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
# 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 self._read() def _read(self): 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 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
- Readable -- each class is short
- Maintainable -- each class knows only about interfaces
- Dependencies between code parts are minimized
- Example: writing a new IFingerService is easy
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:
- Code (in the module)
- Configuration (file above)
- Presentation (templates)
- Content (/etc/users)
- Deployment (twistd)
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:
- Spaghetti: each piece of code interacts with every other piece of code [can be implemented with GOTO, functions, objects]
- Lasagna: code has carefully designed layers. Each layer is, in theory independent. However low-level layers usually cannot be used easily, and high-level layers depend on low-level layers.
- Ravioli: each part of the code is useful by itself. There is a thin layer of interfaces between various parts [the sauce]. Each part can be usefully be used elsewhere.
- ...but sometimes, the user just wants to order
Ravioli
, so one coarse-grain easily definable layer of abstraction on top of it all can be useful.
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!