Twisted from Scratch, or The Evolution of Finger

  1. Introduction
  2. Refuse Connections
  3. Do Nothing
  4. Drop Connections
  5. Read Username, Drop Connections
  6. Read Username, Output Error, Drop Connections
  7. Output From Empty Factory
  8. Output from Non-empty Factory
  9. Use Deferreds
  10. Run 'finger' Locally
  11. Read Status from the Web
  12. Use Application
  13. twistd
  14. Setting Message By Local Users
  15. Use Services to Make Dependencies Sane
  16. Read Status File
  17. Announce on Web, Too
  18. Announce on IRC, Too
  19. Add XML-RPC Support
  20. Write Readable Code
  21. Write Maintainable Code
  22. Advantages of Latest Version
  23. Another Back-end
  24. Yet Another Back-end: Doing the Standard Thing
  25. Aspect-Oriented Programming
  26. Use Woven
  27. Use Perspective Broker
  28. Support HTTPS
  29. Finger Proxy
  30. Organization
  31. Easy Configuration
  32. Plugins
  33. OS Integration

Introduction

Twisted is a big system. People are often daunted when they approach it. It's hard to know where to start looking.

This guide builds a full-fledged Twisted application from the ground up, using most of the important bits of the framework. There is a lot of code, but don't be afraid.

The application we are looking at is a finger service, along the lines of the familiar service traditionally provided by UNIX™ servers. We will extend this service slightly beyond the standard, in order to demonstrate some of Twisted's higher-level features.

Refuse Connections

from twisted.internet import reactor
reactor.run()

This example only runs the reactor. Nothing at all will happen until we interrupt the program. It will consume almost no CPU resources. Not very useful, perhaps -- but this is the skeleton inside which the Twisted program will grow.

The Reactor

You don't call Twisted, Twisted calls you. The reactor is Twisted's main event loop. There is exactly one reactor in any running Twisted application. Once started it loops over and over again, responding to network events, and making scheduled calls to code.

Do Nothing

from twisted.internet import protocol, reactor
class FingerProtocol(protocol.Protocol):
    pass
class FingerFactory(protocol.ServerFactory):
    protocol = FingerProtocol
reactor.listenTCP(1079, FingerFactory())
reactor.run()

Here, we start listening on port 1079. The 1079 is a reminder that eventually, we want to run on port 79, the standard port for finger servers. We define a protocol which does not respond to any events. Thus, connections to 1079 will be accepted, but the input ignored.

Drop Connections

from twisted.internet import protocol, reactor
class FingerProtocol(protocol.Protocol):
    def connectionMade(self):
        self.transport.loseConnection()
class FingerFactory(protocol.ServerFactory):
    protocol = FingerProtocol
reactor.listenTCP(1079, FingerFactory())
reactor.run()

Here we add to the protocol the ability to respond to the event of beginning a connection -- by terminating it. Perhaps not an interesting behavior, but it is already close to behaving according to the letter of the protocol. After all, there is no requirement to send any data to the remote connection in the standard. The only problem, as far as the standard is concerned, is that we terminate the connection too soon. A client which is slow enough will see his send() of the username result in an error.

Read Username, Drop Connections

from twisted.internet import protocol, reactor
from twisted.protocols import basic
class FingerProtocol(basic.LineReceiver):
    def lineReceived(self, user):
        self.transport.loseConnection()
class FingerFactory(protocol.ServerFactory):
    protocol = FingerProtocol
reactor.listenTCP(1079, FingerFactory())
reactor.run()

Here we make FingerProtocol inherit from LineReceiver, so that we get data-based events on a line-by-line basis. We respond to the event of receiving the line with shutting down the connection.

Congratulations, this is the first standard-compliant version of the code. However, usually people actually expect some data about users to be transmitted.

Read Username, Output Error, Drop Connections

from twisted.internet import protocol, reactor
from twisted.protocols import basic
class FingerProtocol(basic.LineReceiver):
    def lineReceived(self, user):
        self.transport.write("No such user\r\n")
        self.transport.loseConnection()
class FingerFactory(protocol.ServerFactory):
    protocol = FingerProtocol
reactor.listenTCP(1079, FingerFactory())
reactor.run()

Finally, a useful version. Granted, the usefulness is somewhat limited by the fact that this version only prints out a No such user message. It could be used for devastating effect in honey-pots, of course.

Output From Empty Factory

# Read username, output from empty factory, drop connections
from twisted.internet import protocol, reactor
from twisted.protocols import basic
class FingerProtocol(basic.LineReceiver):
    def lineReceived(self, user):
        self.transport.write(self.factory.getUser(user)+"\r\n")
        self.transport.loseConnection()
class FingerFactory(protocol.ServerFactory):
    protocol = FingerProtocol
    def getUser(self, user): return "No such user"
reactor.listenTCP(1079, FingerFactory())
reactor.run()

The same behavior, but finally we see what usefulness the factory has: as something that does not get constructed for every connection, it can be in charge of the user database. In particular, we won't have to change the protocol if the user database back-end changes.

Output from Non-empty Factory

# Read username, output from non-empty factory, drop connections
from twisted.internet import protocol, reactor
from twisted.protocols import basic
class FingerProtocol(basic.LineReceiver):
    def lineReceived(self, user):
        self.transport.write(self.factory.getUser(user)+"\r\n")
        self.transport.loseConnection()
class FingerFactory(protocol.ServerFactory):
    protocol = FingerProtocol
    def __init__(self, **kwargs): self.users = kwargs
    def getUser(self, user):
        return self.users.get(user, "No such user")
reactor.listenTCP(1079, FingerFactory(moshez='Happy and well'))
reactor.run()

Finally, a really useful finger database. While it does not supply information about logged in users, it could be used to distribute things like office locations and internal office numbers. As hinted above, the factory is in charge of keeping the user database: note that the protocol instance has not changed. This is starting to look good: we really won't have to keep tweaking our protocol.

Use Deferreds

# Read username, output from non-empty factory, drop connections
# Use deferreds, to minimize synchronicity assumptions
from twisted.internet import protocol, reactor, defer
from twisted.protocols import basic
class FingerProtocol(basic.LineReceiver):
    def lineReceived(self, user):
        self.factory.getUser(user
        ).addErrback(lambda _: "Internal error in server"
        ).addCallback(lambda m:
            (self.transport.write(m+"\r\n"),
             self.transport.loseConnection()))
class FingerFactory(protocol.ServerFactory):
    protocol = FingerProtocol
    def __init__(self, **kwargs): self.users = kwargs
    def getUser(self, user):
        return defer.succeed(self.users.get(user, "No such user"))
reactor.listenTCP(1079, FingerFactory(moshez='Happy and well'))
reactor.run()

But, here we tweak it just for the hell of it. Yes, while the previous version worked, it did assume the result of getUser is always immediately available. But what if instead of an in memory database, we would have to fetch result from a remote Oracle? Or from the web? Or, or...

Run 'finger' Locally

# Read username, output from factory interfacing to OS, drop connections
from twisted.internet import protocol, reactor, defer, utils
from twisted.protocols import basic
class FingerProtocol(basic.LineReceiver):
    def lineReceived(self, user):
        self.factory.getUser(user
        ).addErrback(lambda _: "Internal error in server"
        ).addCallback(lambda m:
            (self.transport.write(m+"\r\n"),
             self.transport.loseConnection()))
class FingerFactory(protocol.ServerFactory):
    protocol = FingerProtocol
    def getUser(self, user):
        return utils.getProcessOutput("finger", [user])
reactor.listenTCP(1079, FingerFactory())
reactor.run()

...from running a local command? Yes, this version runs finger locally with whatever arguments it is given, and returns the standard output. This is probably insecure, so you probably don't want a real server to do this without a lot more validation of the user input. This will do exactly what the standard version of the finger server does.

Read Status from the Web

The web. That invention which has infiltrated homes around the world finally gets through to our invention. Here we use the built-in Twisted web client, which also returns a deferred. Finally, we manage to have examples of three different database back-ends, which do not change the protocol class. In fact, we will not have to change the protocol again until the end of this tutorial: we have achieved, here, one truly usable class.

# Read username, output from factory interfacing to web, drop connections
from twisted.internet import protocol, reactor, defer, utils
from twisted.protocols import basic
from twisted.web import client
class FingerProtocol(basic.LineReceiver):
    def lineReceived(self, user):
        self.factory.getUser(user
        ).addErrback(lambda _: "Internal error in server"
        ).addCallback(lambda m:
            (self.transport.write(m+"\r\n"),
             self.transport.loseConnection()))
class FingerFactory(protocol.ServerFactory):
    protocol = FingerProtocol
    def __init__(self, prefix): self.prefix=prefix
    def getUser(self, user):
        return client.getPage(self.prefix+user)
reactor.listenTCP(1079, FingerFactory(prefix='http://livejournal.com/~'))
reactor.run()

Use Application

Up until now, we faked. We kept using port 1079, because really, who wants to run a finger server with root privileges? Well, the common solution is privilege shedding: after binding to the network, become a different, less privileged user. We could have done it ourselves, but Twisted has a built-in way to do it. Create a snippet as above, defining an application object. That object will have uid and gid attributes. When running it (later we will see how) it will bind to ports, shed privileges and then run.

# Read username, output from non-empty factory, drop connections
# Use deferreds, to minimize synchronicity assumptions
# Write application. Save in 'finger.tpy'
from twisted.application import internet, service
from twisted.internet import protocol, reactor, defer
from twisted.protocols import basic
class FingerProtocol(basic.LineReceiver):
    def lineReceived(self, user):
        self.factory.getUser(user
        ).addErrback(lambda _: "Internal error in server"
        ).addCallback(lambda m:
            (self.transport.write(m+"\r\n"),
             self.transport.loseConnection()))
class FingerFactory(protocol.ServerFactory):
    protocol = FingerProtocol
    def __init__(self, **kwargs): self.users = kwargs
    def getUser(self, user):
        return defer.succeed(self.users.get(user, "No such user"))

application = service.Application('finger', uid=1, gid=1)
factory = FingerFactory(moshez='Happy and well')
internet.TCPServer(79, factory).setServiceParent(
    service.IServiceCollection(application))

twistd

This is how to run Twisted Applications -- files which define an 'application'. twistd (TWISTed Daemonizer) does everything a daemon can be expected to -- shuts down stdin/stdout/stderr, disconnects from the terminal and can even change runtime directory, or even the root filesystems. In short, it does everything so the Twisted application developer can concentrate on writing his networking code.

root% twistd -ny finger.tac # just like before
root% twistd -ny finger.tac  # also works
root% twistd -ny finger.tac # usually a .tac is more of an app
root% twistd -y finger.tac # daemonize, keep pid in twistd.pid
root% twistd -y finger.tac --pidfile=finger.pid
root% twistd -y finger.tac --rundir=/
root% twistd -y finger.tac --chroot=/var
root% twistd -y finger.tac -l /var/log/finger.log
root% twistd -y finger.tac --syslog # just log to syslog
root% twistd -y finger.tac --syslog --prefix=twistedfinger # use given prefix

Setting Message By Local Users

Now that port 1079 is free, maybe we can run on it a different server, one which will let people set their messages. It does no access control, so anyone who can login to the machine can set any message. We assume this is the desired behavior in our case. Testing it can be done by simply:

% nc localhost 1079   # or telnet localhost 1079
moshez
Giving a tutorial now, sorry!
^D
# But let's try and fix setting away messages, shall we?
from twisted.application import internet, service
from twisted.internet import protocol, reactor, defer
from twisted.protocols import basic
class FingerProtocol(basic.LineReceiver):
    def lineReceived(self, user):
        self.factory.getUser(user).addErrback(
            lambda _:"Internal error in server"
            ).addCallback(
            lambda m: (self.transport.write(m+"\r\n"),
                       self.transport.loseConnection()))

class FingerFactory(protocol.ServerFactory):
    protocol = FingerProtocol
    def __init__(self, **kwargs): self.users = kwargs
    def getUser(self, user):
        return defer.succeed(self.users.get(user, "No such user"))

class FingerSetterProtocol(basic.LineReceiver):
    def connectionMade(self): self.lines = []
    def lineReceived(self, line): self.lines.append(line)
    def connectionLost(self, reason):
        self.factory.setUser(*self.lines[:2])
        # first line: user    second line: status

class FingerSetterFactory(protocol.ServerFactory):
    protocol = FingerSetterProtocol
    def __init__(self, ff): self.setUser = ff.users.__setitem__

ff = FingerFactory(moshez='Happy and well')
fsf = FingerSetterFactory(ff)

application = service.Application('finger', uid=1, gid=1)
serviceCollection = service.IServiceCollection(application)
internet.TCPServer(79,ff).setServiceParent(serviceCollection)
internet.TCPServer(1079,fsf).setServiceParent(serviceCollection)

Use Services to Make Dependencies Sane

The previous version had the setter poke at the innards of the finger factory. It's usually not a good idea: this version makes both factories symmetric by making them both look at a single object. Services are useful for when an object is needed which is not related to a specific network server. Here, we moved all responsibility for manufacturing factories into the service. Note that we stopped subclassing: the service simply puts useful methods and attributes inside the factories. We are getting better at protocol design: none of our protocol classes had to be changed, and neither will have to change until the end of the tutorial.

