Python echo output constantly searches but never ends

Question

For our assignment, when we run our little bot, it gets stuck in an endless loop and we can't get it to end. All it does is constantly look for new bots i.e:

Waiting for connection...
Enter command: p2p echo
Finding another bot...
Found bot on port 1338
No bot was listening on port 1338
Found bot on port 1339
No bot was listening on port 1339
Found bot on port 1340
No bot was listening on port 1340
Found bot on port 1341
No bot was listening on port 1341
Found bot on port 1342

Code below

import socket
import threading

from lib.comms import StealthConn
from lib.files import p2p_download_file

# Keep track of where our server is
# This is primarily so we don't try to talk to ourselves
server_port = 1337

def find_bot():
    print("Finding another bot...")
    port = 1337
    conn = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    while 1:
        if port == server_port:
            # Don't connect to yourself, silly bot!
            port += 1
        else:
            try:
                print("Found bot on port %d" % port)
                conn.connect(("localhost", port))
                sconn = StealthConn(conn, client=True)
                return sconn
            except socket.error:
                print("No bot was listening on port %d" % port)
                port += 1

def echo_server(sconn):
    while 1:
        data = sconn.recv()
        print("ECHOING>", data)
        sconn.send(data)
        if data == b'X' or data == b'exit' or data == b'quit':
            print("Closing connection...")
            sconn.close()
            return

def accept_connection(conn):
    try:
        sconn = StealthConn(conn, server=True)
        # The sender is either going to chat to us or send a file
        cmd = sconn.recv()
        if cmd == b'ECHO':
            echo_server(sconn)
        elif cmd == b'FILE':
            p2p_download_file(sconn)
    except socket.error:
        print("Connection closed unexpectedly")

def bot_server():
    global server_port
    # Every bot is both client & server, so needs to listen for
    # connections. This is to allow for peer to peer traffic.
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    # Real worms use shifting ports but for simplicity, we won't.
    # We'll also assume you may run another bot on your computer
    # so if something else is using 1337, we'll keep going up.
    while True:
        try:
            s.bind(("localhost", server_port))
            print("Listening on port %d" % server_port)
            break
        except socket.error:
            # Someone is already using that port -- let's go up one
            print("Port %d not available" % server_port)
            server_port += 1
    s.listen(5)

    while 1:
        print("Waiting for connection...")
        conn, address = s.accept()
        print("Accepted a connection from %s..." % (address,))
        # Start a new thread per connection
        # We don't need to specify it's a daemon thread as daemon status is inherited
        threading.Thread(target=accept_connection, args=(conn,)).start()

Looked around and can't seem to find anything like it.

Answer 1

You're getting an exception in your try-except

        try:
            print("Found bot on port %d" % port)
            conn.connect(("localhost", port))
            sconn = StealthConn(conn, client=True)
            return sconn
        except socket.error:
            print("No bot was listening on port %d" % port)
            port += 1

You print out the "Found bot" part before attempting to connect to the bot. There's an exception somewhere between print("Found bot on port %d" % port) and return sconn. You're not hitting that return statement, thus the infinite loop. While is always true.

Assuming sconn returns some value if you find a bot, you just need to rearrange things.

        try:
            conn.connect(("localhost", port))
            sconn = StealthConn(conn, client=True)
            if sconn: # Check for a return value that makes sense whatever
                      # StealthConn is
                print("Found bot on port %d" % port)
                return sconn
        except socket.error:
            print("No bot was listening on port %d" % port)
            port += 1