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dnsquery.c
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/*
* =====================================================================================
*
* Filename: dnsquery.c
*
* Description: 对外层接口:getaddrinfo_v6()
* 1.host输入为ipv4地址时，申请解析ipv4only.arpa的ip地址，判断前缀-提取前缀合成
* 2.host输入为域名时，首先通过自己实现的getaddrinfo，如果返回失败，再调用系统api getaddrinfo
* 内部:th_gethostbyname()，解析地址
* 1.现在只知道3个dns64服务器的地址，开3个线程解析地址，某线程首先获取到该域名下所对应的IP地址列表即返回
*
*
* Version: 1.0
* Created: 2017/04.17
* Compiler: gcc
* Author: ZQ
*
* =====================================================================================
*/
#include "dnsquery.h"
#define TRAFFIC_LIMIT_RET_CODE (INT_MIN)
#define DNS_PORT (53)
#define DEFAULT_TIMEOUT (3000)
#define NAME_SVR ("nameserver")
#define NAME_SVR_LEN (40)
// Type field of Query and Answer
#define A 1 /* host address */
#define NS 2 /* authoritative server */
#define CNAME 5 /* canonical name */
#define SOA 6 /* start of authority zone */
#define PTR 12 /* domain name pointer */
#define MX 15 /* mail routing information */
#define AAAA 0x1c
#define min(a,b) ((a)<(b))?(a):(b)
#define false 0
#define true 1
#define dbg printf
typedef unsigned char uint8_t;
// DNS header structure
#pragma pack(push, 1)
struct DNS_HEADER {
unsigned short id; // identification number
unsigned char rd : 1; // recursion desired
unsigned char tc : 1; // truncated message
unsigned char aa : 1; // authoritive answer
unsigned char opcode : 4; // purpose of message
unsigned char qr : 1; // query/response flag
unsigned char rcode : 4; // response code
unsigned char cd : 1; // checking disabled
unsigned char ad : 1; // authenticated data
unsigned char z : 1; // its z! reserved
unsigned char ra : 1; // recursion available
unsigned short q_count; // number of question entries
unsigned short ans_count; // number of answer entries
unsigned short auth_count; // number of authority entries
unsigned short add_count; // number of resource entries
};
static pthread_mutex_t dnsquery_mutex,dnsquery_mutex1;
//static pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
static int DNS64SERVERNUM =3;
static int dnsquery_failcount=0;
struct multi_dns
{
const char* _host;
struct socket_ipinfo_t* _ipinfo;
int _timeout;
const char *_dnsserver;
};
// Constant sized fields of query structure
struct QUESTION {
unsigned short qtype;
unsigned short qclass;
};
// Constant sized fields of the resource record structure
struct R_DATA {
unsigned short type;
unsigned short _class;
unsigned int ttl;
unsigned short data_len;
};
#pragma pack(pop)
// Pointers to resource record contents
struct RES_RECORD {
unsigned char* name;
struct R_DATA* resource;
unsigned char* rdata;
};
// Structure of a Query
typedef struct {
unsigned char* name;
struct QUESTION* ques;
} QUERY;