# Fix asymmetry
from twisted.application import internet, service
from twisted.internet import protocol, reactor, defer
from twisted.protocols import basic
class FingerProtocol(basic.LineReceiver):
    def lineReceived(self, user):
        self.factory.getUser(user
        ).addErrback(lambda _: "Internal error in server"
        ).addCallback(lambda m:
                      (self.transport.write(m+"\r\n"),
                       self.transport.loseConnection()))

class FingerSetterProtocol(basic.LineReceiver):
    def connectionMade(self): self.lines = []
    def lineReceived(self, line): self.lines.append(line)
    def connectionLost(self,reason): self.factory.setUser(*self.lines[:2])
    # first line: user   second line: status

class FingerService(service.Service):
    def __init__(self, *args, **kwargs):
        self.parent.__init__(self, *args)
        self.users = kwargs
    def getUser(self, user):
        return defer.succeed(self.users.get(user, "No such user"))
    def getFingerFactory(self):
        f = protocol.ServerFactory()
        f.protocol, f.getUser = FingerProtocol, self.getUser
        return f
    def getFingerSetterFactory(self):
        f = protocol.ServerFactory()
        f.protocol, f.setUser = FingerSetterProtocol, self.users.__setitem__
        return f

application = service.Application('finger', uid=1, gid=1)
f = FingerService('finger', moshez='Happy and well')
serviceCollection = service.IServiceCollection(application)
internet.TCPServer(79,f.getFingerFactory()
                   ).setServiceParent(serviceCollection)
internet.TCPServer(1079,f.getFingerSetterFactory()
                   ).setServiceParent(serviceCollection)

Read Status File

This version shows how, instead of just letting users set their messages, we can read those from a centrally managed file. We cache results, and every 30 seconds we refresh it. Services are useful for such scheduled tasks.

moshez: happy and well
shawn: alive 
sample /etc/users file - listings/finger/etc.users
# Read from file
from twisted.application import internet, service
from twisted.internet import protocol, reactor, defer
from twisted.protocols import basic
class FingerProtocol(basic.LineReceiver):
    def lineReceived(self, user):
        self.factory.getUser(user
        ).addErrback(lambda _: "Internal error in server"
        ).addCallback(lambda m:
                      (self.transport.write(m+"\r\n"),
                       self.transport.loseConnection()))

class FingerService(service.Service):
    def __init__(self, filename):
        self.users = {}
        self.filename = filename
    def startService(self):
        def _read(self):
            for line in file(self.file):
                user, status = line.split(':', 1)
                user=user.strip()
                status=status.strip()
                self.users[user] = status
            self.call = reactor.callLater(30, _read)
        _read()
        service.Service.startService(self)
    def stopService(self):
        service.Service.stopService(self)
        self.call.cancel()
    def getUser(self, user):
        return defer.succeed(self.users.get(user, "No such user"))
    def getFingerFactory(self):
        f = protocol.ServerFactory()
        f.protocol, f.getUser = FingerProtocol, self.getUser,
        f.startService = self.startService
        return f

application = service.Application('finger', uid=1, gid=1)
f = FingerService('/etc/users')
finger = internet.TCPServer(79, f.getFingerFactory())
finger.setServiceParent(service.IServiceCollection(application))

Announce on Web, Too

The same kind of service can also produce things useful for other protocols. For example, in twisted.web, the factory itself (the site) is almost never subclassed -- instead, it is given a resource, which represents the tree of resources available via URLs. That hierarchy is navigated by site, and overriding it dynamically is possible with getChild.

# Read from file, announce on the web!
from twisted.application import internet, service
from twisted.internet import protocol, reactor, defer
from twisted.protocols import basic
from twisted.web import resource, server, static
import cgi

class FingerProtocol(basic.LineReceiver):
    def lineReceived(self, user):
        self.factory.getUser(user
        ).addErrback(lambda _: "Internal error in server"
        ).addCallback(lambda m:
         (self.transport.write(m+"\r\n"),self.transport.loseConnection()))


class FingerService(service.Service):
    def __init__(self, file):
        self.file = file
        self._read()
    def _read(self):
        self.users = {}
        for line in file(self.file):
            user, status = line.split(':', 1)
            user=user.strip()
            status=status.strip()
            self.users[user] = status
        self.call = reactor.callLater(30, self._read)
    def getUser(self, user):
        return defer.succeed(self.users.get(user, "No such user"))
    def getFingerFactory(self):
        f = protocol.ServerFactory()
        f.protocol, f.getUser = FingerProtocol, self.getUser
        f.startService = self.startService
        return f
    def getResource(self):
        r = resource.Resource()
        r.getChild = (lambda path, request:
                      static.Data('<h1>%s</h1><p>%s</p>' %
                      tuple(map(cgi.escape,
                      [path,self.users.get(path,
                      "No such user.<p/>http://this.site/user")])),
                      'text/html'))
        return r

application = service.Application('finger', uid=1, gid=1)
f = FingerService('/etc/users')
serviceCollection = service.IServiceCollection(application)
internet.TCPServer(79,f.getFingerFactory()
                   ).setServiceParent(serviceCollection)
internet.TCPServer(8000,server.Site(f.getResource())
                   ).setServiceParent(serviceCollection)

Announce on IRC, Too

This is the first time there is client code. IRC clients often act a lot like servers: responding to events from the network. The reconnecting client factory will make sure that severed links will get re-established, with intelligent tweaked exponential back-off algorithms. The IRC client itself is simple: the only real hack is getting the nickname from the factory in connectionMade.

# Read from file, announce on the web, irc
from twisted.application import internet, service
from twisted.internet import protocol, reactor, defer
from twisted.protocols import basic, irc
from twisted.web import resource, server, static
import cgi
class FingerProtocol(basic.LineReceiver):
    def lineReceived(self, user):
        self.factory.getUser(user
        ).addErrback(lambda _: "Internal error in server"
        ).addCallback(lambda m:
         (self.transport.write(m+"\r\n"),self.transport.loseConnection()))
class FingerSetterProtocol(basic.LineReceiver):
    def connectionMade(self): self.lines = []
    def lineReceived(self, line): self.lines.append(line)
    def connectionLost(self,reason): self.factory.setUser(*self.lines[:2])
class IRCReplyBot(irc.IRCClient):
    def connectionMade(self):
        self.nickname = self.factory.nickname
        irc.IRCClient.connectionMade(self)
    def privmsg(self, user, channel, msg):
        user = user.split('!')[0]
        if self.nickname.lower() == channel.lower():
            self.factory.getUser(msg
            ).addErrback(lambda _: "Internal error in server"
            ).addCallback(lambda m: irc.IRCClient.msg(self, user, msg+': '+m))


class FingerService(service.Service):
    def __init__(self, file):
        self.file = file
        self._read()
    def _read(self):
        self.users = {}
        for line in file(self.file):
            user, status = line.split(':', 1)
            user = user.strip()
            status = status.strip()
            self.users[user] = status
        self.call = reactor.callLater(30, self._read)
    def getUser(self, user):
        return defer.succeed(self.users.get(user, "No such user"))
    def getFingerFactory(self):
        f = protocol.ServerFactory()
        f.protocol, f.getUser = FingerProtocol, self.getUser
        return f
    def getResource(self):
        r = resource.Resource()
        r.getChild = (lambda path, request:
                      static.Data('<h1>%s</h1><p>%s</p>' %
                      tuple(map(cgi.escape,
                      [path,self.users.get(path,
                      "No such user <p/> usage: site/user")])),
                      'text/html'))
        return r

    def getIRCBot(self, nickname):
        f = protocol.ReconnectingClientFactory()
        f.protocol,f.nickname,f.getUser = IRCReplyBot,nickname,self.getUser
        return f

application = service.Application('finger', uid=1, gid=1)
f = FingerService('/etc/users')
serviceCollection = service.IServiceCollection(application)
internet.TCPServer(79,f.getFingerFactory()
                   ).setServiceParent(serviceCollection)
internet.TCPServer(8000,server.Site(f.getResource())
                   ).setServiceParent(serviceCollection)
internet.TCPClient('irc.freenode.org', 6667, f.getIRCBot('fingerbot')
                   ).setServiceParent(serviceCollection)

Add XML-RPC Support

In Twisted, XML-RPC support is handled just as though it was another resource. That resource will still support GET calls normally through render(), but that is usually left unimplemented. Note that it is possible to return deferreds from XML-RPC methods. The client, of course, will not get the answer until the deferred is triggered.

# Read from file, announce on the web, irc, xml-rpc
from twisted.application import internet, service
from twisted.internet import protocol, reactor, defer
from twisted.protocols import basic, irc
from twisted.web import resource, server, static, xmlrpc
import cgi
class FingerProtocol(basic.LineReceiver):
    def lineReceived(self, user):
        self.factory.getUser(user
         ).addErrback(lambda _: "Internal error in server"
         ).addCallback(lambda m:
          (self.transport.write(m+"\r\n"),self.transport.loseConnection()))
class FingerSetterProtocol(basic.LineReceiver):
    def connectionMade(self): self.lines = []
    def lineReceived(self, line): self.lines.append(line)
    def connectionLost(self,reason): self.factory.setUser(*self.lines[:2])
class IRCReplyBot(irc.IRCClient):
    def connectionMade(self):
        self.nickname = self.factory.nickname
        irc.IRCClient.connectionMade(self)
    def privmsg(self, user, channel, msg):
        user = user.split('!')[0]
        if self.nickname.lower() == channel.lower():
            self.factory.getUser(msg
            ).addErrback(lambda _: "Internal error in server"
            ).addCallback(lambda m: irc.IRCClient.msg(self, user, msg+': '+m))
class FingerService(service.Service):
    def __init__(self, filename):
        self.filename = filename
        self._read()
    def _read(self):
        self.users = {}
        for line in file(self.filename):
            user, status = line.split(':', 1)
            user = user.strip()
            status = status.strip()
            self.users[user] = status
        self.call = reactor.callLater(30, self._read)
    def getUser(self, user):
        return defer.succeed(self.users.get(user, "No such user"))
    def getFingerFactory(self):
        f = protocol.ServerFactory()
        f.protocol, f.getUser = FingerProtocol, self.getUser
        return f
    def getResource(self):
        r = resource.Resource()
        r.getChild = (lambda path, request:
                      static.Data('<h1>%s</h1><p>%s</p>' %
                      tuple(map(cgi.escape,
                      [path,self.users.get(path, "No such user")])),
                      'text/html'))
        x = xmlrpc.XMLRPC()
        x.xmlrpc_getUser = self.getUser
        r.putChild('RPC2', x)
        return r
    def getIRCBot(self, nickname):
        f = protocol.ReconnectingClientFactory()
        f.protocol,f.nickname,f.getUser = IRCReplyBot,nickname,self.getUser
        return f

application = service.Application('finger', uid=1, gid=1)
f = FingerService('/etc/users')
serviceCollection = service.IServiceCollection(application)
internet.TCPServer(79, f.getFingerFactory()
                   ).setServiceParent(serviceCollection)
internet.TCPServer(8000, server.Site(f.getResource())
                   ).setServiceParent(serviceCollection)
internet.TCPClient('irc.freenode.org', 6667, f.getIRCBot('fingerbot')
                   ).setServiceParent(serviceCollection)

A simple client to test the XMLRPC finger:

# testing xmlrpc finger

import xmlrpclib
server = xmlrpclib.Server('http://127.0.0.1:8000/RPC2')
print server.getUser('moshez')

Write Readable Code

The last version of the application had a lot of hacks. We avoided sub-classing, didn't support things like user listings over the web, and removed all blank lines -- all in the interest of code which is shorter. Here we take a step back, subclass what is more naturally a subclass, make things which should take multiple lines take them, etc. This shows a much better style of developing Twisted applications, though the hacks in the previous stages are sometimes used in throw-away prototypes.

