df: pass back 'close_to' for completed/commitment secured channels

When commitments are secured, also return the 'close_to' script if we've
got a local_upfront_shutdown_script set.

doc/lightning-openchannel_update.7

@@ -35,6 +35,20 @@ complete \fIpsbt\fR for this channel's funding transaction; and the flag
 If \fIcommitments_secured\fR is true, caller should proceed with signing the
 returned PSBT and calling \fBopenchannel_signed\fR to complete the channel open\.
 
+
+If \fIcommitments_secured\fR is true, will also return:
+
+.RS
+.IP \[bu]
+The derived \fIchannel_id\fR\.
+.IP \[bu]
+A \fIclose_to\fR script, iff a \fBclose_to\fR address was provided to
+\fBopenchannel_init\fR and the peer supports \fBoption_upfront_shutdownscript\fR\.
+.IP \[bu]
+The \fIfunding_outnum\fR, the index of the funding output for this channel
+in the funding transaction\.
+
+.RE
 .RS
 .IP \[bu]
 -32602: If the given parameters are wrong\.
@@ -63,4 +77,4 @@ lightning-fundchannel_\fBstart\fR(7), lightning-fundchannel_\fBcomplete\fR(7),
 
 Main web site: \fIhttps://github.com/ElementsProject/lightning\fR
 
-\" SHA256STAMP:ab3d19be91c8b2e651a6f4a23552f21323c4f0096ceda8026bb2450c2f9c616c
+\" SHA256STAMP:de370bb6e61a0390a50a85e97f533238f379c908cddd822436d0ac4c72b43d6e

doc/lightning-openchannel_update.7.md

@@ -34,6 +34,14 @@ complete *psbt* for this channel's funding transaction; and the flag
 If *commitments_secured* is true, caller should proceed with signing the
 returned PSBT and calling `openchannel_signed` to complete the channel open.
 
+If *commitments_secured* is true, will also return:
+- The derived *channel_id*.
+- A *close_to* script, iff a `close_to` address was provided to
+  `openchannel_init` and the peer supports `option_upfront_shutdownscript`.
+- The *funding_outnum*, the index of the funding output for this channel
+  in the funding transaction.
+
+
 - -32602: If the given parameters are wrong.
 - -1: Catchall nonspecific error.
 - 305: Peer is not connected.

lightningd/dual_open_control.c

@@ -933,6 +933,9 @@ static void opener_commit_received(struct subd *dualopend,
 	json_add_bool(response, "commitments_secured", true);
 	/* For convenience sake, we include the funding outnum */
 	json_add_num(response, "funding_outnum", funding_outnum);
+	if (local_upfront_shutdown_script)
+		json_add_hex_talarr(response, "close_to",
+				    local_upfront_shutdown_script);
 	/* Now that we've got the final PSBT, save it */
 	channel->psbt = tal_steal(channel, psbt);
 	wallet_channel_save(uc->fc->cmd->ld->wallet, channel);

plugins/spender/openchannel.c

@@ -715,7 +715,7 @@ openchannel_update_ok(struct command *cmd,
 			   json_tok_full(buf, result));
 
 	if (done) {
-		const jsmntok_t *outnum_tok;
+		const jsmntok_t *outnum_tok, *close_to_tok;
 
 		outnum_tok = json_get_member(buf, result, "funding_outnum");
 		if (!outnum_tok)
@@ -732,6 +732,14 @@ openchannel_update_ok(struct command *cmd,
 			   json_tok_full_len(result),
 			   json_tok_full(buf, result));
 
+		close_to_tok = json_get_member(buf, result, "close_to");
+		if (close_to_tok)
+			dest->close_to_script =
+				json_tok_bin_from_hex(dest->mfc, buf,
+						      close_to_tok);
+		else
+			dest->close_to_script = NULL;
+
 		/* It's possible they beat us to the SIGNED flag,
 		 * in which case we just let that be the more senior
 		 * state position */