recently had the unfortunate task of setting up a basic SOAP server for the purposes of some cross-University communication. Java tends to be very good at this (or as good as you can be, dealing with SOAP) but it’s still quite long-winded and, to save time, I also wanted something I could easily deploy to Heroku.

After spending a little while looking at some options, I settled on Python and rpclib. This let me create a SOAP server without any pain, and of course it was simple to deploy to Heroku as well. The biggest time-saver is that rpclib is not by necessity a contract-first SOAP server - so you don’t need to write your own WSDL, but can simply write a service class in Python and have rpclib autogenerate the WSDL.

I can’t imagine there’s many people who’ll need to know how to do this (a SOAP server sitting on Heroku? How common is that?) but I’m throwing it up here for future reference. Although if I ever have to work with SOAP again I may shoot myself.

What to do

We’ll create a new directory for our app:

mkdir minisoap && cd minisoap

And then create a virtual environment and source it:

virtualenv venv --distribute
source venv/bin/activate

Now we can install rpclib and its dependencies:

pip install rpclib

Finally, create app.py which will contain all our code. Here are all the imports you’ll need:

import logging
import os

from rpclib.application import Application
from rpclib.decorator import srpc
from rpclib.interface.wsdl import Wsdl11
from rpclib.protocol.soap import Soap11
from rpclib.service import ServiceBase
from rpclib.model.complex import Iterable
from rpclib.model.primitive import Integer
from rpclib.model.primitive import String
from rpclib.server.wsgi import WsgiApplication

And next, our service:

class MessageService(ServiceBase):
  @srpc(String, Integer, _returns=Iterable(String))
  def send_message(msg):
    yield 'Your message: %s' % msg

And finally, a chunk of boilerplate to configure rpclib, tell it to use the service we just created and then serve forever as a wsgi application.

if __name__=='__main__':
  try:
      from wsgiref.simple_server import make_server
  except ImportError:
      print "Error: server requires Python >= 2.5"

  logging.basicConfig(level=logging.INFO)
  logging.getLogger('rpclib.protocol.xml').setLevel(logging.DEBUG)

  application = Application([MessageService], 'org.temporary.soap',
              interface=Wsdl11(), in_protocol=Soap11(), out_protocol=Soap11())

  port = int(os.environ.get('PORT', 5000))

  server = make_server('0.0.0.0', port, WsgiApplication(application))

  print "listening to http://0.0.0.0:%s" % port
  print "wsdl is at: http://0.0.0.0:%s/?wsdl" % port

  server.serve_forever()

From here you should be able to run python app.py and then you can hit http://localhost:5000/?wsdl to view your glorious WSDL.

Deploying to Heroku

It’s easy to get this on Heroku. Do a pip freeze to get the requirements.txt:

pip freeze > requirements.txt

And then create the file Procfile and stick this inside:

web: python app.py

From here, it’s as straightforward as any other Heroku Cedar deployment. Stick it in a git repository and then push it up to Heroku, as described in the Heroku docs. Enjoy!

You can find the source for this example over on Github.