# Do everything properly
from twisted.application import internet, service
from twisted.internet import protocol, reactor, defer
from twisted.protocols import basic, irc
from twisted.web import resource, server, static, xmlrpc
import cgi

def catchError(err):
    return "Internal error in server"

class FingerProtocol(basic.LineReceiver):

    def lineReceived(self, user):
        d = self.factory.getUser(user)
        d.addErrback(catchError)
        def writeValue(value):
            self.transport.write(value+'\n')
            self.transport.loseConnection()
        d.addCallback(writeValue)


class FingerSetterProtocol(basic.LineReceiver):

    def connectionMade(self):
        self.lines = []

    def lineReceived(self, line):
        self.lines.append(line)

    def connectionLost(self,reason):
        self.factory.setUser(*self.lines[:2])


class IRCReplyBot(irc.IRCClient):

    def connectionMade(self):
        self.nickname = self.factory.nickname
        irc.IRCClient.connectionMade(self)

    def privmsg(self, user, channel, msg):
        user = user.split('!')[0]
        if self.nickname.lower() == channel.lower():
            d = self.factory.getUser(msg)
            d.addErrback(catchError)
            d.addCallback(lambda m: "Status of %s: %s" % (msg, m))
            d.addCallback(lambda m: self.msg(user,m))


class UserStatusTree(resource.Resource):
    def __init__(self, service):
        resource.Resource.__init__(self)
        self.service = service

    def render(self, request):
        d = self.service.getUsers()
        def formatUsers(users):
            l = ['<li><a href="%s">%s</a></li>' % (user, user)
                 for user in users]
            return '<ul>'+''.join(l)+'</ul>'
        d.addCallback(formatUsers)
        d.addCallback(request.write)
        d.addCallback(lambda _: request.finish())
        return server.NOT_DONE_YET

    def getChild(self, path, request):
        if path=="":
            return UserStatusTree(self.service)
        else:
            return UserStatus(path, self.service)

class UserStatus(resource.Resource):

    def __init__(self, user, service):
        resource.Resource.__init__(self)
        self.user = user
        self.service = service

    def render(self, request):
        d = self.service.getUser(self.user)
        d.addCallback(cgi.escape)
        d.addCallback(lambda m:
                      '<h1>%s</h1>'%self.user+'<p>%s</p>'%m)
        d.addCallback(request.write)
        d.addCallback(lambda _: request.finish())
        return server.NOT_DONE_YET


class UserStatusXR(xmlrpc.XMLRPC):

    def __init__(self, service):
        xmlrpc.XMLRPC.__init__(self)
        self.service = service

    def xmlrpc_getUser(self, user):
        return self.service.getUser(user)


class FingerService(service.Service):

    def __init__(self, filename):
        self.filename = filename
        self._read()

    def _read(self):
        self.users = {}
        for line in file(self.filename):
            user, status = line.split(':', 1)
            user = user.strip()
            status = status.strip()
            self.users[user] = status
        self.call = reactor.callLater(30, self._read)

    def getUser(self, user):
        return defer.succeed(self.users.get(user, "No such user"))

    def getUsers(self):
        return defer.succeed(self.users.keys())

    def getFingerFactory(self):
        f = protocol.ServerFactory()
        f.protocol = FingerProtocol
        f.getUser = self.getUser
        return f

    def getResource(self):
        r = UserStatusTree(self)
        x = UserStatusXR(self)
        r.putChild('RPC2', x)
        return r

    def getIRCBot(self, nickname):
        f = protocol.ReconnectingClientFactory()
        f.protocol = IRCReplyBot
        f.nickname = nickname
        f.getUser = self.getUser
        return f

application = service.Application('finger', uid=1, gid=1)
f = FingerService('/etc/users')
serviceCollection = service.IServiceCollection(application)
internet.TCPServer(79, f.getFingerFactory()
                   ).setServiceParent(serviceCollection)
internet.TCPServer(8000, server.Site(f.getResource())
                   ).setServiceParent(serviceCollection)
internet.TCPClient('irc.freenode.org', 6667, f.getIRCBot('fingerbot')
                   ).setServiceParent(serviceCollection)

Write Maintainable Code

In the last version, the service class was three times longer than any other class, and was hard to understand. This was because it turned out to have multiple responsibilities. It had to know how to access user information, by rereading the file every half minute, but also how to display itself in a myriad of protocols. Here, we used the component-based architecture that Twisted provides to achieve a separation of concerns. All the service is responsible for, now, is supporting getUser/getUsers. It declares its support via the __implements__ keyword. Then, adapters are used to make this service look like an appropriate class for various things: for supplying a finger factory to TCPServer, for supplying a resource to site's constructor, and to provide an IRC client factory for TCPClient. All the adapters use are the methods in FingerService they are declared to use: getUser/getUsers. We could, of course, skip the interfaces and let the configuration code use things like FingerFactoryFromService(f) directly. However, using interfaces provides the same flexibility inheritance gives: future subclasses can override the adapters.

# Do everything properly, and componentize
from twisted.application import internet, service
from twisted.internet import protocol, reactor, defer
from twisted.protocols import basic, irc
from twisted.python import components
from twisted.web import resource, server, static, xmlrpc
import cgi

class IFingerService(components.Interface):

    def getUser(self, user):
        """Return a deferred returning a string"""

    def getUsers(self):
        """Return a deferred returning a list of strings"""

class IFingerSetterService(components.Interface):

    def setUser(self, user, status):
        """Set the user's status to something"""

def catchError(err):
    return "Internal error in server"


class FingerProtocol(basic.LineReceiver):

    def lineReceived(self, user):
        d = self.factory.getUser(user)
        d.addErrback(catchError)
        def writeValue(value):
            self.transport.write(value+'\n')
            self.transport.loseConnection()
        d.addCallback(writeValue)


class IFingerFactory(components.Interface):

    def getUser(self, user):
        """Return a deferred returning a string"""

    def buildProtocol(self, addr):
        """Return a protocol returning a string"""


class FingerFactoryFromService(protocol.ServerFactory):

    __implements__ = IFingerFactory,

    protocol = FingerProtocol

    def __init__(self, service):
        self.service = service

    def getUser(self, user):
        return self.service.getUser(user)

components.registerAdapter(FingerFactoryFromService,
                           IFingerService,
                           IFingerFactory)



class FingerSetterProtocol(basic.LineReceiver):

      def connectionMade(self):
          self.lines = []

      def lineReceived(self, line):
          self.lines.append(line)

      def connectionLost(self,reason):
          if len(self.lines) == 2:
              self.factory.setUser(*self.lines)


class IFingerSetterFactory(components.Interface):

    def setUser(self, user, status):
        """Return a deferred returning a string"""

    def buildProtocol(self, addr):
        """Return a protocol returning a string"""


class FingerSetterFactoryFromService(protocol.ServerFactory):

    __implements__ = IFingerSetterFactory,

    protocol = FingerSetterProtocol

    def __init__(self, service):
        self.service = service

    def setUser(self, user, status):
        self.service.setUser(user, status)



components.registerAdapter(FingerSetterFactoryFromService,
                           IFingerSetterService,
                           IFingerSetterFactory)

class IRCReplyBot(irc.IRCClient):

    def connectionMade(self):
        self.nickname = self.factory.nickname
        irc.IRCClient.connectionMade(self)

    def privmsg(self, user, channel, msg):
        user = user.split('!')[0]
        if self.nickname.lower() == channel.lower():
            d = self.factory.getUser(msg)
            d.addErrback(catchError)
            d.addCallback(lambda m: "Status of %s: %s" % (msg, m))
            d.addCallback(lambda m: self.msg(user, m))


class IIRCClientFactory(components.Interface):

    '''
    @ivar nickname
    '''       

    def getUser(self, user):
        """Return a deferred returning a string"""

    def buildProtocol(self, addr):
        """Return a protocol"""


class IRCClientFactoryFromService(protocol.ClientFactory):

    __implements__ = IIRCClientFactory,

    protocol = IRCReplyBot
    nickname = None

    def __init__(self, service):
        self.service = service

    def getUser(self, user):
        return self.service.getUser(user)

components.registerAdapter(IRCClientFactoryFromService, IFingerService,
                           IIRCClientFactory)

class UserStatusTree(resource.Resource):

    __implements__ = resource.IResource,

    def __init__(self, service):
        resource.Resource.__init__(self)
        self.service = service
        self.putChild('RPC2', UserStatusXR(self.service))


    def render(self, request):
        d = self.service.getUsers()
        def formatUsers(users):
            l = ['<li><a href="%s">%s</a></li>' % (user, user)
                 for user in users]
            return '<ul>'+''.join(l)+'</ul>'
        d.addCallback(formatUsers)
        d.addCallback(request.write)
        d.addCallback(lambda _: request.finish())
        return server.NOT_DONE_YET

    def getChild(self, path, request):
        if path=="":
            return UserStatusTree(self.service)
        else:
            return UserStatus(path, self.service)

components.registerAdapter(UserStatusTree, IFingerService,
                           resource.IResource)

class UserStatus(resource.Resource):

    def __init__(self, user, service):
        resource.Resource.__init__(self)
        self.user = user
        self.service = service

    def render(self, request):
        d = self.service.getUser(self.user)
        d.addCallback(cgi.escape)
        d.addCallback(lambda m:
                      '<h1>%s</h1>'%self.user+'<p>%s</p>'%m)
        d.addCallback(request.write)
        d.addCallback(lambda _: request.finish())
        return server.NOT_DONE_YET


class UserStatusXR(xmlrpc.XMLRPC):

    def __init__(self, service):
        xmlrpc.XMLRPC.__init__(self)
        self.service = service

    def xmlrpc_getUser(self, user):
        return self.service.getUser(user)


class FingerService(service.Service):

