why telnetlib write function not working in my python code?
Question: I was learning python for a few weeks, I was trying to build a chat app, I
chose twisted and felt comfortable with it, but I run into a strange problem
in client tesing code.

Here is my server code:

    
    
    from twisted.internet.protocol import Factory
    from twisted.protocols.basic import LineReceiver
    from twisted.internet import reactor
    
    class ChatServer(LineReceiver):
    
        def __init__(self, users):
            self.users = users
            self.name = None
            self.state = "GETNAME"
    
        def connectionMade(self):
            self.sendLine("What's your name?")
            print 'DEBUG: Name Input Request Send Back To Client.'
    
        def connectionLost(self, reason):
            if self.users.has_key(self.name):
                del self.users[self.name]
    
        def lineReceived(self, line):
            print 'DEBUG: A Message Recieved From Client.'
            if self.state == "GETNAME":
                self.handle_GETNAME(line)
            else:
                self.handle_CHAT(line)
    
        def handle_GETNAME(self, name):
            if self.users.has_key(name):
                self.sendLine("Name taken, please choose another.")
                return
            self.sendLine("Welcome, %s!" % (name,))
            print 'DEBUG: Welcome Message Send Back To Client.'
            self.name = name
            self.users[name] = self
            self.state = "CHAT"
    
        def handle_CHAT(self, message):
            message = "<%s> %s" % (self.name, message)
            for name, protocol in self.users.iteritems():
                if protocol != self:
                    protocol.sendLine(message)
    
    class ChatServerFactory(Factory):
    
        def __init__(self):
            self.users = {}
    
        def buildProtocol(self, addr):
            return ChatServer(self.users)
    
    reactor.listenTCP(8123, ChatServerFactory())
    reactor.run()
    

and this is my client testing code, I tried to test server in telnet way.

    
    
    import telnetlib
    import cmd
    import sys
    import time
    
    def test_telnet(Host, Port):     
        # connected to the server
        tn = telnetlib.Telnet(Host, Port)  
        print 'Client Connecton Made.'
        # tn.set_debuglevel(2)
    
        # read back from server
        greeting = tn.read_until("What's your name?")
        print 'Recieved Name Input Request From Server'
        print greeting
        print "DEBUG: Before telnet write data"
        username = 'amber'
        tn.write(username + '\n')
        print "DEBUG: After telnet write data"
        # welcome = tn.read_until('see', 5)
        # print 'Recieved Welcome Message From Server'
        # print welcome
    
        time.sleep(7)
        tn.write("exit\n")
        print 'Client Connection Lost.'
    
    test_telnet('localhost', 8123)
    

However, tn.write() send message, but in server console, I noticed that
lineReceived is never get called, but in real telnet, it's called, why is
that? Many thanks!


Answer: [`LineReceiver`](http://twistedmatrix.com/documents/current/api/twisted.protocols.basic.LineReceiver.html)
expects lines end with
[`\r\n`](http://twistedmatrix.com/documents/current/api/twisted.protocols.basic.LineReceiver.html#delimiter),
not `\n`.

Replacing `\n` in the code with `\r\n` solves the problem.

* * *

Alternatively you can change the line delimiter:

    
    
    class ChatServer(LineReceiver):
        delimiter = '\n' # <----
        ...
    

