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

@@ -318,9 +318,20 @@ struct find_best_peer_data {
 				     const struct chaninfo *,
 				     void *);
 	u64 needed_features;
+	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,
@@ -366,6 +377,18 @@ 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;
@@ -400,6 +423,7 @@ static struct command_result *listincoming_done(struct command *cmd,
 
 struct command_result *find_best_peer_(struct command *cmd,
 				       u64 needed_features,
+				       const struct pubkey *fronting_only,
 				       struct command_result *(*cb)(struct command *,
 								    const struct chaninfo *,
 								    void *),
@@ -410,6 +434,7 @@ struct command_result *find_best_peer_(struct command *cmd,
 	data->cb = cb;
 	data->arg = arg;
 	data->needed_features = needed_features;
+	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,
 				       u64 needed_features,
+				       const struct pubkey *fronting_only,
 				       struct command_result *(*cb)(struct command *,
 								    const struct chaninfo *,
 								    void *),
 				       void *arg);
 
-#define find_best_peer(cmd, needed_features, cb, arg)			\
-	find_best_peer_((cmd), (needed_features),			\
+#define find_best_peer(cmd, needed_features, fronting_only, cb, arg)	\
+	find_best_peer_((cmd), (needed_features), (fronting_only),	\
 			typesafe_cb_preargs(struct command_result *, void *, \
 					    (cb), (arg),		\
 					    struct command *,		\

plugins/offers_invreq_hook.c

@@ -393,7 +393,7 @@ static struct command_result *add_blindedpaths(struct command *cmd,
 	 * us onion messaging. */
 	return find_best_peer(cmd,
 			      (1ULL << OPT_ROUTE_BLINDING) | (1ULL << OPT_ONION_MESSAGES),
-			      found_best_peer, ir);
+			      NULL, found_best_peer, ir);
 }
 
 static struct command_result *cancel_invoice(struct command *cmd,

plugins/offers_offer.c

@@ -342,6 +342,7 @@ static struct command_result *maybe_add_path(struct command *cmd,
 							     tal_count(od->fronting_nodes));
 			} else {
 				return find_best_peer(cmd, 1ULL << OPT_ONION_MESSAGES,
+						      NULL,
 						      found_best_peer, offinfo);
 			}
 		}
@@ -776,7 +777,7 @@ struct command_result *json_invoicerequest(struct command *cmd,
 		idata->single_use = *single_use;
 		idata->label = label;
 		return find_best_peer(cmd, 1ULL << OPT_ONION_MESSAGES,
-				      found_best_peer_invrequest, idata);
+				      NULL, found_best_peer_invrequest, idata);
 	}
 
 	return call_createinvoicerequest(cmd, invreq, *single_use, label);