tlv value length check

Author: Evanfeenstra

src/payment/spontaneous.rs

@@ -119,9 +119,16 @@ impl SpontaneousPayment {
 		};
 
 		let recipient_fields = match custom_tlv {
-			Some((tlv_type, tlv_value)) => RecipientOnionFields::spontaneous_empty()
-				.with_custom_tlvs(vec![(tlv_type, tlv_value)])
-				.map_err(|_| Error::PaymentSendingFailed)?,
+			Some((tlv_type, tlv_value)) => {
+				if tlv_value.len() > 1300 {
+					// The real limit is lower, but we can't know without the full route.
+					// This is just an early check to avoid trying a payment that will fail.
+					return Err(Error::PaymentSendingFailed);
+				}
+				RecipientOnionFields::spontaneous_empty()
+					.with_custom_tlvs(vec![(tlv_type, tlv_value)])
+					.map_err(|_| Error::PaymentSendingFailed)?
+			},
 			None => RecipientOnionFields::spontaneous_empty(),
 		};