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 1

LineReceiver expects lines end with \r\n, 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' # <----
    ...