Configuration option to specify "fronting nodes" for routehints/blinded paths.

doc/lightningd-config.5.md

@@ -530,6 +530,10 @@ delete the others.
 
 ### Payment and invoice control options:
 
+* **payment-fronting-node**=*nodeid*
+
+  Always use this *nodeid* as the entry point when we generate invoices or offers.  For BOLT11 invoices, this node must be a neighbor: we will use a routehint with the alias for the short channel id to provide limited privacy (we still reveal our node id).  For BOLT12 invoices and offers , we provide a blinded path from the node to us, to provide better privacy.
+
 * **disable-mpp** [plugin `pay`]
 
   Disable the multi-part payment sending support in the `pay` plugin. By default

lightningd/invoice.c

@@ -662,6 +662,25 @@ static struct route_info **select_inchan_mpp(const tal_t *ctx,
 	return routehints;
 }
 
+static struct route_info **select_inchan_all(const tal_t *ctx,
+					     struct lightningd *ld,
+					     struct routehint_candidate
+					     *candidates)
+{
+	struct route_info **routehints;
+
+	log_debug(ld->log, "Selecting all %zu candidates",
+		  tal_count(candidates));
+
+	routehints = tal_arr(ctx, struct route_info *, tal_count(candidates));
+	for (size_t i = 0; i < tal_count(candidates); i++) {
+		routehints[i] = tal_dup(routehints, struct route_info,
+					candidates[i].r);
+	}
+
+	return routehints;
+}
+
 /* Encapsulating struct while we wait for gossipd to give us incoming channels */
 struct chanhints {
 	bool expose_all_private;
@@ -723,6 +742,10 @@ add_routehints(struct invoice_info *info,
 
 	needed = info->b11->msat ? *info->b11->msat : AMOUNT_MSAT(1);
 
+	/* --payment-fronting-node means use all candidates. */
+	if (tal_count(info->cmd->ld->fronting_nodes))
+		info->b11->routes = select_inchan_all(info->b11, info->cmd->ld, candidates);
+
 	/* If we are not completely unpublished, try with reservoir
 	 * sampling first.
 	 *
@@ -738,7 +761,7 @@ add_routehints(struct invoice_info *info,
 	 * should make an effort to avoid overlapping incoming
 	 * channels, which is done by select_inchan_mpp.
 	 */
-	if (!node_unpublished)
+	else if (!node_unpublished)
 		info->b11->routes = select_inchan(info->b11,
 						  info->cmd->ld,
 						  needed,

lightningd/lightningd.c

@@ -378,6 +378,7 @@ static struct lightningd *new_lightningd(const tal_t *ctx)
 	/* The gossip seeker automatically connects to a this many peers */
 	ld->autoconnect_seeker_peers = 10;
 
+	ld->fronting_nodes = tal_arr(ld, struct node_id, 0);
 	return ld;
 }
 

lightningd/lightningd.h

@@ -426,6 +426,9 @@ struct lightningd {
 
 	/* Minimum number of peers seeker should maintain. */
 	u32 autoconnect_seeker_peers;
+
+	/* Nodes to use for invoices / offers */
+	struct node_id *fronting_nodes;
 };
 
 /* Turning this on allows a tal allocation to return NULL, rather than aborting.

lightningd/options.c

@@ -1278,6 +1278,16 @@ static char *opt_add_api_beg(const char *arg, struct lightningd *ld)
 	return NULL;
 }
 
+static char *opt_add_node_id(const char *arg, struct node_id **arr)
+{
+	struct node_id n;
+	if (!node_id_from_hexstr(arg, strlen(arg), &n))
+		return "Unparsable nodeid";
+
+	tal_arr_expand(arr, n);
+	return NULL;
+}
+
 char *hsm_secret_arg(const tal_t *ctx,
 		     const char *arg,
 		     const u8 **hsm_secret)
@@ -1598,6 +1608,10 @@ static void register_opts(struct lightningd *ld)
 		       ld,
 		       "Re-enable a long-deprecated API (which will be removed entirely next version!)");
 	opt_register_logging(ld);
+	clnopt_witharg("--payment-fronting-node",
+		       OPT_MULTI,
+		       opt_add_node_id, NULL,
+		       &ld->fronting_nodes, "Put this node in all invoices and offers, and use blinded path (bolt12) or route hints (bolt11) to route to this node.  Must be a neighboring node.  Can be specified multiple times.");
 
