gossip: Use gossiped node_announcement to locate nodes.

So we can get via address hint, DNS seed, or node_announcement
gossip.

gossipd/gossip.c

@@ -1811,6 +1811,34 @@ seed_resolve_addr(const tal_t *ctx, const struct pubkey *id, const u16 port)
 	}
 }
 
+/* Resolve using gossiped wireaddr stored in routemap. */
+static struct addrhint *
+gossip_resolve_addr(const tal_t *ctx,
+		    struct routing_state *rstate,
+		    const struct pubkey *id)
+{
+	struct node *node;
+	struct addrhint *a;
+
+	/* Get from routing state. */
+	node = get_node(rstate, id);
+
+	/* No matching node? */
+	if (!node)
+		return NULL;
+	/* Node has no addresses? */
+	if (tal_count(node->addresses) == 0)
+		return NULL;
+
+	/* FIXME: When struct addrhint can contain more than one address,
+	 * we should copy all addresses.
+	 * For now getting first address should be fine. */
+	a = tal(ctx, struct addrhint);
+	a->addr = node->addresses[0];
+
+	return a;
+}
+
 static void try_reach_peer(struct daemon *daemon, const struct pubkey *id,
 			   bool master_needs_response)
 {
@@ -1847,6 +1875,11 @@ static void try_reach_peer(struct daemon *daemon, const struct pubkey *id,
 
 	a = find_addrhint(daemon, id);
 
+	if (!a)
+		a = gossip_resolve_addr(tmpctx,
+					daemon->rstate,
+					id);
+
 	if (!a)
 		a = seed_resolve_addr(tmpctx, id, 9735);
 

tests/test_lightningd.py

@@ -109,8 +109,12 @@ class NodeFactory(object):
         self.executor = executor
         self.bitcoind = bitcoind
 
+    def get_next_port(self):
+        return 16330 + self.next_id
+
     def get_node(self, disconnect=None, options=None, may_fail=False, may_reconnect=False, random_hsm=False, fake_bitcoin_cli=False):
         node_id = self.next_id
+        port = self.get_next_port()
         self.next_id += 1
 
         lightning_dir = os.path.join(
@@ -120,7 +124,6 @@ class NodeFactory(object):
             shutil.rmtree(lightning_dir)
 
         socket_path = os.path.join(lightning_dir, "lightning-rpc").format(node_id)
-        port = 16330 + node_id
         daemon = utils.LightningD(lightning_dir, self.bitcoind.bitcoin_dir, port=port, random_hsm=random_hsm)
         # If we have a disconnect string, dump it to a file for daemon.
         if disconnect:
@@ -633,6 +636,31 @@ class LightningDTests(BaseLightningDTests):
                                "Cryptographic handshake: ",
                                l1.rpc.connect, '032cf15d1ad9c4a08d26eab1918f732d8ef8fdc6abb9640bf3db174372c491304e', 'localhost', l2.info['port'])
 
+    def test_connect_by_gossip(self):
+        """Test connecting to an unknown peer using node gossip
+        """
+        l1 = self.node_factory.get_node()
+        l2 = self.node_factory.get_node()
+        # Force l3 to give its address.
+        l3port = self.node_factory.get_next_port()
+        l3 = self.node_factory.get_node(options={"ipaddr": "127.0.0.1:{}".format(l3port)})
+
+        l2.rpc.connect(l3.info['id'], 'localhost', l3.info['port'])
+
+        # Nodes are gossiped only if they have channels
+        chanid = self.fund_channel(l2, l3, 10**6)
+        # Let channel reach announcement depth
+        self.wait_for_routes(l2, [chanid])
+        # Make sure l3 has given node announcement to l2.
+        l2.daemon.wait_for_logs(['Received node_announcement for node {}'.format(l3.info['id'])])
+
+        # Let l1 learn of l3 by node gossip
+        l1.rpc.connect(l2.info['id'], 'localhost', l2.info['port'])
+        l1.daemon.wait_for_logs(['Received node_announcement for node {}'.format(l3.info['id'])])
+
+        # Have l1 connect to l3 without explicit host and port.
+        l1.rpc.connect(l3.info['id'])
+
     def test_connect_standard_addr(self):
         """Test standard node@host:port address
         """