周日花了大概3-4个小时把代码巧了遍，理解了下。做完前面的netcat理解大致原理和流程就不难了。不过要期末考试了，我就不费心费力去调代码了，里面肯定有很多bug。。以我先前对netcat的代码调试经验来看。
核心就一个，中间代理上两个socket，一个和远程主机通信，一个和本地客户端通信，就这么简单。代码献上，有兴趣的朋友可以试着调试下。
import sys
import socket
import threading#打开server端口，listen,处理传进来的数据
def server_loop(local_host,local_port,remote_host,remote_port,receive_first):server = socket.socket(socket.AF_INET,socket.SOCK_STREAM)try:server.bind(local_host,local_port)except:print('[!!] Failed to listen on %s:%d'%(local_host,local_port))print('[!!] Check for other listening sockets or correct permissions')sys.exit(0)print('[*] Listening on %s:%d'%(local_host,local_port))server.listen(5)while True():client_socket,addr = server.accept()print('[==>] Received incoming connection from %s:%d'%(addr[0],addr[1]))proxy_thread = threading.Thread(target = proxy_handler,args = (client_socket,remote_host,remote_port,receive_first))proxy_thread.start()#这个函数定义了代理服务器的主要处理方法
def proxy_handler(client_socket,remote_host,remote_port,receive_first):#连接上远程主机remote_socket = socket.socket(socket.AF_INET,socket.SOCK_STREAM)remote_socket.connect((remote_host,remote_port))#如果receive_first为true说明要先从远程主机接收数据if receive_first:remote_buffer = receive_from(remote_socket)#看一看远程主机过来的内容有没有想要的东西^_^偷窥下hexdump(remote_buffer)#将接收到的数据处理下remote_buffer = response_handler(remote_buffer)#remote_buffer处理过后长度不为0说明要把数据传给客户端if len(remote_buffer):print('[<==] Sending %d bytes to local_host.'%len(remote_buffer))client_socket.send(remote_buffer)#不断地接收来自远程主机和客户端的信息然后发送给对方while True:local_buffer = receive_from(client_socket)if len(local_buffer):print('[==>] Received %d bites from local_host.'%len(local_buffer))hexdump(local_buffer)local_buffer = request_handler(local_buffer)remote_socket.send(local_buffer)print('[==>] Sent to remote')remote_buffer = receive_from(remote_socket)if len(remote_buffer):print('[<==] Received %d bytes from remote.'%len(remote_buffer))hexdump(remote_buffer)remote_buffer = response_handler(remote_buffer)client_socket.send(remote_buffer)print('[<== Sent to local_host]')#两边都没有数据，关闭连接，我怀疑这里会出问题if not len(local_buffer) or not len(remote_buffer):client_socket.close()remote_buffer.close()print('[*] No more data. Closing connections.')break#这个函数不大懂意思，后面仔细研究下
def hexdump(src,length = 16):result = []digits = 4 if isinstance(src,unincode) else 2 #我的理解是中文4，外文2#xrange不会直接生成list，而是生成一个对象，要用的时候再去调用对象里面的东西for i in xrange(0,len(src),length):s = src[i:i+length]hexa = b' '.join(['%0*x'%(digits,ord(x)) for x in s])text = b''.join([x if 0x20 <= ord(x) <= 0x7F else b'.' for x in s])result.append(b'%04X %-*s %s'%(i,length*(digits + 1),hexa,text))print(b'\n'.join(result))def receive_from(connection):buffer = ''#设置两秒超时connection.settimeout(2)try:while True:data = connection.recv(4096)if not data:breakbuffer += dataexcept:passreturn buffer#定义远程和本地主机消息处理函数，这里没有需要，不做操作
def request_handler(buffer):return(buffer)
def response_handler(buffer):return(buffer)def main():#从命令行读入参数，如果数目不对则报错if len(sys.argv(1:)) != 5:print('Usage: python tcp_proxy.py [local_host] [local_port] [remote_host] [remote_port] [receive_first]')print('Example: python tcp_proxy.py 127.0.0.1')sys.exit(0)#设置监听参数local_host = sys.argv[1]local_port = int(sys.argv[2])#设置远程目标remote_host = sys.argv[3]remote_port = int(sys.argv[4])#告诉代理在发送数据前接收连接和接收数据，不大懂，先存疑receive_first = sys.argv[5]if 'True' in receive_first:receive_first = Trueelse:receive_first = False#开始监听，然后代理开始工作！server_loop(local_host,local_port,remote_host,remote_port,receive_first)main()