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:

The response was successfully parsed.
The response was malformatted.
The response did not contain an answer to the query.
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,
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)
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 = "";
if (argc > 1)
domain = argv[1];
ares_channel channel;
if ((err = ares_init (&channel)) != ARES_SUCCESS)
printf ("ares_init() failed (%i)\n", err);
ares_query (channel, domain,
1, /* ns_c_in */
257, /* T_CAA */
dns_callback, domain);
main_loop (&channel);
ares_destroy (channel);

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

ares_query(3) ares_free_data(3)

Written by Danny Sonnenschein <>, on behalf of platynum,

16 September 2020