offers: handle scid in blinded reply path first_node_id field.

Signed-off-by: Rusty Russell <[email protected]>
Changelog-EXPERIMENTAL: offers: we now understand blinded paths which use a short-channel-id(+direction) as entry point.

plugins/Makefile

@@ -211,7 +211,7 @@ $(PLUGIN_KEYSEND_OBJS): $(PLUGIN_PAY_LIB_HEADER)
 
 plugins/spenderp: bitcoin/block.o bitcoin/preimage.o bitcoin/psbt.o common/psbt_open.o common/json_channel_type.o common/channel_type.o common/features.o wire/peer_wiregen.o $(PLUGIN_SPENDER_OBJS) $(PLUGIN_LIB_OBJS) $(PLUGIN_COMMON_OBJS) $(JSMN_OBJS)
 
-plugins/offers: $(PLUGIN_OFFERS_OBJS) $(PLUGIN_LIB_OBJS) $(PLUGIN_COMMON_OBJS) common/addr.o common/bolt12.o common/bolt12_merkle.o common/bolt11_json.o common/iso4217.o $(WIRE_OBJS) $(WIRE_BOLT12_OBJS) bitcoin/block.o common/channel_id.o bitcoin/preimage.o common/blindedpath.o common/invoice_path_id.o common/blinding.o common/hmac.o common/json_blinded_path.o $(JSMN_OBJS)
+plugins/offers: $(PLUGIN_OFFERS_OBJS) $(PLUGIN_LIB_OBJS) $(PLUGIN_COMMON_OBJS) common/addr.o common/bolt12.o common/bolt12_merkle.o common/bolt11_json.o common/iso4217.o $(WIRE_OBJS) $(WIRE_BOLT12_OBJS) bitcoin/block.o common/channel_id.o bitcoin/preimage.o common/blindedpath.o common/invoice_path_id.o common/blinding.o common/hmac.o common/json_blinded_path.o common/gossmap.o common/fp16.o $(JSMN_OBJS)
 
 plugins/fetchinvoice: $(PLUGIN_FETCHINVOICE_OBJS) $(PLUGIN_LIB_OBJS) $(PLUGIN_COMMON_OBJS) common/bolt12.o common/bolt12_merkle.o common/iso4217.o $(WIRE_OBJS) $(WIRE_BOLT12_OBJS) bitcoin/block.o common/channel_id.o bitcoin/preimage.o $(JSMN_OBJS) common/gossmap.o common/fp16.o common/dijkstra.o common/route.o common/blindedpath.o common/hmac.o common/blinding.o common/gossmods_listpeerchannels.o
 

plugins/fetchinvoice.c

@@ -38,6 +38,9 @@ struct sent {
 	/* Path to use (including self) */
 	struct pubkey *path;
 
+	/* When creating blinded return path, use scid not pubkey for intro node. */
+	struct short_channel_id_dir *dev_path_use_scidd;
+
 	/* The invreq we sent, OR the invoice we sent */
 	struct tlv_invoice_request *invreq;
 
@@ -597,6 +600,7 @@ send_modern_message(struct command *cmd,
 static struct blinded_path *blinded_path(const tal_t *ctx,
 					 struct command *cmd,
 					 const struct pubkey *ids,
+					 const struct short_channel_id_dir *first_scidd,
 					 const struct secret *pathsecret)
 {
 	struct privkey first_blinding, blinding_iter;
@@ -608,7 +612,10 @@ static struct blinded_path *blinded_path(const tal_t *ctx,
 	nhops = tal_count(ids);
 
 	assert(nhops > 0);
-	sciddir_or_pubkey_from_pubkey(&path->first_node_id, &ids[0]);
+	if (first_scidd)
+		sciddir_or_pubkey_from_scidd(&path->first_node_id, first_scidd);
+	else
+		sciddir_or_pubkey_from_pubkey(&path->first_node_id, &ids[0]);
 	assert(pubkey_eq(&ids[nhops-1], &local_id));
 
 	randombytes_buf(&first_blinding, sizeof(first_blinding));
@@ -673,7 +680,8 @@ static struct command_result *make_reply_path(struct command *cmd,
 	for (int i = nhops - 2; i >= 0; i--)
 		ids[nhops - 2 - i] = sending->sent->path[i];
 
-	rpath = blinded_path(cmd, cmd, ids, sending->sent->reply_secret);
+	rpath = blinded_path(cmd, cmd, ids, sending->sent->dev_path_use_scidd,
+			     sending->sent->reply_secret);
 	return send_modern_message(cmd, rpath, sending);
 }
 
@@ -927,6 +935,22 @@ static struct command_result *invreq_done(struct command *cmd,
 	return send_outreq(cmd->plugin, req);
 }
 
+static struct command_result *param_dev_scidd(struct command *cmd, const char *name,
+					      const char *buffer, const jsmntok_t *tok,
+					      struct short_channel_id_dir **scidd)
+{
+	if (!plugin_developer_mode(cmd->plugin))
+		return command_fail_badparam(cmd, name, buffer, tok,
+					     "not available outside --developer mode");
+
+	*scidd = tal(cmd, struct short_channel_id_dir);
+	if (short_channel_id_dir_from_str(buffer + tok->start, tok->end - tok->start, *scidd))
+		return NULL;
+
+	return command_fail_badparam(cmd, name, buffer, tok,
+				     "should be a short_channel_id of form NxNxN/dir");
+}
+
 /* Fetches an invoice for this offer, and makes sure it corresponds. */
 static struct command_result *json_fetchinvoice(struct command *cmd,
 						const char *buffer,
@@ -950,6 +974,7 @@ static struct command_result *json_fetchinvoice(struct command *cmd,
 		   p_opt("recurrence_label", param_string, &rec_label),
 		   p_opt_def("timeout", param_number, &timeout, 60),
 		   p_opt("payer_note", param_string, &payer_note),
+		   p_opt("dev_path_use_scidd", param_dev_scidd, &sent->dev_path_use_scidd),
 		   NULL))
 		return command_param_failed();
 