static const uint8_t kWellKnownV4Addr1[4] = {192, 0, 0, 170};
static const uint8_t kWellKnownV4Addr2[4] = {192, 0, 0, 171};
static const uint8_t kOurDefineV4Addr[4] = {192, 0, 2, 1};
//根据rfc6052，第64-72位必需为0;
//insert 0 after first byte
static const uint8_t kWellKnownV4Addr1_index1[5] = {192, 0, 0, 0, 170};
static const uint8_t kWellKnownV4Addr2_index1[5] = {192, 0, 0, 0, 171};
static const uint8_t kOurDefineV4Addr_index1[5] = {192, 0, 0, 2, 1};
//insert 0 after second byte
static const uint8_t kWellKnownV4Addr1_index2[5] = {192, 0, 0, 0, 170};
static const uint8_t kWellKnownV4Addr2_index2[5] = {192, 0, 0, 0, 171};
static const uint8_t kOurDefineV4Addr_index2[5] = {192, 0, 0, 2, 1};
//insert 0 after third byte
static const uint8_t kWellKnownV4Addr1_index3[5] = {192, 0, 0, 0, 170};
static const uint8_t kWellKnownV4Addr2_index3[5] = {192, 0, 0, 0, 171};
static const uint8_t kOurDefineV4Addr_index3[5] = {192, 0, 2, 0, 1};
//函数原型声明
static int isValidIpv4Address(char* _ipaddress);
static void ChangetoDnsNameFormat(unsigned char*,char *);
static unsigned char* ReadName(unsigned char*, unsigned char*, int*);
static void PrepareDnsQueryPacket(unsigned char* _buf, struct DNS_HEADER* _dns, unsigned char* _qname, char * _host);
static void ReadRecvAnswer(unsigned char* _buf, struct DNS_HEADER* _dns, unsigned char* _reader, struct RES_RECORD* _answers);
static int RecvWithinTime(int _fd, char* _buf, size_t _buf_n, struct sockaddr* _addr, socklen_t* _len, unsigned int _sec, unsigned _usec);
static int SendWithinTime(int _fd, char* _buf, size_t _buf_n, struct sockaddr* _addr, socklen_t* _len, unsigned int _sec, unsigned _usec);
static void FreeAll(struct RES_RECORD* _answers);
static int GetSuffixZeroCount(uint8_t* _buf, int _buf_len);
static int IsNat64AddrValid(struct in6_addr* _replaced_nat64_addr);
static void ReplaceNat64WithV4IP(struct in6_addr* _replaced_nat64_addr,struct in_addr* _v4_addr);
static int IsNat64AddrValid(struct in6_addr* _replaced_nat64_addr) {
int suffix_zero_count = GetSuffixZeroCount((uint8_t*)_replaced_nat64_addr, sizeof(struct in6_addr));
int is_valid = false;
switch(suffix_zero_count) {
case 3:
//Pref64::/64
if (0==memcmp(((uint8_t*)_replaced_nat64_addr)+9, kWellKnownV4Addr1, 4)
|| 0==memcmp(((uint8_t*)_replaced_nat64_addr)+9, kWellKnownV4Addr2, 4)) {
is_valid = true;
}
break;
case 4:
//Pref64::/56
if (0==memcmp(((uint8_t*)_replaced_nat64_addr)+7, kWellKnownV4Addr1_index1, 5)
|| 0==memcmp(((uint8_t*)_replaced_nat64_addr)+7, kWellKnownV4Addr2_index1, 5)) {
is_valid = true;
}
break;
case 5:
//Pref64::/48
if (0==memcmp(((uint8_t*)_replaced_nat64_addr)+6, kWellKnownV4Addr1_index2, 5)
|| 0==memcmp(((uint8_t*)_replaced_nat64_addr)+6, kWellKnownV4Addr2_index2, 5)) {
is_valid = true;
}
break;
case 6:
//Pref64::/40
if (0==memcmp(((uint8_t*)_replaced_nat64_addr)+5, kWellKnownV4Addr1_index3, 5)