    __implements__ = IFingerService,

    def __init__(self, filename):
        self.filename = filename
        self._read()

    def _read(self):
        self.users = {}
        for line in file(self.filename):
            user, status = line.split(':', 1)
            user = user.strip()
            status = status.strip()
            self.users[user] = status
        self.call = reactor.callLater(30, self._read)

    def getUser(self, user):
        return defer.succeed(self.users.get(user, "No such user"))

    def getUsers(self):
        return defer.succeed(self.users.keys())


application = service.Application('finger', uid=1, gid=1)
f = FingerService('/etc/users')
serviceCollection = service.IServiceCollection(application)
internet.TCPServer(79, IFingerFactory(f)
                   ).setServiceParent(serviceCollection)
internet.TCPServer(8000, server.Site(resource.IResource(f))
                   ).setServiceParent(serviceCollection)
i = IIRCClientFactory(f)
i.nickname = 'fingerbot'
internet.TCPClient('irc.freenode.org', 6667, i
                   ).setServiceParent(serviceCollection)

Advantages of Latest Version

class IFingerSetterService(components.Interface):

    def setUser(self, user, status):
        """Set the user's status to something"""


# Advantages of latest version

class MemoryFingerService(service.Service):

    __implements__ = IFingerService, IFingerSetterService

    def __init__(self, **kwargs):
        self.users = kwargs

    def getUser(self, user):
        return defer.succeed(self.users.get(user, "No such user"))

    def getUsers(self):
        return defer.succeed(self.users.keys())

    def setUser(self, user, status):
        self.users[user] = status


f = MemoryFingerService(moshez='Happy and well')
serviceCollection = service.IServiceCollection(application)
internet.TCPServer(1079, IFingerSetterFactory(f), interface='127.0.0.1'
                   ).setServiceParent(serviceCollection)

Full source code here:

# Do everything properly, and componentize
from twisted.application import internet, service
from twisted.internet import protocol, reactor, defer
from twisted.protocols import basic, irc
from twisted.python import components
from twisted.web import resource, server, static, xmlrpc
import cgi

class IFingerService(components.Interface):

    def getUser(self, user):
        """Return a deferred returning a string"""

    def getUsers(self):
        """Return a deferred returning a list of strings"""

class IFingerSetterService(components.Interface):

    def setUser(self, user, status):
        """Set the user's status to something"""

class IFingerSetterService(components.Interface):

    def setUser(self, user, status):
        """Set the user's status to something"""


def catchError(err):
    return "Internal error in server"


class FingerProtocol(basic.LineReceiver):

    def lineReceived(self, user):
        d = self.factory.getUser(user)
        d.addErrback(catchError)
        def writeValue(value):
            self.transport.write(value+'\n')
            self.transport.loseConnection()
        d.addCallback(writeValue)


class IFingerFactory(components.Interface):

    def getUser(self, user):
        """Return a deferred returning a string"""

    def buildProtocol(self, addr):
        """Return a protocol returning a string"""


class FingerFactoryFromService(protocol.ServerFactory):

    __implements__ = IFingerFactory,

    protocol = FingerProtocol

    def __init__(self, service):
        self.service = service

    def getUser(self, user):
        return self.service.getUser(user)

components.registerAdapter(FingerFactoryFromService,
                           IFingerService,
                           IFingerFactory)



class FingerSetterProtocol(basic.LineReceiver):

      def connectionMade(self):
          self.lines = []

      def lineReceived(self, line):
          self.lines.append(line)

      def connectionLost(self,reason):
          if len(self.lines) == 2:
              self.factory.setUser(*self.lines)


class IFingerSetterFactory(components.Interface):

    def setUser(self, user, status):
        """Return a deferred returning a string"""

    def buildProtocol(self, addr):
        """Return a protocol returning a string"""


class FingerSetterFactoryFromService(protocol.ServerFactory):

    __implements__ = IFingerSetterFactory,

    protocol = FingerSetterProtocol

    def __init__(self, service):
        self.service = service

    def setUser(self, user, status):
        self.service.setUser(user, status)



components.registerAdapter(FingerSetterFactoryFromService,
                           IFingerSetterService,
                           IFingerSetterFactory)

class IRCReplyBot(irc.IRCClient):

    def connectionMade(self):
        self.nickname = self.factory.nickname
        irc.IRCClient.connectionMade(self)

    def privmsg(self, user, channel, msg):
        user = user.split('!')[0]
        if self.nickname.lower() == channel.lower():
            d = self.factory.getUser(msg)
            d.addErrback(catchError)
            d.addCallback(lambda m: "Status of %s: %s" % (msg, m))
            d.addCallback(lambda m: self.msg(user, m))


class IIRCClientFactory(components.Interface):

    '''
    @ivar nickname
    '''       

    def getUser(self, user):
        """Return a deferred returning a string"""

    def buildProtocol(self, addr):
        """Return a protocol"""


class IRCClientFactoryFromService(protocol.ClientFactory):

    __implements__ = IIRCClientFactory,

    protocol = IRCReplyBot
    nickname = None

    def __init__(self, service):
        self.service = service

    def getUser(self, user):
        return self.service.getUser(user)

components.registerAdapter(IRCClientFactoryFromService, IFingerService,
                           IIRCClientFactory)

class UserStatusTree(resource.Resource):

    __implements__ = resource.IResource,

    def __init__(self, service):
        resource.Resource.__init__(self)
        self.service = service
        self.putChild('RPC2', UserStatusXR(self.service))


    def render(self, request):
        d = self.service.getUsers()
        def formatUsers(users):
            l = ['<li><a href="%s">%s</a></li>' % (user, user)
                 for user in users]
            return '<ul>'+''.join(l)+'</ul>'
        d.addCallback(formatUsers)
        d.addCallback(request.write)
        d.addCallback(lambda _: request.finish())
        return server.NOT_DONE_YET

    def getChild(self, path, request):
        if path=="":
            return UserStatusTree(self.service)
        else:
            return UserStatus(path, self.service)

components.registerAdapter(UserStatusTree, IFingerService,
                           resource.IResource)

class UserStatus(resource.Resource):

    def __init__(self, user, service):
        resource.Resource.__init__(self)
        self.user = user
        self.service = service

    def render(self, request):
        d = self.service.getUser(self.user)
        d.addCallback(cgi.escape)
        d.addCallback(lambda m:
                      '<h1>%s</h1>'%self.user+'<p>%s</p>'%m)
        d.addCallback(request.write)
        d.addCallback(lambda _: request.finish())
        return server.NOT_DONE_YET


class UserStatusXR(xmlrpc.XMLRPC):

    def __init__(self, service):
        xmlrpc.XMLRPC.__init__(self)
        self.service = service

    def xmlrpc_getUser(self, user):
        return self.service.getUser(user)


class FingerService(service.Service):

    __implements__ = IFingerService,

    def __init__(self, filename):
        self.filename = filename
        self._read()

    def _read(self):
        self.users = {}
        for line in file(self.filename):
            user, status = line.split(':', 1)
            user = user.strip()
            status = status.strip()
            self.users[user] = status
        self.call = reactor.callLater(30, self._read)

    def getUser(self, user):
        return defer.succeed(self.users.get(user, "No such user"))

    def getUsers(self):
        return defer.succeed(self.users.keys())

# Advantages of latest version

class MemoryFingerService(service.Service):

    __implements__ = IFingerService, IFingerSetterService

    def __init__(self, **kwargs):
        self.users = kwargs

    def getUser(self, user):
        return defer.succeed(self.users.get(user, "No such user"))

    def getUsers(self):
        return defer.succeed(self.users.keys())

    def setUser(self, user, status):
        self.users[user] = status



application = service.Application('finger', uid=1, gid=1)
f = MemoryFingerService(moshez='Happy and well')
serviceCollection = service.IServiceCollection(application)
internet.TCPServer(79, IFingerFactory(f)
                   ).setServiceParent(serviceCollection)
internet.TCPServer(8000, server.Site(resource.IResource(f))
                   ).setServiceParent(serviceCollection)
i = IIRCClientFactory(f)
i.nickname = 'fingerbot'
internet.TCPClient('irc.freenode.org', 6667, i
                   ).setServiceParent(serviceCollection)
internet.TCPServer(1079, IFingerSetterFactory(f), interface='127.0.0.1'
                   ).setServiceParent(serviceCollection)

Here we show just how convenient it is to implement new back-ends when we move to a component based architecture. Note that here we also use an interface we previously wrote, FingerSetterFactory, by supporting one single method. We manage to preserve the service's ignorance of the network.

Another Back-end

from twisted.internet import protocol, reactor, defer, utils
import pwd

# Another back-end

class LocalFingerService(service.Service):

    __implements__ = IFingerService

    def getUser(self, user):
    # need a local finger daemon running for this to work
        return utils.getProcessOutput("finger", [user])

    def getUsers(self):
        return defer.succeed([])


f = LocalFingerService()

Full source code here:

# Do everything properly, and componentize
from twisted.application import internet, service
from twisted.internet import protocol, reactor, defer, utils
from twisted.protocols import basic, irc
from twisted.python import components
from twisted.web import resource, server, static, xmlrpc
import cgi
import pwd

class IFingerService(components.Interface):

    def getUser(self, user):
        """Return a deferred returning a string"""

    def getUsers(self):
        """Return a deferred returning a list of strings"""

class IFingerSetterService(components.Interface):

    def setUser(self, user, status):
        """Set the user's status to something"""

class IFingerSetterService(components.Interface):

    def setUser(self, user, status):
        """Set the user's status to something"""


def catchError(err):
    return "Internal error in server"


class FingerProtocol(basic.LineReceiver):

    def lineReceived(self, user):
        d = self.factory.getUser(user)
        d.addErrback(catchError)
        def writeValue(value):
            self.transport.write(value+'\n')
            self.transport.loseConnection()
        d.addCallback(writeValue)


class IFingerFactory(components.Interface):

    def getUser(self, user):
        """Return a deferred returning a string"""

    def buildProtocol(self, addr):
        """Return a protocol returning a string"""


class FingerFactoryFromService(protocol.ServerFactory):

    __implements__ = IFingerFactory,

    protocol = FingerProtocol

    def __init__(self, service):
        self.service = service

    def getUser(self, user):
        return self.service.getUser(user)

components.registerAdapter(FingerFactoryFromService,
                           IFingerService,
                           IFingerFactory)



class FingerSetterProtocol(basic.LineReceiver):

      def connectionMade(self):
          self.lines = []

      def lineReceived(self, line):
          self.lines.append(line)

      def connectionLost(self,reason):
          if len(self.lines) == 2:
              self.factory.setUser(*self.lines)


class IFingerSetterFactory(components.Interface):

    def setUser(self, user, status):
        """Return a deferred returning a string"""

    def buildProtocol(self, addr):
        """Return a protocol returning a string"""


class FingerSetterFactoryFromService(protocol.ServerFactory):

    __implements__ = IFingerSetterFactory,

    protocol = FingerSetterProtocol

    def __init__(self, service):
        self.service = service

    def setUser(self, user, status):
        self.service.setUser(user, status)



components.registerAdapter(FingerSetterFactoryFromService,
                           IFingerSetterService,
                           IFingerSetterFactory)

class IRCReplyBot(irc.IRCClient):

    def connectionMade(self):
        self.nickname = self.factory.nickname
        irc.IRCClient.connectionMade(self)

    def privmsg(self, user, channel, msg):
        user = user.split('!')[0]
        if self.nickname.lower() == channel.lower():
            d = self.factory.getUser(msg)
            d.addErrback(catchError)
            d.addCallback(lambda m: "Status of %s: %s" % (msg, m))
            d.addCallback(lambda m: self.msg(user, m))


class IIRCClientFactory(components.Interface):

    '''
    @ivar nickname
    '''       

    def getUser(self, user):
        """Return a deferred returning a string"""

    def buildProtocol(self, addr):
        """Return a protocol"""


class IRCClientFactoryFromService(protocol.ClientFactory):

    __implements__ = IIRCClientFactory,

    protocol = IRCReplyBot
    nickname = None

    def __init__(self, service):
        self.service = service

    def getUser(self, user):
        return self.service.getUser(user)

components.registerAdapter(IRCClientFactoryFromService, IFingerService,
                           IIRCClientFactory)

class UserStatusTree(resource.Resource):

