Manpages - ares_parse_caa_reply.3

ares_parse_caa_reply - Parse a reply to a DNS query of type CAA

  #include <ares.h>

  int ares_parse_caa_reply(const unsigned char* abuf, int alen,
                           struct ares_caa_reply **caa_out);

The ares_parse_caa_reply function parses the response to a query of type CAA into a linked list (one element per sub-string) of struct ares_caa_reply The parameters abuf and alen give the contents of the response. The result is stored in allocated memory and a pointer to it stored into the variable pointed to by caa_out. It is the caller’s responsibility to free the resulting caa_out structure when it is no longer needed using the function ares_free_data(3)

The structure ares_caa_reply(3) contains the following fields:

  struct ares_caa_reply {
    struct ares_caa_reply *next;
    int                    critical;
    unsigned char         *property;
    size_t                 plength; /* plength excludes null */
    unsigned char         *value;
    size_t                 length;  /* length excludes null */
  };

ares_parse_caa_reply can return any of the following values:

ARES_SUCCESS

The response was successfully parsed.

ARES_EBADRESP

The response was malformatted.

ARES_ENODATA

The response did not contain an answer to the query.

ARES_ENOMEM

Memory was exhausted.

  #include <arpa/inet.h>
  #include <time.h>
  #include <sys/time.h>
  #include <netdb.h>

  #include <unistd.h>
  #include <stdio.h>
  #include <stdlib.h>

  #include "ares.h"

  static void dns_callback(void *arg,
                           int status,
                           int timeouts,
                           unsigned char *abuf,
                           int alen)
    {
      struct ares_caa_reply *caa_out;
      int err;

      err = ares_parse_caa_reply (abuf, alen, &caa_out);
      if (err == ARES_SUCCESS)
        {
          struct ares_caa_reply *caa_curr;
          for (caa_curr=caa_out; caa_curr; caa_curr=caa_curr->next)
            printf ("%s. CAA %i %s \"%s\"\n", arg,
                                              caa_curr->critical,
                                              caa_curr->property,
                                              caa_curr->value);
        }
      else
        {
          printf ("err=%i\n", err);
        }
      ares_free_data (caa_out);
    }

  static void main_loop(ares_channel *channel)
    {
      int nfds, count;
      fd_set readers, writers;
      struct timeval tv, *tvp;
      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);
        }
    }

  int main(int argc, char **argv)
    {
      const char *sversion;
      int iversion;
      int err;

      sversion = ares_version (&iversion);
      printf ("c-ares version %s\n", sversion);

      char *domain = "wikipedia.org";
      if (argc > 1)
        domain = argv[1];

      ares_channel channel;
      if ((err = ares_init (&channel)) != ARES_SUCCESS)
        {
          printf ("ares_init() failed (%i)\n", err);
          exit (EXIT_FAILURE);
        }

      ares_query (channel, domain,
                  1,   /* ns_c_in */
                  257, /* T_CAA */
                  dns_callback, domain);

      main_loop (&channel);

      ares_destroy (channel);

      exit (EXIT_SUCCESS);
    }

This function was first introduced in c-ares version 1.17.0.

*ares_query*(3) *ares_free_data*(3)

Written by Danny Sonnenschein <my.card.god@web.de>, on behalf of platynum, https://platynum.ch