dual-open: use tx-abort instead of warning/errors

When a channel open fails, we use tx-abort instead of warning/error.

This means that the peer won't disconnect! And instead when a new
message arrives, we'll need to rebuild the dualopend subd (if missing).

Makes opens a bit easer to retry (no reconnect needed), as well as keeps
the connection alive for other channels we may have with that peer.

Changelog-Changed: Experimental-Dual-Fund: open failures don't disconnect, but instead fail the opening process

common/peer_failed.c

@@ -11,7 +11,7 @@
 #include <common/wire_error.h>
 
 /* Fatal error here, return peer control to lightningd */
-static void NORETURN
+void NORETURN
 peer_fatal_continue(const u8 *msg TAKES, const struct per_peer_state *pps)
 {
  	int reason = fromwire_peektype(msg);

common/peer_failed.h

@@ -7,6 +7,9 @@
 struct channel_id;
 struct per_peer_state;
 
+/* peer_fatal_continue - Send a message to master, we've failed */
+void NORETURN peer_fatal_continue(const u8 *msg TAKES, const struct per_peer_state *pps);
+
 /**
  * peer_failed_warn - Send a warning msg and close the connection.
  * @pps: the per-peer state.

common/wire_error.c

@@ -93,6 +93,8 @@ char *sanitize_error(const tal_t *ctx, const u8 *errmsg,
 		warning = false;
 	else if (fromwire_warning(ctx, errmsg, channel_id, &data))
 		warning = true;
+	else if (fromwire_tx_abort(ctx, errmsg, channel_id, &data))
+		warning = false;
 	else
 		return tal_fmt(ctx, "Invalid ERROR message '%s'",
 			       tal_hex(ctx, errmsg));

lightningd/dual_open_control.c

@@ -2379,9 +2379,33 @@ json_openchannel_bump(struct command *cmd,
 				    type_to_string(tmpctx, struct amount_sat,
 						   &chainparams->max_funding));
 
-	if (!channel->owner)
-		return command_fail(cmd, FUNDING_PEER_NOT_CONNECTED,
-				      "Peer not connected.");
+	/* It's possible that the last open failed/was aborted.
+	 * So now we restart the attempt! */
+	if (!channel->owner) {
+		int fds[2];
+		if (socketpair(AF_LOCAL, SOCK_STREAM, 0, fds) != 0) {
+			log_broken(channel->log,
+				   "Failed to create socketpair: %s",
+				   strerror(errno));
+			return command_fail(cmd, FUNDING_PEER_NOT_CONNECTED,
+					    "Unable to create socket: %s",
+					    strerror(errno));
+		}
+
+		if (!peer_restart_dualopend(channel->peer,
+					    new_peer_fd(tmpctx, fds[0]),
+					    channel)) {
+			close(fds[1]);
+			return command_fail(cmd, FUNDING_PEER_NOT_CONNECTED,
+					      "Peer not connected.");
+		}
+		subd_send_msg(cmd->ld->connectd,
+			      take(towire_connectd_peer_connect_subd(NULL,
+								     &channel->peer->id,
+								     channel->peer->connectd_counter,
+								     &channel->cid)));
+		subd_send_fd(cmd->ld->connectd, fds[1]);
+	}
 
 	if (channel->open_attempt)
 		return command_fail(cmd, FUNDING_STATE_INVALID,

lightningd/peer_control.c

@@ -362,7 +362,7 @@ void channel_errmsg(struct channel *channel,
 
 	if (channel_unsaved(channel)) {
 		log_info(channel->log, "%s", "Unsaved peer failed."
-			 " Disconnecting and deleting channel.");
+			 " Deleting channel.");
 		delete_channel(channel);
 		return;
 	}
@@ -1485,8 +1485,26 @@ void peer_spoke(struct lightningd *ld, const u8 *msg)
 
 		/* If channel is active, we raced, so ignore this:
 		 * subd will get it soon. */
-		if (channel_active(channel))
+		if (channel_active(channel)) {
+			log_debug(channel->log,
+				  "channel already active");
+			if (!channel->owner) {
+				assert(channel->state == DUALOPEND_AWAITING_LOCKIN);
+				if (socketpair(AF_LOCAL, SOCK_STREAM, 0, fds) != 0) {
+					log_broken(ld->log,
+						   "Failed to create socketpair: %s",
+						   strerror(errno));
+					error = towire_warningfmt(tmpctx, &channel_id,
+								  "Trouble in paradise?");
+					goto send_error;
+				}
+				if (peer_restart_dualopend(peer, new_peer_fd(tmpctx, fds[0]), channel))
+					goto tell_connectd;
+			/* FIXME: Send informative error? */
+				close(fds[1]);
+			}
 			return;
+		}
 
 		if (msgtype == WIRE_CHANNEL_REESTABLISH) {
 			log_debug(channel->log,