/*
* ares_query_completed_cb() is the callback that ares will call when
* the host query initiated by ares_gethostbyname() from Curl_getaddrinfo(),
* when using ares, is completed either successfully or with failure.
*/
static void query_completed_cb(void *arg, /* (struct connectdata *) */
int status,
#ifdef HAVE_CARES_CALLBACK_TIMEOUTS
int timeouts,
#endif
struct hostent *hostent)
{
struct connectdata *conn = (struct connectdata *)arg;
struct ResolverResults *res;
#ifdef HAVE_CARES_CALLBACK_TIMEOUTS
(void)timeouts; /* ignored */
#endif
if(ARES_EDESTRUCTION == status)
/* when this ares handle is getting destroyed, the 'arg' pointer may not
be valid so only defer it when we know the 'status' says its fine! */
return;
res = (struct ResolverResults *)conn->async.os_specific;
res->num_pending--;
if(CURL_ASYNC_SUCCESS == status) {
Curl_addrinfo *ai = Curl_he2ai(hostent, conn->async.port);
if(ai) {
compound_results(res, ai);
}
}
/* A successful result overwrites any previous error */
if(res->last_status != ARES_SUCCESS)
res->last_status = status;
}
/*
* ares_query_completed_cb() is the callback that ares will call when
* the host query initiated by ares_gethostbyname() from Curl_getaddrinfo(),
* when using ares, is completed either successfully or with failure.
*/
static void query_completed_cb(void *arg, /* (struct connectdata *) */
int status,
#ifdef HAVE_CARES_CALLBACK_TIMEOUTS
int timeouts,
#endif
struct hostent *hostent)
{
struct connectdata *conn = (struct connectdata *)arg;
struct ResolverResults *res;
#ifdef HAVE_CARES_CALLBACK_TIMEOUTS
(void)timeouts; /* ignored */
#endif
if(ARES_EDESTRUCTION == status)
/* when this ares handle is getting destroyed, the 'arg' pointer may not
be valid so only defer it when we know the 'status' says its fine! */
return;
res = (struct ResolverResults *)conn->async.os_specific;
if(res) {
res->num_pending--;
if(CURL_ASYNC_SUCCESS == status) {
Curl_addrinfo *ai = Curl_he2ai(hostent, conn->async.port);
if(ai) {
compound_results(res, ai);
}
}
/* A successful result overwrites any previous error */
if(res->last_status != ARES_SUCCESS)
res->last_status = status;
/* If there are responses still pending, we presume they must be the
complementary IPv4 or IPv6 lookups that we started in parallel in
Curl_resolver_getaddrinfo() (for Happy Eyeballs). If we've got a
"definitive" response from one of a set of parallel queries, we need to
think about how long we're willing to wait for more responses. */
if(res->num_pending
/* Only these c-ares status values count as "definitive" for these
purposes. For example, ARES_ENODATA is what we expect when there is
no IPv6 entry for a domain name, and that's not a reason to get more
aggressive in our timeouts for the other response. Other errors are
either a result of bad input (which should affect all parallel
requests), local or network conditions, non-definitive server
responses, or us cancelling the request. */
&& (status == ARES_SUCCESS || status == ARES_ENOTFOUND)) {
/* Right now, there can only be up to two parallel queries, so don't
bother handling any other cases. */
DEBUGASSERT(res->num_pending == 1);
/* It's possible that one of these parallel queries could succeed
quickly, but the other could always fail or timeout (when we're
talking to a pool of DNS servers that can only successfully resolve
IPv4 address, for example).
It's also possible that the other request could always just take
longer because it needs more time or only the second DNS server can
fulfill it successfully. But, to align with the philosophy of Happy
Eyeballs, we don't want to wait _too_ long or users will think
requests are slow when IPv6 lookups don't actually work (but IPv4 ones
do).
So, now that we have a usable answer (some IPv4 addresses, some IPv6
addresses, or "no such domain"), we start a timeout for the remaining
pending responses. Even though it is typical that this resolved
request came back quickly, that needn't be the case. It might be that
this completing request didn't get a result from the first DNS server
or even the first round of the whole DNS server pool. So it could
already be quite some time after we issued the DNS queries in the
first place. Without modifying c-ares, we can't know exactly where in
its retry cycle we are. We could guess based on how much time has
gone by, but it doesn't really matter. Happy Eyeballs tells us that,
given usable information in hand, we simply don't want to wait "too
much longer" after we get a result.
We simply wait an additional amount of time equal to the default
c-ares query timeout. That is enough time for a typical parallel
response to arrive without being "too long". Even on a network
where one of the two types of queries is failing or timing out
constantly, this will usually mean we wait a total of the default
c-ares timeout (5 seconds) plus the round trip time for the successful
request, which seems bearable. The downside is that c-ares might race
with us to issue one more retry just before we give up, but it seems
better to "waste" that request instead of trying to guess the perfect
timeout to prevent it. After all, we don't even know where in the
c-ares retry cycle each request is.
*/
res->happy_eyeballs_dns_time = Curl_now();
Curl_expire(
conn->data, HAPPY_EYEBALLS_DNS_TIMEOUT, EXPIRE_HAPPY_EYEBALLS_DNS);
}
}
}