Python: DNS Client implementation

In the past two days, I tested IPv6 and DNS, checked the materials at night, and wrote a DNS Client. For the request message encoding section, refer to the online instance.

The encoding has just been completed and the function has not been tested.

1. Code:

#! /Usr/bin/ENV Python #-*-coding: UTF-8-*-import configparserimport socketimport time import stringimport osimport reimport structdef dns_codec (hostname): ''' function: request message encoding input: Hostname: host name, such as www.baidu.com output: encoded byte stream Author: Socrates Date: 2012-12-14 ''' Index = OS. urandom (2) hoststr = ''. join (CHR (LEN (x) + X for X in hostname. split ('. ') Data =' % s \ x01 \ x00 \ x00 \ x01 \ x00 \ x00 \ x00 \ x00 \ x00 \ x00 % s \ x0 0 \ x00 \ x01 \ x00 \ x01 '% (index, hoststr) Data = struct. Pack ('! H ', Len (data) + data return datadef dns_decode (in_sock): ''' function: Return Message decoding input: in_sock: Socket output for receiving messages: decoded content Author: Socrates Date: 2012-12-14 ''' rfile = in_sock.makefile ('rb') size = struct. unpack ('! H', rfile. read (2) [0] DATA = rfile. read (size) iplist = Re. findall ('\ xc0. \ x00 \ x01 \ x00 \ x01. {6 }(. {4}) ', data) return ['. '. join (STR (ord (x) for X in S) for S in iplist] def dns_sendmsg (): ''' function: Send DNS query message input: None output: none Author: Socrates Date: 2012-12-14 ''' ens_client_config = configparser. configparser () # Read the configuration file try: ens_client_config.readfp (open ('ens _ client_config.ini ') using t configparser. error: Print 'read ens_client_config.ini failed. '# obtain the required information server_ip_1 = ens_client_config.get ("server_info", "ip_1") server_port_1 = forward ("server_info", "port_1") sockettype_1 = ens_client_config.get ("server_info ", "sockettype_1") heartbeat_1 = ens_client_config.get ("server_info", "heartbeat_1") msg_1 = forward ("server_info", "msg_1") # IP type address_family = {true: socket. af_inet6, false: socket. af_inet} [':' In server_ip_1] # transmission type socket_type = {true: socket. sock_stream, false: socket. sock_dgram} ['tcp '= sockettype_1.upper ()] Try: sock = socket. socket (address_family, socket_type) cannot socket. error, E: Print 'create socket return error. errno = % d, errmsg = % s' % (E. ARGs [0], E. ARGs [1]) # connect to the server and send the message try: # connect to the server sock. connect (server_ip_1, String. atoi (server_port_1) while true: # Sending frequency time. sleep (string. atoi (heartbeat_1) # Send the sock message. sendall (dns_codec (msg_1) # receives and prints the message print dns_decode (sock) handle T socket. error, E: Print 'connect server failed. errno = % d, errmsg = % s' % (E. ARGs [0], E. ARGs [1]) sock. close () If _ name _ = '_ main _': dns_sendmsg ()

2. configuration file:

File Name: ens_client_config.ini

Content:

[server_info]ip_1=192.168.1.1port_1=53sockettype_1=UDPheartbeat_1=2msg_1=www.google.com

3. In the morning, the DNS Client under UDP protocol is tested, and the function is available normally.

A. Wireshark packet capture:

Request:

Response:

B. Code running result: