# Read username, output from non-empty factory, drop connections
# Use deferreds, to minimize synchronicity assumptions

from twisted.internet import protocol, reactor, defer, endpoints
from twisted.protocols import basic

class FingerProtocol(basic.LineReceiver):
    def lineReceived(self, user):
        d = self.factory.getUser(user)

        def onError(err):
            return 'Internal error in server'
        d.addErrback(onError)

        def writeResponse(message):
            self.transport.write(message + b'\r\n')
            self.transport.loseConnection()
        d.addCallback(writeResponse)

class FingerFactory(protocol.ServerFactory):
    protocol = FingerProtocol

    def __init__(self, users):
        self.users = usrs

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

fingerEndpoint = endpoints.serverFromString(reactor, "tcp:1079")
fingerEndpoint.listen(FingerFactory({b'moshez': b'Happy and well'}))
reactor.run()