plugins/offers.c

@@ -10,11 +10,14 @@
 #include <common/bolt11.h>
 #include <common/bolt11_json.h>
 #include <common/bolt12_merkle.h>
+#include <common/gossmap.h>
 #include <common/invoice_path_id.h>
 #include <common/iso4217.h>
 #include <common/json_blinded_path.h>
 #include <common/json_param.h>
 #include <common/json_stream.h>
+#include <common/memleak.h>
+#include <errno.h>
 #include <plugins/offers.h>
 #include <plugins/offers_inv_hook.h>
 #include <plugins/offers_invreq_hook.h>
@@ -29,6 +32,32 @@ u32 blockheight;
 u16 cltv_final;
 bool offers_enabled;
 struct secret invoicesecret_base;
+static struct gossmap *global_gossmap;
+
+static void init_gossmap(struct plugin *plugin)
+{
+	size_t num_cupdates_rejected;
+	global_gossmap
+		= notleak_with_children(gossmap_load(plugin,
+						     GOSSIP_STORE_FILENAME,
+						     &num_cupdates_rejected));
+	if (!global_gossmap)
+		plugin_err(plugin, "Could not load gossmap %s: %s",
+			   GOSSIP_STORE_FILENAME, strerror(errno));
+	if (num_cupdates_rejected)
+		plugin_log(plugin, LOG_DBG,
+			   "gossmap ignored %zu channel updates",
+			   num_cupdates_rejected);
+}
+
+static struct gossmap *get_gossmap(struct plugin *plugin)
+{
+	if (!global_gossmap)
+		init_gossmap(plugin);
+	else
+		gossmap_refresh(global_gossmap, NULL);
+	return global_gossmap;
+}
 
 static struct command_result *finished(struct command *cmd,
 				       const char *buf,
@@ -52,6 +81,32 @@ static struct command_result *sendonionmessage_error(struct command *cmd,
 	return command_hook_success(cmd);
 }
 
+/* So, you gave us a reply scid?  Let's do the lookup then!  And no,
+ * we won't accept private channels, just public ones.
+ */
+static bool convert_to_scidd(struct command *cmd,
+			     struct sciddir_or_pubkey *sciddpk)
+{
+	struct gossmap *gossmap = get_gossmap(cmd->plugin);
+	struct gossmap_chan *chan;
+	struct gossmap_node *node;
+	struct node_id id;
+
+	chan = gossmap_find_chan(gossmap, &sciddpk->scidd.scid);
+	if (!chan)
+		return false;
+
+	node = gossmap_nth_node(gossmap, chan, sciddpk->scidd.dir);
+	gossmap_node_get_id(gossmap, node, &id);
+	if (!sciddir_or_pubkey_from_node_id(sciddpk, &id)) {
+		plugin_log(cmd->plugin, LOG_BROKEN,
+			   "Could not convert node %s to pubkey?",
+			   fmt_node_id(tmpctx, &id));
+		return false;
+	}
+	return true;
+}
+
 struct command_result *
 send_onion_reply(struct command *cmd,
 		 struct blinded_path *reply_path,
@@ -60,6 +115,13 @@ send_onion_reply(struct command *cmd,
 	struct out_req *req;
 	size_t nhops;
 
+	if (!reply_path->first_node_id.is_pubkey
+	    && !convert_to_scidd(cmd, &reply_path->first_node_id)) {
+		plugin_log(cmd->plugin, LOG_INFORM, "Unknown reply scid %s: cannot send reply",
+			   fmt_short_channel_id_dir(tmpctx, &reply_path->first_node_id.scidd));
+		return command_hook_success(cmd);
+	}
+
 	req = jsonrpc_request_start(cmd->plugin, cmd, "sendonionmessage",
 				    finished, sendonionmessage_error, NULL);
 
@@ -111,13 +173,6 @@ static struct command_result *onion_message_modern_call(struct command *cmd,
 			plugin_err(cmd->plugin, "Invalid reply path %.*s?",
 				   json_tok_full_len(replytok),
 				   json_tok_full(buf, replytok));
-
-		/* FIXME: support this! */
-		if (!reply_path->first_node_id.is_pubkey) {
-			plugin_log(cmd->plugin, LOG_DBG,
-				   "reply_blindedpath uses scid");
-			return command_hook_success(cmd);
-		}
 	}
 
 	invreqtok = json_get_member(buf, om, "invoice_request");

tests/test_pay.py

@@ -5588,3 +5588,16 @@ def test_pay_partial_msat(node_factory, executor):
 
     l1pay.result(TIMEOUT)
     l3pay.result(TIMEOUT)
+
+
+def test_blinded_reply_path_scid(node_factory):
+    """Check that we handle a blinded path which begins with a scid instead of a nodeid"""
+    l1, l2 = node_factory.line_graph(2, wait_for_announce=True,
+                                     opts={'experimental-offers': None})
+    offer = l2.rpc.offer(amount='2msat', description='test_blinded_reply_path_scid')
+
+    chan = only_one(l1.rpc.listpeerchannels()['channels'])
+    scidd = "{}/{}".format(chan['short_channel_id'], chan['direction'])
+    inv = l1.rpc.fetchinvoice(offer=offer['bolt12'], dev_path_use_scidd=scidd)['invoice']
+
+    l1.rpc.pay(inv)