Copyright 2020 Danny Sonnenschein <[email protected]>

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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:

15 ARES_SUCCESS The response was successfully parsed.

15 ARES_EBADRESP The response was malformatted.

15 ARES_ENODATA The response did not contain an answer to the query.

15 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 <[email protected]>, on behalf of platynum, https://platynum.ch