resolved: add cache-flush bit to answers in mDNS announcements

See the section 10.2 of RFC6762 for details.

Signed-off-by: Dmitry Rozhkov <dmitry.rozhkov@linux.intel.com>

8 files changed, 24 insertions, 20 deletions

diff --git a/src/resolve/resolved-dns-answer.h b/src/resolve/resolved-dns-answer.h
index 4a92bd1150..c0a819873a 100644
--- a/src/resolve/resolved-dns-answer.h
+++ b/src/resolve/resolved-dns-answer.h
@@ -36,6 +36,7 @@ typedef enum DnsAnswerFlags {
         DNS_ANSWER_AUTHENTICATED = 1, /* Item has been authenticated */
         DNS_ANSWER_CACHEABLE     = 2, /* Item is subject to caching */
         DNS_ANSWER_SHARED_OWNER  = 4, /* For mDNS: RRset may be owner by multiple peers */
+        DNS_ANSWER_CACHE_FLUSH   = 8, /* For mDNS: sets cache-flush bit in the rrclass of response records */
 } DnsAnswerFlags;
 
 struct DnsAnswerItem {
diff --git a/src/resolve/resolved-dns-cache.c b/src/resolve/resolved-dns-cache.c
index 9233fb0ac1..c43a7865dc 100644
--- a/src/resolve/resolved-dns-cache.c
+++ b/src/resolve/resolved-dns-cache.c
@@ -980,7 +980,7 @@ int dns_cache_export_shared_to_packet(DnsCache *cache, DnsPacket *p) {
                         if (!j->shared_owner)
                                 continue;
 
-                        r = dns_packet_append_rr(p, j->rr, NULL, NULL);
+                        r = dns_packet_append_rr(p, j->rr, 0, NULL, NULL);
                         if (r == -EMSGSIZE && p->protocol == DNS_PROTOCOL_MDNS) {
                                 /* For mDNS, if we're unable to stuff all known answers into the given packet,
                                  * allocate a new one, push the RR into that one and link it to the current one.
@@ -995,7 +995,7 @@ int dns_cache_export_shared_to_packet(DnsCache *cache, DnsPacket *p) {
 
                                 /* continue with new packet */
                                 p = p->more;
-                                r = dns_packet_append_rr(p, j->rr, NULL, NULL);
+                                r = dns_packet_append_rr(p, j->rr, 0, NULL, NULL);
                         }
 
                         if (r < 0)
diff --git a/src/resolve/resolved-dns-packet.c b/src/resolve/resolved-dns-packet.c
index 337a8c473f..8231c21450 100644
--- a/src/resolve/resolved-dns-packet.c
+++ b/src/resolve/resolved-dns-packet.c
@@ -569,8 +569,9 @@ fail:
         return r;
 }
 
-int dns_packet_append_key(DnsPacket *p, const DnsResourceKey *k, size_t *start) {
+int dns_packet_append_key(DnsPacket *p, const DnsResourceKey *k, const DnsAnswerFlags flags, size_t *start) {
         size_t saved_size;
+        uint16_t class;
         int r;
 
         assert(p);
@@ -586,7 +587,8 @@ int dns_packet_append_key(DnsPacket *p, const DnsResourceKey *k, size_t *start)
         if (r < 0)
                 goto fail;
 
-        r = dns_packet_append_uint16(p, k->class, NULL);
+        class = flags & DNS_ANSWER_CACHE_FLUSH ? k->class | MDNS_RR_CACHE_FLUSH : k->class;
+        r = dns_packet_append_uint16(p, class, NULL);
         if (r < 0)
                 goto fail;
 
@@ -791,7 +793,7 @@ int dns_packet_truncate_opt(DnsPacket *p) {
         return 1;
 }
 
-int dns_packet_append_rr(DnsPacket *p, const DnsResourceRecord *rr, size_t *start, size_t *rdata_start) {
+int dns_packet_append_rr(DnsPacket *p, const DnsResourceRecord *rr, const DnsAnswerFlags flags, size_t *start, size_t *rdata_start) {
 
         size_t saved_size, rdlength_offset, end, rdlength, rds;
         int r;
@@ -801,7 +803,7 @@ int dns_packet_append_rr(DnsPacket *p, const DnsResourceRecord *rr, size_t *star
 
         saved_size = p->size;
 
-        r = dns_packet_append_key(p, rr->key, NULL);
+        r = dns_packet_append_key(p, rr->key, flags, NULL);
         if (r < 0)
                 goto fail;
 
@@ -1143,7 +1145,7 @@ int dns_packet_append_question(DnsPacket *p, DnsQuestion *q) {
         assert(p);
 
         DNS_QUESTION_FOREACH(key, q) {
-                r = dns_packet_append_key(p, key, NULL);
+                r = dns_packet_append_key(p, key, 0, NULL);
                 if (r < 0)
                         return r;
         }
@@ -1153,12 +1155,13 @@ int dns_packet_append_question(DnsPacket *p, DnsQuestion *q) {
 
 int dns_packet_append_answer(DnsPacket *p, DnsAnswer *a) {
         DnsResourceRecord *rr;
+        DnsAnswerFlags flags;
         int r;
 
         assert(p);
 
