gossip: Returning a gossip-client upon peer_ready

This fd is handed to the owner of the peer so that it can talk to the
gossip daemon.

lightningd/gossip/gossip.c

@@ -62,6 +62,9 @@ struct peer {
 	u8 **msg_out;
 	/* Is it time to continue the staggered broadcast? */
 	bool gossip_sync;
+
+	/* The peer owner will use this to talk to gossipd */
+	int proxy_fd;
 };
 
 static void destroy_peer(struct peer *peer)
@@ -227,10 +230,21 @@ static bool has_even_bit(const u8 *bitmap)
 	return false;
 }
 
+static int peer_create_gossip_client(struct peer *peer)
+{
+	int fds[2];
+	if (socketpair(AF_LOCAL, SOCK_STREAM, 0, fds) != 0) {
+		return -1;
+	}
+	peer->proxy_fd = fds[0];
+	return fds[1];
+}
+
 static struct io_plan *peer_parse_init(struct io_conn *conn,
 				       struct peer *peer, u8 *msg)
 {
 	u8 *gfeatures, *lfeatures;
+	int client_fd;
 
 	if (!fromwire_init(msg, msg, NULL, &gfeatures, &lfeatures)) {
 		peer->error = tal_fmt(msg, "Bad init: %s", tal_hex(msg, msg));
@@ -255,12 +269,19 @@ static struct io_plan *peer_parse_init(struct io_conn *conn,
 		return io_close(conn);
 	}
 
+	client_fd = peer_create_gossip_client(peer);
+	if (client_fd == -1) {
+		peer->error = tal_fmt(msg, "Internal error");
+		return io_close(conn);
+	}
+
 	/* BOLT #1:
 	 *
 	 * Each node MUST wait to receive `init` before sending any other
 	 * messages.
 	 */
 	status_send(towire_gossipstatus_peer_ready(msg, peer->unique_id));
+	status_send_fd(client_fd);
 
 	/* Need to go duplex here, otherwise backpressure would mean
 	 * we both wait indefinitely */

lightningd/gossip_control.c

@@ -71,7 +71,7 @@ static void peer_nongossip(struct subd *gossip, const u8 *msg, int fd)
 	peer_accept_open(peer, &cs, inner);
 }
 
-static void peer_ready(struct subd *gossip, const u8 *msg)
+static void peer_ready(struct subd *gossip, const u8 *msg, int fd)
 {
 	u64 unique_id;
 	struct peer *peer;
@@ -98,6 +98,8 @@ static void peer_ready(struct subd *gossip, const u8 *msg)
 		peer->connect_cmd = NULL;
 	}
 
+	peer->gossip_client_fd = fd;
+
 	peer_set_condition(peer, "Exchanging gossip");
 }
 
@@ -128,7 +130,10 @@ static enum subd_msg_ret gossip_msg(struct subd *gossip,
 		peer_nongossip(gossip, msg, fd);
 		break;
 	case WIRE_GOSSIPSTATUS_PEER_READY:
-		peer_ready(gossip, msg);
+		if (fd == -1) {
+			return SUBD_NEED_FD;
+		}
+		peer_ready(gossip, msg, fd);
 		break;
 	}
 	return SUBD_COMPLETE;

lightningd/peer_control.h

@@ -52,6 +52,9 @@ struct peer {
 
 	/* Secret seed (FIXME: Move to hsm!) */
 	struct privkey *seed;
+
+	/* Gossip client fd, forwarded to the respective owner */
+	int gossip_client_fd;
 };
 
 struct peer *peer_by_unique_id(struct lightningd *ld, u64 unique_id);