dns

main.c (6120B)

---

 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <curl/curl.h>
 #define LIB_STR_IMPL
 #include <libstr.h>
 
 #define DNS_ENV_UPDATE  "DNS_UPDATE_URL"
 #define DNS_ENV_LOOKUP  "DNS_LOOKUP_URL"
 #define DNS_ENV_RESOLVE "DNS_RESOLVE_URL"
 
 #define DNS_SYMBOL_HOST    "HOST"
 #define DNS_SYMBOL_DOMAIN  "DOMAIN"
 #define DNS_SYMBOL_IP_ADDR "IP_ADDR"
 #define DNS_SYMBOL_PASSWD  "PASSWD"
 
 #define DNS_DOMAIN_WILDCARD "@"
 
 typedef enum {
   DNS_ERR_OK,
   DNS_ERR_FAIL,
 } dns_error_t;
 
 typedef struct {
   char *host;
   char *domain;
   char *passwd;
 } dns_domain_t;
 
 size_t dns_curl_write(void *ptr, size_t size, size_t nmemb, void *data) {
   size_t len = size * nmemb;
   char **curl_data = (char **) data;
   str_append_len(curl_data, ptr, len);
   return len;
 }
 
 dns_error_t dns_update(char *url, dns_domain_t *domain, char *ip_addr) {
   CURL *curl = curl_easy_init();
   if (!curl) {
     fprintf(stderr, "CURL init failed!\n");
     return DNS_ERR_FAIL;
   }
   char *resolved_url = url;
   resolved_url = str_replace_all(resolved_url, "{" DNS_SYMBOL_HOST "}", domain->host);
   resolved_url = str_replace_all(resolved_url, "{" DNS_SYMBOL_DOMAIN "}", domain->domain);
   resolved_url = str_replace_all(resolved_url, "{" DNS_SYMBOL_PASSWD "}", domain->passwd);
   resolved_url = str_replace_all(resolved_url, "{" DNS_SYMBOL_IP_ADDR "}", ip_addr);
   char *curl_data = NULL;
   curl_easy_setopt(curl, CURLOPT_URL, resolved_url);
   curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, dns_curl_write);
   curl_easy_setopt(curl, CURLOPT_WRITEDATA, &curl_data);
   CURLcode code = curl_easy_perform(curl);
   free(resolved_url);
   if (code != CURLE_OK) {
     curl_easy_cleanup(curl);
     fprintf(stderr, "CURL fetch failed!\n%s\n", curl_easy_strerror(code));
     return DNS_ERR_FAIL;
   }
   curl_easy_cleanup(curl);
   for (size_t i = 0; i < strlen(curl_data); i++) {
     if (strncmp(curl_data + i, "<ErrCount>0</ErrCount>", 22) == 0) {
       free(curl_data);
       return DNS_ERR_OK;
     }
   }
   fprintf(stderr, "DNS update error:\n%s\n", curl_data);
   if (curl_data != NULL) {
     free(curl_data);
   }
   return DNS_ERR_FAIL;
 }
 
 dns_error_t dns_lookup(char *url, dns_domain_t *domain, char **ip_addr) {
   CURL *curl = curl_easy_init();
   if (!curl) {
     fprintf(stderr, "CURL init failed!\n");
     return DNS_ERR_FAIL;
   }
   char *resolved_url = url;
   resolved_url = str_replace_all(resolved_url, "{" DNS_SYMBOL_HOST "}", domain->host);
   resolved_url = str_replace_all(resolved_url, "{" DNS_SYMBOL_DOMAIN "}", domain->domain);
   char *curl_data = NULL;
   curl_easy_setopt(curl, CURLOPT_URL, resolved_url);
   curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, dns_curl_write);
   curl_easy_setopt(curl, CURLOPT_WRITEDATA, &curl_data);
   CURLcode code = curl_easy_perform(curl);
   free(resolved_url);
   if (code != CURLE_OK) {
     curl_easy_cleanup(curl);
     fprintf(stderr, "CURL fetch failed!\n%s\n", curl_easy_strerror(code));
     return DNS_ERR_FAIL;
   }
   curl_easy_cleanup(curl);
   size_t set = 0;
   for (size_t i = 0; i < strlen(curl_data);) {
     if (strncmp(curl_data + i, "\"data\":\"", 8) == 0) {
       i += 8;
       set = i;
       continue;
     }
     if (set > 0 && curl_data[i] == '"') {
       str_append_len(ip_addr, curl_data + set, i - set);
       break;
     }
     i++;
   }
   if (curl_data != NULL) {
     free(curl_data);
   }
   return DNS_ERR_OK;
 }
 
