connect to telnet in python with a quizz as login?

Question

I need to connect to a remote server via telnet. To authenticate to the server I have to answer like a 100 questions. So I tried to automate this task in python using telnetlib but the prompt halts without returning any message.

here is what I did

import telnetlib 

port = 2002
host = "23.23.190.204"

tn = telnetlib.Telnet(host, port)
tn.read_until("""
Welcome to EULER!
                 =================
                                  Answer 100 simple questions to authenticate yourself
""")
print tn.read_all()
tn.close()

in the command line prompt I get this message

Welcome to EULER!
=================
Answer 100 simple questions to authenticate yourself

then I am getting asked a question if the answer is correct I get the next question till I finished the 100. But in the python program I not getting neither the message nor the questions! what to do?

EDIT:

after setting the debug level for telnet, I get the answer of the server. Could you please explain why is that?

tn.set_debuglevel(9)

Answer 1

This is a fake telnet server using netcat (ncat from Nmap):

$ ncat -l 9000 < msg.txt > log.txt

listing on port 9000 and passes a file named msg.txt (the questions) and log the input into log.txt (the answers), it should simulate your server.

The file msg.txt content:

Welcome to EULER!
=================
Answer 100 simple questions to authenticate yourself
What is your name?
How old are you?
Do you use Python?

the file content in hex (using hexdump msg.txt):

00000000: 0A 57 65 6C 63 6F 6D 65 20 74 6F 20 45 55 4C 45 | Welcome to EULE|
00000010: 52 21 0A 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D |R! =============|
00000020: 3D 3D 3D 3D 0A 41 6E 73 77 65 72 20 31 30 30 20 |==== Answer 100 |
00000030: 73 69 6D 70 6C 65 20 71 75 65 73 74 69 6F 6E 73 |simple questions|
00000040: 20 74 6F 20 61 75 74 68 65 6E 74 69 63 61 74 65 | to authenticate|
00000050: 20 79 6F 75 72 73 65 6C 66 0A 57 68 61 74 20 69 | yourself What i|
00000060: 73 20 79 6F 75 72 20 6E 61 6D 65 3F 0A 48 6F 77 |s your name? How|
00000070: 20 6F 6C 64 20 61 72 65 20 79 6F 75 3F 0A 44 6F | old are you? Do|
00000080: 20 79 6F 75 20 75 73 65 20 50 79 74 68 6F 6E 3F | you use Python?|
00000090: 0A                                              |                |
00000091;                                                 |                |

notice the new line character, it's \x0A or \n (it can also be \x0D\x0A or \n\r).

The client:

import telnetlib 

port = 9000
host = "127.0.0.1"

tn = telnetlib.Telnet(host, port)
r = tn.read_until("""\nWelcome to EULER!
=================
Answer 100 simple questions to authenticate yourself\n""")

tn.read_until("What is your name?\n")
tn.write("foo\n") # The client sends `\n`, notice the server may expects `\n\r`.
print("Question 1 answered.")

tn.read_until("How old are you?\n")
tn.write("100\n")
print("Question 2 answered.")

tn.read_until("Do you use Python?\n")
tn.write("yep\n")
print("Question 3 answered.")

tn.close()

now lets test it, on the client side:

$ python client.py
Question 1 answered.
Question 2 answered.
Question 3 answered.
$

on the server side, dump the log file content:

$ ncat -l 9000 < msg.txt > log.txt
$
$ cat log.txt # or `type log.txt` on windows
foo
100
yep

$
$ hexdump log.txt
00000000: 66 6F 6F 0A 31 30 30 0A 79 65 70 0A             |foo 100 yep |
0000000c;
$

put it together you should get the idea.