Python implements proxy server port mapping function

a code

1. Simulate the server code

import sys
import socket
import threading
#Reply message, return as is
def replyMessage(conn):
    while True:
        data = conn.recv(1024)
        conn.send(data)
        if data.decode().lower() == 'bye':
            break
    conn.close()
def main():
    sockScr = socket.socket (socket.AF_INET, socket.SOCK_STREAM)
    sockScr.bind(('', port))
    sockScr.listen(200)
    while True:
        try:
            conn, addr = sockScr.accept()
            #Only allow specific hosts to access this server
            if addr[0] != onlyYou:
                conn.close()
                continue
            #Create and start the thread
            t = threading.Thread(target=replyMessage, args=(conn,))
            t.start()        
        except:
            print('error')
if __name__ == '__main__':
    try:
        #Get command line parameters
        port = int(sys.argv[1])
        onlyYou = sys.argv[2]
        main()
    except:
        print('Must give me a number as port')

2. Simulate proxy server code

import sys
import socket
import threading
def middle(conn, addr):
    #Server-oriented Socket
    sockDst = socket.socket (socket.AF_INET, socket.SOCK_STREAM)
    sockDst.connect((ipServer,portServer))
    while True:
        data = conn.recv(1024).decode()
        print('Received client message: '+data)
        if data == 'don't send to server':
            conn.send('The message has been filtered by the proxy server'.encode())
            print('The message has been filtered')
        elif data.lower() == 'bye':
            print(str(addr)+'client closes connection')
            break
        else:
            sockDst.send(data.encode())
            print('Forwarded server')
            data_fromServer = sockDst.recv(1024).decode()
            print('Received a message from the server: '+data_fromServer)
            if data_fromServer == '不要发给客户端':
                conn.send('该消息已被代理服务器修改'.encode())
                print('消息已被篡改')
            else:
                conn.send(b'Server reply:'+data_fromServer.encode())
                print('已转发服务器消息给客户端')
        
    conn.close()
    sockDst.close()
def main():
    sockScr = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    sockScr.bind(('', portScr))
    sockScr.listen(200)
    print('代理已启动')
    while True:
        try:
            conn, addr = sockScr.accept()
            t = threading.Thread(target=middle, args=(conn, addr))
            t.start()
            print('新客户：'+str(addr))
        except:
            pass
        
if __name__ == '__main__':
    try:
        #(本机IP地址,portScr)<==>(ipServer,portServer)
        #代理服务器监听端口
        portScr = int(sys.argv[1])
        #服务器IP地址与端口号
        ipServer = sys.argv[2]
        portServer = int(sys.argv[3])
        main()
    except:
        print('Sth error')

3、模拟客户端代码

import sys
import socket
def main():
    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    sock.connect((ip, port))
    while True:
        data = input('What do you want to ask:')
        sock.send(data.encode())
        print(sock.recv(1024).decode())
        if data.lower() == 'bye':
            break
    sock.close()
if __name__ == '__main__':
    try:
        #代理服务器的IP地址和端口号
        ip = sys.argv[1]
        port = int(sys.argv[2])
        main()
    except:
        print('Sth error')

二运行结果

三运行说明

从结果可以看出，代理服务器代码能够对客户端和服务器之间的内容进行记录，也能够修改双方通信内容，这样实际存在潜在危险。只要代理服务想这样做，客户在网络上的通信就没有什么隐私可言了，因此如果涉及金钱交易，最好不要使用代理服务器。

Python implements proxy server port mapping function

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