 dns_error_t dns_resolve(char *url, char **ip_addr) {
   CURL *curl = curl_easy_init();
   if (!curl) {
     fprintf(stderr, "CURL init failed!\n");
     return DNS_ERR_FAIL;
   }
   char *curl_data = NULL;
   curl_easy_setopt(curl, CURLOPT_URL, url);
   curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, dns_curl_write);
   curl_easy_setopt(curl, CURLOPT_WRITEDATA, &curl_data);
   CURLcode code = curl_easy_perform(curl);
   if (code != CURLE_OK) {
     curl_easy_cleanup(curl);
     fprintf(stderr, "CURL fetch failed!\n%s\n", curl_easy_strerror(code));
     return DNS_ERR_FAIL;
   }
   curl_easy_cleanup(curl);
   for (size_t i = 0; i < strlen(curl_data); i++) {
     if (curl_data[i] == '\n') {
       str_append_len(ip_addr, curl_data, i);
       break;
     }
   }
   if (curl_data != NULL) {
     free(curl_data);
   }
   return DNS_ERR_OK;
 }
 
 int main(int argc, char **argv) {
   if (argc != 4) {
     fprintf(stderr, "Invalid arguments!\nUsage: dns <host> <domain> <passwd>\n");
     return EXIT_FAILURE;
   }
   dns_domain_t domain = {
     .host = argv[1],
     .domain = argv[2],
     .passwd = argv[3],
   };
   if (strcmp(domain.host, DNS_DOMAIN_WILDCARD) == 0) {
     fprintf(stdout, "DNS domain: %s\n", domain.domain);
   }
   else {
     fprintf(stdout, "DNS domain: %s.%s\n", domain.host, domain.domain);
   }
   char *dns_update_url = getenv(DNS_ENV_UPDATE);
   if (dns_update_url == NULL) {
     fprintf(stderr, "Environment variable missing!\nDefine: " DNS_ENV_UPDATE "\n");
     return EXIT_FAILURE;
   }
   char *dns_lookup_url = getenv(DNS_ENV_LOOKUP);
   if (dns_lookup_url == NULL) {
     fprintf(stderr, "Environment variable missing!\nDefine: " DNS_ENV_LOOKUP "\n");
     return EXIT_FAILURE;
   }
   char *dns_resolve_url = getenv(DNS_ENV_RESOLVE);
   if (dns_resolve_url == NULL) {
     fprintf(stderr, "Environment variable missing!\nDefine: " DNS_ENV_RESOLVE "\n");
     return EXIT_FAILURE;
   }
   char *ip_addr = NULL;
   if (dns_resolve(dns_resolve_url, &ip_addr) != DNS_ERR_OK) {
     fprintf(stderr, "IP address resolution failed!\n");
     return EXIT_FAILURE;
   }
   fprintf(stdout, "DNS resolve IP_ADDR: %s\n", ip_addr);
   char *domain_ip_addr = NULL;
   if (dns_lookup(dns_lookup_url, &domain, &domain_ip_addr) != DNS_ERR_OK) {
     fprintf(stderr, "DNS lookup failed!\n");
     return EXIT_FAILURE;
   }
   fprintf(stdout, "DNS lookup DOMAIN_IP_ADDR: %s\n", domain_ip_addr);
   if (strcmp(ip_addr, domain_ip_addr) != 0) {
     if (dns_update(dns_update_url, &domain, ip_addr) != DNS_ERR_OK) {
       free(ip_addr);
       free(domain_ip_addr);
       fprintf(stderr, "DNS update FAILED!\n");
       return EXIT_FAILURE;
     }
     fprintf(stdout, "DNS update SUCCESSFUL.\n");
   }
   else {
     fprintf(stdout, "DNS domain already UP-TO-DATE.\n");
   }
   free(ip_addr);
   free(domain_ip_addr);
   return EXIT_SUCCESS;
 }