|| 0==memcmp(((uint8_t*)_replaced_nat64_addr)+5, kWellKnownV4Addr2_index3, 5)) {
is_valid = true;
}
break;
case 8: //7bytes suffix and 1 bytes u(RFC6052)
//Pref64::/32
if (0==memcmp(((uint8_t*)_replaced_nat64_addr)+4, kWellKnownV4Addr1, 4)
|| 0==memcmp(((uint8_t*)_replaced_nat64_addr)+4, kWellKnownV4Addr2, 4)) {
is_valid = true;
}
break;
case 0:
//Pref64::/96
if ((0==memcmp(((uint8_t*)_replaced_nat64_addr)+12, kWellKnownV4Addr1, 4))||( 0==memcmp(((uint8_t*)_replaced_nat64_addr)+12, kWellKnownV4Addr2, 4))) {
is_valid = true;
}
break;
}
return true;
}
static void ReplaceNat64WithV4IP(struct in6_addr* _replaced_nat64_addr, struct in_addr* _v4_addr) {
int suffix_zero_count = GetSuffixZeroCount((uint8_t*)_replaced_nat64_addr, sizeof(struct in6_addr));
uint8_t zero = (uint8_t)0;
switch(suffix_zero_count) {
case 3:
//Pref64::/64
memcpy(((uint8_t*)_replaced_nat64_addr)+9, (uint8_t*)_v4_addr, 4);
break;
case 4:
//Pref64::/56
memcpy(((uint8_t*)_replaced_nat64_addr)+7, (uint8_t*)_v4_addr, 1);
memcpy(((uint8_t*)_replaced_nat64_addr)+8, &zero, 1);
memcpy(((uint8_t*)_replaced_nat64_addr)+9, ((uint8_t*)_v4_addr)+1, 3);
break;
case 5:
//Pref64::/48
memcpy(((uint8_t*)_replaced_nat64_addr)+6, (uint8_t*)_v4_addr, 2);
memcpy(((uint8_t*)_replaced_nat64_addr)+8, &zero, 1);
memcpy(((uint8_t*)_replaced_nat64_addr)+9, ((uint8_t*)_v4_addr)+2, 2);
break;
case 6:
//Pref64::/40
memcpy(((uint8_t*)_replaced_nat64_addr)+5, (uint8_t*)_v4_addr, 3);
memcpy(((uint8_t*)_replaced_nat64_addr)+8, &zero, 1);
memcpy(((uint8_t*)_replaced_nat64_addr)+9, ((uint8_t*)_v4_addr)+3, 1);
break;
case 8:
//Pref64::/32
memcpy(((uint8_t*)_replaced_nat64_addr)+4, (uint8_t*)_v4_addr, 4);
break;
case 0:
//Pref64::/96
memcpy(((uint8_t*)_replaced_nat64_addr)+12, (uint8_t*)_v4_addr, 4);
break;
default:
memcpy(((uint8_t*)_replaced_nat64_addr)+12, (uint8_t*)_v4_addr, 4);
}
}
static int GetSuffixZeroCount(uint8_t* _buf, int _buf_len) {
int zero_count = 0;
for(int i=0; i<_buf_len; i++) {
if ((uint8_t)0==_buf[_buf_len-1-i])
zero_count++;
else
break;
}
return zero_count;
}
static int getaddrinfo_api(char *_host,struct socket_ipinfo_t* _ipinfo)
{
struct addrinfo hints, *res=NULL, *res0=NULL;
int error = 0;
int ret = -1;
memset(&hints, 0, sizeof(hints));
hints.ai_family = PF_INET6;
hints.ai_socktype = SOCK_STREAM;
hints.ai_flags = AI_ADDRCONFIG;
error = getaddrinfo(_host, NULL, &hints, &res0);
if (error==0) {
for (res = res0; res; res = res->ai_next) {
char ip_buf[64] = {0};
if (AF_INET6 == res->ai_family) {
memcpy ( (char*)&(_ipinfo->v6_addr[_ipinfo->size].s6_addr32), (char*)&((((struct sockaddr_in6*)res->ai_addr)->sin6_addr).s6_addr32), 12);
//_ipinfo->v6_addr[_ipinfo->size]=res->ai_addr->s6_addr;
_ipinfo->size+=1;
ret = 0;
break;
}
else {
ret = -1;
}
}
} else {
ret = -1;
}
freeaddrinfo(res0);
return ret;
}
void *th_socket_gethostbyname(void *data) {
