繼上一篇計算checksum校驗和，本章通過socket套接字，struct字節打包成二進制，select返回套接字的文件描述符的結合，實現一個簡單的ping工具。

#!/usr/bin/python3.6.4#!coding:utf-8__author__ = 'Rosefinch'__date__ = '2018/5/31 22:27'import timeimport structimport socketimport selectimport sysdef chesksum(data):  """  校驗  """  n = len(data)  m = n % 2  sum = 0   for i in range(0, n - m ,2):    sum += (data[i]) + ((data[i+1]) << 8)#傳入data以每兩個字節（十六進制）通過ord轉十進制，第一字節在低位，第二個字節在高位  if m:    sum += (data[-1])  #將高于16位與低16位相加  sum = (sum >> 16) + (sum & 0xffff)  sum += (sum >> 16) #如果還有高于16位，將繼續與低16位相加  answer = ~sum & 0xffff  #主機字節序轉網絡字節序列（參考小端序轉大端序）  answer = answer >> 8 | (answer << 8 & 0xff00)  return answer   '''  連接套接字,并將數據發送到套接字  '''def raw_socket(dst_addr,imcp_packet):  rawsocket = socket.socket(socket.AF_INET,socket.SOCK_RAW,socket.getprotobyname("icmp"))  send_request_ping_time = time.time()  #send data to the socket  rawsocket.sendto(imcp_packet,(dst_addr,80))  return send_request_ping_time,rawsocket,dst_addr  '''  request ping  '''def request_ping(data_type,data_code,data_checksum,data_ID,data_Sequence,payload_body):  #把字節打包成二進制數據  imcp_packet = struct.pack('>BBHHH32s',data_type,data_code,data_checksum,data_ID,data_Sequence,payload_body)  icmp_chesksum = chesksum(imcp_packet)#獲取校驗和  imcp_packet = struct.pack('>BBHHH32s',data_type,data_code,icmp_chesksum,data_ID,data_Sequence,payload_body)  return imcp_packet  '''  reply ping  '''def reply_ping(send_request_ping_time,rawsocket,data_Sequence,timeout = 2):  while True:    started_select = time.time()    what_ready = select.select([rawsocket], [], [], timeout)    wait_for_time = (time.time() - started_select)    if what_ready[0] == []: # Timeout      return -1    time_received = time.time()    received_packet, addr = rawsocket.recvfrom(1024)    icmpHeader = received_packet[20:28]    type, code, checksum, packet_id, sequence = struct.unpack(      ">BBHHH", icmpHeader    )    if type == 0 and sequence == data_Sequence:      return time_received - send_request_ping_time    timeout = timeout - wait_for_time    if timeout <= 0:      return -1  '''  實現 ping 主機/ip  '''def ping(host):  data_type = 8 # ICMP Echo Request  data_code = 0 # must be zero  data_checksum = 0 # "...with value 0 substituted for this field..."  data_ID = 0 #Identifier  data_Sequence = 1 #Sequence number  payload_body = b'abcdefghijklmnopqrstuvwabcdefghi' #data  dst_addr = socket.gethostbyname(host)#將主機名轉ipv4地址格式，返回以ipv4地址格式的字符串，如果主機名稱是ipv4地址，則它將保持不變  print("正在 Ping {0} [{1}] 具有 32 字節的數據:".format(host,dst_addr))  for i in range(0,4):    icmp_packet = request_ping(data_type,data_code,data_checksum,data_ID,data_Sequence + i,payload_body)    send_request_ping_time,rawsocket,addr = raw_socket(dst_addr,icmp_packet)    times = reply_ping(send_request_ping_time,rawsocket,data_Sequence + i)    if times > 0:      print("來自 {0} 的回復: 字節=32 時間={1}ms".format(addr,int(times*1000)))      time.sleep(0.7)    else:      print("請求超時。")if __name__ == "__main__":  if len(sys.argv) < 2:    sys.exit('Usage: ping.py <host>')  ping(sys.argv[1])