我不明白为什么我的端口扫描仪 Python 程序出错

Question

I have recently started to learn Python and I tried to make a port scanner with Python but I am facing a few errors. Could someone help me understand where I went wrong?

#!/usr/bin/python3

from socket import *
import optparse
from threading import *

def connScan(tgHost,tgPort):
        try:
                sock=socket(AF_NET,SOCK_STREAM)
                sock.connect((tgHost,tgPort))
                print('[+]%d/tcp Open'%tgPort)
        except:
                print('[-]%d/tcp Closed'%tgPort)
        finally:
                sock.close()

def portscan(tgHost,tgPort):
        try:
                tgIP=gethostbyname(tgHost)
        except:
                print('[!] Unkonown Host %s'%tgHost)
        try:
                tgName=gethostbyaddr(tgIP)
                print('[+] Scan Result :' + tgName[0])
        except:
                print('[+]Scan Reults for:' + tgIP)
        setdefaulttimeout(0)
        for port in tgPort:
                t=Thread(target=connScan,args=(tgHost,int(port)))
                t.start()

def main():
        parser=optparse.OptionParser("Usage of Program :" + " -H <target host> -p <target port> ")
        parser.add_option('-H',dest='tgHost',type='string',help='specify target host')
        parser.add_option('-p',dest='tgPort',type='string',help='specify target port separated by comma')
        (options,args)=parser.parse_args()
        tgHost=options.tgHost
        tgPort=str(options.tgPort).split(',')

        if (tgHost==None) | (tgPort[0]==None):
                print (parser.usage)
                exit(0)

        portscan(tgHost,tgPort)

if __name__=='__main__':
        main()

Sample Input:

python portscan.py -H 192.168.0.102 -p 80

Sample Output:

[+]Scan Reults for:192.168.0.102 
    [-]80/tcp Closed
    Exception in thread Thread-1:
    Traceback (most recent call last):
      File "C:\python3.9.4\lib\threading.py", line 954, in _bootstrap_inner
        self.run()
      File "C:\python3.9.4\lib\threading.py", line 892, in run
        self._target(*self._args, **self._kwargs)
      File "C:\Users\DEBGANDHAR\pytools\adv.py", line 15, in connScan
        sock.close()
    UnboundLocalError: local variable 'sock' referenced before assignment

Answer 1

The error message should be self-evident; the variable you are attempting to use in the finally: block is undefined, because the error in the try: block occurred before the variable was assigned.

You have a similar error where you would try to use tgIP even though you just found that no IP address can be resolved.

More generally you should avoid import * when you can; your code only uses socket in a few places, so spelling it out is a minor inconvenience, while it makes your code clearer. Ditto for threading .

Similarly, you should avoid blanket except: blocks, and only trap exceptions which you actually know how to handle.

The optparse module is obsolescent, and should usually be replaced with argparse in new code; but your arguments are not optional in the first place, so perhaps don't use a separate module for this trivial task.

#!/usr/bin/python3

import socket as s
import threading

def connScan(tgHost, tgPort):
        sock = None
        try:
                # Notice typo fix AF_INET
                sock = s.socket(AF_INET, SOCK_STREAM)
                sock.connect((tgHost,tgPort))
                print('[+]%d/tcp Open'%tgPort)
        except s.error:
                print('[-]%d/tcp Closed'%tgPort)
        finally:
                if sock is not None:
                    sock.close()

def portscan(tgHost,tgPorts):
        try:
                tgIP = s.gethostbyname(tgHost)
        except s.gaierror:
                print('[!] Unknown Host %s'%tgHost)
                # Give up
                return None
        try:
                tgName = s.gethostbyaddr(tgIP)
                print('[+] Scan Result :' + tgName[0])
        except s.gaierror:
                print('[+]Scan Results for:' + tgIP)
        s.setdefaulttimeout(0)
        for port in tgPorts:
                t = threading.Thread(target=connScan,args=(tgHost,int(port)))
                t.start()

def main():
    from sys import argv
    import logging
    if len(argv) < 3:
        logging.error("Usage of Program: %s <target host> <target port> ...", argv[0].split('/')[-1])
        exit(2)
    portscan(argv[1], argv[2:])

if __name__=='__main__':
        main()

Notice how the list of ports is now just whitespace-separated. (Notice also the correct spelling of "separate".)