funding: add RPC arg to specify a 'close_to' address

Takes advantage of upfront-shutdown-script to permit users to
specify the close-to address for a channel at open, by adding
a `close_to` field to `fundchannel_start`.

Note that this only is in effect if `fundchannel_start` returns
with `close_to` set -- otherwise, peer doesn't
support `option_upfront_shutdown_script`.

CHANGELOG.md

@@ -16,6 +16,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - JSON API: `fundchannel_start` now includes field `scriptpubkey`
 - JSON API: New method `listtransactions`
 - JSON API: `signmessage` will now create a signature from your node on a message; `checkmessage` will verify it.
+- JSON API: `fundchannel_start` now accepts an optional parameter `close_to`, the address to which these channel funds should be sent to on close. Returns `using_close_to` if will use.
 - Plugin: new notifications `sendpay_success` and `sendpay_failure`.
 - Protocol: nodes now announce features in `node_announcement` broadcasts.
 - Protocol: we now offer `option_gossip_queries_ex` for finegrained gossip control.

contrib/pylightning/lightning/lightning.py

@@ -568,12 +568,13 @@ def fundchannel_start(self, node_id, *args, **kwargs):
         if 'satoshi' in kwargs:
             return self._deprecated_fundchannel_start(node_id, *args, **kwargs)
 
-        def _fundchannel_start(node_id, amount, feerate=None, announce=True):
+        def _fundchannel_start(node_id, amount, feerate=None, announce=True, close_to=None):
             payload = {
                 "id": node_id,
                 "amount": amount,
                 "feerate": feerate,
-                "announce": announce
+                "announce": announce,
+                "close_to": close_to,
             }
             return self.call("fundchannel_start", payload)
 

doc/lightning-fundchannel_start.7

@@ -3,7 +3,7 @@
 lightning-fundchannel_start - Command for initiating channel establishment for a lightning channel
 .SH SYNOPSIS
 
-\fBfundchannel_start\fR \fIid\fR \fIamount\fR [\fIfeerate\fR \fIannounce\fR]
+\fBfundchannel_start\fR \fIid\fR \fIamount\fR [\fIfeerate\fR \fIannounce\fR \fIclose_to\fR]
 
 .SH DESCRIPTION
 
@@ -26,6 +26,11 @@ commitment transactions\.
 \fIannounce\fR whether or not to announce this channel\.
 
 
+\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\.
+
+
 Note that the funding transaction MUST NOT be broadcast until after
 channel establishment has been successfully completed by running
 \fBfundchannel_complete\fR, as the commitment transactions for this channel
@@ -35,6 +40,8 @@ transaction before that can lead to unrecoverable loss of funds\.
 .SH RETURN VALUE
 
 On success, returns the \fIfunding_address\fR and the \fIscriptpubkey\fR for the channel funding output\.
+If a \fBclose_to\fR address was provided, will close to this address iff the \fBclose_to\fR address is
+returned in the response\. Otherwise, the peer does not support \fBoption_upfront_shutdownscript\fR\.
 
 
 On failure, returns an error\.
@@ -52,7 +59,3 @@ lightning-fundchannel_\fBcomplete\fR(7), lightning-fundchannel_\fBcancel\fR(7)
 
 Main web site: \fIhttps://github.com/ElementsProject/lightning\fR
 
-.HL
-
-Last updated 2019-06-12 11:16:20 CEST
-

doc/lightning-fundchannel_start.7.md

@@ -4,7 +4,7 @@ lightning-fundchannel\_start -- Command for initiating channel establishment for
 SYNOPSIS
 --------
 
-**fundchannel\_start** *id* *amount* \[*feerate* *announce*\]
+**fundchannel\_start** *id* *amount* \[*feerate* *announce* *close_to*\]
 
 DESCRIPTION
 -----------
@@ -23,6 +23,10 @@ commitment transactions.
 
 *announce* whether or not to announce this channel.
 
+*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.
+
 Note that the funding transaction MUST NOT be broadcast until after
 channel establishment has been successfully completed by running
 `fundchannel_complete`, as the commitment transactions for this channel
@@ -33,6 +37,8 @@ RETURN VALUE
 ------------
 
 On success, returns the *funding\_address* and the *scriptpubkey* for the channel funding output.
+If a `close_to` address was provided, will close to this address iff the `close_to` address is
+returned in the response. Otherwise, the peer does not support `option_upfront_shutdownscript`.
 
 On failure, returns an error.
 

lightningd/channel.c

@@ -170,7 +170,7 @@ struct channel *new_channel(struct peer *peer, u64 dbid,
 			    const struct channel_info *channel_info,
 			    /* NULL or stolen */
 			    u8 *remote_shutdown_scriptpubkey,
-			    u8 *local_shutdown_scriptpubkey,
+			    const u8 *local_shutdown_scriptpubkey,
 			    u64 final_key_idx,
 			    bool last_was_revoke,
 			    /* NULL or stolen */

lightningd/channel.h

@@ -89,8 +89,8 @@ struct channel {
 	/* Our funding tx pubkey. */
 	struct pubkey local_funding_pubkey;
 
-	/* Their scriptpubkey if they sent shutdown. */
-	u8 *shutdown_scriptpubkey[NUM_SIDES];
+	/* scriptpubkey for shutdown, if applicable. */
+	const u8 *shutdown_scriptpubkey[NUM_SIDES];
 	/* Address for any final outputs */
 	u64 final_key_idx;
 
