1 端口映射
举个例子来说明一下端口映射的作用。
有A、B、C三台计算机,A、B互通,B、C互通,但是A、C不通,这个时候在C上开了一个Web服务,如何让A访问C的Web服务?
最简单有效的办法就是在B上开一个端口映射服务,然后让A访问B的某个端口,B将这个端口上的所有流量全部转发到C的Web服务端口上,同时将C上Web服务返回的流量也全部转发给A。这样对A来说,以B为跳板,实现了间接访问C上Web服务的目的。
2 实现流程
端口映射的原理并不复杂,本文以TCP为例介绍一下实现过程,简单画了个时序图(如下),这里就不再用文字赘述了。
需要注意的是,由于端口映射只是单纯的流量转发,对应用层数据不进行处理,所以对于多通道协议是无法支持的(如FTP协议)。
3 代码示例
按照上面的流程,Python实现如下(建议从后向前看):
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# -*- coding: utf-8 -*-
# tcp mapping created by hutaow(hutaow.com) at 2014-08-31
import socket
import threading
# 端口映射配置信息
CFG_REMOTE_IP = '192.168.0.10'
CFG_REMOTE_PORT = 22
CFG_LOCAL_IP = '0.0.0.0'
CFG_LOCAL_PORT = 10022
# 接收数据缓存大小
PKT_BUFF_SIZE = 2048
# 调试日志封装
def send_log(content):
print content
return
# 单向流数据传递
def tcp_mapping_worker(conn_receiver, conn_sender):
while True :
try :
data = conn_receiver.recv(PKT_BUFF_SIZE)
except Exception:
send_log( 'Event: Connection closed.' )
break
if not data:
send_log( 'Info: No more data is received.' )
break
try :
conn_sender.sendall(data)
except Exception:
send_log( 'Error: Failed sending data.' )
break
# send_log('Info: Mapping data > %s ' % repr(data))
send_log( 'Info: Mapping > %s -> %s > %d bytes.' % (conn_receiver.getpeername(), conn_sender.getpeername(), len (data)))
conn_receiver.close()
conn_sender.close()
return
# 端口映射请求处理
def tcp_mapping_request(local_conn, remote_ip, remote_port):
remote_conn = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
try :
remote_conn.connect((remote_ip, remote_port))
except Exception:
local_conn.close()
send_log( 'Error: Unable to connect to the remote server.' )
return
threading.Thread(target = tcp_mapping_worker, args = (local_conn, remote_conn)).start()
threading.Thread(target = tcp_mapping_worker, args = (remote_conn, local_conn)).start()
return
# 端口映射函数
def tcp_mapping(remote_ip, remote_port, local_ip, local_port):
local_server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
local_server.bind((local_ip, local_port))
local_server.listen( 5 )
send_log( 'Event: Starting mapping service on ' + local_ip + ':' + str (local_port) + ' ...' )
while True :
try :
(local_conn, local_addr) = local_server.accept()
except KeyboardInterrupt, Exception:
local_server.close()
send_log( 'Event: Stop mapping service.' )
break
threading.Thread(target = tcp_mapping_request, args = (local_conn, remote_ip, remote_port)).start()
send_log( 'Event: Receive mapping request from %s:%d.' % local_addr)
return
# 主函数
if __name__ = = '__main__' :
tcp_mapping(CFG_REMOTE_IP, CFG_REMOTE_PORT, CFG_LOCAL_IP, CFG_LOCAL_PORT)
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4 运行
运行效果如下,192.168.0.20通过连接映射服务器的10022端口,成功访问192.168.0.10的SSH服务(22端口):