实例探究Python以并发方式编写高性能端口扫描器的方法
关于端口扫描器
端口扫描工具（Port Scanner）指用于探测服务器或主机开放端口情况的工具。常被计算机管理员用于确认安全策略，同时被攻击者用于识别目标主机上的可运作的网络服务。
端口扫描定义是客户端向一定范围的服务器端口发送对应请求，以此确认可使用的端口。虽然其本身并不是恶意的网络活动，但也是网络攻击者探测目标主机服务，以利用该服务的已知漏洞的重要手段。端口扫描的主要用途仍然只是确认远程机器某个服务的可用性。
扫描多个主机以获取特定的某个端口被称为端口清扫（Portsweep），以此获取特定的服务。例如，基于SQL服务的计算机蠕虫就会清扫大量主机的同一端口以在 1433 端口上建立TCP连接。
Python实现
端口扫描器原理很简单，无非就是操作socket，能connect就认定这个端口开放着。
import socket
def scan(port):
s = socket.socket()
if s.connect_ex(('localhost', port)) == 0:
print port, 'open'
s.close()
if __name__ == '__main__':
map(scan,range(1,65536))
这样一个最简单的端口扫描器出来了。
等等喂，半天都没反应，那是因为socket是阻塞的，每次连接要等很久才超时。
我们自己给它加上的超时。
s.settimeout(0.1)
再跑一遍，感觉快多了。
多线程版本
import socket
import threading
def scan(port):
s = socket.socket()
s.settimeout(0.1)
if s.connect_ex(('localhost', port)) == 0:
print port, 'open'
s.close()
if __name__ == '__main__':
threads = [threading.Thread(target=scan, args=(i,)) for i in xrange(1,65536)]
map(lambda x:x.start(),threads)
运行一下，哇，好快，快到抛出错误了。thread.error: can't start new thread。
想一下，这个进程开启了65535个线程，有两种可能，一种是超过最大线程数了，一种是超过最大socket句柄数了。在linux可以通过ulimit来修改。
如果不修改最大限制，怎么用多线程不报错呢？
加个queue,变成生产者-消费者模式,开固定线程。
多线程+队列版本
import socket
import threading
from Queue import Queue
def scan(port):
s = socket.socket()
s.settimeout(0.1)
if s.connect_ex(('localhost', port)) == 0:
print port, 'open'
s.close()
def worker():
while not q.empty():
port = q.get()
try:
scan(port)
finally:
q.task_done()
if __name__ == '__main__':
q = Queue()
map(q.put,xrange(1,65535))
threads = [threading.Thread(target=worker) for i in xrange(500)]
map(lambda x:x.start(),threads)
q.join()
这里开500个线程，不停的从队列取任务来做。
multiprocessing+队列版本
总不能开65535个进程吧？还是用生产者消费者模式
import multiprocessing
def scan(port):
s = socket.socket()
s.settimeout(0.1)
if s.connect_ex(('localhost', port)) == 0:
print port, 'open'
s.close()
def worker(q):
while not q.empty():
port = q.get()
try:
scan(port)
finally:
q.task_done()
if __name__ == '__main__':
q = multiprocessing.JoinableQueue()
map(q.put,xrange(1,65535))
jobs = [multiprocessing.Process(target=worker, args=(q,)) for i in xrange(100)]
map(lambda x:x.start(),jobs)
注意这里把队列作为一个参数传入到worker中去，因为是process safe的queue，不然会报错。
还有用的是JoinableQueue()，顾名思义就是可以join()的。
gevent的spawn版本
from gevent import monkey; monkey.patch_all(); import gevent import socket ... if __name__ == '__main__': threads = [gevent.spawn(scan, i) for i in xrange(1,65536)] gevent.joinall(threads)
注意monkey patch必须在被patch的东西之前import,不然会Exception KeyError.比如不能先import threading,再monkey patch.
gevent的Pool版本
from gevent import monkey; monkey.patch_all(); import socket from gevent.pool import Pool ... if __name__ == '__main__': pool = Pool(500) pool.map(scan,xrange(1,65536)) pool.join()
concurrent.futures版本
import socket
from Queue import Queue
from concurrent.futures import ThreadPoolExecutor
...
if __name__ == '__main__':
q = Queue()
map(q.put,xrange(1,65536))
with ThreadPoolExecutor(max_workers=500) as executor:
for i in range(500):
executor.submit(worker,q)
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