# The Evolution of Finger: a web frontend

## Introduction

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

In this part, we demonstrate adding a web frontend using simple `twisted.web.resource.Resource` objects: `UserStatusTree` , which will produce a listing of all users at the base URL (`/` ) of our site; `UserStatus` , which gives the status of each user at the location `/username` ; and `UserStatusXR` , which exposes an XMLRPC interface to `getUser` and `getUsers` functions at the URL `/RPC2` .

In this example we construct HTML segments manually. If the web interface was less trivial, we would want to use more sophisticated web templating and design our system so that HTML rendering and logic were clearly separated.

`finger20.tac`

    # Do everything properly, and componentize
    import cgi

    from zope.interface import Interface, implementer

    from twisted.application import internet, service, strports
    from twisted.internet import defer, endpoints, protocol, reactor
    from twisted.protocols import basic
    from twisted.python import components
    from twisted.web import resource, server, static, xmlrpc
    from twisted.words.protocols import irc

    class IFingerService(Interface):
        def getUser(user):
            """
            Return a deferred returning L{bytes}.
            """

        def getUsers():
            """
            Return a deferred returning a L{list} of L{bytes}.
            """

    class IFingerSetterService(Interface):
        def setUser(user, status):
            """
            Set the user's status to something.
            """

    def catchError(err):
        return b"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 + b"\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.
            """

    @implementer(IFingerFactory)
    class FingerFactoryFromService(protocol.ServerFactory):

        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.
            """

    @implementer(IFingerSetterFactory)
    class FingerSetterFactoryFromService(protocol.ServerFactory):

        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: f"Status of {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.
            """

    @implementer(IIRCClientFactory)
    class IRCClientFactoryFromService(protocol.ClientFactory):

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

            # add a specific child for the path "RPC2"
            self.putChild(b"RPC2", UserStatusXR(self.service))

            # need to do this for resources at the root of the site
            self.putChild(b"", self)

        def _cb_render_GET(self, users, request):
            userOutput = "".join(
                [f'<li><a href="{user}">{user}</a></li>' for user in users]
            )
            request.write(
                """
                <html><head><title>Users</title></head><body>
                <h1>Users</h1>
                <ul>
                %s
                </ul></body></html>"""
                % userOutput
            )
            request.finish()

        def render_GET(self, request):
            d = self.service.getUsers()
            d.addCallback(self._cb_render_GET, request)

            # signal that the rendering is not complete
            return server.NOT_DONE_YET

        def getChild(self, path, request):
            return UserStatus(user=path, service=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 _cb_render_GET(self, status, request):
            request.write(
                b"""<html><head><title>%s</title></head>
            <body><h1>%s</h1>
            <p>%s</p>
            </body></html>"""
                % (self.user, self.user, status)
            )
            request.finish()

        def render_GET(self, request):
            d = self.service.getUser(self.user)
            d.addCallback(self._cb_render_GET, request)

            # signal that the rendering is not complete
            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)

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

    @implementer(IFingerService)
    class FingerService(service.Service):
        def __init__(self, filename):
            self.filename = filename
            self.users = {}

        def _read(self):
            self.users.clear()
            with open(self.filename, "rb") as f:
                for line in f:
                    user, status = line.split(b":", 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, b"No such user"))

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

        def startService(self):
            self._read()
            service.Service.startService(self)

        def stopService(self):
            service.Service.stopService(self)
            self.call.cancel()

    application = service.Application("finger", uid=1, gid=1)
    f = FingerService("/etc/users")
    serviceCollection = service.IServiceCollection(application)
    f.setServiceParent(serviceCollection)
    strports.service("tcp:79", IFingerFactory(f)).setServiceParent(serviceCollection)
    strports.service("tcp:8000", server.Site(resource.IResource(f))).setServiceParent(
        serviceCollection
    )
    i = IIRCClientFactory(f)
    i.nickname = "fingerbot"
    internet.ClientService(
        endpoints.clientFromString(reactor, "tcp:irc.freenode.org:6667"), i
    ).setServiceParent(serviceCollection)