resolved: rework server feature level logic

This changes the DnsServer logic to count failed UDP and TCP failures separately. This is useful so that we don't end
up downgrading the feature level from one UDP level to a lower UDP level just because a TCP connection we did because
of a TC response failed.

This also adds accounting of truncated packets. If we detect incoming truncated packets, and count too many failed TCP
connections (which is the normal fall back if we get a trucnated UDP packet) we downgrade the feature level, given that
the responses at the current levels don't get through, and we somehow need to make sure they become smaller, which they
will do if we don't request DNSSEC or EDNS support.

This makes resolved work much better with crappy DNS servers that do not implement TCP and only limited UDP packet
sizes, but otherwise support DNSSEC RRs. They end up choking on the generally larger DNSSEC RRs and there's no way to
retrieve the full data.

1 files changed, 7 insertions, 3 deletions

diff --git a/src/resolve/resolved-dns-server.h b/src/resolve/resolved-dns-server.h
index da21e6571a..3ad6a0d38f 100644
--- a/src/resolve/resolved-dns-server.h
+++ b/src/resolve/resolved-dns-server.h
@@ -67,7 +67,10 @@ struct DnsServer {
         DnsServerFeatureLevel verified_feature_level;
         DnsServerFeatureLevel possible_feature_level;
         size_t received_udp_packet_max;
-        unsigned n_failed_attempts;
+        unsigned n_failed_udp;
+        unsigned n_failed_tcp;
+        bool packet_failed:1;
+        bool packet_truncated:1;
         usec_t verified_usec;
         usec_t features_grace_period_usec;
 
@@ -99,9 +102,10 @@ DnsServer* dns_server_unref(DnsServer *s);
 void dns_server_unlink(DnsServer *s);
 void dns_server_move_back_and_unmark(DnsServer *s);
 
-void dns_server_packet_received(DnsServer *s, DnsServerFeatureLevel level, usec_t rtt, size_t size);
-void dns_server_packet_lost(DnsServer *s, DnsServerFeatureLevel level, usec_t usec);
+void dns_server_packet_received(DnsServer *s, int protocol, DnsServerFeatureLevel level, usec_t rtt, size_t size);
+void dns_server_packet_lost(DnsServer *s, int protocol, DnsServerFeatureLevel level, usec_t usec);
 void dns_server_packet_failed(DnsServer *s, DnsServerFeatureLevel level);
+void dns_server_packet_truncated(DnsServer *s, DnsServerFeatureLevel level);
 void dns_server_packet_rrsig_missing(DnsServer *s);
 
 DnsServerFeatureLevel dns_server_possible_feature_level(DnsServer *s);