嵌入式Linux网络编程之：实验内容——NTP协议实现

/*获取NTP时间*/

intget_ntp_time(intsk,structaddrinfo*addr,structntp_packet*ret_time)

{

fd_setpending_data;

structtimevalblock_time;

chardata[NTP_PCK_LEN*8];

intpacket_len,data_len=addr->ai_addrlen,count=0,result,i,re;

if(!(packet_len=construct_packet(data)))

{

return0;

}

/*客户端给服务器端发送NTP协议数据包*/

if((result=sendto(sk,data,

packet_len,0,addr->ai_addr,data_len))0)

{

perror(sendto);

return0;

}

/*调用select()函数，并设定超时时间为1s*/

FD_ZERO(pending_data);

FD_SET(sk,pending_data);

block_time.tv_sec=10;

block_time.tv_usec=0;

if(select(sk+1,pending_data,NULL,NULL,block_time)>0)

{

/*接收服务器端的信息*/

if((count=recvfrom(sk,data,

NTP_PCK_LEN*8,0,addr->ai_addr,data_len))0)

{

perror(recvfrom);

return0;

}

if(protocol==TIME)

{

memcpy(ret_time->transmit_timestamp,data,4);

return1;

}

elseif(countNTP_PCK_LEN)

{

return0;

}

/*设置接收NTP包的数据结构*/

ret_time->leap_ver_mode=ntohl(data[0]);

ret_time->startum=ntohl(data[1]);

ret_time->poll=ntohl(data[2]);

ret_time->precision=ntohl(data[3]);

ret_time->root_delay=ntohl(*(int*)(data[4]));

ret_time->root_dispersion=ntohl(*(int*)(data[8]));

ret_time->reference_identifier=ntohl(*(int*)(data[12]));

ret_time->reference_timestamp.coarse=ntohl*(int*)(data[16]));

ret_time->reference_timestamp.fine=ntohl(*(int*)(data[20]));

ret_time->originage_timestamp.coarse=ntohl(*(int*)(data[24]));

ret_time->originage_timestamp.fine=ntohl(*(int*)(data[28]));

ret_time->receive_timestamp.coarse=ntohl(*(int*)(data[32]));

ret_time->receive_timestamp.fine=ntohl(*(int*)(data[36]));

ret_time->transmit_timestamp.coarse=ntohl(*(int*)(data[40]));

ret_time->transmit_timestamp.fine=ntohl(*(int*)(data[44]));

return1;

}/*endofifselect*/

return0;

}