lightningd: immediately close without broadcast whenever we close a withheld channel.

There's no funding tx to spend.

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

Author: rustyrussell

lightningd/channel.c

@@ -1075,21 +1075,31 @@ static void channel_fail_perm(struct channel *channel,
 
 	channel_set_owner(channel, NULL);
 
-	if (channel_state_wants_onchain_fail(channel->state))
+	if (channel->withheld) {
+		channel_set_state(channel,
+				  channel->state,
+				  CLOSED,
+				  reason,
+				  why);
+	} else if (channel_state_wants_onchain_fail(channel->state)) {
 		channel_set_state(channel,
 				  channel->state,
 				  AWAITING_UNILATERAL,
 				  reason,
 				  why);
+	}
+
+	if (channel_state_open_uncommitted(channel->state)) {
+		delete_channel(channel, false);
+		return;
+	}
 
 	/* Drop non-cooperatively (unilateral) to chain. If we detect
 	 * the close from the blockchain, then we can observe
 	 * passively, and not broadcast our own unilateral close, as
 	 * it doesn't stand a chance anyway. */
 	drop_to_chain(ld, channel, false, spent_by);
 
-	if (channel_state_open_uncommitted(channel->state))
-		delete_channel(channel, false);
 }
 
 void channel_fail_permanent(struct channel *channel,

lightningd/closing_control.c

@@ -38,13 +38,18 @@ static void
 resolve_one_close_command(struct close_command *cc, bool cooperative,
 			  const struct bitcoin_tx **close_txs)
 {
-	assert(tal_count(close_txs));
 	struct json_stream *result = json_stream_success(cc->cmd);
-	const struct bitcoin_tx *close_tx = close_txs[tal_count(close_txs) - 1];
+	const struct bitcoin_tx *close_tx;
 
-	if (command_deprecated_out_ok(cc->cmd, "tx", "v24.11", "v25.12"))
+	/* Withheld funding channels can have no close_txs! */
+	if (tal_count(close_txs) != 0)
+		close_tx = close_txs[tal_count(close_txs) - 1];
+	else
+		close_tx = NULL;
+
+	if (close_tx && command_deprecated_out_ok(cc->cmd, "tx", "v24.11", "v25.12"))
 		json_add_tx(result, "tx", close_tx);
-	if (!invalid_last_tx(close_tx)) {
+	if (close_tx && !invalid_last_tx(close_tx)) {
 		struct bitcoin_txid txid;
 		bitcoin_txid(close_tx, &txid);
 		if (command_deprecated_out_ok(cc->cmd, "txid", "v24.11", "v25.12"))

lightningd/peer_control.c

@@ -348,6 +348,17 @@ void drop_to_chain(struct lightningd *ld, struct channel *channel,
 	struct channel_inflight *inflight;
 	const char *cmd_id;
 
+	/* If we withheld the funding tx, we simply close */
+	if (channel->withheld) {
+		log_info(channel->log,
+			 "Withheld channel: not sending a close transaction");
+		resolve_close_command(ld, channel, cooperative,
+				      tal_arr(tmpctx, const struct bitcoin_tx *, 0));
+		free_htlcs(ld, channel);
+		delete_channel(channel, false);
+		return;
+	}
+
 	/* If we're not already (e.g. close before channel fully open),
 	 * make sure we're watching for the funding spend */
 	if (!channel->funding_spend_watch) {

plugins/spender/openchannel.c

@@ -1096,17 +1096,22 @@ static void list_awaiting_channels(struct command *init_cmd)
 		struct channel_id cid;
 		struct command *aux_cmd;
 		struct wally_psbt *psbt;
+		bool withheld;
 
-		if (json_scan(tmpctx, buf, t, "{state:%,channel_id:%,funding:{psbt:%}}",
+		if (json_scan(tmpctx, buf, t, "{state:%,channel_id:%,funding:{withheld:%,psbt:%}}",
 			      JSON_SCAN_TAL(tmpctx, json_strdup, &state),
 			      JSON_SCAN(json_tok_channel_id, &cid),
+			      JSON_SCAN(json_to_bool, &withheld),
 			      JSON_SCAN_TAL(tmpctx, json_to_psbt, &psbt)) != NULL)
 			continue;
 
 		if (!streq(state, "CHANNELD_AWAITING_LOCKIN")
 		    && !streq(state, "DUALOPEND_AWAITING_LOCKIN"))
 			continue;
 
+		if (withheld)
+			continue;
+
 		/* Don't do this sync, as it can reasonably fail! */
 		aux_cmd = aux_command(init_cmd);
 		req = jsonrpc_request_start(aux_cmd, "signpsbt",