 	dev_register_opts(ld);
 }
@@ -1854,6 +1868,7 @@ bool is_known_opt_cb_arg(char *(*cb_arg)(const char *, void *))
 		|| cb_arg == (void *)opt_subd_dev_disconnect
 		|| cb_arg == (void *)opt_set_crash_timeout
 		|| cb_arg == (void *)opt_add_api_beg
+		|| cb_arg == (void *)opt_add_node_id
 		|| cb_arg == (void *)opt_force_featureset
 		|| cb_arg == (void *)opt_force_privkey
 		|| cb_arg == (void *)opt_force_bip32_seed

lightningd/plugin.c

@@ -2124,12 +2124,8 @@ void plugins_init(struct plugins *plugins)
 	setenv("LIGHTNINGD_PLUGIN", "1", 1);
 	setenv("LIGHTNINGD_VERSION", version(), 1);
 
-	if (plugins_send_getmanifest(plugins, NULL)) {
-		void *ret;
-		ret = io_loop_with_timers(plugins->ld);
-		log_debug(plugins->ld->log, "io_loop_with_timers: %s", __func__);
-		assert(ret == plugins);
-	}
+	if (plugins_send_getmanifest(plugins, NULL))
+		io_loop_with_timers(plugins->ld);
 }
 
 static void plugin_config_cb(const char *buffer,

lightningd/routehint.c

@@ -17,6 +17,16 @@ static bool scid_in_arr(const struct short_channel_id *scidarr,
 	return false;
 }
 
+static bool is_fronting_node(const struct lightningd *ld,
+			     const struct node_id *node)
+{
+	for (size_t i = 0; i < tal_count(ld->fronting_nodes); i++) {
+		if (node_id_eq(&ld->fronting_nodes[i], node))
+			return true;
+	}
+	return false;
+}
+
 struct routehint_candidate *
 routehint_candidates(const tal_t *ctx,
 		     struct lightningd *ld,
@@ -62,7 +72,7 @@ routehint_candidates(const tal_t *ctx,
 		struct routehint_candidate candidate;
 		struct amount_msat fee_base, htlc_max;
 		struct route_info *r;
-		bool is_public;
+		bool is_public, is_fronting;
 
 		r = tal(tmpctx, struct route_info);
 
@@ -92,6 +102,17 @@ routehint_candidates(const tal_t *ctx,
 			      json_tok_full(buf, toks));
 		}
 
+		/* If they specify fronting nodes, always use them. */
+		if (tal_count(ld->fronting_nodes)) {
+			if (!is_fronting_node(ld, &r->pubkey)) {
+				log_debug(ld->log, "%s: not a fronting node",
+					  fmt_node_id(tmpctx, &r->pubkey));
+				continue;
+			}
+			is_fronting = true;
+		} else
+			is_fronting = false;
+
 		/* Note: listincoming returns real scid or local alias if no real scid. */
 		candidate.c = any_channel_by_scid(ld, r->short_channel_id, true);
 		if (!candidate.c) {
@@ -133,6 +154,10 @@ routehint_candidates(const tal_t *ctx,
 		if (expose_all_private != NULL && *expose_all_private)
 			is_public = true;
 
+		/* Also, consider fronting nodes public */
+		if (is_fronting)
+			is_public = true;
+
 		r->fee_base_msat = fee_base.millisatoshis; /* Raw: route_info */
 		/* Could wrap: if so ignore */
 		if (!amount_msat_eq(amount_msat(r->fee_base_msat), fee_base)) {
@@ -156,7 +181,7 @@ routehint_candidates(const tal_t *ctx,
 				continue;
 			}
 			/* If they give us a hint, we use even if capacity 0 */
-		} else if (amount_msat_is_zero(capacity)) {
+		} else if (!is_fronting && amount_msat_is_zero(capacity)) {
 			log_debug(ld->log, "%s: deadend",
 				  fmt_short_channel_id(tmpctx,
 						       r->short_channel_id));
@@ -166,8 +191,8 @@ routehint_candidates(const tal_t *ctx,
 			continue;
 		}
 
-		/* Is it offline? */
-		if (candidate.c->owner == NULL) {
+		/* Is it offline?  Leave it if it's fronting. */
+		if (!is_fronting && candidate.c->owner == NULL) {
 			log_debug(ld->log, "%s: offline",
 				  fmt_short_channel_id(tmpctx,
 						       r->short_channel_id));

plugins/fetchinvoice.c

@@ -576,6 +576,7 @@ static struct command_result *establish_path_fail(struct command *cmd,
 static struct command_result *try_establish(struct command *cmd,
 					    struct establishing_paths *epaths)
 {
+	const struct offers_data *od = get_offers_data(cmd->plugin);
 	struct pubkey target;
 
 	if (epaths->sent->direct_dest) {
@@ -596,8 +597,8 @@ static struct command_result *try_establish(struct command *cmd,
 			epaths->sent->issuer_key = &bpath->path[tal_count(bpath->path)-1]->blinded_node_id;
 	}
 
