The Evolution of Finger: cleaning up the finger code¶
Introduction¶
This is the third part of the Twisted tutorial Twisted from Scratch, or The Evolution of Finger .
In this section of the tutorial, we’ll clean up our code so that it is closer to a readable and extensible style.
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
import html
from twisted.application import internet, service, strports
from twisted.internet import defer, endpoints, protocol, reactor
from twisted.protocols import basic
from twisted.web import resource, server, static, xmlrpc
from twisted.words.protocols import irc
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 + b"\r\n")
self.transport.loseConnection()
d.addCallback(writeValue)
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.encode("ascii"))
d.addErrback(catchError)
d.addCallback(lambda m: f"Status of {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_GET(self, request):
d = self.service.getUsers()
def formatUsers(users):
l = [f'<li><a href="{user}">{user}</a></li>' 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_GET(self, request):
d = self.service.getUser(self.user)
d.addCallback(html.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.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 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.ClientFactory()
f.protocol = IRCReplyBot
f.nickname = nickname
f.getUser = self.getUser
return f
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", f.getFingerFactory()).setServiceParent(serviceCollection)
strports.service("tcp:8000", server.Site(f.getResource())).setServiceParent(
serviceCollection
)
internet.ClientService(
endpoints.clientFromString(reactor, "tcp:irc.freenode.org:6667"),
f.getIRCBot("fingerbot"),
).setServiceParent(serviceCollection)