The Evolution of Finger: pluggable backends

  1. Introduction
  2. Another Back-end
  3. Yet Another Back-end: Doing the Standard Thing

Introduction

This is the fifth part of the Twisted tutorial Twisted from Scratch, or The Evolution of Finger.

In this part we will add new several new backends to our finger service using the component-based architecture developed in The Evolution of Finger: moving to a component based architecture. This will 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()
Source listing - listings/finger/finger19b_changes.py

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.words.protocols import irc
from twisted.protocols import basic
from twisted.python import components
from twisted.web import resource, server, static, xmlrpc
from zope.interface import Interface, implements
import cgi
import pwd

class IFingerService(Interface):

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

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

class IFingerSetterService(Interface):

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

class IFingerSetterService(Interface):

    def setUser(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+'\r\n')
            self.transport.loseConnection()
        d.addCallback(writeValue)


class IFingerFactory(Interface):

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

    def buildProtocol(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(Interface):

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

    def buildProtocol(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(Interface):

    """
    @ivar nickname
    """

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

    def buildProtocol(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_GET(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_GET(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)
Source listing - listings/finger/finger19b.py

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()
Source listing - listings/finger/finger19c_changes.py

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.words.protocols import irc
from twisted.protocols import basic
from twisted.python import components
from twisted.web import resource, server, static, xmlrpc
from zope.interface import Interface, implements
import cgi
import pwd
import os

class IFingerService(Interface):

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

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

class IFingerSetterService(Interface):

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

class IFingerSetterService(Interface):

    def setUser(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+'\r\n')
            self.transport.loseConnection()
        d.addCallback(writeValue)


class IFingerFactory(Interface):

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

    def buildProtocol(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(Interface):

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

    def buildProtocol(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.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(Interface):

    """
    @ivar nickname
    """

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

    def buildProtocol(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_GET(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_GET(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)
Source listing - listings/finger/finger19c.py

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!

Index

Version: 2.5.0