Created
August 30, 2017 15:15
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DNS resolve using c-ares
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| #include <ares.h> | |
| #include <stdio.h> | |
| #include <netdb.h> | |
| #include <assert.h> | |
| #include <stdlib.h> | |
| #include <unistd.h> | |
| #include <sys/select.h> | |
| #define HOST_TO_RESOLVE "yandex.ru" | |
| #define GOOGLE_DNS_SERVER 0x08080808 | |
| #define DNS_WATCH_SERVER 0x54C84550 | |
| static void ares_lookup_completed(void * arg, int status, int timeouts, struct hostent * hostent) | |
| { | |
| if (status != ARES_SUCCESS) | |
| { | |
| printf("Unable to resolve host %s\n", HOST_TO_RESOLVE); | |
| goto done; | |
| } | |
| printf("Resolved host: %u.%u.%u.%u for %s\n", (unsigned char)hostent->h_addr[0], | |
| (unsigned char)hostent->h_addr[1], | |
| (unsigned char)hostent->h_addr[2], | |
| (unsigned char)hostent->h_addr[3], | |
| hostent->h_name); | |
| done: | |
| return; | |
| } | |
| int main() | |
| { | |
| ares_channel channel; | |
| int nfds, count; | |
| fd_set readers, writers; | |
| struct timeval tv, *tvp; | |
| struct in_addr dns_servers[] = { | |
| { .s_addr = GOOGLE_DNS_SERVER }, | |
| { .s_addr = DNS_WATCH_SERVER }, | |
| }; | |
| struct ares_options options = { | |
| .servers = dns_servers, | |
| .nservers = 2 | |
| }; | |
| printf("Initializing c-ares..."); | |
| assert(ARES_SUCCESS == ares_init_options(&channel, &options, ARES_OPT_SERVERS)); | |
| printf("\tOK\n"); | |
| printf("Trying to resolve host %s...\n", HOST_TO_RESOLVE); | |
| ares_gethostbyname(channel, HOST_TO_RESOLVE, AF_INET, ares_lookup_completed, NULL); | |
| while (1) | |
| { | |
| FD_ZERO(&readers); | |
| FD_ZERO(&writers); | |
| nfds = ares_fds(channel, &readers, &writers); | |
| if (nfds == 0) | |
| { | |
| break; | |
| } | |
| tvp = ares_timeout(channel, NULL, &tv); | |
| count = select(nfds, &readers, &writers, NULL, tvp); | |
| ares_process(channel, &readers, &writers); | |
| sleep(1); | |
| } | |
| printf("Destroying c-ares..."); | |
| ares_destroy(channel); | |
| printf("\tOK\n"); | |
| return EXIT_SUCCESS; | |
| } |
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