@@ -157,7 +157,7 @@ struct channel *new_channel(struct peer *peer, u64 dbid,
 			    const struct channel_info *channel_info,
 			    /* NULL or stolen */
 			    u8 *remote_shutdown_scriptpubkey,
-			    u8 *local_shutdown_scriptpubkey,
+			    const u8 *local_shutdown_scriptpubkey,
 			    u64 final_key_idx,
 			    bool last_was_revoke,
 			    /* NULL or stolen */

lightningd/opening_control.c

@@ -77,6 +77,7 @@ struct funding_channel {
 	struct amount_msat push;
 	struct amount_sat funding;
 	u8 channel_flags;
+	const u8 *our_upfront_shutdown_script;
 
 	/* Variables we need to compose fields in cmd's response */
 	const char *hextx;
@@ -165,6 +166,7 @@ wallet_commit_channel(struct lightningd *ld,
 		      u8 channel_flags,
 		      struct channel_info *channel_info,
 		      u32 feerate,
+		      const u8 *our_upfront_shutdown_script,
 		      const u8 *remote_upfront_shutdown_script)
 {
 	struct channel *channel;
@@ -247,7 +249,7 @@ wallet_commit_channel(struct lightningd *ld,
 			      NULL, /* No HTLC sigs yet */
 			      channel_info,
 			      NULL, /* No shutdown_scriptpubkey[REMOTE] yet */
-			      NULL, /* No shutdown_scriptpubkey[LOCAL] yet. Generate the default one. */
+			      our_upfront_shutdown_script,
 			      final_key_idx, false,
 			      NULL, /* No commit sent yet */
 			      /* If we're fundee, could be a little before this
@@ -290,7 +292,8 @@ static void funding_success(struct channel *channel)
 }
 
 static void funding_started_success(struct funding_channel *fc,
-				    u8 *scriptPubkey)
+				    u8 *scriptPubkey,
+				    bool supports_shutdown)
 {
 	struct json_stream *response;
 	struct command *cmd = fc->cmd;
@@ -303,6 +306,8 @@ static void funding_started_success(struct funding_channel *fc,
 	if (out) {
 		json_add_string(response, "funding_address", out);
 		json_add_hex_talarr(response, "scriptpubkey", scriptPubkey);
+		if (fc->our_upfront_shutdown_script)
+			json_add_hex_talarr(response, "close_to", fc->our_upfront_shutdown_script);
 	}
 
 	/* Clear this so cancel doesn't think it's still in progress */
@@ -315,9 +320,11 @@ static void opening_funder_start_replied(struct subd *openingd, const u8 *resp,
 					 struct funding_channel *fc)
 {
 	u8 *funding_scriptPubkey;
+	bool supports_shutdown_script;
 
 	if (!fromwire_opening_funder_start_reply(resp, resp,
-						 &funding_scriptPubkey)) {
+						 &funding_scriptPubkey,
+						 &supports_shutdown_script)) {
 		log_broken(fc->uc->log,
 			   "bad OPENING_FUNDER_REPLY %s",
 			   tal_hex(resp, resp));
@@ -327,7 +334,12 @@ static void opening_funder_start_replied(struct subd *openingd, const u8 *resp,
 		goto failed;
 	}
 
-	funding_started_success(fc, funding_scriptPubkey);
+	/* If we're not using the upfront shutdown script, forget it */
+	if (!supports_shutdown_script)
+		fc->our_upfront_shutdown_script =
+			tal_free(fc->our_upfront_shutdown_script);
+
+	funding_started_success(fc, funding_scriptPubkey, supports_shutdown_script);
 
 	/* Mark that we're in-flight */
 	fc->inflight = true;
@@ -401,6 +413,7 @@ static void opening_funder_finished(struct subd *openingd, const u8 *resp,
 					fc->channel_flags,
 					&channel_info,
 					feerate,
+					fc->our_upfront_shutdown_script,
 					remote_upfront_shutdown_script);
 	if (!channel) {
 		was_pending(command_fail(fc->cmd, LIGHTNINGD,
@@ -496,6 +509,7 @@ static void opening_fundee_finished(struct subd *openingd,
 					channel_flags,
 					&channel_info,
 					feerate,
+					NULL,
 					remote_upfront_shutdown_script);
 	if (!channel) {
 		uncommitted_channel_disconnect(uc, "Commit channel failed");
@@ -1078,6 +1092,7 @@ static struct command_result *json_fund_channel_start(struct command *cmd,
 			   p_req("amount", param_sat, &amount),
 			   p_opt("feerate", param_feerate, &feerate_per_kw),
 			   p_opt_def("announce", param_bool, &announce_channel, true),
+			   p_opt("close_to", param_bitcoin_address, &fc->our_upfront_shutdown_script),
 			   NULL))
 			return command_param_failed();
 	} else {
@@ -1101,6 +1116,9 @@ static struct command_result *json_fund_channel_start(struct command *cmd,
 				return command_fail(cmd, JSONRPC2_INVALID_PARAMS,
 						    "Need set 'amount' field");
 		}
+
+		/* No upfront shutdown script option for deprecated API */
+		fc->our_upfront_shutdown_script = NULL;
 	}
 
 	if (amount_sat_greater(*amount, max_funding_satoshi))
@@ -1161,9 +1179,15 @@ static struct command_result *json_fund_channel_start(struct command *cmd,
 	peer->uncommitted_channel->fc = tal_steal(peer->uncommitted_channel, fc);
 	fc->uc = peer->uncommitted_channel;
 
+	/* Needs to be stolen away from cmd */
+	if (fc->our_upfront_shutdown_script)
+		fc->our_upfront_shutdown_script
+			= tal_steal(fc, fc->our_upfront_shutdown_script);
+
 	msg = towire_opening_funder_start(NULL,
 					  *amount,
 					  fc->push,
+					  fc->our_upfront_shutdown_script,
 					  *feerate_per_kw,
 					  fc->channel_flags);