一、简介

代理服务器大多被用来连接 （国际互联网）和 INTRANET（企业内部网）。在多个局域网中需设置不同的代理服务器参数来使浏览器访问网络。在微软 ( )5.0 以上版本中的功能中已经具备了自动切换代理服务器的功能。网络管理员需要事先部署代理服务器配置文件，然而用户方的设置却很简单。在这一功能中使用了被称为“WPAD”(Web Proxy Auto-Discovery protocol)的协议。

 

网络代理自发现协议(Web Proxy Auto-Discovery Protocol，WPAD)，通过让浏览器自动发现代理服务器，使代理服务器对用户来说是透明的，进而轻松访问互联网。

 

参考：

 

二、实现

WPAD实现源码

/*************************************************************************** wpad.cpp** CREATE ON:  2013-03-14 * BY             :  Wayne Qu (qwquwei@cn.ibm.com)* * This demo is for Proxy auto defection(WPAD) feature development & UT. **************************************************************************/#include
     
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                /* Useful definitions */#define DHCP_SERVER_PORT 67#define DHCP_CLIENT_PORT 68#define MAGIC_COOKIE 0x63825363#define DHCP_INFORM 8/* Sizes for DHCP options */#define MTU_MAX 1500#define DHCP_CHADDR_LEN 16#define SERVERNAME_LEN 64#define BOOTFILE_LEN 128#define DHCP_UDP_LEN (14 + 20 + 8)#define DHCP_FIXED_LEN (DHCP_UDP_LEN + 226)#define DHCP_OPTION_LEN (MTU_MAX - DHCP_FIXED_LEN)/* DHCP options */enum DHO { DHO_MESSAGETYPE = 53, DHO_PARAMETERREQUESTLIST = 55, DHO_PACFILELOCATION = 252, DHO_END = 255};typedef struct dhcp_message_ { uint8_t op; /* message type */ uint8_t hwtype; /* hardware address type */ uint8_t hwlen; /* hardware address length */ uint8_t hwopcount; /* should be zero in client message */ uint32_t xid; /* transaction id */ uint16_t secs; /* elapsed time in sec. from boot */ uint16_t flags; uint32_t ciaddr; /* (previously allocated) client IP */ uint32_t yiaddr; /* 'your' client IP address */ uint32_t siaddr; /* should be zero in client's messages */ uint32_t giaddr; /* should be zero in client's messages */ uint8_t chaddr[DHCP_CHADDR_LEN]; /* client's hardware address */ uint8_t servername[SERVERNAME_LEN]; /* server host name */ uint8_t bootfile[BOOTFILE_LEN]; /* boot file name */ uint32_t cookie; uint8_t options[DHCP_OPTION_LEN]; /* message options - cookie */}dhcp_message;void * xzalloc(size_t s){ void *value = malloc(s); if (value != NULL) { bzero(value,s); } return value;}uint32_t GetIPV4Ciaddr(const std::string& ip_addr){ if( 3!=std::count(ip_addr.begin(), ip_addr.end(), '.') ) { std::cout << "invalid IP Format : " << ip_addr; return 0; } std::string::size_type beg = 0; std::string::size_type end = 0; std::string tmp_str[4]; uint32_t tmp_int[4]; for(int i=0; i<4; i++) { end = ip_addr.find(".", beg); tmp_str[i] = ip_addr.substr(beg,end-beg); tmp_int[i] = atoi(tmp_str[i].c_str()); if( tmp_int[i] > 255) { std::cout << "invalid IP Format : " << ip_addr; return 0; } //std::cout<< tmp_int[i] << " "; beg = end+1; } return (uint8_t)tmp_int[0] | ((uint8_t)tmp_int[1]<<8) | ((uint8_t)tmp_int[2]<<16) | ((uint8_t)tmp_int[3]<<24);}uint32_t GetCiaddr(const std::string& ip_addr){ //Just Ipv4 Now return GetIPV4Ciaddr(ip_addr);}uint32_t GetChaddr(const std::string& mac_addr, uint8_t* chaddr){ if( 5!=std::count(mac_addr.begin(), mac_addr.end(), ':') ) { std::cout << "invalid MAC Format : " << mac_addr; return 0; } std::string::size_type beg = 0; std::string::size_type end = 0; std::string tmp_str[6]; uint32_t tmp_int[6]; for(int i=0; i<6; i++) { end = mac_addr.find(":", beg); tmp_str[i] = mac_addr.substr(beg,end-beg); std::stringstream tmp_stream; tmp_stream << "0x" << tmp_str[i]; tmp_stream >> std::hex >> tmp_int[i]; if( tmp_int[i] > 255) { std::cout << "invalid MAC Format : " << mac_addr; return 0; } chaddr[i] = tmp_int[i]; //std::cout<< std::hex << (int)chaddr[i] << " "; beg = end+1; }}// Format: ipaddr - 9.125.90.117 macaddr E4:1F:13:DA:12:7Evoid make_message(const std::string& ip_addr, const std::string& mac_addr, dhcp_message **message){ dhcp_message* dhcp; dhcp = (dhcp_message*)xzalloc(sizeof (*dhcp)); bzero(dhcp, sizeof(dhcp_message)); dhcp->op = 1; dhcp->hwtype = 1; //ARPHRD_ETHER dhcp->hwlen = 6; //MAC ADDR LENGTH dhcp->xid = 1983; //random dhcp->ciaddr = GetCiaddr(ip_addr); GetChaddr(mac_addr, dhcp->chaddr); dhcp->cookie = htonl(MAGIC_COOKIE); uint8_t *p = dhcp->options; //option 53 *p++ = DHO_MESSAGETYPE; *p++ = 1; *p++ = DHCP_INFORM; //option 55 *p++ = DHO_PARAMETERREQUESTLIST; *p++ = 1; *p++ = DHO_PACFILELOCATION; *p++ = DHO_END; *message = dhcp;}int open_send_socket(){ int sockfd; struct sockaddr_in addr; if((sockfd = socket(AF_INET,SOCK_DGRAM,0))<0) { //TBI } int bBroadcast=1; setsockopt(sockfd, SOL_SOCKET, SO_BROADCAST, &bBroadcast, sizeof(bBroadcast)); return sockfd;}int open_recv_socket(char* ipaddr){ int sockfd; struct sockaddr_in addr; if((sockfd = socket(AF_INET,SOCK_DGRAM,0))<0) { std::cout << "setup socket failed" << std::endl;//TBI } bzero(&addr,sizeof(addr)); addr.sin_family = AF_INET; addr.sin_port = htons(DHCP_CLIENT_PORT); addr.sin_addr.s_addr = inet_addr(ipaddr); const int retry_cnt = 10; int retry_num = retry_cnt; while(bind(sockfd, (struct sockaddr *)&addr, sizeof(addr))<0 && (retry_num > 0)) { std::cout << "bind to " << ipaddr << ":" << DHCP_CLIENT_PORT<< " failed!"<
                
                 options[i]) << " "; }*/ std::cout << "dhcp->xid = " << dhcp_recv->xid << std::endl; std::cout << "wpad url = " << dhcp_parser(dhcp_recv->options) << std::endl; close(send_socket_fd); close(recv_socket_fd);}