JSONRPC: add optional short_channel_id argument to listchannels

In order to just list one (though it may return two entries, one for each
channel direction!).

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

gossipd/gossip.c

@@ -1066,11 +1066,19 @@ static struct io_plan *getchannels_req(struct io_conn *conn, struct daemon *daem
 	struct gossip_getchannels_entry *entries;
 	struct node *n;
 	struct node_map_iter i;
+	struct short_channel_id *scid;
+
+	fromwire_gossip_getchannels_request(msg, msg, NULL, &scid);
 
 	entries = tal_arr(tmpctx, struct gossip_getchannels_entry, num_chans);
 	n = node_map_first(daemon->rstate->nodes, &i);
 	while (n != NULL) {
 		for (j=0; j<tal_count(n->out); j++){
+			if (scid &&
+			    !short_channel_id_eq(scid,
+						 &n->out[j]->short_channel_id)) {
+				continue;
+			}
 			tal_resize(&entries, num_chans + 1);
 			entries[num_chans].source = n->out[j]->src->id;
 			entries[num_chans].destination = n->out[j]->dst->id;

gossipd/gossip_wire.csv

@@ -105,6 +105,9 @@ gossip_getroute_reply,,num_hops,u16
 gossip_getroute_reply,,hops,num_hops*struct route_hop
 
 gossip_getchannels_request,3007
+# In practice, 0 or 1.
+gossip_getchannels_request,,num,u16
+gossip_getchannels_request,,short_channel_id,num*struct short_channel_id
 
 gossip_getchannels_reply,3107
 gossip_getchannels_reply,,num_channels,u16

lightningd/gossip_control.c

@@ -386,7 +386,26 @@ static void json_listchannels_reply(struct subd *gossip, const u8 *reply,
 static void json_listchannels(struct command *cmd, const char *buffer,
 			     const jsmntok_t *params)
 {
-	u8 *req = towire_gossip_getchannels_request(cmd);
+	u8 *req;
+	jsmntok_t *idtok;
+	struct short_channel_id *id = NULL;
+
+	if (!json_get_params(buffer, params,
+			     "?short_channel_id", &idtok,
+			     NULL)) {
+		command_fail(cmd, "Invalid arguments");
+		return;
+	}
+
+	if (idtok) {
+		id = tal_arr(cmd, struct short_channel_id, 1);
+		if (!json_tok_short_channel_id(buffer, idtok, id)) {
+			command_fail(cmd, "Invalid short_channel_id");
+			return;
+		}
+	}
+
+	req = towire_gossip_getchannels_request(cmd, id);
 	subd_req(cmd->ld->gossip, cmd->ld->gossip,
 		 req, -1, 0, json_listchannels_reply, cmd);
 	command_still_pending(cmd);

tests/test_lightningd.py

@@ -1775,6 +1775,17 @@ class LightningDTests(BaseLightningDTests):
                                .format(bitcoind.rpc.getblockcount() + 9 + shadow_route))
         assert l3.rpc.listinvoice('test_forward_different_fees_and_cltv')[0]['complete'] == True
 
+        # Check that we see all the channels
+        shortids = set(c['short_channel_id'] for c in l2.rpc.listchannels()['channels'])
+        for scid in shortids:
+            c = l1.rpc.listchannels(scid)['channels']
+            # We get one entry for each direction.
+            assert len(c) == 2
+            assert c[0]['short_channel_id'] == scid
+            assert c[1]['short_channel_id'] == scid
+            assert c[0]['source'] == c[1]['destination']
+            assert c[1]['source'] == c[0]['destination']
+        
     @unittest.skipIf(not DEVELOPER, "needs DEVELOPER=1 for --dev-broadcast-interval")
     def test_forward_pad_fees_and_cltv(self):
         """Test that we are allowed extra locktime delta, and fees"""