+ log_debug_errno(r, "Failed to send reply packet: %m");
+ return;
+ }
+}
+
+DnsTransaction *dns_scope_find_transaction(DnsScope *scope, DnsQuestion *question, bool cache_ok) {
+ DnsTransaction *t;
+
+ assert(scope);
+ assert(question);
+
+ /* Try to find an ongoing transaction that is a equal or a
+ * superset of the specified question */
+
+ LIST_FOREACH(transactions_by_scope, t, scope->transactions) {
+
+ /* Refuse reusing transactions that completed based on
+ * cached data instead of a real packet, if that's
+ * requested. */
+ if (!cache_ok &&
+ IN_SET(t->state, DNS_TRANSACTION_SUCCESS, DNS_TRANSACTION_FAILURE) &&
+ !t->received)
+ continue;
+
+ if (dns_question_is_superset(t->question, question) > 0)
+ return t;
+ }
+
+ return NULL;
+}
+
+static int dns_scope_make_conflict_packet(
+ DnsScope *s,
+ DnsResourceRecord *rr,
+ DnsPacket **ret) {
+
+ _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
+ int r;
+
+ assert(s);
+ assert(rr);
+ assert(ret);
+
+ r = dns_packet_new(&p, s->protocol, 0);
+ if (r < 0)
+ return r;
+
+ DNS_PACKET_HEADER(p)->flags = htobe16(DNS_PACKET_MAKE_FLAGS(
+ 0 /* qr */,
+ 0 /* opcode */,
+ 1 /* conflict */,
+ 0 /* tc */,
+ 0 /* t */,
+ 0 /* (ra) */,
+ 0 /* (ad) */,
+ 0 /* (cd) */,
+ 0));
+ random_bytes(&DNS_PACKET_HEADER(p)->id, sizeof(uint16_t));
+ DNS_PACKET_HEADER(p)->qdcount = htobe16(1);
+ DNS_PACKET_HEADER(p)->arcount = htobe16(1);
+
+ r = dns_packet_append_key(p, rr->key, NULL);
+ if (r < 0)
+ return r;
+
+ r = dns_packet_append_rr(p, rr, NULL);
+ if (r < 0)
+ return r;
+
+ *ret = p;
+ p = NULL;
+
+ return 0;
+}
+
+static int on_conflict_dispatch(sd_event_source *es, usec_t usec, void *userdata) {
+ DnsScope *scope = userdata;
+ int r;
+
+ assert(es);
+ assert(scope);
+
+ scope->conflict_event_source = sd_event_source_unref(scope->conflict_event_source);
+
+ for (;;) {
+ _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
+ _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
+
+ rr = ordered_hashmap_steal_first(scope->conflict_queue);
+ if (!rr)
+ break;
+
+ r = dns_scope_make_conflict_packet(scope, rr, &p);
+ if (r < 0) {
+ log_error_errno(r, "Failed to make conflict packet: %m");
+ return 0;
+ }
+
+ r = dns_scope_emit(scope, p);
+ if (r < 0)
+ log_debug_errno(r, "Failed to send conflict packet: %m");
+ }
+
+ return 0;
+}
+
+int dns_scope_notify_conflict(DnsScope *scope, DnsResourceRecord *rr) {
+ usec_t jitter;
+ int r;
+
+ assert(scope);
+ assert(rr);
+
+ /* We don't send these queries immediately. Instead, we queue
+ * them, and send them after some jitter delay. */
+ r = ordered_hashmap_ensure_allocated(&scope->conflict_queue, &dns_resource_key_hash_ops);
+ if (r < 0) {
+ log_oom();
+ return r;
+ }
+
+ /* We only place one RR per key in the conflict
+ * messages, not all of them. That should be enough to
+ * indicate where there might be a conflict */
+ r = ordered_hashmap_put(scope->conflict_queue, rr->key, rr);
+ if (r == -EEXIST || r == 0)
+ return 0;
+ if (r < 0) {
+ log_debug_errno(r, "Failed to queue conflicting RR: %m");
+ return r;
+ }
+
+ dns_resource_record_ref(rr);
+
+ if (scope->conflict_event_source)
+ return 0;
+
+ random_bytes(&jitter, sizeof(jitter));
+ jitter %= LLMNR_JITTER_INTERVAL_USEC;
+
+ r = sd_event_add_time(scope->manager->event,
+ &scope->conflict_event_source,
+ clock_boottime_or_monotonic(),
+ now(clock_boottime_or_monotonic()) + jitter,
+ LLMNR_JITTER_INTERVAL_USEC,
+ on_conflict_dispatch, scope);
+ if (r < 0) {
+ log_debug_errno(r, "Failed to add conflict dispatch event: %m");
+ return r;
+ }
+
+ return 0;
+}
+
+void dns_scope_check_conflicts(DnsScope *scope, DnsPacket *p) {
+ unsigned i;
+ int r;
+
+ assert(scope);
+ assert(p);
+
+ if (p->protocol != DNS_PROTOCOL_LLMNR)
+ return;
+
+ if (DNS_PACKET_RRCOUNT(p) <= 0)
+ return;
+
+ if (DNS_PACKET_C(p) != 0)
+ return;
+
+ if (DNS_PACKET_T(p) != 0)
+ return;
+
+ if (manager_our_packet(scope->manager, p))
+ return;
+
+ r = dns_packet_extract(p);
+ if (r < 0) {
+ log_debug_errno(r, "Failed to extract packet: %m");