-	return establish_onion_path(cmd, get_gossmap(cmd->plugin), &id, &target,
-				    disable_connect,
+	return establish_onion_path(cmd, get_gossmap(cmd->plugin), &od->id, &target,
+				    od->disable_connect,
 				    establish_path_done,
 				    establish_path_fail,
 				    epaths);
@@ -799,15 +800,16 @@ static struct command_result *param_dev_reply_path(struct command *cmd, const ch
 	return NULL;
 }
 
-static bool payer_key(const u8 *public_tweak, size_t public_tweak_len,
+static bool payer_key(const struct offers_data *od,
+		      const u8 *public_tweak, size_t public_tweak_len,
 		      struct pubkey *key)
 {
 	struct sha256 tweakhash;
 
-	bolt12_alias_tweak(&nodealias_base, public_tweak, public_tweak_len,
+	bolt12_alias_tweak(&od->nodealias_base, public_tweak, public_tweak_len,
 			   &tweakhash);
 
-	*key = id;
+	*key = od->id;
 	return secp256k1_ec_pubkey_tweak_add(secp256k1_ctx,
 					     &key->pubkey,
 					     tweakhash.u.u8) == 1;
@@ -818,6 +820,7 @@ struct command_result *json_fetchinvoice(struct command *cmd,
 					 const char *buffer,
 					 const jsmntok_t *params)
 {
+	const struct offers_data *od = get_offers_data(cmd->plugin);
 	struct amount_msat *msat;
 	const char *rec_label, *payer_note;
 	u8 *payer_metadata;
@@ -988,7 +991,7 @@ struct command_result *json_fetchinvoice(struct command *cmd,
 		       rec_label,
 		       strlen(rec_label));
 
-		bolt12_alias_tweak(&nodealias_base,
+		bolt12_alias_tweak(&od->nodealias_base,
 				   tweak_input,
 				   tal_bytelen(tweak_input),
 				   &tweak);
@@ -1054,7 +1057,7 @@ struct command_result *json_fetchinvoice(struct command *cmd,
 
 	/* We derive transient payer_id from invreq_metadata */
 	invreq->invreq_payer_id = tal(invreq, struct pubkey);
-	if (!payer_key(invreq->invreq_metadata,
+	if (!payer_key(od, invreq->invreq_metadata,
 		       tal_bytelen(invreq->invreq_metadata),
 		       invreq->invreq_payer_id)) {
 		/* Doesn't happen! */
@@ -1345,6 +1348,7 @@ struct command_result *json_sendinvoice(struct command *cmd,
 					const char *buffer,
 					const jsmntok_t *params)
 {
+	const struct offers_data *od = get_offers_data(cmd->plugin);
 	struct amount_msat *msat;
 	u32 *timeout;
 	struct sent *sent = tal(cmd, struct sent);
@@ -1417,7 +1421,7 @@ struct command_result *json_sendinvoice(struct command *cmd,
 	 *   - MUST set `invoice_node_id` to the final `blinded_node_id` on the path it received the invoice request
 	 */
 	sent->inv->invoice_node_id = tal(sent->inv, struct pubkey);
-	sent->inv->invoice_node_id->pubkey = id.pubkey;
+	sent->inv->invoice_node_id->pubkey = od->id.pubkey;
 
 	/* BOLT #12:
 	 * - if the expiry for accepting payment is not 7200 seconds

plugins/libplugin.c

@@ -62,6 +62,8 @@ struct plugin_option {
 	const char *depr_start, *depr_end;
 	/* If true, allow setting after plugin has initialized */
 	bool dynamic;
+	/* If true, allow multiple settings. */
+	bool multi;
 };
 
 struct plugin {
@@ -1262,6 +1264,7 @@ handle_getmanifest(struct command *getmanifest_cmd,
 		json_add_string(params, "description", p->opts[i].description);
 		json_add_deprecated(params, "deprecated", p->opts[i].depr_start, p->opts[i].depr_end);
 		json_add_bool(params, "dynamic", p->opts[i].dynamic);
+		json_add_bool(params, "multi", p->opts[i].multi);
 		if (p->opts[i].jsonfmt)
 			p->opts[i].jsonfmt(p, params, "default", p->opts[i].arg);
 		json_object_end(params);
@@ -1598,9 +1601,19 @@ static struct command_result *handle_init(struct command *cmd,
 		if (!popt)
 			plugin_err(p, "lightningd specified unknown option '%s'?", name);
 
