common: tighten restrictions on periods, as per latest draft.

common/bolt12.c

@@ -171,6 +171,7 @@ struct tlv_offer *offer_decode(const tal_t *ctx,
 	const u8 *data;
 	size_t dlen;
 	const struct tlv_field *badf;
+	const struct recurrence *recurr;
 
 	data = string_to_data(tmpctx, b12, b12len, "lno", &dlen, fail);
 	if (!data)
@@ -242,6 +243,46 @@ struct tlv_offer *offer_decode(const tal_t *ctx,
 		}
 	}
 
+	/* BOLT-recurrence #12
+	 *   - if `offer_recurrence_optional` or `offer_recurrence_compulsory` are set:
+	 *     - if `time_unit` is not one of 0, 1, or 2:
+	 *        - MUST NOT respond to the offer.
+	 *     - if `period` is 0:
+	 *        - MUST NOT respond to the offer.
+	 *     - if `offer_recurrence_limit` is set and `max_period_index` is 0:
+	 *        - MUST NOT respond to the offer.
+	 */
+	recurr = offer_recurrence(offer);
+	if (recurr) {
+		if (recurr->time_unit != 0
+		    && recurr->time_unit != 1
+		    && recurr->time_unit != 2) {
+			*fail = tal_fmt(ctx, "Offer contains invalid recurrence time_unit %u", recurr->time_unit);
+			return tal_free(offer);
+		}
+		if (recurr->period == 0) {
+			*fail = tal_fmt(ctx, "Offer contains invalid recurrence period %u", recurr->period);
+			return tal_free(offer);
+		}
+		if (offer->offer_recurrence_limit && *offer->offer_recurrence_limit == 0) {
+			*fail = tal_fmt(ctx, "Offer contains invalid recurrence limit %u",
+					*offer->offer_recurrence_limit);
+			return tal_free(offer);
+		}
+	} else {
+		/* BOLT-recurrence #12
+		 *   - otherwise: (no recurrence):
+		 *     - if it `offer_recurrence_paywindow`, `offer_recurrence_limit` or `offer_recurrence_base` are set:
+		 *        - MUST NOT respond to the offer.
+		 */
+		if (offer->offer_recurrence_paywindow
+		    || offer->offer_recurrence_limit
+		    || offer->offer_recurrence_base) {
+			*fail = tal_strdup(ctx, "Offer contains recurrence fields but no recurrence");
+			return tal_free(offer);
+		}
+	}
+
 	return offer;
 }