dbg("[%s] -- [%d] -- th_socket_gethostbyname enter\r\n", __FUNCTION__, __LINE__);
struct multi_dns *tmp = (struct multi_dns *)data;
if(socket_gethostbyname(tmp->_host,tmp->_ipinfo,tmp->_timeout,tmp->_dnsserver)==-1)
{
pthread_mutex_lock(&dnsquery_mutex1);
dnsquery_failcount++;
pthread_mutex_unlock(&dnsquery_mutex1);
}
dbg("[%s] -- [%d] -- th_socket_gethostbyname out \r\n", __FUNCTION__, __LINE__);
}
static int th_gethostbyname(char* _host, struct socket_ipinfo_t* _ipinfo, int _timeout /*ms*/)
{
int ret=-1;
dbg("[%s] -- [%d] -- th_gethostbyname enter\r\n", __FUNCTION__, __LINE__);
struct multi_dns *data=(struct multi_dns *)malloc(sizeof(struct multi_dns));
pthread_t dnsserver1,dnsserver2,dnsserver3;
pthread_mutex_init(&dnsquery_mutex,NULL);
pthread_mutex_init(&dnsquery_mutex1,NULL);
data->_host=_host;
data->_ipinfo=_ipinfo;
data->_timeout=_timeout;
data->_dnsserver = "2001:67c:27e4:15::64";
if(pthread_create(&dnsserver1,NULL,th_socket_gethostbyname,data))
{
dbg("[%s] -- [%d] -- pthread_create failed\r\n", __FUNCTION__, __LINE__);
DNS64SERVERNUM--;
}
data->_dnsserver = "2001:67c:27e4:15::6411";
if(pthread_create(&dnsserver2,NULL,th_socket_gethostbyname,data))
{
dbg("[%s] -- [%d] -- pthread_create failed\r\n", __FUNCTION__, __LINE__);
DNS64SERVERNUM--;
}
data->_dnsserver = "2001:67c:27e4::60";
if(pthread_create(&dnsserver3,NULL,th_socket_gethostbyname,data))
{
dbg("[%s] -- [%d] -- pthread_create failed\r\n", __FUNCTION__, __LINE__);
DNS64SERVERNUM--;
}
do
{
if(_ipinfo->size>0)
{
dbg("[%s] -- [%d] -- _ipinfo->size[%d]\r\n", __FUNCTION__, __LINE__,_ipinfo->size);
free(data);
return 0;
}
usleep(1);
if(dnsquery_failcount==DNS64SERVERNUM)
{
dbg("[%s] -- [%d] -- pthreadNUM[%d]==dnsquery_failcount\r\n", __FUNCTION__, __LINE__,dnsquery_failcount);
free(data);
return -1;
}
}while(1);
}
/**
*函数名: getaddrinfo_v6
*功能: 输入域名，可得到该域名下所对应的IP地址列表保存在结构体_ipinfo中
*输入: _host：输入的要查询的主机域名
*输入: _timeout：设置查询超时时间，单位为毫秒
*输出: _ipinfo为要输出的ip信息结构体
*返回值: 当返回-1表示查询失败，当返回0则表示查询成功
*
*/
int getaddrinfo_v6(const char* _host, struct socket_ipinfo_t* _ipinfo, int _timeout /*ms*/)
{
dbg("[%s] -- [%d] -- getaddrinfo_v6 enter\r\n", __FUNCTION__, __LINE__);
if (NULL == _host)
{
dbg("[%s] -- [%d] -- NULL == _host \r\n", __FUNCTION__, __LINE__);
return -1;
}
if (NULL == _ipinfo) {
dbg("[%s] -- [%d] -- NULL == _ipinfo \r\n", __FUNCTION__, __LINE__);
return -1;
}
int re=-1;
char host[64];
memset(host, 0, sizeof(host));
strncpy(host, _host, strlen(_host));
_ipinfo->size = 0;
if(isValidIpv4Address(host))//输入的是ipv4地址
{
struct in_addr _v4_addr = {0};
inet_pton(AF_INET,host,&_v4_addr);
char ipv4_host[20]="ipv4only.arpa";
if(th_gethostbyname(ipv4_host,_ipinfo, _timeout)!=0)
{
dbg("[%s] -- [%d] -- socket_gethostbyname failed\r\n", __FUNCTION__, __LINE__);
return -1;
}
_ipinfo->size=1;
if(IsNat64AddrValid(&(_ipinfo->v6_addr[0]))==true) {