-		problem = popt->handle(p, json_strdup(tmpctx, buf, t+1), false, popt->arg);
-		if (problem)
-			plugin_err(p, "option '%s': %s", popt->name, problem);
+		if (popt->multi) {
+			size_t j;
+			const jsmntok_t *opt;
+			json_for_each_arr(j, opt, t+1) {
+				problem = popt->handle(p, json_strdup(tmpctx, buf, opt), false, popt->arg);
+				if (problem)
+					plugin_err(p, "option '%s': %s", popt->name, problem);
+			}
+		} else {
+			problem = popt->handle(p, json_strdup(tmpctx, buf, t+1), false, popt->arg);
+			if (problem)
+				plugin_err(p, "option '%s': %s", popt->name, problem);
+		}
 	}
 
 	if (p->init) {
@@ -2449,6 +2462,7 @@ static struct plugin *new_plugin(const tal_t *ctx,
 		o.depr_start = va_arg(ap, const char *);
 		o.depr_end = va_arg(ap, const char *);
 		o.dynamic = va_arg(ap, int); /* bool gets promoted! */
+		o.multi = va_arg(ap, int); /* bool gets promoted! */
 		tal_arr_expand(&p->opts, o);
 	}
 

plugins/libplugin.h

@@ -577,7 +577,7 @@ void *plugin_get_data_(struct plugin *plugin);
 #define plugin_get_data(plugin, type) ((type *)(plugin_get_data_(plugin)))
 
 /* Macro to define arguments */
-#define plugin_option_(name, type, description, set, jsonfmt, arg, dev_only, depr_start, depr_end, dynamic) \
+#define plugin_option_(name, type, description, set, jsonfmt, arg, dev_only, depr_start, depr_end, dynamic, multi) \
 	(name),								\
 	(type),								\
 	(description),							\
@@ -594,23 +594,27 @@ void *plugin_get_data_(struct plugin *plugin);
 	(dev_only),							\
 	(depr_start),							\
 	(depr_end),							\
-	(dynamic)
+	(dynamic),							\
+	(multi)
 
 /* jsonfmt can be NULL, but then default won't be printed */
 #define plugin_option(name, type, description, set, jsonfmt, arg)	\
-	plugin_option_((name), (type), (description), (set), (jsonfmt), (arg), false, NULL, NULL, false)
+	plugin_option_((name), (type), (description), (set), (jsonfmt), (arg), false, NULL, NULL, false, false)
 
 #define plugin_option_dev(name, type, description, set, jsonfmt, arg)	\
-	plugin_option_((name), (type), (description), (set), (jsonfmt), (arg), true, NULL, NULL, false)
+	plugin_option_((name), (type), (description), (set), (jsonfmt), (arg), true, NULL, NULL, false, false)
 
 #define plugin_option_dev_dynamic(name, type, description, set, jsonfmt, arg) \
-	plugin_option_((name), (type), (description), (set), (jsonfmt), (arg), true, NULL, NULL, true)
+	plugin_option_((name), (type), (description), (set), (jsonfmt), (arg), true, NULL, NULL, true, false)
 
 #define plugin_option_dynamic(name, type, description, set, jsonfmt, arg) \
-	plugin_option_((name), (type), (description), (set), (jsonfmt), (arg), false, NULL, NULL, true)
+	plugin_option_((name), (type), (description), (set), (jsonfmt), (arg), false, NULL, NULL, true, false)
 
 #define plugin_option_deprecated(name, type, description, depr_start, depr_end, set, jsonfmt, arg) \
-	plugin_option_((name), (type), (description), (set), (jsonfmt), (arg), false, (depr_start), (depr_end), false)
+	plugin_option_((name), (type), (description), (set), (jsonfmt), (arg), false, (depr_start), (depr_end), false, false)
+
+#define plugin_option_multi(name, type, description, set, jsonfmt, arg)	\
+	plugin_option_((name), (type), (description), (set), (jsonfmt), (arg), false, NULL, NULL, false, true)
 
 /* Standard helpers */
 char *u64_option(struct plugin *plugin, const char *arg, bool check_only, u64 *i);