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Python:DNS客户端实现

这两天在测试IPV6与DNS,晚上查了下资料,写了个DNS客户端,其中请求消息编码部分参考网上实例。

刚完成了编码,功能还没有测试。

1、代码:

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import ConfigParser
import socket
import time   
import string
import os
import re
import struct

def dns_codec(hostname):
    """
    Function:请求消息编码
    Input:hostname:主机名,如www.baidu.com
    Output: 编码后的字节流
    author: socrates
    date:2012-12-14
    """
    index = os.urandom(2)
    hoststr = "".join(chr(len(x))+x for x in hostname.split("."))
    data = "%sx01x00x00x01x00x00x00x00x00x00%sx00x00x01x00x01" % (index, hoststr)
    data = struct.pack("!H", len(data)) + data
    return data

def dns_decode(in_sock):
    """
    Function:响应消息解码
    Input:in_sock:接收消息的socket
    Output:解码后的内容
    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.x00x01x00x01.{6}(.{4})", data)
    return [".".join(str(ord(x)) for x in s) for s in iplist]  
    
def dns_sendmsg():
    """
    Function:通过socket发送DNS查询消息
    Input:None
    Output:None
    author: socrates
    date:2012-12-14
    """
    ens_client_config = ConfigParser.ConfigParser()
    
    #读取配置文件
    try:
        ens_client_config.readfp(open("ens_client_config.ini"))
    except ConfigParser.Error:
        print "read ens_client_config.ini failed."
    
    #获取需要的信息
    server_ip_1 = ens_client_config.get("server_info","ip_1")
    server_port_1 = ens_client_config.get("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 = ens_client_config.get("server_info","msg_1")
    
    #IP类型
    address_family = {True:socket.AF_INET6, False:socket.AF_INET}[":" in server_ip_1]
    #传输类型
    socket_type = {True:socket.SOCK_STREAM , False:socket.SOCK_DGRAM}["TCP" == sockettype_1.upper()]
    
    try:
        sock = socket.socket(address_family, socket_type)  
    except socket.error, e:
        print "create socket return error. errno = %d, errmsg = %s" % (e.args[0], e.args[1])
    
    #连接服务器并发送消息        
    try:
        #连接服务端
        sock.connect((server_ip_1, string.atoi(server_port_1)))  
        
        while True:
            
            #发送频率
            time.sleep(string.atoi(heartbeat_1)) 
            
            #发送消息 
            sock.sendall(dns_codec(msg_1))  
            
            #接收并打印消息
            print dns_decode(sock)  
            
    except 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、配置文件:

文件名:ens_client_config.ini

内容:

[server_info]
ip_1=192.168.1.1
port_1=53
sockettype_1=UDP
heartbeat_1=2
msg_1=www.google.com

3、早上测试了下UDP协议下的DNS客户端,功能正常可用。

a、wireshark抓包:

请求:

QQ截图20121216114223

响应:

QQ截图20121216114223

b、代码运行结果:

QQ截图20121216114223