    __implements__ = resource.IResource,

    def __init__(self, service):
        resource.Resource.__init__(self)
        self.service = service
        self.putChild('RPC2', UserStatusXR(self.service))


    def render(self, request):
        d = self.service.getUsers()
        def formatUsers(users):
            l = ['<li><a href="%s">%s</a></li>' % (user, user)
                 for user in users]
            return '<ul>'+''.join(l)+'</ul>'
        d.addCallback(formatUsers)
        d.addCallback(request.write)
        d.addCallback(lambda _: request.finish())
        return server.NOT_DONE_YET

    def getChild(self, path, request):
        if path=="":
            return UserStatusTree(self.service)
        else:
            return UserStatus(path, self.service)

components.registerAdapter(UserStatusTree, IFingerService,
                           resource.IResource)

class UserStatus(resource.Resource):

    def __init__(self, user, service):
        resource.Resource.__init__(self)
        self.user = user
        self.service = service

    def render(self, request):
        d = self.service.getUser(self.user)
        d.addCallback(cgi.escape)
        d.addCallback(lambda m:
                      '<h1>%s</h1>'%self.user+'<p>%s</p>'%m)
        d.addCallback(request.write)
        d.addCallback(lambda _: request.finish())
        return server.NOT_DONE_YET


class UserStatusXR(xmlrpc.XMLRPC):

    def __init__(self, service):
        xmlrpc.XMLRPC.__init__(self)
        self.service = service

    def xmlrpc_getUser(self, user):
        return self.service.getUser(user)


class FingerService(service.Service):

    __implements__ = IFingerService,

    def __init__(self, filename):
        self.filename = filename
        self._read()

    def _read(self):
        self.users = {}
        for line in file(self.filename):
            user, status = line.split(':', 1)
            user = user.strip()
            status = status.strip()
            self.users[user] = status
        self.call = reactor.callLater(30, self._read)

    def getUser(self, user):
        return defer.succeed(self.users.get(user, "No such user"))

    def getUsers(self):
        return defer.succeed(self.users.keys())

# Another back-end

class LocalFingerService(service.Service):

    __implements__ = IFingerService

    def getUser(self, user):
    # need a local finger daemon running for this to work
        return utils.getProcessOutput("finger", [user])

    def getUsers(self):
        return defer.succeed([])


application = service.Application('finger', uid=1, gid=1)
f = LocalFingerService()
serviceCollection = service.IServiceCollection(application)
internet.TCPServer(79, IFingerFactory(f)
                   ).setServiceParent(serviceCollection)
internet.TCPServer(8000, server.Site(resource.IResource(f))
                   ).setServiceParent(serviceCollection)
i = IIRCClientFactory(f)
i.nickname = 'fingerbot'
internet.TCPClient('irc.freenode.org', 6667, i
                   ).setServiceParent(serviceCollection)

We've already written this, but now we get more for less work: the network code is completely separate from the back-end.

Yet Another Back-end: Doing the Standard Thing

from twisted.internet import protocol, reactor, defer, utils
import pwd
import os


# Yet another back-end

class LocalFingerService(service.Service):

    __implements__ = IFingerService

    def getUser(self, user):
        user = user.strip()
        try:
            entry = pwd.getpwnam(user)
        except KeyError:
            return defer.succeed("No such user")
        try:
            f = file(os.path.join(entry[5],'.plan'))
        except (IOError, OSError):
            return defer.succeed("No such user")
        data = f.read()
        data = data.strip()
        f.close()
        return defer.succeed(data)

    def getUsers(self):
        return defer.succeed([])



f = LocalFingerService()

Full source code here:

# Do everything properly, and componentize
from twisted.application import internet, service
from twisted.internet import protocol, reactor, defer, utils
from twisted.protocols import basic, irc
from twisted.python import components
from twisted.web import resource, server, static, xmlrpc
import cgi
import pwd
import os

class IFingerService(components.Interface):

    def getUser(self, user):
        """Return a deferred returning a string"""

    def getUsers(self):
        """Return a deferred returning a list of strings"""

class IFingerSetterService(components.Interface):

    def setUser(self, user, status):
        """Set the user's status to something"""

class IFingerSetterService(components.Interface):

    def setUser(self, user, status):
        """Set the user's status to something"""


def catchError(err):
    return "Internal error in server"


class FingerProtocol(basic.LineReceiver):

    def lineReceived(self, user):
        d = self.factory.getUser(user)
        d.addErrback(catchError)
        def writeValue(value):
            self.transport.write(value)
            self.transport.write('\n\n')
            self.transport.loseConnection()
        d.addCallback(writeValue)


class IFingerFactory(components.Interface):

    def getUser(self, user):
        """Return a deferred returning a string"""

    def buildProtocol(self, addr):
        """Return a protocol returning a string"""


class FingerFactoryFromService(protocol.ServerFactory):

    __implements__ = IFingerFactory,

    protocol = FingerProtocol

    def __init__(self, service):
        self.service = service

    def getUser(self, user):
        return self.service.getUser(user)

components.registerAdapter(FingerFactoryFromService,
                           IFingerService,
                           IFingerFactory)



class FingerSetterProtocol(basic.LineReceiver):

      def connectionMade(self):
          self.lines = []

      def lineReceived(self, line):
          self.lines.append(line)

      def connectionLost(self,reason):
          if len(self.lines) == 2:
              self.factory.setUser(*self.lines)


class IFingerSetterFactory(components.Interface):

    def setUser(self, user, status):
        """Return a deferred returning a string"""

    def buildProtocol(self, addr):
        """Return a protocol returning a string"""


class FingerSetterFactoryFromService(protocol.ServerFactory):

    __implements__ = IFingerSetterFactory,

    protocol = FingerSetterProtocol

    def __init__(self, service):
        self.service = service

    def setUser(self, user, status):
        self.service.setUser(user, status)



components.registerAdapter(FingerSetterFactoryFromService,
                           IFingerSetterService,
                           IFingerSetterFactory)

class IRCReplyBot(irc.IRCClient):

    def connectionMade(self):
        self.nickname = self.factory.nickname
        irc.IRCClient.connectionMade(self)

    def privmsg(self, user, channel, msg):
        user = user.split('!')[0]
        if self.nickname.lower() == channel.lower():
            d = self.factory.getUser(msg)
            d.addErrback(catchError)
            d.addCallback(lambda m: "Status of %s: %s" % (msg, m))
            d.addCallback(lambda m: self.msg(user, m))


class IIRCClientFactory(components.Interface):

    '''
    @ivar nickname
    '''       

    def getUser(self, user):
        """Return a deferred returning a string"""

    def buildProtocol(self, addr):
        """Return a protocol"""


class IRCClientFactoryFromService(protocol.ClientFactory):

    __implements__ = IIRCClientFactory,

    protocol = IRCReplyBot
    nickname = None

    def __init__(self, service):
        self.service = service

    def getUser(self, user):
        return self.service.getUser(user)

components.registerAdapter(IRCClientFactoryFromService, IFingerService,
                           IIRCClientFactory)

class UserStatusTree(resource.Resource):

    __implements__ = resource.IResource,

    def __init__(self, service):
        resource.Resource.__init__(self)
        self.service = service
        self.putChild('RPC2', UserStatusXR(self.service))


    def render(self, request):
        d = self.service.getUsers()
        def formatUsers(users):
            l = ['<li><a href="%s">%s</a></li>' % (user, user)
                 for user in users]
            return '<ul>'+''.join(l)+'</ul>'
        d.addCallback(formatUsers)
        d.addCallback(request.write)
        d.addCallback(lambda _: request.finish())
        return server.NOT_DONE_YET

    def getChild(self, path, request):
        if path=="":
            return UserStatusTree(self.service)
        else:
            return UserStatus(path, self.service)

components.registerAdapter(UserStatusTree, IFingerService,
                           resource.IResource)

class UserStatus(resource.Resource):

    def __init__(self, user, service):
        resource.Resource.__init__(self)
        self.user = user
        self.service = service

    def render(self, request):
        d = self.service.getUser(self.user)
        d.addCallback(cgi.escape)
        d.addCallback(lambda m:
                      '<h1>%s</h1>'%self.user+'<p>%s</p>'%m)
        d.addCallback(request.write)
        d.addCallback(lambda _: request.finish())
        return server.NOT_DONE_YET


class UserStatusXR(xmlrpc.XMLRPC):

    def __init__(self, service):
        xmlrpc.XMLRPC.__init__(self)
        self.service = service

    def xmlrpc_getUser(self, user):
        return self.service.getUser(user)


class FingerService(service.Service):

    __implements__ = IFingerService,

    def __init__(self, filename):
        self.filename = filename
        self._read()

    def _read(self):
        self.users = {}
        for line in file(self.filename):
            user, status = line.split(':', 1)
            user = user.strip()
            status = status.strip()
            self.users[user] = status
        self.call = reactor.callLater(30, self._read)

    def getUser(self, user):
        return defer.succeed(self.users.get(user, "No such user"))

    def getUsers(self):
        return defer.succeed(self.users.keys())

# Yet another back-end

class LocalFingerService(service.Service):

    __implements__ = IFingerService

    def getUser(self, user):
        user = user.strip()
        try:
            entry = pwd.getpwnam(user)
        except KeyError:
            return defer.succeed("No such user")
        try:
            f = file(os.path.join(entry[5],'.plan'))
        except (IOError, OSError):
            return defer.succeed("No such user")
        data = f.read()
        data = data.strip()
        f.close()
        return defer.succeed(data)

    def getUsers(self):
        return defer.succeed([])


application = service.Application('finger', uid=1, gid=1)
f = LocalFingerService()
serviceCollection = service.IServiceCollection(application)
internet.TCPServer(79, IFingerFactory(f)
                   ).setServiceParent(serviceCollection)
internet.TCPServer(8000, server.Site(resource.IResource(f))
                   ).setServiceParent(serviceCollection)
i = IIRCClientFactory(f)
i.nickname = 'fingerbot'
internet.TCPClient('irc.freenode.org', 6667, i
                   ).setServiceParent(serviceCollection)

Not much to say except that now we can be churn out backends like crazy. Feel like doing a back-end for Advogato, for example? Dig out the XML-RPC client support Twisted has, and get to work!

Aspect-Oriented Programming

At last, an example of aspect-oriented programming that isn't about logging or timing. This code is actually useful! Watch how aspect-oriented programming helps you write less code and have fewer dependencies!

Use Woven

Here we convert to using Woven, instead of manually constructing HTML snippets. Woven is a sophisticated web templating system. Its main features are to disallow any code inside the HTML, and transparent integration with deferred results.

# Do everything properly, and componentize
from twisted.application import internet, service
from twisted.internet import protocol, reactor, defer
from twisted.protocols import basic, irc
from twisted.python import components
from twisted.web import resource, server, static, xmlrpc, microdom
from twisted.web.woven import page, model, interfaces #,widgets
import cgi

class IFingerService(components.Interface):

    def getUser(self, user):
        """Return a deferred returning a string"""

    def getUsers(self):
        """Return a deferred returning a list of strings"""

class IFingerSetterService(components.Interface):

    def setUser(self, user, status):
        """Set the user's status to something"""

def catchError(err):
    return "Internal error in server"


class FingerProtocol(basic.LineReceiver):

    def lineReceived(self, user):
        d = self.factory.getUser(user)
        d.addErrback(catchError)
        def writeValue(value):
            self.transport.write(value+"\n")
            self.transport.loseConnection()
        d.addCallback(writeValue)


class IFingerFactory(components.Interface):

    def getUser(self, user):
        """Return a deferred returning a string"""

    def buildProtocol(self, addr):
        """Return a protocol returning a string"""


class FingerFactoryFromService(protocol.ServerFactory):

    __implements__ = IFingerFactory,

    protocol = FingerProtocol

    def __init__(self, service):
        self.service = service

    def getUser(self, user):
        return self.service.getUser(user)

components.registerAdapter(FingerFactoryFromService, IFingerService,
                           IFingerFactory)


class FingerSetterProtocol(basic.LineReceiver):

      def connectionMade(self):
          self.lines = []

      def lineReceived(self, line):
          self.lines.append(line)

      def connectionLost(self, reason):
          if len(self.lines) == 2:
              self.factory.setUser(*self.lines)


class IFingerSetterFactory(components.Interface):

    def setUser(self, user, status):
        """Return a deferred returning a string"""

    def buildProtocol(self, addr):
        """Return a protocol returning a string"""


class FingerSetterFactoryFromService(protocol.ServerFactory):

    __implements__ = IFingerSetterFactory,

    protocol = FingerSetterProtocol

    def __init__(self, service):
        self.service = service

    def setUser(self, user, status):
        self.service.setUser(user, status)


components.registerAdapter(FingerSetterFactoryFromService,
                           IFingerSetterService,
                           IFingerSetterFactory)

class IRCReplyBot(irc.IRCClient):

    def connectionMade(self):
        self.nickname = self.factory.nickname
        irc.IRCClient.connectionMade(self)

    def privmsg(self, user, channel, msg):
        user = user.split('!')[0]
        if self.nickname.lower() == channel.lower():
            d = self.factory.getUser(msg)
            d.addErrback(catchError)
            d.addCallback(lambda m: "Status of %s: %s " % (msg, m))
            d.addCallback(lambda m: self.msg(user, m))


class IIRCClientFactory(components.Interface):

    """
    @ivar nickname
    """       

    def getUser(self, user):
        """Return a deferred returning a string"""

    def buildProtocol(self, addr):
        """Return a protocol"""


class IRCClientFactoryFromService(protocol.ClientFactory):

   __implements__ = IIRCClientFactory,

   protocol = IRCReplyBot
   nickname = None

   def __init__(self, service):
       self.service = service


   def getUser(self, user):
        return self.service.getUser(user)

components.registerAdapter(IRCClientFactoryFromService, IFingerService,
                           IIRCClientFactory)


class UsersModel(model.MethodModel):

    def initialize(self, *args, **kwargs):
        self.service=args[0]

    def wmfactory_users(self, request):
        return self.service.getUsers()

components.registerAdapter(UsersModel, IFingerService, interfaces.IModel)

class UserStatusTree(page.Page):

    template = """<html><head><title>Users</title></head><body>
    <h1>Users</h1>
    <ul model="users" view="List">
    <li pattern="listItem"><a view="Anchor" /></li>
    </ul></body></html>"""                          


    def initialize(self, *args, **kwargs):
        self.service=args[0]

    def getDynamicChild(self, path, request):
        return UserStatus(user=path, service=self.service)

    def wchild_RPC2 (self, request):
        return UserStatusXR(self.service)


components.registerAdapter(UserStatusTree, IFingerService, resource.IResource)


class UserStatus(page.Page):

    template='''<html><head><title view="Text" model="user"/></head>
    <body><h1 view="Text" model="user"/>
    <p model="status" view="Text" />
    </body></html>'''                     

    def initialize(self, **kwargs):
        self.user = kwargs['user']
        self.service = kwargs['service']

    def wmfactory_user(self, request):
        return self.user

    def wmfactory_status(self, request):
        return self.service.getUser(self.user)


class UserStatusXR(xmlrpc.XMLRPC):

    def __init__(self, service):
        xmlrpc.XMLRPC.__init__(self)
        self.service = service

    def xmlrpc_getUser(self, user):
        return self.service.getUser(user)

    def xmlrpc_getUsers(self):
        return self.service.getUsers()


class FingerService(service.Service):

    __implements__ = IFingerService,

    def __init__(self, filename):
        self.filename = filename
        self._read()

    def _read(self):
        self.users = {}
        for line in file(self.filename):
            user, status = line.split(':', 1)
            user = user.strip()
            status = status.strip()
            self.users[user] = status
        self.call = reactor.callLater(30, self._read)

    def getUser(self, user):
        return defer.succeed(self.users.get(user, "No such user"))

    def getUsers(self):
        return defer.succeed(self.users.keys())


application = service.Application('finger', uid=1, gid=1)
f = FingerService('/etc/users')
serviceCollection = service.IServiceCollection(application)
internet.TCPServer(79, IFingerFactory(f)
                   ).setServiceParent(serviceCollection)
internet.TCPServer(8000, server.Site(resource.IResource(f))
                   ).setServiceParent(serviceCollection)
i = IIRCClientFactory(f)
i.nickname = 'fingerbot'
internet.TCPClient('irc.freenode.org', 6667, i
                   ).setServiceParent(serviceCollection)

Use Perspective Broker

We add support for perspective broker, Twisted's native remote object protocol. Now, Twisted clients will not have to go through XML-RPCish contortions to get information about users.

# Do everything properly, and componentize
from twisted.application import internet, service
from twisted.internet import protocol, reactor, defer
from twisted.protocols import basic, irc
from twisted.python import components
from twisted.web import resource, server, static, xmlrpc, microdom
from twisted.web.woven import page, model, interfaces
from twisted.spread import pb
import cgi

class IFingerService(components.Interface):

    def getUser(self, user):
        """Return a deferred returning a string"""

    def getUsers(self):
        """Return a deferred returning a list of strings"""

class IFingerSetterService(components.Interface):

    def setUser(self, user, status):
        """Set the user's status to something"""

def catchError(err):
    return "Internal error in server"


class FingerProtocol(basic.LineReceiver):

    def lineReceived(self, user):
        d = self.factory.getUser(user)
        d.addErrback(catchError)
        def writeValue(value):
            self.transport.write(value)
            self.transport.write('\n\n')
            self.transport.loseConnection()
        d.addCallback(writeValue)


class IFingerFactory(components.Interface):

    def getUser(self, user):
        """Return a deferred returning a string"""

    def buildProtocol(self, addr):
        """Return a protocol returning a string"""


class FingerFactoryFromService(protocol.ServerFactory):

    __implements__ = IFingerFactory,

    protocol = FingerProtocol

    def __init__(self, service):
        self.service = service

    def getUser(self, user):
        return self.service.getUser(user)

components.registerAdapter(FingerFactoryFromService,
                           IFingerService,
                           IFingerFactory)


class FingerSetterProtocol(basic.LineReceiver):

    def connectionMade(self):
        self.lines = []

    def lineReceived(self, line):
        self.lines.append(line)

    def connectionLost(self, reason):
        if len(self.lines) == 2:
            self.factory.setUser(*self.lines)


class IFingerSetterFactory(components.Interface):

    def setUser(self, user, status):
        """Return a deferred returning a string"""

    def buildProtocol(self, addr):
        """Return a protocol returning a string"""


class FingerSetterFactoryFromService(protocol.ServerFactory):

    __implements__ = IFingerSetterFactory,

    protocol = FingerSetterProtocol

    def __init__(self, service):
        self.service = service

    def setUser(self, user, status):
        self.service.setUser(user, status)


components.registerAdapter(FingerSetterFactoryFromService,
                           IFingerSetterService,
                           IFingerSetterFactory)

class IRCReplyBot(irc.IRCClient):

    def connectionMade(self):
        self.nickname = self.factory.nickname
        irc.IRCClient.connectionMade(self)

    def privmsg(self, user, channel, msg):
        user = user.split('!')[0]
        if self.nickname.lower() == channel.lower():
            d = self.factory.getUser(msg)
            d.addErrback(catchError)
            d.addCallback(lambda m: "Status of %s: %s" % (msg, m))
            d.addCallback(lambda m: self.msg(user, m))


class IIRCClientFactory(components.Interface):

    """
    @ivar nickname
    """       

    def getUser(self, user):
        """Return a deferred returning a string"""

    def buildProtocol(self, addr):
        """Return a protocol"""


class IRCClientFactoryFromService(protocol.ClientFactory):

    __implements__ = IIRCClientFactory,

    protocol = IRCReplyBot
    nickname = None

    def __init__(self, service):
        self.service = service

    def getUser(self, user):
        return self.service.getUser(user)

components.registerAdapter(IRCClientFactoryFromService,
                           IFingerService,
                           IIRCClientFactory)

class UsersModel(model.MethodModel):
    def initialize(self, *args, **kwargs):
        self.service=args[0]

    def wmfactory_users(self, request):
        return self.service.getUsers()

components.registerAdapter(UsersModel, IFingerService, interfaces.IModel)


class UserStatusTree(page.Page):

    template = """<html><head><title>Users</title></head><body>
    <h1>Users</h1>
    <ul model="users" view="List">
    <li pattern="listItem"><a view="Anchor" /></li>
    </ul></body></html>"""                          

    def initialize(self, *args, **kwargs):
        self.service=args[0]

    def getDynamicChild(self, path, request):
        return UserStatus(user=path, service=self.service)

    def wchild_RPC2 (self, request):
        return UserStatusXR(self.service)

components.registerAdapter(UserStatusTree, IFingerService, resource.IResource)


class UserStatus(page.Page):

    template='''<html><head><title view="Text" model="user"/></head>
    <body><h1 view="Text" model="user"/>
    <p model="status" view="Text" />
    </body></html>'''                     

    def initialize(self, **kwargs):
        self.user = kwargs['user']
        self.service = kwargs['service']

    def wmfactory_user(self, request):
        return self.user

    def wmfactory_status(self, request):
        return self.service.getUser(self.user)


class UserStatusXR(xmlrpc.XMLRPC):

    def __init__(self, service):
        xmlrpc.XMLRPC.__init__(self)
        self.service = service

    def xmlrpc_getUser(self, user):
        return self.service.getUser(user)

    def xmlrpc_getUsers(self):
        return self.service.getUsers()


class IPerspectiveFinger(components.Interface):

    def remote_getUser(self, username):
        """return a user's status"""

    def remote_getUsers(self):
        """return a user's status"""

# need to write a little script to test this PB shit

class PerspectiveFingerFromService(pb.Root):

    __implements__ = pb.Root.__implements__, IPerspectiveFinger

    def __init__ (self, *args):
        self.service = args[0]

    def remote_getUser(self, username):
        return self.service.getUser(username)

    def remote_getUsers(self):
        return self.service.getUsers()

components.registerAdapter(PerspectiveFingerFromService,
                           IFingerService,
                           IPerspectiveFinger)


class FingerService(service.Service):

    __implements__ = IFingerService,

    def __init__(self, filename):
        self.filename = filename
        self._read()

    def _read(self):
        self.users = {}
        for line in file(self.filename):
            user, status = line.split(':', 1)
            user = user.strip()
            status = status.strip()
            self.users[user] = status
        self.call = reactor.callLater(30, self._read)

    def getUser(self, user):
        return defer.succeed(self.users.get(user, "No such user"))

    def getUsers(self):
        return defer.succeed(self.users.keys())



application = service.Application('finger', uid=1, gid=1)
f = FingerService('/etc/users')
serviceCollection = service.IServiceCollection(application)
internet.TCPServer(79, IFingerFactory(f)
                   ).setServiceParent(serviceCollection)
internet.TCPServer(8000,server.Site(resource.IResource(f))
                   ).setServiceParent(serviceCollection)
i = IIRCClientFactory(f)
i.nickname = 'fingerbot'
internet.TCPClient('irc.freenode.org', 6667, i
                   ).setServiceParent(serviceCollection)
internet.TCPServer(8889, pb.PBServerFactory(IPerspectiveFinger(f))
                   ).setServiceParent(serviceCollection)

A simple client to test the perspective broker finger:

# test the PB finger on port 8889
# this code is essentially the same as
# the first example in howto/pb-usage

from twisted.spread import pb
from twisted.internet import reactor

def gotObject(object):
    print "got object:", object
    object.callRemote("getUser","moshez").addCallback(gotData)
# or
#   object.callRemote("getUsers").addCallback(gotData)

def gotData(data):
    print 'server sent:', data
    reactor.stop()

def gotNoObject(reason):
    print "no object:",reason
    reactor.stop()

factory = pb.PBClientFactory()
reactor.connectTCP("127.0.0.1",8889, factory)
factory.getRootObject().addCallbacks(gotObject,gotNoObject)
reactor.run()

Support HTTPS

All we need to do to code an HTTPS site is just write a context factory (in this case, which loads the certificate from a certain file) and then use the twisted.application.internet.SSLServer method. Note that one factory (in this case, a site) can listen on multiple ports with multiple protocols.