ReplaceNat64WithV4IP((&_ipinfo->v6_addr[0]) , &_v4_addr);
return 0;
} else {
dbg("[%s] -- [%d] -- isValidIpv4Address failed\r\n", __FUNCTION__, __LINE__);
return -1;
}
}
else
{
re=th_gethostbyname(host,_ipinfo,_timeout);
if(-1 == re) {
dbg("[%s] -- [%d] -- socket_gethostbyname failed\r\n", __FUNCTION__, __LINE__);
re=getaddrinfo_api(host,_ipinfo);
}
}
//dbg("re : %d\r\n",re);
return re;
/*getaddrinfo*/
}
/**
*函数名: socket_gethostbyname
*功能: 输入域名，可得到该域名下所对应的IP地址列表
*输入: _host：输入的要查询的主机域名
*输入: _timeout：设置查询超时时间，单位为毫秒
*输入: _dnsserver 指定的dns服务器的IP
*输出: _ipinfo为要输出的ip信息结构体
*返回值: 当返回-1表示查询失败，当返回0则表示查询成功
*
*/
int socket_gethostbyname(char* _host, struct socket_ipinfo_t* _ipinfo, int _timeout /*ms*/, const char* _dnsserver) {
dbg("[%s] -- [%d] -- socket_gethostbyname enter\r\n", __FUNCTION__, __LINE__);
if(NULL==_dnsserver) {
dbg("[%s] -- [%d] -- NULL==_dnsserver \r\n", __FUNCTION__, __LINE__);
return -1;
}
if (_timeout <= 0) _timeout = DEFAULT_TIMEOUT;
int sockfd = socket(AF_INET6,SOCK_DGRAM,IPPROTO_UDP);
if (sockfd < 0)
{
dbg("[%s] -- [%d] -- socket failed\r\n", __FUNCTION__, __LINE__);
return -1;
}
//dbg("sockfd:%d\n",sockfd);
struct sockaddr_in6 dest = {0};
dest.sin6_family = AF_INET6;
inet_pton(AF_INET6, _dnsserver, &(dest.sin6_addr));
dest.sin6_port = htons(DNS_PORT);
struct RES_RECORD answers[SOCKET_MAX_IP_COUNT]; // the replies from the DNS server
memset(answers, 0, sizeof(struct RES_RECORD)*SOCKET_MAX_IP_COUNT);
int ret = -1;
do {
unsigned int BUF_LEN=2048;
unsigned char send_buf[2048] = {0};
unsigned char recv_buf[2048] = {0};//C99标准引入了变长数组，它允许使用变量定义数组各维。变长数组必须是自动存储类，而且声明时不可以进行初始化。
struct DNS_HEADER* dns = (struct DNS_HEADER*)send_buf;
unsigned char* qname = (unsigned char*)&send_buf[sizeof(struct DNS_HEADER)];
PrepareDnsQueryPacket(send_buf, dns, qname, _host);
unsigned long send_packlen = sizeof(struct DNS_HEADER) + (strlen((const char*)qname) + 1) + sizeof(struct QUESTION);
int sendfd;
struct sockaddr_in6 recv_src = {0};
int recvPacketLen = 0;
for(int i=0;i<3;i++)
{
sendfd = sendto(sockfd, (char*)send_buf, send_packlen, 0, (struct sockaddr*)&dest, sizeof(dest));
//dbg("sendPacketlen:%d\n",sendfd);
if (sendfd==-1)
{
dbg("[%s] -- [%d] -- sendto failed\r\n", __FUNCTION__, __LINE__);
break;
}
socklen_t recv_src_len = sizeof(recv_src);
if ((recvPacketLen = RecvWithinTime(sockfd, (char*)recv_buf, BUF_LEN, (struct sockaddr*)&recv_src, &recv_src_len, _timeout / 1000, (_timeout % 1000) * 1000)) > -1)
{
break;
}
else {
dbg("[%s] -- [%d] -- RecvWithinTime failed\r\n", __FUNCTION__, __LINE__);
}
}
// move ahead of the dns header and the query field
unsigned char* reader = &recv_buf[sizeof(struct DNS_HEADER) + (strlen((const char*)qname) + 1) + sizeof(struct QUESTION)];
dns = (struct DNS_HEADER*)recv_buf; // 指向recv_buf的header
ReadRecvAnswer(recv_buf, dns, reader, answers);
