offers: modify find_best_peer() to only select from fronting nodes if set.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

Author: rustyrussell

plugins/offers.c

@@ -316,9 +316,20 @@ struct find_best_peer_data {
 				     const struct chaninfo *,
 				     void *);
 	int needed_feature;
+	const struct pubkey *fronting_only;
 	void *arg;
 };
 
+static bool is_in_pubkeys(const struct pubkey *pubkeys,
+			  const struct pubkey *k)
+{
+	for (size_t i = 0; i < tal_count(pubkeys); i++) {
+		if (pubkey_eq(&pubkeys[i], k))
+			return true;
+	}
+	return false;
+}
+
 static struct command_result *listincoming_done(struct command *cmd,
 						const char *method,
 						const char *buf,
@@ -363,6 +374,18 @@ static struct command_result *listincoming_done(struct command *cmd,
 		}
 		ci.feebase = feebase.millisatoshis; /* Raw: feebase */
 
+		if (data->fronting_only) {
+			if (!is_in_pubkeys(data->fronting_only, &ci.id))
+				continue;
+
+			/* If disconnected, don't eliminate, simply
+			 * consider it last. */
+			if (!enabled) {
+				ci.capacity = AMOUNT_MSAT(0);
+				enabled = true;
+			}
+		}
+
 		/* Don't pick a peer which is disconnected */
 		if (!enabled)
 			continue;
@@ -388,6 +411,7 @@ static struct command_result *listincoming_done(struct command *cmd,
 
 struct command_result *find_best_peer_(struct command *cmd,
 				       int needed_feature,
+				       const struct pubkey *fronting_only,
 				       struct command_result *(*cb)(struct command *,
 								    const struct chaninfo *,
 								    void *),
@@ -398,6 +422,7 @@ struct command_result *find_best_peer_(struct command *cmd,
 	data->cb = cb;
 	data->arg = arg;
 	data->needed_feature = needed_feature;
+	data->fronting_only = fronting_only;
 	req = jsonrpc_request_start(cmd, "listincoming",
 				    listincoming_done, forward_error, data);
 	return send_outreq(req);

plugins/offers.h

@@ -86,13 +86,14 @@ struct chaninfo {
 /* Calls listpeerchannels, then cb with best peer (if any!) which has needed_feature */
 struct command_result *find_best_peer_(struct command *cmd,
 				       int needed_feature,
+				       const struct pubkey *fronting_only,
 				       struct command_result *(*cb)(struct command *,
 								    const struct chaninfo *,
 								    void *),
 				       void *arg);
 
-#define find_best_peer(cmd, needed_feature, cb, arg)			\
-	find_best_peer_((cmd), (needed_feature),			\
+#define find_best_peer(cmd, needed_feature, fronting_only, cb, arg)	\
+	find_best_peer_((cmd), (needed_feature), (fronting_only),	\
 			typesafe_cb_preargs(struct command_result *, void *, \
 					    (cb), (arg),		\
 					    struct command *,		\

plugins/offers_invreq_hook.c

@@ -390,7 +390,7 @@ static struct command_result *add_blindedpaths(struct command *cmd,
 	if (!we_want_blinded_path(cmd->plugin, true))
 		return create_invoicereq(cmd, ir);
 
-	return find_best_peer(cmd, OPT_ROUTE_BLINDING,
+	return find_best_peer(cmd, OPT_ROUTE_BLINDING, NULL,
 			      found_best_peer, ir);
 }
 

plugins/offers_offer.c

@@ -343,6 +343,7 @@ static struct command_result *maybe_add_path(struct command *cmd,
 							     tal_count(od->fronting_nodes));
 			} else {
 				return find_best_peer(cmd, OPT_ONION_MESSAGES,
+						      NULL,
 						      found_best_peer, offinfo);
 			}
 		}
@@ -776,7 +777,7 @@ struct command_result *json_invoicerequest(struct command *cmd,
 		idata->invreq = invreq;
 		idata->single_use = *single_use;
 		idata->label = label;
-		return find_best_peer(cmd, OPT_ONION_MESSAGES,
+		return find_best_peer(cmd, OPT_ONION_MESSAGES, NULL,
 				      found_best_peer_invrequest, idata);
 	}