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This is a first cut at combining the [http://peak.telecommunity.com PEAK] and [http://twistedmatrix.com/ Twisted] frameworks. We've taken the echoserver example from the doc/examples directory in the Twisted distribution, and "PEAK-ified" the Echo protocol to be a PEAK component. This example also shows a trivial use of the ZConfig machinery, which sets the Port to 8080 in the file config/tp.zcfg (It is port 8090 by default). To run using the zconfig machinery, use the run-tp-schema script(port 8080), to run using a hard-coded EventDriven command object, use the run-tp script(port 8090).
#format rst
Getting Started
---------------
PEAK and Twisted work very well together thanks to the the
peak.commands.EventDriven class, a top level container for
reactor-based applications. The following shows an XML-RPC server
based on Twisted's XML-RPC HOWTO__::
from peak.api import binding, commands, running
from twisted.web import xmlrpc, server
class Example(xmlrpc.XMLRPC):
"""An example object to be published."""
def xmlrpc_echo(self, x):
"""Return all passed args."""
return x
def xmlrpc_add(self, a, b):
"""Return sum of arguments."""
return a + b
class App(commands.EventDriven):
example = binding.Make(Example)
server = binding.Make(lambda self: server.Site(self.example))
port = binding.Make(lambda: 7080)
reactor = binding.Obtain(running.ITwistedReactor)
__onStart = binding.Make(
lambda self: self.reactor.listenTCP(self.port, self.server),
uponAssembly=True
)
__ http://twistedmatrix.com/projects/web/documentation/howto/xmlrpc.html
The Example class is lifted verbatim from the HOWTO. Note how the
Twisted reactor is obtained in the App class, and how the __onStart
method tells the reactor to listen with the given server object and
port number.
If saved in a file called ``twistedpeak.py``, this code can be run as
follows (on Unix/Linux systems)::
PYTHONPATH=. peak import:twistedpeak.App
The example client code from the HOWTO works exactly the same::
>>> import xmlrpclib
>>> s = xmlrpclib.Server('http://localhost:7080/')
>>> s.echo("lala")
'lala'
>>> s.add(1, 2)
3
This code can be used as a starting point for any kind of Twisted
application.
Configuration and Binding
-------------------------
The code above is slightly longer than the example shown in the HOWTO,
but because of PEAK's component-oriented features, especially its
configuration and binding facilities, it is much more flexible. Since
``commands.EventDriven`` is a descendent of PEAK's base component
class, the ``App`` class is also a component class. This primarily
means two things:
- instances of it can be located in a hierarchy of other components;
components can find each other in various ways without needing to
know anything about the structure of the application as a
whole. This promotes loose coupling, which can lead to more flexible
applications and more reusable code. Components can optionally
"offer" their properties for use by other components in the system.
- component objects are easily configurable by various means,
including external configuration files (.ini-style, ZConfig),
internally via "property names", and through keyword parameters when
directly instantiated.
A component hierarchy always has a "root" object. In our example the
root object is created by the ``peak`` script, which is installed to
an executable directory by PEAK's ``setup.py`` installer script. The
``peak`` script is a simple launcher which takes a URL-like recipe for
finding a "runnable" object to load and run.
...
Notes
-----
This page is a replacement for the one originally created by Joel
Boehland in July 2003. Unfortunately his code examples were included
in a separate tar archive which has since been lost. Without the
code, config files, and shell scripts, the page was no longer usable.
-- John Landahl, March 2005.
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