f Rebase on lightningdevkit#596

Author: TheBlueMatt

lightning/src/ln/channelmanager.rs

@@ -3051,9 +3051,13 @@ impl<ChanSigner: ChannelKeys, M: Deref + Sync + Send, T: Deref + Sync + Send, K:
 		for (source, payment_hash, value) in timed_out_htlcs.drain(..) {
 			// Call it preimage_unknown as the issue, ultimately, is that the user failed to
 			// provide us a preimage within the cltv_expiry time window.
+			let mut htlc_msat_height_data = byte_utils::be64_to_array(value).to_vec();
+			htlc_msat_height_data.extend_from_slice(&byte_utils::be32_to_array(
+				self.latest_block_height.load(Ordering::Acquire) as u32,
+			));
 			self.fail_htlc_backwards_internal(self.channel_state.lock().unwrap(), source, &payment_hash, HTLCFailReason::Reason {
 				failure_code: 0x4000 | 15,
-				data: byte_utils::be64_to_array(value).to_vec()
+				data: htlc_msat_height_data
 			});
 		}
 		self.latest_block_height.store(height as usize, Ordering::Release);

lightning/src/ln/functional_tests.rs

@@ -3695,11 +3695,22 @@ fn test_htlc_timeout() {
 	nodes[0].node.handle_update_fail_htlc(&nodes[1].node.get_our_node_id(), &htlc_timeout_updates.update_fail_htlcs[0]);
 	commitment_signed_dance!(nodes[0], nodes[1], htlc_timeout_updates.commitment_signed, false);
 	let events = nodes[0].node.get_and_clear_pending_events();
-	match events[0] {
-		Event::PaymentFailed { payment_hash, rejected_by_dest, error_code } => {
+	match &events[0] {
+		&Event::PaymentFailed { payment_hash, rejected_by_dest, error_code, ref error_data } => {
 			assert_eq!(payment_hash, our_payment_hash);
 			assert!(rejected_by_dest);
 			assert_eq!(error_code.unwrap(), 0x4000 | 15);
+			// 100_000 msat as u64, followed by a height of 122 as u32
+			assert_eq!(&error_data.as_ref().unwrap()[..], &[
+				((100_000u64 >> 7*8) & 0xff) as u8,
+				((100_000u64 >> 6*8) & 0xff) as u8,
+				((100_000u64 >> 5*8) & 0xff) as u8,
+				((100_000u64 >> 4*8) & 0xff) as u8,
+				((100_000u64 >> 3*8) & 0xff) as u8,
+				((100_000u64 >> 2*8) & 0xff) as u8,
+				((100_000u64 >> 1*8) & 0xff) as u8,
+				((100_000u64 >> 0*8) & 0xff) as u8,
+				0, 0, 0, 122]);
 		},
 		_ => panic!("Unexpected event"),
 	}