// 把查询到的IP放入返回参数_ipinfo结构体中
int answer_count = min(SOCKET_MAX_IP_COUNT, (int)ntohs(dns->ans_count));
pthread_mutex_lock(&dnsquery_mutex);
for (int i = 0; i < answer_count; ++i) {
if (AAAA == ntohs(answers[i].resource->type)) { // IPv6 address
for(int p=0;p<16;p++)
{
_ipinfo->v6_addr[_ipinfo->size].s6_addr[p]=answers[i].rdata[p];
}
_ipinfo->size++;
//pthread_mutex_unlock(&mutex);
}
}
if (0 >= _ipinfo->size) {
pthread_mutex_unlock(&dnsquery_mutex);
dbg("[%s] -- [%d] -- _ipinfo->size <= 0\r\n", __FUNCTION__, __LINE__);
break;
}
ret = 0;
} while (false);
FreeAll(answers);
close(sockfd);
dbg("[%s] -- [%d] -- socket_gethostbyname out\r\n", __FUNCTION__, __LINE__);
return ret; //* 查询DNS服务器超时
}
static int isValidIpv4Address(char* _ipaddress) {
struct sockaddr_in sa;
int result =inet_pton(AF_INET, _ipaddress, (void*) & (sa.sin_addr));
return result != 0;
}
void FreeAll(struct RES_RECORD* _answers) {
int i;
for (i = 0; i < SOCKET_MAX_IP_COUNT; i++) {
if (_answers[i].name != NULL)
free(_answers[i].name);
if (_answers[i].rdata != NULL)
free(_answers[i].rdata);
}
}
void ReadRecvAnswer(unsigned char* _buf, struct DNS_HEADER* _dns, unsigned char* _reader, struct RES_RECORD* _answers) {
// reading answers
int i, j, stop = 0;
int answer_count =min(SOCKET_MAX_IP_COUNT, (int)ntohs(_dns->ans_count));
for (i = 0; i < answer_count; i++) {
_answers[i].name = ReadName(_reader, _buf, &stop);
_reader = _reader + stop;
_answers[i].resource = (struct R_DATA*)(_reader);
_reader = _reader + sizeof(struct R_DATA);//指针偏移
// if (ntohs(_answers[i].resource->type) == 1) { // if its an ipv4 address
if (ntohs(_answers[i].resource->type) == AAAA) { // if its an ipv6 address
_answers[i].rdata = (unsigned char*)malloc(ntohs(_answers[i].resource->data_len));
if (NULL == _answers[i].rdata)
{
return;
}
for (j = 0 ; j < ntohs(_answers[i].resource->data_len) ; j++)
{ _answers[i].rdata[j] = _reader[j];
}
_answers[i].rdata[ntohs(_answers[i].resource->data_len)] = '\0';
_reader = _reader + ntohs(_answers[i].resource->data_len);
} else {
_answers[i].rdata = ReadName(_reader, _buf, &stop);
_reader = _reader + stop;
}
}
}
unsigned char* ReadName(unsigned char* _reader, unsigned char* _buffer, int* _count) {
unsigned char* name;
unsigned int p = 0, jumped = 0, offset;
const unsigned int INIT_SIZE = 256, INCREMENT = 64;
int timesForRealloc = 0;
int i , j;
*_count = 1;
name = (unsigned char*)malloc(INIT_SIZE);
if (NULL == name) {
return NULL;
}
name[0] = '\0';
// read the names in 3www6google3com format
while (*_reader != 0) {
if (*_reader >= 192) { // 192 = 11000000 ,如果该字节前两位bit为11，则表示使用的是地址偏移来表示name
offset = (*_reader) * 256 + *(_reader + 1) - 49152; // 49152 = 11000000 00000000 计算相对于报文起始地址的偏移字节数，即去除两位为11的bit，剩下的14位表示的值
_reader = _buffer + offset - 1;
jumped = 1; // we have jumped to another location so counting wont go up!
