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I'm currently working on a CTF challenge which runs on server, here is the part I need help with:

....
while True:
    menu() #display 4 options
    cmd = int(input(">> "))
    if cmd == 1:   #do something
    elif cmd == 2: #do something
    elif cmd == 3: #do something
    elif cmd == 4: #do something
....

I tried to use socket.send() and socket.recv() to send and receive data, but it seems like my code only allows me to type in 1 value and then it freezes.

Here is my solve.py:

import socket

HOST = '127.0.0.1'
PORT = 9000

with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
    s.connect((HOST, PORT))
    received_data = s.recv(1024).decode()    #this will receive the menu() display
    print(received_data)                     #print it out
    data = input()                           #I typed "1"
    s.send(data.encode())                    #send "1"
    received_data = s.recv(1024).decode()    #It should receive the option 1 action but it didn't
    print('Received: ',received_data)        #Print out '' when I force stop the program (nothing)
    s.close()

When I force stop the server, it returned EOFError: EOF when reading a line. I have found out that the problem was the input() is in while loop. The loop need multiple input while my solve.py only send 1 input.

But now I wonder what is the best solution for this. Using socket is my priority, but others should also be fine ( pwn, requests, ...)

P/s: The server is fixed. Any change on the server.py is not allowed.

LilLee
  • 11
  • Without seeing the server code or documented protocol, hard to say the solution. You have to follow the server’s protocol (assuming it is even written correctly). Your client is assuming TCP is message-based, but it is not. From the error it appears the server wants a newline-terminated response. – Mark Tolonen Jul 13 '23 at 23:05

0 Answers0