# Do everything properly, and componentize
from twisted.application import internet, service
from twisted.internet import protocol, reactor, defer
from twisted.protocols import basic, irc
from twisted.python import components
from twisted.web import resource, server, static, xmlrpc, microdom
from twisted.web.woven import page, model, interfaces
from twisted.spread import pb
#from OpenSSL import SSL
import cgi

class IFingerService(components.Interface):
    def getUser(self, user):
        """Return a deferred returning a string"""

    def getUsers(self):
        """Return a deferred returning a list of strings"""

class IFingerSetterService(components.Interface):

    def setUser(self, user, status):
        """Set the user's status to something"""

def catchError(err):
    return "Internal error in server"


class FingerProtocol(basic.LineReceiver):

    def lineReceived(self, user):
        d = self.factory.getUser(user)
        d.addErrback(catchError)
        def writeValue(value):
            self.transport.write(value)
            self.transport.write('\n\n')
            self.transport.loseConnection()
        d.addCallback(writeValue)


class IFingerFactory(components.Interface):
    def getUser(self, user):
        """Return a deferred returning a string"""

    def buildProtocol(self, addr):
        """Return a protocol returning a string"""


class FingerFactoryFromService(protocol.ServerFactory):
    __implements__ = IFingerFactory,

    protocol = FingerProtocol

    def __init__(self, service):
        self.service = service

    def getUser(self, user):
        return self.service.getUser(user)

components.registerAdapter(FingerFactoryFromService,
                           IFingerService,
                           IFingerFactory)

class FingerSetterProtocol(basic.LineReceiver):

    def connectionMade(self):
        self.lines = []

    def lineReceived(self, line):
        self.lines.append(line)

    def connectionLost(self, reason):
        if len(self.lines) == 2:
            self.factory.setUser(*self.lines)


class IFingerSetterFactory(components.Interface):

    def setUser(self, user, status):
        """Return a deferred returning a string"""

    def buildProtocol(self, addr):
        """Return a protocol returning a string"""


class FingerSetterFactoryFromService(protocol.ServerFactory):

    __implements__ = IFingerSetterFactory,

    protocol = FingerSetterProtocol

    def __init__(self, service):
        self.service = service

    def setUser(self, user, status):
        self.service.setUser(user, status)

components.registerAdapter(FingerSetterFactoryFromService,
                           IFingerSetterService,
                           IFingerSetterFactory)

class IRCReplyBot(irc.IRCClient):

    def connectionMade(self):
        self.nickname = self.factory.nickname
        irc.IRCClient.connectionMade(self)

    def privmsg(self, user, channel, msg):
        user = user.split('!')[0]
        if self.nickname.lower() == channel.lower():
            d = self.factory.getUser(msg)
            d.addErrback(catchError)
            d.addCallback(lambda m: "Status of %s: %s" % (msg, m))
            d.addCallback(lambda m: self.msg(user, m))


class IIRCClientFactory(components.Interface):

    """
    @ivar nickname
    """       

    def getUser(self, user):
        """Return a deferred returning a string"""

    def buildProtocol(self, addr):
        """Return a protocol"""


class IRCClientFactoryFromService(protocol.ClientFactory):

    __implements__ = IIRCClientFactory,

    protocol = IRCReplyBot
    nickname = None

    def __init__(self, service):
        self.service = service

    def getUser(self, user):
        return self.service.getUser(user)

components.registerAdapter(IRCClientFactoryFromService,
                           IFingerService,
                           IIRCClientFactory)


class UsersModel(model.MethodModel):

    def initialize(self, *args, **kwargs):
        self.service=args[0]

    def wmfactory_users(self, request):
        return self.service.getUsers()

components.registerAdapter(UsersModel, IFingerService, interfaces.IModel)

class UserStatusTree(page.Page):

    template = """<html><head><title>Users</title></head><body>
    <h1>Users</h1>
    <ul model="users" view="List">
    <li pattern="listItem"><a view="Anchor" /></li>
    </ul></body></html>"""                          

    def initialize(self, *args, **kwargs):
        self.service=args[0]

    def getDynamicChild(self, path, request):
        return UserStatus(user=path, service=self.service)

    def wchild_RPC2 (self, request):
        return UserStatusXR(self.service)

components.registerAdapter(UserStatusTree, IFingerService, resource.IResource)

class UserStatus(page.Page):

    template='''<html><head><title view="Text" model="user"/></head>
    <body><h1 view="Text" model="user"/>
    <p model="status" view="Text" />
    </body></html>'''                     

    def initialize(self, **kwargs):
        self.user = kwargs['user']
        self.service = kwargs['service']

    def wmfactory_user(self, request):
        return self.user

    def wmfactory_status(self, request):
        return self.service.getUser(self.user)

class UserStatusXR(xmlrpc.XMLRPC):

    def __init__(self, service):
        xmlrpc.XMLRPC.__init__(self)
        self.service = service

    def xmlrpc_getUser(self, user):
        return self.service.getUser(user)

    def xmlrpc_getUsers(self):
        return self.service.getUsers()


class IPerspectiveFinger(components.Interface):

    def remote_getUser(self, username):
        """return a user's status"""

    def remote_getUsers(self):
        """return a user's status"""


class PerspectiveFingerFromService(pb.Root):

    __implements__ = pb.Root.__implements__, IPerspectiveFinger

    def __init__(self, service):
        self.service = service

    def remote_getUser(self, username):
        return self.service.getUser(username)

    def remote_getUsers(self):
        return self.service.getUsers()

components.registerAdapter(PerspectiveFingerFromService,
                           IFingerService,
                           IPerspectiveFinger)


class FingerService(service.Service):

    __implements__ = IFingerService,

    def __init__(self, filename):
        self.filename = filename
        self._read()

    def _read(self):
        self.users = {}
        for line in file(self.filename):
            user, status = line.split(':', 1)
            user = user.strip()
            status = status.strip()
            self.users[user] = status
        self.call = reactor.callLater(30, self._read)

    def getUser(self, user):
        return defer.succeed(self.users.get(user, "No such user"))

    def getUsers(self):
        return defer.succeed(self.users.keys())


class ServerContextFactory:

    def getContext(self):
        """Create an SSL context.

        This is a sample implementation that loads a certificate from a file
        called 'server.pem'."""                               
        ctx = SSL.Context(SSL.SSLv23_METHOD)
        ctx.use_certificate_file('server.pem')
        ctx.use_privatekey_file('server.pem')
        return ctx


application = service.Application('finger', uid=1, gid=1)
f = FingerService('/etc/users')
serviceCollection = service.IServiceCollection(application)
internet.TCPServer(79, IFingerFactory(f)
                   ).setServiceParent(serviceCollection)
site = server.Site(resource.IResource(f))
internet.TCPServer(8000, site
                   ).setServiceParent(serviceCollection)
internet.SSLServer(443, site, ServerContextFactory()
                   ).setServiceParent(serviceCollection)
i = IIRCClientFactory(f)
i.nickname = 'fingerbot'
internet.TCPClient('irc.freenode.org', 6667, i
                   ).setServiceParent(serviceCollection)
internet.TCPServer(8889, pb.PBServerFactory(IPerspectiveFinger(f))
                   ).setServiceParent(serviceCollection)

Finger Proxy

Writing new clients with Twisted is much like writing new servers. We implement the protocol, which just gathers up all the data, and give it to the factory. The factory keeps a deferred which is triggered if the connection either fails or succeeds. When we use the client, we first make sure the deferred will never fail, by producing a message in that case. Implementing a wrapper around client which just returns the deferred is a common pattern. While less flexible than using the factory directly, it's also more convenient.

# finger proxy
from twisted.application import internet, service
from twisted.internet import defer, protocol, reactor
from twisted.protocols import basic
from twisted.python import components


def catchError(err):
    return "Internal error in server"

class IFingerService(components.Interface):

    def getUser(self, user):
        """Return a deferred returning a string"""

    def getUsers(self):
        """Return a deferred returning a list of strings"""


class IFingerFactory(components.Interface):

    def getUser(self, user):
        """Return a deferred returning a string"""

    def buildProtocol(self, addr):
        """Return a protocol returning a string"""

class FingerProtocol(basic.LineReceiver):

    def lineReceived(self, user):
        d = self.factory.getUser(user)
        d.addErrback(catchError)
        def writeValue(value):
            self.transport.write(value)
            self.transport.loseConnection()
        d.addCallback(writeValue)



class FingerFactoryFromService(protocol.ClientFactory):

    __implements__ = IFingerFactory,

    protocol = FingerProtocol

    def __init__(self, service):
        self.service = service

    def getUser(self, user):
        return self.service.getUser(user)


components.registerAdapter(FingerFactoryFromService,
                           IFingerService,
                           IFingerFactory)

class FingerClient(protocol.Protocol):

    def connectionMade(self):
        self.transport.write(self.factory.user+"\r\n")
        self.buf = []

    def dataReceived(self, data):
        self.buf.append(data)

    def connectionLost(self):
        self.factory.gotData(''.join(self.buf))

class FingerClientFactory(protocol.ClientFactory):

    protocol = FingerClient

    def __init__(self, user):
        self.user = user
        self.d = defer.Deferred()

    def clientConnectionFailed(self, _, reason):
        self.d.errback(reason)

    def gotData(self, data):
        self.d.callback(data)


def finger(user, host, port=79):
    f = FingerClientFactory(user)
    reactor.connectTCP(host, port, f)
    return f.d


class ProxyFingerService(service.Service):
    __implements__ = IFingerService

    def getUser(self, user):
        try:
            user, host = user.split('@', 1)
        except:
            user = user.strip()
            host = '127.0.0.1'
        ret = finger(user, host)
        ret.addErrback(lambda _: "Could not connect to remote host")
        return ret

    def getUsers(self):
        return defer.succeed([])

application = service.Application('finger', uid=1, gid=1)
f = ProxyFingerService()
internet.TCPServer(7779, IFingerFactory(f)).setServiceParent(
    service.IServiceCollection(application))

Organization

Now this code, while quite modular and well-designed, isn't properly organized. Everything above the application= belongs in a module, and the HTML templates all belong in separate files.

We can use the templateFile and templateDirectory attributes to indicate what HTML template file to use for each Page, and where to look for it.

# organized-finger.tac
# eg:  twistd -ny organized-finger.tac

import finger

from twisted.internet import protocol, reactor, defer
from twisted.spread import pb
from twisted.web import resource, server
from twisted.application import internet, service, strports
from twisted.python import log

application = service.Application('finger', uid=1, gid=1)
f = finger.FingerService('/etc/users')
serviceCollection = service.IServiceCollection(application)
internet.TCPServer(79, finger.IFingerFactory(f)
                   ).setServiceParent(serviceCollection)

site = server.Site(resource.IResource(f))
internet.TCPServer(8000, site
                   ).setServiceParent(serviceCollection)

internet.SSLServer(443, site, ServerContextFactory()
                   ).setServiceParent(serviceCollection)

i = finger.IIRCClientFactory(f)
i.nickname = 'fingerbot'
internet.TCPClient('irc.freenode.org', 6667, i
                   ).setServiceParent(serviceCollection)

internet.TCPServer(8889, pb.PBServerFactory(finger.IPerspectiveFinger(f))
                   ).setServiceParent(serviceCollection)

Note that our program is now quite separated. We have:

Prototypes don't need this level of separation, so our earlier examples all bunched together. However, real applications do. Thankfully, if we write our code correctly, it is easy to achieve a good separation of parts.

