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asyn-ares: acknowledge CURLOPT_DNS_SERVERS set to NULL

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Since c-ares has no function to restore this value to default, it
instead closes and re-inits the c-ares channel.

Reported-by: Deniz Sökmen
Fixes #16015
Closes #16016
This commit is contained in:
Daniel Stenberg 2025-01-16 08:45:45 +01:00
parent f241ccf714
commit 13afb1128f
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GPG Key ID: 5CC908FDB71E12C2
1 changed files with 19 additions and 7 deletions
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26
lib/asyn-ares.c
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@ -838,14 +838,26 @@ CURLcode Curl_set_dns_servers(struct Curl_easy *data,
CURLcode result = CURLE_NOT_BUILT_IN;
int ares_result;
/* If server is NULL or empty, this would purge all DNS servers
* from ares library, which will cause any and all queries to fail.
* So, just return OK if none are configured and do not actually make
* any changes to c-ares. This lets c-ares use its defaults, which
* it gets from the OS (for instance from /etc/resolv.conf on Linux).
/* If server is NULL, this purges all DNS servers from c-ares. Reset it to
* default.
*/
if(!(servers && servers[0]))
return CURLE_OK;
if(!servers) {
Curl_resolver_cleanup(data->state.async.resolver);
result = Curl_resolver_init(data, &data->state.async.resolver);
if(!result) {
/* this now needs to restore the other options set to c-ares */
if(data->set.str[STRING_DNS_INTERFACE])
(void)Curl_set_dns_interface(data,
data->set.str[STRING_DNS_INTERFACE]);
if(data->set.str[STRING_DNS_LOCAL_IP4])
(void)Curl_set_dns_local_ip4(data,
data->set.str[STRING_DNS_LOCAL_IP4]);
if(data->set.str[STRING_DNS_LOCAL_IP6])
(void)Curl_set_dns_local_ip6(data,
data->set.str[STRING_DNS_LOCAL_IP6]);
}
return result;
}
#ifdef HAVE_CARES_SERVERS_CSV
#ifdef HAVE_CARES_PORTS_CSV