Writing a twistd Plugin¶
This document describes adding subcommands to the
as a way to facilitate the deployment of your applications.
The target audience of this document are those that have developed a Twisted application which needs a command line-based deployment mechanism.
There are a few prerequisites to understanding this document:
A basic understanding of the Twisted Plugin System (i.e., the
twisted.pluginmodule) is necessary, however, step-by-step instructions will be given. Reading The Twisted Plugin System is recommended, in particular the “Extending an Existing Program” section.
The Application infrastructure is used in
twistdplugins; in particular, you should know how to expose your program’s functionality as a Service.
In order to parse command line arguments, the
twistdplugin mechanism relies on
twisted.python.usage, which is documented in Using usage.Options .
After reading this document,
the reader should be able to expose their Service-using application as a subcommand of
taking into consideration whatever was passed on the command line.
Alternatives to twistd Plugins¶
The major alternative to the twistd plugin mechanism is the
which is a simple script to be used with the twistd
The twistd plugin mechanism exists to offer a more extensible command-line-driven interface to your application.
For more information on
see the document Using the Twisted Application Framework .
Creating the Plugin¶
The following directory structure is assumed of your project:
MyProject- Top level directory
myproject- Python package
During development of your project,
Twisted plugins can be loaded from a special directory in your project,
assuming your top level directory ends up in
Create a directory named
twisted containing a directory named
and add a file named
myproject_plugin.py to it.
This file will contain your plugin.
Note that you must not add any
__init__.py files to this directory structure,
and the plugin file should not be named
(because that would conflict with your project’s module name).
tapname attribute of your IServiceMaker provider will be used as the subcommand name in a command like
twistd [subcommand] [args...] ,
(which should be a
will be used to parse the given args.
from zope.interface import implementer from twisted.python import usage from twisted.plugin import IPlugin from twisted.application.service import IServiceMaker from twisted.application import internet from myproject import MyFactory class Options(usage.Options): optParameters = [["port", "p", 1235, "The port number to listen on."]] @implementer(IServiceMaker, IPlugin) class MyServiceMaker(object): tapname = "myproject" description = "Run this! It'll make your dog happy." options = Options def makeService(self, options): """ Construct a TCPServer from a factory defined in myproject. """ return internet.TCPServer(int(options["port"]), MyFactory()) # Now construct an object which *provides* the relevant interfaces # The name of this variable is irrelevant, as long as there is *some* # name bound to a provider of IPlugin and IServiceMaker. serviceMaker = MyServiceMaker()
twistd --help should print
myproject in the list of available subcommands,
followed by the description that we specified in the plugin.
twistd -n myproject would,
assuming we defined a
MyFactory factory inside
start a listening server on port 1235 with that factory.
cred with your TAP¶
Twisted ships with a robust authentication framework to use with your application. If your server needs authentication functionality, and you haven’t read about twisted.cred yet, read up on it first.
If you are building a twistd plugin and you want to support a wide variety of authentication patterns,
Twisted provides an easy-to-use mixin for your Options subclass:
The following code is an example of using this mixin:
from twisted.cred import credentials, portal, strcred from twisted.python import usage from twisted.plugin import IPlugin from twisted.application.service import IServiceMaker from myserver import myservice class ServerOptions(usage.Options, strcred.AuthOptionMixin): # This part is optional; it tells AuthOptionMixin what # kinds of credential interfaces the user can give us. supportedInterfaces = (credentials.IUsernamePassword,) optParameters = [ ["port", "p", 1234, "Server port number"], ["host", "h", "localhost", "Server hostname"]] @implementer(IServiceMaker, IPlugin) class MyServerServiceMaker(object): tapname = "myserver" description = "This server does nothing productive." options = ServerOptions def makeService(self, options): """Construct a service object.""" # The realm is a custom object that your server defines. realm = myservice.MyServerRealm(options["host"]) # The portal is something Cred can provide, as long as # you have a list of checkers that you'll support. This # list is provided my AuthOptionMixin. portal = portal.Portal(realm, options["credCheckers"]) # OR, if you know you might get multiple interfaces, and # only want to give your application one of them, you # also have that option with AuthOptionMixin: interface = credentials.IUsernamePassword portal = portal.Portal(realm, options["credInterfaces"][interface]) # The protocol factory is, like the realm, something you implement. factory = myservice.ServerFactory(realm, portal) # Finally, return a service that will listen for connections. return internet.TCPServer(int(options["port"]), factory) # As in our example above, we have to construct an object that # provides the IPlugin and IServiceMaker interfaces. serviceMaker = MyServerServiceMaker()
Now that you have your TAP configured to support any authentication we can throw at it,
you’re ready to use it.
Here is an example of starting your server using the
/etc/passwd file for authentication.
(Clearly, this won’t work on servers with shadow passwords.)
$ twistd myserver --auth passwd:/etc/passwd
For a full list of cred plugins supported,
or use the command-line help:
$ twistd myserver --help-auth $ twistd myserver --help-auth-type passwd
Deploy your Application Using Python Packages¶
To deploy your application one possibility is to wrap it up in a Python package.
For this you need to write a special file
setup.py, which contains metadata
of the package. You would have to extend the layout of your files like this:
MyProject- Top level directory
setup.py- Description file for the package
myproject- Python package
myproject_plugins.py- Dropin file containing the actual plugin
from setuptools import setup, find_packages setup( name='MyApplication', version='0.1dev', # it is necesary to extend the found package list with the twisted.plugin # directory. It cannot be automatically detected, because it should not # contain a __init__.py file. packages=find_packages() + ['twisted.plugins'], install_requires=[ 'twisted', ], )
To create the Python package from the directory the standard setup tools can be used:
$ python3 setup.py sdist
This command creates a
dist directory in your project folder with the
compressed archive file
MyApplication-0.1dev.tar.gz. This archive contains
all the code and additional files if specified. This file can be copied and used
To install the application just use pip. It will also install all requirements
$ pip install MyApplication-0.1dev.tar.gz
You should now be able to
Create a twistd plugin
Incorporate authentication into your plugin
Use it from your development environment
Install it correctly and use it in deployment