Easy Configuration

We can also supply easy configuration for common cases with a makeService method that will also help build .tap files later:

# Easy configuration
# makeService from finger module

def makeService(config):
    # finger on port 79
    s = service.MultiService()
    f = FingerService(config['file'])
    h = internet.TCPServer(79, IFingerFactory(f))
    h.setServiceParent(s)

    # website on port 8000
    r = resource.IResource(f)
    r.templateDirectory = config['templates']
    site = server.Site(r)
    j = internet.TCPServer(8000, site)
    j.setServiceParent(s)

    # ssl on port 443
    if config.get('ssl'):
        k = internet.SSLServer(443, site, ServerContextFactory())
        k.setServiceParent(s)

    # irc fingerbot
    if config.has_key('ircnick'):
        i = IIRCClientFactory(f)
        i.nickname = config['ircnick']
        ircserver = config['ircserver']
        b = internet.TCPClient(ircserver, 6667, i)
        b.setServiceParent(s)

    # Pespective Broker on port 8889
    if config.has_key('pbport'):
        m = internet.TCPServer(
            int(config['pbport']),
            pb.PBServerFactory(IPerspectiveFinger(f)))
        m.setServiceParent(s)

    return s

And we can write simpler files now:

# simple-finger.tac
# eg:  twistd -ny simple-finger.tac

from twisted.application import service

import finger

options = { 'file': '/etc/users',
            'templates': '/usr/share/finger/templates',
            'ircnick': 'fingerbot',
            'ircserver': 'irc.freenode.net',
            'pbport': 8889,
            'ssl': 'ssl=0' }

ser = finger.makeService(options)
application = service.Application('finger', uid=1, gid=1)
ser.setServiceParent(service.IServiceCollection(application))
% twisted -ny simple-finger.tac

Note: the finger user still has ultimate power: he can use makeService, or he can use the lower-level interface if he has specific needs (maybe an IRC server on some other port? maybe we want the non-SSL webserver to listen only locally? etc. etc.) This is an important design principle: never force a layer of abstraction: allow usage of layers of abstractions.

The pasta theory of design:

Plugins

So far, the user had to be somewhat of a programmer to be able to configure stuff. Maybe we can eliminate even that? Move old code to finger/__init__.py and...

Full source code for finger module here:

# finger.py module

from twisted.application import internet, service, strports
from twisted.internet import protocol, reactor, defer
from twisted.protocols import basic, irc
from twisted.python import components
from twisted.web import resource, server, static, xmlrpc, microdom
from twisted.web.woven import page, model, interfaces
from twisted.spread import pb
#from OpenSSL import SSL
import cgi

class IFingerService(components.Interface):
    def getUser(self, user):
        """Return a deferred returning a string"""

    def getUsers(self):
        """Return a deferred returning a list of strings"""

class IFingerSetterService(components.Interface):

    def setUser(self, user, status):
        """Set the user's status to something"""

def catchError(err):
    return "Internal error in server"


class FingerProtocol(basic.LineReceiver):

    def lineReceived(self, user):
        d = self.factory.getUser(user)
        d.addErrback(catchError)
        def writeValue(value):
            self.transport.write(value)
            self.transport.write('\n\n')
            self.transport.loseConnection()
        d.addCallback(writeValue)


class IFingerFactory(components.Interface):
    def getUser(self, user):
        """Return a deferred returning a string"""

    def buildProtocol(self, addr):
        """Return a protocol returning a string"""


class FingerFactoryFromService(protocol.ServerFactory):
    __implements__ = protocol.ServerFactory.__implements__, IFingerFactory

    protocol = FingerProtocol

    def __init__(self, service):
        self.service = service

    def getUser(self, user):
        return self.service.getUser(user)

components.registerAdapter(FingerFactoryFromService,
                           IFingerService,
                           IFingerFactory)

class FingerSetterProtocol(basic.LineReceiver):

    def connectionMade(self):
        self.lines = []

    def lineReceived(self, line):
        self.lines.append(line)

    def connectionLost(self, reason):
        if len(self.lines) == 2:
            self.factory.setUser(*self.lines)


class IFingerSetterFactory(components.Interface):

    def setUser(self, user, status):
        """Return a deferred returning a string"""

    def buildProtocol(self, addr):
        """Return a protocol returning a string"""


class FingerSetterFactoryFromService(protocol.ServerFactory):

    __implements__ = protocol.ServerFactory.__implements__,IFingerSetterFactory

    protocol = FingerSetterProtocol

    def __init__(self, service):
        self.service = service

    def setUser(self, user, status):
        self.service.setUser(user, status)

components.registerAdapter(FingerSetterFactoryFromService,
                           IFingerSetterService,
                           IFingerSetterFactory)

class IRCReplyBot(irc.IRCClient):

    def connectionMade(self):
        self.nickname = self.factory.nickname
        irc.IRCClient.connectionMade(self)

    def privmsg(self, user, channel, msg):
        user = user.split('!')[0]
        if self.nickname.lower() == channel.lower():
            d = self.factory.getUser(msg)
            d.addErrback(catchError)
            d.addCallback(lambda m: "Status of %s: %s" % (msg, m))
            d.addCallback(lambda m: self.msg(user, m))


class IIRCClientFactory(components.Interface):

    """
    @ivar nickname
    """       

    def getUser(self, user):
        """Return a deferred returning a string"""

    def buildProtocol(self, addr):
        """Return a protocol"""


class IRCClientFactoryFromService(protocol.ClientFactory):

    __implements__ = protocol.ClientFactory.__implements__, IIRCClientFactory

    protocol = IRCReplyBot
    nickname = None

    def __init__(self, service):
        self.service = service

    def getUser(self, user):
        return self.service.getUser(user)

components.registerAdapter(IRCClientFactoryFromService,
                           IFingerService,
                           IIRCClientFactory)


class UsersModel(model.MethodModel):

    def initialize(self, *args, **kwargs):
        self.service=args[0]

    def wmfactory_users(self, request):
        return self.service.getUsers()

components.registerAdapter(UsersModel, IFingerService, interfaces.IModel)

class UserStatusTree(page.Page):

    template = """<html><head><title>Users</title></head><body>
    <h1>Users</h1>
    <ul model="users" view="List">
    <li pattern="listItem"><a view="Anchor" /></li>
    </ul></body></html>"""                          

    def initialize(self, *args, **kwargs):
        self.service=args[0]

    def getDynamicChild(self, path, request):
        return UserStatus(user=path, service=self.service)

    def wchild_RPC2 (self, request):
        return UserStatusXR(self.service)

components.registerAdapter(UserStatusTree, IFingerService, resource.IResource)

class UserStatus(page.Page):

    template='''<html><head><title view="Text" model="user"/></head>
    <body><h1 view="Text" model="user"/>
    <p model="status" view="Text" />
    </body></html>'''                     

    def initialize(self, **kwargs):
        self.user = kwargs['user']
        self.service = kwargs['service']

    def wmfactory_user(self, request):
        return self.user

    def wmfactory_status(self, request):
        return self.service.getUser(self.user)

class UserStatusXR(xmlrpc.XMLRPC):

    def __init__(self, service):
        xmlrpc.XMLRPC.__init__(self)
        self.service = service

    def xmlrpc_getUser(self, user):
        return self.service.getUser(user)

    def xmlrpc_getUsers(self):
        return self.service.getUsers()


class IPerspectiveFinger(components.Interface):

    def remote_getUser(self, username):
        """return a user's status"""

    def remote_getUsers(self):
        """return a user's status"""


class PerspectiveFingerFromService(pb.Root):

    __implements__ = pb.Root.__implements__, IPerspectiveFinger

    def __init__(self, service):
        self.service = service

    def remote_getUser(self, username):
        return self.service.getUser(username)

    def remote_getUsers(self):
        return self.service.getUsers()

components.registerAdapter(PerspectiveFingerFromService,
                           IFingerService,
                           IPerspectiveFinger)


class FingerService(service.Service):

    __implements__ = service.Service.__implements__, IFingerService

    def __init__(self, filename):
        self.filename = filename
        self._read()

    def _read(self):
        self.users = {}
        for line in file(self.filename):
            user, status = line.split(':', 1)
            user = user.strip()
            status = status.strip()
            self.users[user] = status
        self.call = reactor.callLater(30, self._read)

    def getUser(self, user):
        return defer.succeed(self.users.get(user, "No such user"))

    def getUsers(self):
        return defer.succeed(self.users.keys())


class ServerContextFactory:

    def getContext(self):
        """Create an SSL context.

        This is a sample implementation that loads a certificate from a file
        called 'server.pem'."""                               
        ctx = SSL.Context(SSL.SSLv23_METHOD)
        ctx.use_certificate_file('server.pem')
        ctx.use_privatekey_file('server.pem')
        return ctx




# Easy configuration

def makeService(config):
    # finger on port 79
    s = service.MultiService()
    f = FingerService(config['file'])
    h = internet.TCPServer(79, IFingerFactory(f))
    h.setServiceParent(s)


    # website on port 8000
    r = resource.IResource(f)
    r.templateDirectory = config['templates']
    site = server.Site(r)
    j = internet.TCPServer(8000, site)
    j.setServiceParent(s)

    # ssl on port 443
#    if config.get('ssl'):
#        k = internet.SSLServer(443, site, ServerContextFactory())
#        k.setServiceParent(s)

    # irc fingerbot
    if config.has_key('ircnick'):
        i = IIRCClientFactory(f)
        i.nickname = config['ircnick']
        ircserver = config['ircserver']
        b = internet.TCPClient(ircserver, 6667, i)
        b.setServiceParent(s)

    # Pespective Broker on port 8889
    if config.has_key('pbport'):
        m = internet.TCPServer(
            int(config['pbport']),
            pb.PBServerFactory(IPerspectiveFinger(f)))
        m.setServiceParent(s)

    return s

# finger/tap.py
from twisted.application import internet, service
from twisted.internet import interfaces
from twisted.python import usage
import finger

class Options(usage.Options):

    optParameters = [
        ['file', 'f', '/etc/users'],
        ['templates', 't', '/usr/share/finger/templates'],
        ['ircnick', 'n', 'fingerbot'],
        ['ircserver', None, 'irc.freenode.net'],
        ['pbport', 'p', 8889],
        ]

    optFlags = [['ssl', 's']]

def makeService(config):
    return finger.makeService(config)

And register it all:

#finger/plugins.tml
register('finger', 'finger.tap',
 description='Build a finger server tap',
 type='tap', tapname='finger')

And now, the following works

% mktap finger --file=/etc/users --ircnick=fingerbot
% sudo twistd -nf finger.tap

OS Integration

If we already have the finger package installed in PYTHONPATH (e.g. we added it to site-packages), we can achieve easy integration:

Debian

% tap2deb --unsigned -m "Foo <foo@example.com>" --type=python finger.tac
% sudo dpkg -i .build/*.deb

Red Hat / Mandrake

% tap2rpm --type=python finger.tac #[maybe other options needed]
% sudo rpm -i .build/*.rpm

Will properly register the tap/tac, init.d scripts, etc. for the given file.

If it doesn't work on your favorite OS: patches accepted!

Index

Version: 1.1.1