[英]Query a server and get the results as addrinfo struct
我想查詢一個特定的服務器,並以與通過getaddrinfo
獲取它相同的方式獲取結果。 我想獲得一個addrinfo
結構,因此我可以使用ip,端口和一個指向下一個結果的指針。
我正在使用下面的代碼,該代碼查詢我想要的服務器並獲取結果。 但是每個結果都在另一個結構上,它們彼此不指向(不在列表中)。
這是代碼:
static int my_getaddrinfo(const char *dns_server_s, const char *node, const char *service, const struct addrinfo *hints, struct addrinfo **res) {
int retValue = 1;
struct __res_state result;
char ip[16];
memset(ip, '\0', sizeof(ip));
res_ninit(&result);
struct in_addr addr;
inet_aton(dns_server_s, &addr);
result.nsaddr_list[0].sin_addr = addr;
result.nsaddr_list[0].sin_family = AF_INET;
result.nsaddr_list[0].sin_port = htons(NS_DEFAULTPORT);
result.nscount = 1;
u_char answer[NS_PACKETSZ];
int len = res_nquery(&result, node, ns_c_in, ns_t_a, answer, sizeof(answer));
ns_msg handle;
ns_initparse(answer, len, &handle);
if(ns_msg_count(handle, ns_s_an) > 0) {
ns_rr rr;
if(ns_parserr(&handle, ns_s_an, 0, &rr) == 0) {
strcpy(ip, inet_ntoa(*(struct in_addr *)ns_rr_rdata(rr)));
getaddrinfo(ip, service, hints, res);
retValue = 0;
}
}
return retValue;
}
是否有可能以我想要的方式獲得結果? 類似於addrinfo結構?
編輯:我看到我得到三個答案ns_msg_count(handle, ns_s_an) = 3
並訪問每個答案,我應該調用ns_parserr(&handle, ns_s_an, answer_index, &rr)
但是正如我所說,我想將這些答案作為一個列表來獲取就像我通過調用getaddrinfo
獲取它們。
getaddrinfo不僅返回IP地址,還將服務名稱解析為端口號,並且可以支持不同的協議,主要是tcp和udp。 因此,您將需要通過調用getservbyname_r
來解析服務名稱,並為IP,端口和協議的每種組合手動構造結果addrinfo
。 這是一個解析ip和port的簡單版本,但它僅返回TCP的addrinfo。 您可以輕松地將其擴展為包括UDP。
另一個功能是getaddrinfo
也支持IPV6,在這種情況下,您將需要使用T_AAAA
而不是T_A
調用res_nquery
來解析IPV6地址。
這是一個示例,請注意,它像getaddrinfo
一樣返回struct addrinfo
的鏈接列表,因此完成后,結果應該與freeaddrinfo
一起freeaddrinfo
。
static int my_getaddrinfo(const char *dns_server,
const char *node, const char *service,
const struct addrinfo *hints, struct addrinfo **res) {
int ret;
// get dns server sockaddr
struct addrinfo hint = {0};
struct addrinfo *ai = NULL;
hint.ai_family = AF_INET;
hint.ai_socktype = SOCK_DGRAM;
hint.ai_protocol = IPPROTO_UDP;
ret = getaddrinfo(dns_server, "domain", &hint, &ai);
if (ret != 0) {
puts("getaddrinfo dns error");
return 1;
}
if (!ai) {
printf("getaddrinfo returned no result\n");
return 1;
}
freeaddrinfo(ai);
int port = 0;
// get service port
if (service) {
struct servent srv, *sres;
char buf[1024];
ret = getservbyname_r(service, NULL, &srv, buf, sizeof buf, &sres);
if (ret != 0) {
printf("getservbyname error\n");
return 1;
}
port = sres->s_port;
}
struct __res_state p = {0};
res_state state = &p;
unsigned char ans[NS_MAXMSG];
ns_msg msg;
ns_rr rr;
char line[1024];
int len ;
ret = res_ninit(state);
if (ret != 0) {
printf("res_ninit error\n");
return 1;
}
state->nscount = 1;
memset(state->nsaddr_list, 0, sizeof state->nsaddr_list);
memcpy(state->nsaddr_list, ai->ai_addr, sizeof state->nsaddr_list[0]);
ret = res_nquery(state, node, C_IN, T_A, ans, sizeof ans);
if (ret < 0) {
printf("res_nquery error\n");
return 1;
}
len = ret;
ret = ns_initparse(ans, len, &msg);
if (ret != 0) {
printf("ns_initparse error\n");
return 1;
}
len = ns_msg_count(msg, ns_s_an);
if (len == 0) {
printf("no address found\n");
return 0;
}
struct addrinfo *head = NULL;
struct addrinfo *cur = NULL;
struct addrinfo *prev = NULL;
struct sockaddr_in *sin;
for (int i = 0; i < len; i++) {
ret = ns_parserr(&msg, ns_s_an, i, &rr);
if (ret != 0) {
printf("ns_parserr error\n");
}
if (ns_rr_rdlen(rr) != NS_INADDRSZ) {
continue;
}
cur = malloc(sizeof *cur + sizeof(struct sockaddr_in));
memset(cur, 0, sizeof *cur);
cur->ai_family = AF_INET;
cur->ai_socktype = SOCK_STREAM;
cur->ai_protocol = IPPROTO_TCP;
cur->ai_addrlen = sizeof(struct sockaddr_in);
cur->ai_addr = (void*)(cur + 1);
cur->ai_canonname = NULL;
cur->ai_next = NULL;
sin = (struct sockaddr_in*)(cur->ai_addr);
sin->sin_family = cur->ai_family;
sin->sin_port = port;
memcpy(&sin->sin_addr, ns_rr_rdata(rr), sizeof sin->sin_addr);
if (prev)
prev->ai_next = cur;
if (head == NULL)
head = cur;
prev = cur;
}
*res = head;
return 0;
}
int main(int argc, char *argv[])
{
const char *node = "bing.com";
struct addrinfo *res = NULL;
if (argc == 2)
node = argv[1];
int ret = my_getaddrinfo("8.8.8.8", node, "http", NULL, &res);
if (ret != 0) {
puts("getaddrinfo error");
return 1;
}
// do stuff with res
struct addrinfo *rp;
struct sockaddr_in *sin;
char p[1024];
for (rp = res; rp != NULL; rp = rp->ai_next) {
sin = (struct sockaddr_in*)rp->ai_addr;
const char *s = inet_ntop(rp->ai_family,
&sin->sin_addr, p, sizeof p);
printf("Got %s: %d\n", s, ntohs(sin->sin_port));
}
freeaddrinfo(res);
return 0;
}
例:
$ ./a.out bing.com
Got 204.79.197.200: 80
Got 13.107.21.200: 80
$ ./a.out google.com
Got 172.217.24.14: 80
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