fundchannel: take a 'close_to' address

Finally, extends the 'close_to' functionality up to the flagship 'open a
channel' command.

Changelog-Added: JSON-API `fundchannel` now accepts an optional 'close_to' param, a bitcoin address that the channel funding should be sent to on close. Requires `opt_upfront_shutdownscript`

contrib/pyln-client/pyln/client/lightning.py

@@ -657,12 +657,13 @@ class LightningRpc(UnixDomainSocketRpc):
         Only select outputs with {minconf} confirmations.
         If {utxos} is specified (as a list of 'txid:vout' strings),
         fund a channel from these specifics utxos.
+        {close_to} is a valid Bitcoin address.
         """
 
         if 'satoshi' in kwargs:
             return self._deprecated_fundchannel(node_id, *args, **kwargs)
 
-        def _fundchannel(node_id, amount, feerate=None, announce=True, minconf=None, utxos=None, push_msat=None):
+        def _fundchannel(node_id, amount, feerate=None, announce=True, minconf=None, utxos=None, push_msat=None, close_to=None):
             payload = {
                 "id": node_id,
                 "amount": amount,
@@ -670,7 +671,8 @@ class LightningRpc(UnixDomainSocketRpc):
                 "announce": announce,
                 "minconf": minconf,
                 "utxos": utxos,
-                "push_msat": push_msat
+                "push_msat": push_msat,
+                "close_to": close_to,
             }
             return self.call("fundchannel", payload)
 

doc/lightning-fundchannel.7

@@ -4,7 +4,7 @@ lightning-fundchannel - Command for establishing a lightning channel
 .SH SYNOPSIS
 
 \fBfundchannel\fR \fIid\fR \fIamount\fR [\fIfeerate\fR \fIannounce\fR] [\fIminconf\fR]
-[\fIutxos\fR] [\fIpush_msat\fR]
+[\fIutxos\fR] [\fIpush_msat\fR] [\fIclose_to\fR]
 
 .SH DESCRIPTION
 
@@ -66,6 +66,11 @@ open\. Note that this is a gift to the peer -- these satoshis are
 added to the initial balance of the peer at channel start and are largely
 unrecoverable once pushed\.
 
+
+\fIclose_to\fR is a Bitcoin address to which the channel funds should be sent to
+on close\. Only valid if both peers have negotiated \fBoption_upfront_shutdown_script\fR\.
+Returns \fBclose_to\fR set to closing script iff is negotiated\.
+
 .SH RETURN VALUE
 
 On success, the \fItx\fR and \fItxid\fR of the transaction is returned, as well
@@ -74,6 +79,11 @@ as the \fIchannel_id\fR of the newly created channel\. On failure, an error
 is reported and the channel is not funded\.
 
 
+If a \fBclose_to\fR address was provided, will close to this address
+iff the \fBclose_to\fR script is returned in the response\. Otherwise,
+the peer does not support \fBoption_upfront_shutdownscript\fR\.
+
+
 The following error codes may occur:
 
 .RS
@@ -102,4 +112,4 @@ channel parameters (funding limits, channel reserves, fees, etc\.)\.
 
 Main web site: \fIhttps://github.com/ElementsProject/lightning\fR
 
-\" SHA256STAMP:f885008c6e60738b1ec9c5def19cc0877b0f9a72498ffa60e9fb3277ed9d9919
+\" SHA256STAMP:05dff04e52740da20760c2501ed7958d646750284f6a55904ca39c4ca69c46fc

doc/lightning-fundchannel.7.md

@@ -5,7 +5,7 @@ SYNOPSIS
 --------
 
 **fundchannel** *id* *amount* \[*feerate* *announce*\] \[*minconf*\]
-\[*utxos*\] \[*push_msat*\]
+\[*utxos*\] \[*push_msat*\] \[*close_to*\]
 
 DESCRIPTION
 -----------
@@ -60,6 +60,10 @@ open. Note that this is a gift to the peer -- these satoshis are
 added to the initial balance of the peer at channel start and are largely
 unrecoverable once pushed.
 
+*close_to* is a Bitcoin address to which the channel funds should be sent to
+on close. Only valid if both peers have negotiated `option_upfront_shutdown_script`.
+Returns `close_to` set to closing script iff is negotiated.
+
 RETURN VALUE
 ------------
 
@@ -68,6 +72,10 @@ as the *outnum* indicating the output index which creates the channel, as well
 as the *channel\_id* of the newly created channel. On failure, an error
 is reported and the channel is not funded.
 
+If a `close_to` address was provided, will close to this address
+iff the `close_to` script is returned in the response. Otherwise,
+the peer does not support `option_upfront_shutdownscript`.
+
 The following error codes may occur:
 - -1: Catchall nonspecific error.
 - 300: The maximum allowed funding amount is exceeded.

plugins/spender/fundchannel.c

@@ -41,6 +41,7 @@ json_fundchannel(struct command *cmd,
 	const jsmntok_t *minconf;
 	const jsmntok_t *utxos;
 	const jsmntok_t *push_msat;
+	const jsmntok_t *close_to;
 
 	struct out_req *req;
 
@@ -52,6 +53,7 @@ json_fundchannel(struct command *cmd,
 		   p_opt("minconf", param_tok, &minconf),
 		   p_opt("utxos", param_tok, &utxos),
 		   p_opt("push_msat", param_tok, &push_msat),
+		   p_opt("close_to", param_tok, &close_to),
 		   NULL))
 		return command_param_failed();
 
@@ -67,6 +69,8 @@ json_fundchannel(struct command *cmd,
 		json_add_tok(req->js, "announce", announce, buf);
 	if (push_msat)
 		json_add_tok(req->js, "push_msat", push_msat, buf);
+	if (close_to)
+		json_add_tok(req->js, "close_to", close_to, buf);
 	json_object_end(req->js);
 	json_array_end(req->js);
 	if (feerate)
@@ -92,6 +96,7 @@ fundchannel_get_result(struct command *cmd,
 	const jsmntok_t *channel_ids_obj;
 	const jsmntok_t *channel_id;
 	const jsmntok_t *outnum;
+	const jsmntok_t *close_to_script;
 
 	struct json_stream *out;
 
@@ -108,6 +113,10 @@ fundchannel_get_result(struct command *cmd,
 	ok = ok && channel_id;
 	outnum = ok ? json_get_member(buf, channel_ids_obj, "outnum") : NULL;
 	ok = ok && outnum;
+	close_to_script = ok ? json_get_member(buf, channel_ids_obj,
+					       "close_to")
+			     : NULL;
+
 
 	if (!ok)
 		plugin_err(cmd->plugin,
@@ -120,5 +129,7 @@ fundchannel_get_result(struct command *cmd,
 	json_add_tok(out, "txid", txid, buf);
 	json_add_tok(out, "channel_id", channel_id, buf);
 	json_add_tok(out, "outnum", outnum, buf);
+	if (close_to_script)
+		json_add_tok(out, "close_to", close_to_script, buf);
 	return command_finished(cmd, out);
 }