resolved: rework what ResolveHostname() with family == AF_UNSPEC means

Previously, if a hostanem is resolved with AF_UNSPEC specified, this would be used as indication to resolve both an
AF_INET and an AF_INET6 address. With this change this logic is altered: an AF_INET address is only resolved if there's
actually a routable IPv4 address on the specific interface, and similar an AF_INET6 address is only resolved if there's
a routable IPv6 address. With this in place, it's ensured that the returned data is actually connectable by
applications. This logic mimics glibc's resolver behaviour.

Note that if the client asks explicitly for AF_INET or AF_INET6 it will get what it asked for.

This also simplifies the logic how it is determined whether a specific lookup shall take place on a scope.
Specifically, the checks with dns_scope_good_key() are now moved out of the transaction code and into the query code,
so that we don't even create a transaction object on a specific scope if we cannot execute the resolution on it anyway.

1 files changed, 15 insertions, 0 deletions

diff --git a/src/resolve/resolved-manager.c b/src/resolve/resolved-manager.c
index fbd188c2ac..f1dbda1a6a 100644
--- a/src/resolve/resolved-manager.c
+++ b/src/resolve/resolved-manager.c
@@ -1226,3 +1226,18 @@ void manager_dnssec_verdict(Manager *m, DnssecVerdict verdict, const DnsResource
 
         m->n_dnssec_verdict[verdict]++;
 }
+
+bool manager_routable(Manager *m, int family) {
+        Iterator i;
+        Link *l;
+
+        assert(m);
+
+        /* Returns true if the host has at least one interface with a routable address of the specified type */
+
+        HASHMAP_FOREACH(l, m->links, i)
+                if (link_relevant(l, family, false))
+                        return true;
+
+        return false;
+}