ln/fix: return incorrect payment details for incorrect keysend preimage

Per: https://github.com/lightning/blips/blob/master/blip-0003.md

While we're here, move creation of data into a helper function.

Author: carlaKC

lightning/src/ln/channelmanager.rs

@@ -87,6 +87,8 @@ use crate::util::string::UntrustedString;
 use crate::util::ser::{BigSize, FixedLengthReader, LengthReadable, Readable, ReadableArgs, MaybeReadable, Writeable, Writer, VecWriter};
 use crate::util::logger::{Level, Logger, WithContext};
 use crate::util::errors::APIError;
+use super::onion_payment::invalid_payment_err_data;
+
 #[cfg(async_payments)] use {
 	crate::offers::offer::Amount,
 	crate::offers::static_invoice::{DEFAULT_RELATIVE_EXPIRY as STATIC_INVOICE_DEFAULT_RELATIVE_EXPIRY, StaticInvoice, StaticInvoiceBuilder},
@@ -6262,10 +6264,7 @@ where
 								macro_rules! fail_htlc {
 									($htlc: expr, $payment_hash: expr) => {
 										debug_assert!(!committed_to_claimable);
-										let mut htlc_msat_height_data = $htlc.value.to_be_bytes().to_vec();
-										htlc_msat_height_data.extend_from_slice(
-											&self.best_block.read().unwrap().height.to_be_bytes(),
-										);
+										let err_data = invalid_payment_err_data($htlc.value, self.best_block.read().unwrap().height);
 										failed_forwards.push((HTLCSource::PreviousHopData(HTLCPreviousHopData {
 												short_channel_id: $htlc.prev_hop.short_channel_id,
 												user_channel_id: $htlc.prev_hop.user_channel_id,
@@ -6278,7 +6277,7 @@ where
 												blinded_failure,
 												cltv_expiry: Some(cltv_expiry),
 											}), payment_hash,
-											HTLCFailReason::reason(0x4000 | 15, htlc_msat_height_data),
+											HTLCFailReason::reason(0x4000 | 15, err_data),
 											HTLCDestination::FailedPayment { payment_hash: $payment_hash },
 										));
 										continue 'next_forwardable_htlc;
@@ -7231,10 +7230,9 @@ where
 			}
 		} else {
 			for htlc in sources {
-				let mut htlc_msat_height_data = htlc.value.to_be_bytes().to_vec();
-				htlc_msat_height_data.extend_from_slice(&self.best_block.read().unwrap().height.to_be_bytes());
+				let err_data = invalid_payment_err_data(htlc.value, self.best_block.read().unwrap().height);
 				let source = HTLCSource::PreviousHopData(htlc.prev_hop);
-				let reason = HTLCFailReason::reason(0x4000 | 15, htlc_msat_height_data);
+				let reason = HTLCFailReason::reason(0x4000 | 15, err_data);
 				let receiver = HTLCDestination::FailedPayment { payment_hash };
 				self.fail_htlc_backwards_internal(&source, &payment_hash, &reason, receiver);
 			}
@@ -11822,11 +11820,8 @@ where
 					// number of blocks we generally consider it to take to do a commitment update,
 					// just give up on it and fail the HTLC.
 					if height >= htlc.cltv_expiry - HTLC_FAIL_BACK_BUFFER {
-						let mut htlc_msat_height_data = htlc.value.to_be_bytes().to_vec();
-						htlc_msat_height_data.extend_from_slice(&height.to_be_bytes());
-
 						timed_out_htlcs.push((HTLCSource::PreviousHopData(htlc.prev_hop.clone()), payment_hash.clone(),
-							HTLCFailReason::reason(0x4000 | 15, htlc_msat_height_data),
+							HTLCFailReason::reason(0x4000 | 15, invalid_payment_err_data(htlc.value, height)),
 							HTLCDestination::FailedPayment { payment_hash: payment_hash.clone() }));
 						false
 					} else { true }

lightning/src/ln/onion_payment.rs

@@ -36,6 +36,14 @@ pub struct InboundHTLCErr {
 	pub msg: &'static str,
 }
 
+/// Writes payment data for invalid or unknown payment error code.
+pub (super) fn invalid_payment_err_data(amt_msat: u64, current_height: u32) -> Vec<u8>{
+	let mut err_data = Vec::with_capacity(12);
+	err_data.extend_from_slice(&amt_msat.to_be_bytes());
+	err_data.extend_from_slice(&current_height.to_be_bytes());
+	err_data
+}
+
 fn check_blinded_payment_constraints(
 	amt_msat: u64, cltv_expiry: u32, constraints: &PaymentConstraints
 ) -> Result<(), ()> {
@@ -333,11 +341,9 @@ pub(super) fn create_recv_pending_htlc_info(
 	// payment logic has enough time to fail the HTLC backward before our onchain logic triggers a
 	// channel closure (see HTLC_FAIL_BACK_BUFFER rationale).
 	if cltv_expiry <= current_height + HTLC_FAIL_BACK_BUFFER + 1 {
-		let mut err_data = Vec::with_capacity(12);
-		err_data.extend_from_slice(&amt_msat.to_be_bytes());
-		err_data.extend_from_slice(&current_height.to_be_bytes());
 		return Err(InboundHTLCErr {
-			err_code: 0x4000 | 15, err_data,
+			err_code: 0x4000 | 15,
+			err_data: invalid_payment_err_data(amt_msat, current_height),
 			msg: "The final CLTV expiry is too soon to handle",
 		});
 	}
@@ -361,8 +367,8 @@ pub(super) fn create_recv_pending_htlc_info(
 		let hashed_preimage = PaymentHash(Sha256::hash(&payment_preimage.0).to_byte_array());
 		if hashed_preimage != payment_hash {
 			return Err(InboundHTLCErr {
-				err_code: 0x4000|22,
-				err_data: Vec::new(),
+				err_code: 0x4000 | 15,
+				err_data: invalid_payment_err_data(amt_msat, current_height),
 				msg: "Payment preimage didn't match payment hash",
 			});
 		}