channel control: break out separate method for canceling

Break out a method for canceling a channel that will either
loop through contacting the peer to tell them of the error or
just directly cleans up if the peer is currently disconnected.

lightningd/channel_control.c

@@ -235,18 +235,11 @@ static void peer_start_closingd_after_shutdown(struct channel *channel,
 	channel_set_state(channel, CHANNELD_SHUTTING_DOWN, CLOSINGD_SIGEXCHANGE);
 }
 
-static void handle_error_channel(struct channel *channel,
-				 const u8 *msg)
+static void forget(struct channel *channel)
 {
 	struct command **forgets = tal_steal(tmpctx, channel->forgets);
 	channel->forgets = tal_arr(channel, struct command *, 0);
 
-	if (!fromwire_channel_send_error_reply(msg)) {
-		channel_internal_error(channel, "bad send_error_reply: %s",
-				       tal_hex(tmpctx, msg));
-		return;
-	}
-
 	/* Forget the channel. */
 	delete_channel(channel);
 
@@ -262,6 +255,35 @@ static void handle_error_channel(struct channel *channel,
 	tal_free(forgets);
 }
 
+static void handle_error_channel(struct channel *channel,
+				 const u8 *msg)
+{
+	if (!fromwire_channel_send_error_reply(msg)) {
+		channel_internal_error(channel, "bad send_error_reply: %s",
+				       tal_hex(tmpctx, msg));
+		return;
+	}
+
+	forget(channel);
+}
+
+void forget_channel(struct channel *channel, const char *why)
+{
+	struct channel_id cid;
+
+	derive_channel_id(&cid, &channel->funding_txid,
+			  channel->funding_outnum);
+	channel->error = towire_errorfmt(channel, &cid, "%s", why);
+
+	/* If the peer is connected, we let them know. Otherwise
+	 * we just directly remove the channel */
+	if (channel->owner)
+		subd_send_msg(channel->owner,
+			      take(towire_channel_send_error(NULL, why)));
+	else
+		forget(channel);
+}
+
 static unsigned channel_msg(struct subd *sd, const u8 *msg, const int *fds)
 {
 	enum channel_wire_type t = fromwire_peektype(msg);

lightningd/channel_control.h

@@ -30,4 +30,7 @@ struct command_result *cancel_channel_before_broadcast(struct command *cmd,
 						       struct peer *peer,
 						       const jsmntok_t *cidtok);
 
+/* Forget a channel. Deletes the channel and handles all
+ * associated waiting commands, if present. Notifies peer if available */
+void forget_channel(struct channel *channel, const char *err_msg);
 #endif /* LIGHTNING_LIGHTNINGD_CHANNEL_CONTROL_H */