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;
}