如何确定我的端口扫描仪是否正常工作？

Question

I'm making a port scanner that checks if ports are open or closed but I am convinced that it does not work as it lists every port as being closed, even ports I've specifically opened just to check if it is working. Can anyone see anything wrong with my code?

    if  userChoice == "1":
    # code for option 1
    print("You selected Port Scan Tool")
    loop = 0
    subprocess.call('cls', shell=True)
    remoteServer = input("Enter a remote host to scan: ")
    start=input("Enter starting port number: ")
    start = int(start)
    end=input("Enter ending port number: ")
    end = int(end)
    remoteServerIP = socket.gethostbyname(remoteServer)

    # Print a nice banner with information on which host we are about to scan
    print ("-" * 60)
    print("Please wait, scanning remote host", remoteServerIP)
    print("-" * 60)

    # Check what time the scan started
    t1 = datetime.now()
    timestr = time.strftime("%d.%m.%Y-%H.%M.%S")# creates time stamp on text file

    try:
        textFileLocation = timestr + " -  Port Scan Results.txt"# creates and names text file
        for port in range(start, end):  # lets user select range
            sock = (socket.socket(socket.AF_INET, socket.SOCK_STREAM))
            result = sock.connect_ex((remoteServerIP, port))
            if result == 0:
                print("Port {}: \t Open".format(port))
                #print("Port {}: \t Closed".format(port))
                #print("Port {} \t Closed".format(port))
                textFileLocation = timestr + " - Port Scan Results.txt"
                textFile = open(textFileLocation, "a")
                textToWrite = "Open: Port %d\n" % port
                textFile.write(textToWrite)
                textFile.close()
            else:
                print("Port {}: \t Closed".format(port))
                textFileLocation = timestr + " - Port Scan Results.txt"
                textFile = open(textFileLocation, "a")
                textToWrite = "Closed: Port %d\n" % port
                textFile.write(textToWrite)
                textFile.close()
            sock.close()

Answer 1

This only tests whether there is any program listening on said port.

To see whether this works or not, first remove try block to see which error is returned. Then use correct error in exception handling, ie if your machine is not on the network try will fail as well as when being unable to connect. Also you will have to introduce timeouts so that socket doesn't hang trying to connect.

To see if your code is doing anything to the target machine, activate firewall there and set it up to notify you if anyone is doing just what you did. Your code might also fail if your router/switcher is preventing port scanning on your network. You should check its firewall settings too.

You are also missing the except block in your code, and try is in wrong place anyway. You have to test each connection:

for x in range(...):
    try:
        s = socket.socket(...)
        s.connect(...)
        s.close()
    except: pass

Although you should use for instance:

except socket.SocketError as error:

and then check for error number etc. in variable error where exception will be stored.

Oh, BTW, socket.socket.connect() returns None, so your check would always be False. This is not C, its Python.

>>> ...
>>> result = sock.connect(...)
>>> print result
None

Try-except will tell you whether connection passed or failed with a lot more info.