Python Scapy端口扫描器

Question

有人可以解释这段代码的每一行。它使用scapy找到ip的开放端口：

import timeimport 
logginglogging.getLogger("scapy.runtime").setLevel(logging.ERROR) 
# Disable the annoying No Route found warning !
from scapy.all import * 

ip = input("Enter the ip:,ex:'192.168.255.29/24': ")
closed_ports = 0open_ports = [] 

def is_up(ip): 
    """ Tests if host is up """ 
    icmp = IP(dst=ip)/ICMP() 
    resp = sr1(icmp, timeout=10)
    if resp == None: 
        return False 
    else: 
       return True 

      if __name__ == '__main__': 
           conf.verb = 0 
           # Disable verbose in sr(), sr1() methods 
           start_time = time.time() 
           ports = range(1, 1024) 
           if is_up(ip): 
               print "Host %s is up, start scanning" % ip for port in ports: src_port = RandShort() 
               # Getting a random port as source port 
               p = IP(dst=ip)/TCP(sport=src_port, dport=port, flags='S') 
               # Forging SYN packet 
               resp = sr1(p, timeout=2) 
               # Sending packet 
               if str(type(resp)) == "<type 'NoneType'>": 
                   closed += 1 
               elif resp.haslayer(TCP): 
                   if resp.getlayer(TCP).flags == 0x12: 
                        send_rst = sr(IP(dst=ip)/TCP(sport=src_port, dport=port, flags='AR'), timeout=1) openp.append(port) 
               elif resp.getlayer(TCP).flags == 0x14: 
                   closed += 1 
                   duration = time.time()-start_time 
              print "%s Scan Completed in %fs" % (ip, duration) 
              if len(openp) != 0: 
                  for opp in openp: 
                      print "%d open" % pop print "%d closed ports in %d total port scanned" % (closed, len(ports)) 
               else: 
                   print "Host %s is Down" % ip