Try to implement server and proxy server with the shortest Python code

The simplest server
Python has the ability to set up a separate server listening port, just use wsgiref of the standard library.

from wsgiref.simple_server import make_server 
def simple_app(environ, start_response): 
  status = '200 OK' 
  response_headers = [('Content-type','text/plain')] 
  start_response(status, response_headers) 
  return ['Hello world!\n'] 
httpd = make_server('', 80, simple_app) 
httpd.serve_forever() 

50 lines of code to implement proxy server
I encountered a scene before like this:
I need to use the mongodb graphical client on my computer, but the mongodb server address is not open to the outside world. I can only log in to host A first, and then connect to mongodb server B from A.
I originally wanted to forward through the ssh port, but I don't have the permission to connect ssh from machine A to B. So I wrote one myself in Python.
The principle is simple.
1. Open a socket server to listen for connection requests
2. Every time a connection request from a client is accepted, a connection request is created to the address to be forwarded. That is client->proxy->forward. The proxy is both a socket server (listening client) and a socket client (forward request).
3. Bind the two sockets client->proxy and proxy->forward with a dictionary.
4. Pass the data sent/recv intact through this mapped dictionary
Code below.

#coding=utf-8 
import socket 
import select 
import sys 
 
to_addr = ('xxx.xxx.xx.xxx', 10000)#转发的地址 
 
class Proxy: 
  def __init__(self, addr): 
    self.proxy = socket.socket(socket.AF_INET,socket.SOCK_STREAM) 
    self.proxy.bind(addr) 
    self.proxy.listen(10) 
    self.inputs = [self.proxy] 
    self.route = {} 
 
  def serve_forever(self): 
    print 'proxy listen...' 
    while 1: 
      readable, _, _ = select.select(self.inputs, [], []) 
      for self.sock in readable: 
        if self.sock == self.proxy: 
          self.on_join() 
        else: 
          data = self.sock.recv(8096) 
          if not data: 
            self.on_quit() 
          else: 
            self.route[self.sock].send(data) 
 
  def on_join(self): 
    client, addr = self.proxy.accept() 
    print addr,'connect' 
    forward = socket.socket(socket.AF_INET, socket.SOCK_STREAM) 
    forward.connect(to_addr) 
    self.inputs += [client, forward] 
    self.route[client] = forward 
    self.route[forward] = client 
 
  def on_quit(self): 
    for s in self.sock, self.route[self.sock]: 
      self.inputs.remove(s) 
      del self.route[s] 
      s.close() 
 
if __name__ == '__main__': 
  try: 
    Proxy(('',12345)).serve_forever()#代理服务器监听的地址 
  except KeyboardInterrupt: 
    sys.exit(1) 

The screenshot of the effect is as follows.