text: import io
  import os
  import select
  import socket
  import time
  import utils
  
  utils.new_ns()
  
  port = 1
  
  
  s = socket.socket(socket.AF_INET, socket.SOCK_STREAM, 0)
  s.setsockopt(socket.IPPROTO_TCP, socket.TCP_DEFER_ACCEPT, 10)
  
  if False:
      s.setsockopt(socket.IPPROTO_TCP, socket.TCP_USER_TIMEOUT, 5*1000)
      s.setsockopt(socket.SOL_SOCKET, socket.SO_KEEPALIVE, 1)
      s.setsockopt(socket.IPPROTO_TCP, socket.TCP_KEEPCNT, 1)
      s.setsockopt(socket.IPPROTO_TCP, socket.TCP_KEEPIDLE, 1)
      s.setsockopt(socket.IPPROTO_TCP, socket.TCP_KEEPINTVL, 1)
  
  s.bind(('127.0.0.1', port))
  s.listen(16)
  
  tcpdump = utils.tcpdump_start(port)
  c = socket.socket(socket.AF_INET, socket.SOCK_STREAM, 0)
  
  
  t0 = time.time()
  
  # For testing lost ACK
  #    utils.drop_start(dport=port, extra='--tcp-flags SYN,ACK,FIN,RST,PSH ACK')
  
  c.setblocking(False)
  try:
      c.connect(('127.0.0.1', port))
  except io.BlockingIOError:
      pass
  c.setblocking(True)
  
  utils.ss(port)
  time.sleep(2)
  utils.ss(port)
  time.sleep(2)
  utils.ss(port)
  time.sleep(2)
  utils.ss(port)
  time.sleep(2)
  utils.ss(port)
  print("[x] send")
  c.send(b"hello world")
  utils.ss(port)
  time.sleep(2)
  utils.ss(port)
  