dns: only allow one DNS announcement

lightningd/options.c

@@ -196,6 +196,23 @@ static char *opt_set_accept_extra_tlv_types(const char *arg,
 }
 #endif
 
+#if EXPERIMENTAL_FEATURES /* BOLT7 DNS RFC #911 */
+/* Returns the number of wireaddr types already announced */
+static size_t num_announced_types(enum wire_addr_type type, struct lightningd *ld)
+{
+	size_t num = 0;
+	for (size_t i = 0; i < tal_count(ld->proposed_wireaddr); i++) {
+		if (ld->proposed_wireaddr[i].itype != ADDR_INTERNAL_WIREADDR)
+			continue;
+		if (ld->proposed_wireaddr[i].u.wireaddr.type != type)
+			continue;
+		if (ld->proposed_listen_announce[i] & ADDR_ANNOUNCE)
+			num++;
+	}
+	return num;
+}
+#endif
+
 static char *opt_add_addr_withtype(const char *arg,
 				   struct lightningd *ld,
 				   enum addr_listen_announce ala,
@@ -242,6 +259,14 @@ static char *opt_add_addr_withtype(const char *arg,
 #if EXPERIMENTAL_FEATURES /* BOLT7 DNS RFC #911 */
 	/* Add ADDR_TYPE_DNS to announce DNS hostnames */
 	if (is_dnsaddr(address) && ala & ADDR_ANNOUNCE) {
+		/* BOLT-hostnames #7:
+		 * The origin node:
+		 * ...
+		 *   - MUST NOT announce more than one `type 5` DNS hostname.
+		 */
+		if (num_announced_types(ADDR_TYPE_DNS, ld) > 0) {
+			return tal_fmt(NULL, "Only one DNS can be announced");
+		}
 		memset(&wi, 0, sizeof(wi));
 		wi.itype = ADDR_INTERNAL_WIREADDR;
 		wi.u.wireaddr.type = ADDR_TYPE_DNS;

tests/test_gossip.py

@@ -114,7 +114,6 @@ def test_announce_address(node_factory, bitcoind):
     opts = {'disable-dns': None, 'announce-addr':
             ['4acth47i6kxnvkewtm6q7ib2s3ufpo5sqbsnzjpbi7utijcltosqemad.onion',
              '1.2.3.4:1234',
-             'localhost:1235',
              'example.com:1236',
              '::'],
             'log-level': 'io',
@@ -151,24 +150,21 @@ def test_announce_address(node_factory, bitcoind):
     # Also expect the address descriptor types to be sorted!
     # BOLT #7:
     #   - MUST place address descriptors in ascending order.
-    l1.daemon.wait_for_log(r"\[OUT\] 0101.*0063"
+    l1.daemon.wait_for_log(r"\[OUT\] 0101.*0056"
                            "010102030404d2"  # IPv4 01 1.2.3.4:1234
                            "017f000001...."  # IPv4 01 127.0.0.1:wxyz
                            "0200000000000000000000000000000000...."  # IPv6 02 :::<any_port>
                            "04e00533f3e8f2aedaa8969b3d0fa03a96e857bbb28064dca5e147e934244b9ba5023003...."  # TORv3 04
-                           "05096c6f63616c686f737404d3"       # DNS 05 len localhost:1235
                            "050b6578616d706c652e636f6d04d4")  # DNS 05 len example.com:1236
 
     # Check other node can parse these (make sure it has digested msg)
     wait_for(lambda: 'addresses' in l2.rpc.listnodes(l1.info['id'])['nodes'][0])
     addresses = l2.rpc.listnodes(l1.info['id'])['nodes'][0]['addresses']
     addresses_dns = [address for address in addresses if address['type'] == 'dns']
-    assert len(addresses) == 6
-    assert len(addresses_dns) == 2
-    assert addresses_dns[0]['address'] == 'localhost'
-    assert addresses_dns[0]['port'] == 1235
-    assert addresses_dns[1]['address'] == 'example.com'
-    assert addresses_dns[1]['port'] == 1236
+    assert len(addresses) == 5
+    assert len(addresses_dns) == 1
+    assert addresses_dns[0]['address'] == 'example.com'
+    assert addresses_dns[0]['port'] == 1236
 
 
 @unittest.skipIf(not EXPERIMENTAL_FEATURES, "BOLT7 DNS RFC #911")
@@ -236,6 +232,15 @@ def test_announce_and_connect_via_dns(node_factory, bitcoind):
         l4.rpc.connect(l1.info['id'])
 
 
+@unittest.skipIf(not EXPERIMENTAL_FEATURES, "BOLT7 DNS RFC #911")
+@pytest.mark.developer("gossip without DEVELOPER=1 is slow")
+def test_only_announce_one_dns(node_factory, bitcoind):
+    # and test that we can't announce more than one DNS address
+    l1 = node_factory.get_node(may_fail=True, expect_fail=True,
+                               options={'announce-addr': ['localhost.localdomain:12345', 'example.com:12345']})
+    assert l1.daemon.is_in_stderr("Only one DNS can be announced")
+
+
 @pytest.mark.developer("needs DEVELOPER=1")
 def test_gossip_timestamp_filter(node_factory, bitcoind, chainparams):
     # Updates get backdated 5 seconds with --dev-fast-gossip.