resolved: properly handle LLMNR/TCP connection errors

The LLMNR spec suggests to do do reverse address lookups by doing direct LLMNR/TCP connections to the indicated
address, instead of doing any LLMNR multicast queries. When we do this and the peer doesn't actually implement LLMNR
this will result in a TCP connection error, which we need to handle. In contrast to most LLMNR lookups this will give
us a quick response on whether we can find a suitable name. Report this as new transaction state, since this should
mostly be treated like an NXDOMAIN rcode, except that it's not one.

1 files changed, 1 insertions, 0 deletions

diff --git a/src/resolve/resolved-dns-transaction.h b/src/resolve/resolved-dns-transaction.h
index 80a2591fbc..ab5717c4d1 100644
--- a/src/resolve/resolved-dns-transaction.h
+++ b/src/resolve/resolved-dns-transaction.h
@@ -41,6 +41,7 @@ enum DnsTransactionState {
         DNS_TRANSACTION_NO_TRUST_ANCHOR,
         DNS_TRANSACTION_RR_TYPE_UNSUPPORTED,
         DNS_TRANSACTION_NETWORK_DOWN,
+        DNS_TRANSACTION_NOT_FOUND, /* like NXDOMAIN, but when LLMNR/TCP connections fail */
         _DNS_TRANSACTION_STATE_MAX,
         _DNS_TRANSACTION_STATE_INVALID = -1
 };