} else
name[p++] = *_reader;
_reader = _reader + 1;
if (jumped == 0) *_count = *_count + 1; // if we have not jumped to another location then we can count up
if (*_count >= (int)(INIT_SIZE + INCREMENT * timesForRealloc)) {
timesForRealloc++;
unsigned char* more_name = NULL;
more_name = (unsigned char*)realloc(name, (INIT_SIZE + INCREMENT * timesForRealloc));
if (NULL == more_name) {
free(name);
return NULL;
}
name = more_name;
}
}
name[p] = '\0'; // string complete
if (jumped == 1) *_count = *_count + 1; // number of steps we actually moved forward in the packet
// now convert 3www6google3com0 to www.google.com
for (i = 0; i < (int)strlen((const char*)name); i++) {
p = name[i];
for (j = 0; j < (int)p; j++) {
name[i] = name[i + 1];
i = i + 1;
}
name[i] = '.';
}
name[i - 1] = '\0'; // remove the last dot
return name;
}
// this will convert www.google.com to 3www6google3com
void ChangetoDnsNameFormat(unsigned char* _qname, char* _hostname) {
int lock = 0 , i;
strncat(_hostname,".",1);
const char* host = _hostname;
for (i = 0; i < (int)strlen(host); i++) {
if (host[i] == '.') {
*_qname++ = i - lock;
for (; lock < i; lock++) {
*_qname++ = host[lock];
}
lock++;
}
}
*_qname++ = '\0';
}
void PrepareDnsQueryPacket(unsigned char* _buf, struct DNS_HEADER* _dns, unsigned char* _qname, char* _host) {
struct QUESTION* qinfo = NULL;
// Set the DNS structure to standard queries
_dns->id = getpid();
_dns->qr = 0; // This is a query
_dns->opcode = 0; // This is a standard query
_dns->aa = 0; // Not Authoritative
_dns->tc = 0; // This message is not truncated
_dns->rd = 1; // Recursion Desired
_dns->ra = 0; // Recursion not available!
_dns->z = 0;
_dns->ad = 0;
_dns->cd = 0;
_dns->rcode = 0;
_dns->q_count = htons(1); // we have only 1 question
_dns->ans_count = 0;
_dns->auth_count = 0;
_dns->add_count = 0;
// point to the query portion
_qname = (unsigned char*)&_buf[sizeof(struct DNS_HEADER)];
ChangetoDnsNameFormat(_qname, _host); // 将传入的域名host转换为标准的DNS报文可用的格式，存入qname中
qinfo = (struct QUESTION*)&_buf[sizeof(struct DNS_HEADER) + (strlen((const char*)_qname) + 1)]; // fill it
qinfo->qtype = htons(AAAA); //查询 ipv6 address
qinfo->qclass = htons(1); // its internet
}
static int RecvWithinTime(int _fd, char* _buf, size_t _buf_n, struct sockaddr* _addr, socklen_t* _len, unsigned int _sec, unsigned _usec) {
struct timeval tv;
fd_set readfds, exceptfds;
int n = 0;
FD_ZERO(&readfds);
FD_SET(_fd, &readfds);
FD_ZERO(&exceptfds);
FD_SET(_fd, &exceptfds);
tv.tv_sec = _sec;
tv.tv_usec = _usec;
int ret = -1;
label:
ret = select(_fd + 1, &readfds, NULL, &exceptfds, &tv);
if (-1 == ret) {
if (EINTR == errno) {
// select被信号中断 handler
FD_ZERO(&readfds);
FD_SET(_fd, &readfds);
FD_ZERO(&exceptfds);
FD_SET(_fd, &exceptfds);
goto label;
}
}
if (FD_ISSET(_fd, &exceptfds)) {
// socket异常处理
return -1;
}
if (FD_ISSET(_fd, &readfds)) {
if ((n = (int)recvfrom(_fd, _buf, _buf_n, 0, _addr, _len)) >= 0) {
return n;
}
}
return -1; // 超时或者select失败
}