channeld: support private channel creation, fixes #2125

Adds a new 'announce' field for `fundchannel`, which if false
won't broadcast a `channel_announcement`.

channeld/channeld.c

@@ -417,6 +417,22 @@ static void channel_announcement_negotiate(struct peer *peer)
 		peer->channel_local_active = true;
 		make_channel_local_active(peer);
 	}
+
+	/* BOLT #7:
+	 *
+	 * A node:
+	 *   - if the `open_channel` message has the `announce_channel` bit set
+	 *     AND a `shutdown` message has not been sent:
+	 *     - MUST send the `announcement_signatures` message.
+	 *       - MUST NOT send `announcement_signatures` messages until
+	 *         `funding_locked` has been sent AND the funding transaction has
+	 *         at least six confirmations.
+	 *   - otherwise:
+	 *     - MUST NOT send the `announcement_signatures` message.
+	 */
+	if (!(peer->channel_flags & CHANNEL_FLAGS_ANNOUNCE_CHANNEL))
+		return;
+
 	/* BOLT #7:
 	 *
 	 *      - MUST NOT send `announcement_signatures` messages until

contrib/pylightning/lightning/lightning.py

@@ -361,14 +361,17 @@ class LightningRpc(UnixDomainSocketRpc):
         }
         return self.call("listpeers", payload)
 
-    def fundchannel(self, node_id, satoshi, feerate=None):
+    def fundchannel(self, node_id, satoshi, feerate=None, announce=True):
         """
-        Fund channel with {id} using {satoshi} satoshis"
+        Fund channel with {id} using {satoshi} satoshis
+        with feerate of {feerate} (uses default feerate if unset).
+        If {announce} is False, don't send channel announcements.
         """
         payload = {
             "id": node_id,
             "satoshi": satoshi,
-            "feerate": feerate
+            "feerate": feerate,
+            "announce": announce
         }
         return self.call("fundchannel", payload)
 

lightningd/opening_control.c

@@ -770,6 +770,7 @@ static void json_fund_channel(struct command *cmd,
 	struct peer *peer;
 	struct channel *channel;
 	u32 *feerate_per_kw;
+	bool *announce_channel;
 	u8 *msg;
 	u64 max_funding_satoshi = get_chainparams(cmd->ld)->max_funding_satoshi;
 
@@ -780,6 +781,7 @@ static void json_fund_channel(struct command *cmd,
 		   p_req("id", json_tok_pubkey, &id),
 		   p_req("satoshi", json_tok_tok, &sattok),
 		   p_opt("feerate", json_tok_feerate, &feerate_per_kw),
+		   p_opt_def("announce", json_tok_bool, &announce_channel, true),
 		   NULL))
 		return;
 
@@ -826,6 +828,11 @@ static void json_fund_channel(struct command *cmd,
 	/* FIXME: Support push_msat? */
 	fc->push_msat = 0;
 	fc->channel_flags = OUR_CHANNEL_FLAGS;
+	if (!*announce_channel) {
+		fc->channel_flags &= ~CHANNEL_FLAGS_ANNOUNCE_CHANNEL;
+		log_info(peer->ld->log, "Will open private channel with node %s",
+			type_to_string(fc, struct pubkey, id));
+	}
 
 	if (!wtx_select_utxos(&fc->wtx, *feerate_per_kw,
 			      BITCOIN_SCRIPTPUBKEY_P2WSH_LEN))

tests/test_connection.py

@@ -791,6 +791,21 @@ def test_channel_persistence(node_factory, bitcoind, executor):
     l1.daemon.wait_for_log(' to ONCHAIN')
 
 
+def test_private_channel(node_factory):
+    l1, l2 = node_factory.line_graph(2, announce_channels=False, wait_for_announce=False)
+    l3, l4 = node_factory.line_graph(2, announce_channels=True, wait_for_announce=True)
+
+    assert l1.daemon.is_in_log('Will open private channel with node {}'.format(l2.info['id']))
+    assert not l2.daemon.is_in_log('Will open private channel with node {}'.format(l1.info['id']))
+    assert not l3.daemon.is_in_log('Will open private channel with node {}'.format(l4.info['id']))
+
+    l3.daemon.wait_for_log('Received node_announcement for node {}'.format(l4.info['id']))
+    l4.daemon.wait_for_log('Received node_announcement for node {}'.format(l3.info['id']))
+
+    assert not l1.daemon.is_in_log('Received node_announcement for node {}'.format(l2.info['id']))
+    assert not l2.daemon.is_in_log('Received node_announcement for node {}'.format(l1.info['id']))
+
+
 @unittest.skipIf(not DEVELOPER, "needs DEVELOPER=1 for --dev-broadcast-interval")
 def test_channel_reenable(node_factory):
     l1, l2 = node_factory.line_graph(2, opts={'may_reconnect': True}, fundchannel=True, wait_for_announce=True)

tests/utils.py

@@ -788,9 +788,10 @@ class NodeFactory(object):
                 raise
         return node
 
-    def line_graph(self, num_nodes, fundchannel=True, fundamount=10**6, wait_for_announce=False, opts=None):
+    def line_graph(self, num_nodes, fundchannel=True, fundamount=10**6, wait_for_announce=False, opts=None, announce_channels=True):
         """ Create nodes, connect them and optionally fund channels.
         """
+        assert not (wait_for_announce and not announce_channels), "You've asked to wait for an announcement that's not coming. (wait_for_announce=True,announce_channels=False)"
         nodes = self.get_nodes(num_nodes, opts=opts)
         bitcoin = nodes[0].bitcoin
         connections = [(nodes[i], nodes[i + 1]) for i in range(0, num_nodes - 1)]
@@ -813,7 +814,7 @@ class NodeFactory(object):
         bitcoin.generate_block(1)
         for src, dst in connections:
             wait_for(lambda: len(src.rpc.listfunds()['outputs']) > 0)
-            tx = src.rpc.fundchannel(dst.info['id'], fundamount)
+            tx = src.rpc.fundchannel(dst.info['id'], fundamount, announce=announce_channels)
             wait_for(lambda: tx['txid'] in bitcoin.rpc.getrawmempool())
 
         # Confirm all channels and wait for them to become usable