routeboost: expose private channel in invoice iff we have no public ones.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

CHANGELOG.md

@@ -40,6 +40,7 @@ This release named by @molxyz and [@ctrlbreak](https://twitter.com/ctrlbreak).
 - JSON API: use `\n\n` to terminate responses, for simplified parsing (pylightning now relies on this)
 - JSON API: `fundchannel` now includes an `announce` option, when false it will keep channel private. Defaults to true.
 - JSON API: `listpeers`'s `channels` now includes a `private` flag to indicate if channel is announced or not.
+- JSON API: `invoice` route hints may now include private channels if you have no public ones.
 - Plugins: experimental plugin support for `lightningd`, including option passthrough and JSON-RPC passthrough.
 
 ### Changed

gossipd/gossipd.c

@@ -2114,7 +2114,8 @@ static struct io_plan *get_incoming_channels(struct io_conn *conn,
 					     const u8 *msg)
 {
 	struct node *node;
-	struct route_info *r = tal_arr(tmpctx, struct route_info, 0);
+	struct route_info *public = tal_arr(tmpctx, struct route_info, 0);
+	struct route_info *private = tal_arr(tmpctx, struct route_info, 0);
 
 	if (!fromwire_gossip_get_incoming_channels(msg))
 		master_badmsg(WIRE_GOSSIP_GET_INCOMING_CHANNELS, msg);
@@ -2126,10 +2127,6 @@ static struct io_plan *get_incoming_channels(struct io_conn *conn,
 			const struct half_chan *hc;
 			struct route_info ri;
 
-			/* Don't leak private channels. */
-			if (!is_chan_public(c))
-				continue;
-
 			hc = &c->half[half_chan_to(node, c)];
 
 			if (!is_halfchan_enabled(hc))
@@ -2140,11 +2137,19 @@ static struct io_plan *get_incoming_channels(struct io_conn *conn,
 			ri.fee_base_msat = hc->base_fee;
 			ri.fee_proportional_millionths = hc->proportional_fee;
 			ri.cltv_expiry_delta = hc->delay;
-			tal_arr_expand(&r, ri);
+
+			if (is_chan_public(c))
+				tal_arr_expand(&public, ri);
+			else
+				tal_arr_expand(&private, ri);
 		}
 	}
 
-	msg = towire_gossip_get_incoming_channels_reply(NULL, r);
+	/* If no public channels, share private ones. */
+	if (tal_count(public) == 0)
+		msg = towire_gossip_get_incoming_channels_reply(NULL, private);
+	else
+		msg = towire_gossip_get_incoming_channels_reply(NULL, public);
 	daemon_conn_send(daemon->master, take(msg));
 
 	return daemon_conn_read_next(conn, daemon->master);

tests/test_invoices.py

@@ -120,14 +120,7 @@ def test_invoice_preimage(node_factory):
 def test_invoice_routeboost(node_factory, bitcoind):
     """Test routeboost 'r' hint in bolt11 invoice.
     """
-    l1, l2 = node_factory.line_graph(2, fundamount=2 * (10**4))
-
-    # Won't get reference to route until channel is public.
-    inv = l2.rpc.invoice(msatoshi=123456, label="inv0", description="?")
-    assert 'warning_capacity' in inv
-
-    bitcoind.generate_block(5)
-    wait_for(lambda: [c['public'] for c in l2.rpc.listchannels()['channels']] == [True, True])
+    l1, l2 = node_factory.line_graph(2, fundamount=2 * (10**4), wait_for_announce=True)
 
     # Check routeboost.
     # Make invoice and pay it
@@ -162,6 +155,38 @@ def test_invoice_routeboost(node_factory, bitcoind):
     assert 'warning_offline' in inv
 
 
+def test_invoice_routeboost_private(node_factory, bitcoind):
+    """Test routeboost 'r' hint in bolt11 invoice for private channels
+    """
+    l1, l2 = node_factory.line_graph(2, fundamount=10**6, announce_channels=False)
+
+    # Since there's only one route, it will reluctantly hint that even
+    # though it's private
+    inv = l2.rpc.invoice(msatoshi=123456, label="inv0", description="?")
+    assert 'warning_capacity' not in inv
+    assert 'warning_offline' not in inv
+    # Route array has single route with single element.
+    r = only_one(only_one(l1.rpc.decodepay(inv['bolt11'])['routes']))
+    assert r['pubkey'] == l1.info['id']
+    assert r['short_channel_id'] == l1.rpc.listchannels()['channels'][0]['short_channel_id']
+    assert r['fee_base_msat'] == 1
+    assert r['fee_proportional_millionths'] == 10
+    assert r['cltv_expiry_delta'] == 6
+
+    # The existence of a public channel, even without capacity, will suppress
+    # the exposure of private channels.
+    l3 = node_factory.get_node()
+    l3.rpc.connect(l2.info['id'], 'localhost', l2.port)
+    scid = l3.fund_channel(l2, 2 * (10**4))
+    bitcoind.generate_block(5)
+
+    # Make sure channel is totally public.
+    wait_for(lambda: [c['public'] for c in l3.rpc.listchannels(scid)['channels']] == [True, True])
+
+    inv = l2.rpc.invoice(msatoshi=123456000, label="inv1", description="?")
+    assert 'warning_capacity' in inv
+
+
 def test_invoice_expiry(node_factory, executor):
     l1, l2 = node_factory.line_graph(2, fundchannel=True)