resolved: when using the ResolveRecord() bus call, adjust TTL for caching time

When we return the full RR wire data, let's make sure the TTL included in it is
adjusted by the time the RR sat in the cache.

As an optimization we do this only for ResolveRecord() and not for
ResolveHostname() and friends, since adjusting the TTL means copying the RR
object, and we don#t want to do that if there's no reason to.
(ResolveHostname() and friends don't return the TTL hence there's no reason to
in that case)

1 files changed, 16 insertions, 2 deletions

diff --git a/src/resolve/resolved-dns-cache.c b/src/resolve/resolved-dns-cache.c
index 77c42d7aad..0bb5a95188 100644
--- a/src/resolve/resolved-dns-cache.c
+++ b/src/resolve/resolved-dns-cache.c
@@ -790,7 +790,7 @@ static DnsCacheItem *dns_cache_get_by_key_follow_cname_dname_nsec(DnsCache *c, D
         return NULL;
 }
 
-int dns_cache_lookup(DnsCache *c, DnsResourceKey *key, int *rcode, DnsAnswer **ret, bool *authenticated) {
+int dns_cache_lookup(DnsCache *c, DnsResourceKey *key, bool clamp_ttl, int *rcode, DnsAnswer **ret, bool *authenticated) {
         _cleanup_(dns_answer_unrefp) DnsAnswer *answer = NULL;
         char key_str[DNS_RESOURCE_KEY_STRING_MAX];
         unsigned n = 0;
@@ -798,6 +798,7 @@ int dns_cache_lookup(DnsCache *c, DnsResourceKey *key, int *rcode, DnsAnswer **r
         bool nxdomain = false;
         DnsCacheItem *j, *first, *nsec = NULL;
         bool have_authenticated = false, have_non_authenticated = false;
+        usec_t current;
 
         assert(c);
         assert(key);
@@ -892,11 +893,24 @@ int dns_cache_lookup(DnsCache *c, DnsResourceKey *key, int *rcode, DnsAnswer **r
         if (!answer)
                 return -ENOMEM;
 
+        if (clamp_ttl)
+                current = now(clock_boottime_or_monotonic());
+
         LIST_FOREACH(by_key, j, first) {
+                _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
+
                 if (!j->rr)
                         continue;
 
-                r = dns_answer_add(answer, j->rr, j->ifindex, j->authenticated ? DNS_ANSWER_AUTHENTICATED : 0);
+                if (clamp_ttl) {
+                        rr = dns_resource_record_ref(j->rr);
+
+                        r = dns_resource_record_clamp_ttl(&rr, LESS_BY(j->until, current) / USEC_PER_SEC);
+                        if (r < 0)
+                                return r;
+                }
+
+                r = dns_answer_add(answer, rr ?: j->rr, j->ifindex, j->authenticated ? DNS_ANSWER_AUTHENTICATED : 0);
                 if (r < 0)
                         return r;
         }