-        DNS_ANSWER_FOREACH(rr, a) {
-                r = dns_packet_append_rr(p, rr, NULL, NULL);
+        DNS_ANSWER_FOREACH_FLAGS(rr, flags, a) {
+                r = dns_packet_append_rr(p, rr, flags, NULL, NULL);
                 if (r < 0)
                         return r;
         }
diff --git a/src/resolve/resolved-dns-packet.h b/src/resolve/resolved-dns-packet.h
index 054dc88a85..2c92392e4d 100644
--- a/src/resolve/resolved-dns-packet.h
+++ b/src/resolve/resolved-dns-packet.h
@@ -209,8 +209,8 @@ int dns_packet_append_string(DnsPacket *p, const char *s, size_t *start);
 int dns_packet_append_raw_string(DnsPacket *p, const void *s, size_t size, size_t *start);
 int dns_packet_append_label(DnsPacket *p, const char *s, size_t l, bool canonical_candidate, size_t *start);
 int dns_packet_append_name(DnsPacket *p, const char *name, bool allow_compression, bool canonical_candidate, size_t *start);
-int dns_packet_append_key(DnsPacket *p, const DnsResourceKey *key, size_t *start);
-int dns_packet_append_rr(DnsPacket *p, const DnsResourceRecord *rr, size_t *start, size_t *rdata_start);
+int dns_packet_append_key(DnsPacket *p, const DnsResourceKey *key, const DnsAnswerFlags flags, size_t *start);
+int dns_packet_append_rr(DnsPacket *p, const DnsResourceRecord *rr, const DnsAnswerFlags flags, size_t *start, size_t *rdata_start);
 int dns_packet_append_opt(DnsPacket *p, uint16_t max_udp_size, bool edns0_do, int rcode, size_t *start);
 int dns_packet_append_question(DnsPacket *p, DnsQuestion *q);
 int dns_packet_append_answer(DnsPacket *p, DnsAnswer *a);
diff --git a/src/resolve/resolved-dns-rr.c b/src/resolve/resolved-dns-rr.c
index 209d565033..e8c05ed0da 100644
--- a/src/resolve/resolved-dns-rr.c
+++ b/src/resolve/resolved-dns-rr.c
@@ -1262,7 +1262,7 @@ int dns_resource_record_to_wire_format(DnsResourceRecord *rr, bool canonical) {
         if (rr->wire_format && rr->wire_format_canonical == canonical)
                 return 0;
 
-        r = dns_packet_append_rr(&packet, rr, &start, &rds);
+        r = dns_packet_append_rr(&packet, rr, 0, &start, &rds);
         if (r < 0)
                 return r;
 
diff --git a/src/resolve/resolved-dns-scope.c b/src/resolve/resolved-dns-scope.c
index 6616bc4e0e..b47cb79795 100644
--- a/src/resolve/resolved-dns-scope.c
+++ b/src/resolve/resolved-dns-scope.c
@@ -847,11 +847,11 @@ static int dns_scope_make_conflict_packet(
         DNS_PACKET_HEADER(p)->qdcount = htobe16(1);
         DNS_PACKET_HEADER(p)->arcount = htobe16(1);
 
-        r = dns_packet_append_key(p, rr->key, NULL);
+        r = dns_packet_append_key(p, rr->key, 0, NULL);
         if (r < 0)
                 return r;
 
-        r = dns_packet_append_rr(p, rr, NULL, NULL);
+        r = dns_packet_append_rr(p, rr, 0, NULL, NULL);
         if (r < 0)
                 return r;
 
@@ -1086,12 +1086,12 @@ void dns_scope_announce(DnsScope *scope) {
 
         answer = dns_answer_new(4);
         LIST_FOREACH(addresses, a, scope->link->addresses) {
-                r = dns_answer_add(answer, a->mdns_address_rr, 0);
+                r = dns_answer_add(answer, a->mdns_address_rr, 0, DNS_ANSWER_CACHE_FLUSH);
                 if (r < 0) {
                         log_debug_errno(r, "Failed to add address RR to answer: %m");
                         return;
                 }
-                r = dns_answer_add(answer, a->mdns_ptr_rr, 0);
+                r = dns_answer_add(answer, a->mdns_ptr_rr, 0, DNS_ANSWER_CACHE_FLUSH);
                 if (r < 0) {
                         log_debug_errno(r, "Failed to add PTR RR to answer: %m");
                         return;
diff --git a/src/resolve/resolved-dns-stub.c b/src/resolve/resolved-dns-stub.c
index e76de6c06a..932e5b58a2 100644
--- a/src/resolve/resolved-dns-stub.c
+++ b/src/resolve/resolved-dns-stub.c
@@ -86,7 +86,7 @@ static int dns_stub_make_reply_packet(
 
                 continue;
         add:
-                r = dns_packet_append_rr(p, rr, NULL, NULL);
+                r = dns_packet_append_rr(p, rr, 0, NULL, NULL);
                 if (r < 0)
                         return r;
 
diff --git a/src/resolve/resolved-dns-transaction.c b/src/resolve/resolved-dns-transaction.c
index bd36e5e1a1..672f0e4cb2 100644
--- a/src/resolve/resolved-dns-transaction.c
+++ b/src/resolve/resolved-dns-transaction.c
@@ -1369,7 +1369,7 @@ static int dns_transaction_make_packet_mdns(DnsTransaction *t) {
         if (r < 0)
                 return r;
 
-        r = dns_packet_append_key(p, t->key, NULL);
+        r = dns_packet_append_key(p, t->key, 0, NULL);
         if (r < 0)
                 return r;
 
@@ -1401,7 +1401,7 @@ static int dns_transaction_make_packet_mdns(DnsTransaction *t) {
                 if (qdcount >= UINT16_MAX)
                         break;
 
-                r = dns_packet_append_key(p, other->key, NULL);
+                r = dns_packet_append_key(p, other->key, 0, NULL);
 
                 /*
                  * If we can't stuff more questions into the packet, just give up.
@@ -1470,7 +1470,7 @@ static int dns_transaction_make_packet(DnsTransaction *t) {
         if (r < 0)
                 return r;
 
-        r = dns_packet_append_key(p, t->key, NULL);
+        r = dns_packet_append_key(p, t->key, 0, NULL);
         if (r < 0)
                 return r;