Add all_paths_failed field to PaymentFailed

see field docs for details

lightning/src/ln/channelmanager.rs

@@ -2848,6 +2848,7 @@ impl<Signer: Sign, M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelMana
 									payment_hash,
 									rejected_by_dest: false,
 									network_update: None,
+									all_paths_failed: sessions.get().len() == 0,
 									#[cfg(test)]
 									error_code: None,
 									#[cfg(test)]
@@ -2886,12 +2887,14 @@ impl<Signer: Sign, M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelMana
 				let mut session_priv_bytes = [0; 32];
 				session_priv_bytes.copy_from_slice(&session_priv[..]);
 				let mut outbounds = self.pending_outbound_payments.lock().unwrap();
+				let mut all_paths_failed = false;
 				if let hash_map::Entry::Occupied(mut sessions) = outbounds.entry(mpp_id) {
 					if !sessions.get_mut().remove(&session_priv_bytes) {
 						log_trace!(self.logger, "Received duplicative fail for HTLC with payment_hash {}", log_bytes!(payment_hash.0));
 						return;
 					}
 					if sessions.get().len() == 0 {
+						all_paths_failed = true;
 						sessions.remove();
 					}
 				} else {
@@ -2914,6 +2917,7 @@ impl<Signer: Sign, M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelMana
 								payment_hash: payment_hash.clone(),
 								rejected_by_dest: !payment_retryable,
 								network_update,
+								all_paths_failed,
 #[cfg(test)]
 								error_code: onion_error_code,
 #[cfg(test)]
@@ -2939,6 +2943,7 @@ impl<Signer: Sign, M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelMana
 								payment_hash: payment_hash.clone(),
 								rejected_by_dest: path.len() == 1,
 								network_update: None,
+								all_paths_failed,
 #[cfg(test)]
 								error_code: Some(*failure_code),
 #[cfg(test)]

lightning/src/ln/functional_test_utils.rs

@@ -1041,7 +1041,7 @@ macro_rules! expect_payment_failed_with_update {
 		let events = $node.node.get_and_clear_pending_events();
 		assert_eq!(events.len(), 1);
 		match events[0] {
-			Event::PaymentFailed { ref payment_hash, rejected_by_dest, ref network_update, ref error_code, ref error_data } => {
+			Event::PaymentFailed { ref payment_hash, rejected_by_dest, ref network_update, ref error_code, ref error_data, .. } => {
 				assert_eq!(*payment_hash, $expected_payment_hash, "unexpected payment_hash");
 				assert_eq!(rejected_by_dest, $rejected_by_dest, "unexpected rejected_by_dest value");
 				assert!(error_code.is_some(), "expected error_code.is_some() = true");
@@ -1070,7 +1070,7 @@ macro_rules! expect_payment_failed {
 		let events = $node.node.get_and_clear_pending_events();
 		assert_eq!(events.len(), 1);
 		match events[0] {
-			Event::PaymentFailed { ref payment_hash, rejected_by_dest, network_update: _, ref error_code, ref error_data } => {
+			Event::PaymentFailed { ref payment_hash, rejected_by_dest, network_update: _, ref error_code, ref error_data, .. } => {
 				assert_eq!(*payment_hash, $expected_payment_hash, "unexpected payment_hash");
 				assert_eq!(rejected_by_dest, $rejected_by_dest, "unexpected rejected_by_dest value");
 				assert!(error_code.is_some(), "expected error_code.is_some() = true");
@@ -1367,9 +1367,10 @@ pub fn fail_payment_along_route<'a, 'b, 'c>(origin_node: &Node<'a, 'b, 'c>, expe
 			let events = origin_node.node.get_and_clear_pending_events();
 			assert_eq!(events.len(), 1);
 			match events[0] {
-				Event::PaymentFailed { payment_hash, rejected_by_dest, .. } => {
+				Event::PaymentFailed { payment_hash, rejected_by_dest, all_paths_failed, .. } => {
 					assert_eq!(payment_hash, our_payment_hash);
 					assert!(rejected_by_dest);
+					assert_eq!(all_paths_failed, i == expected_paths.len() - 1);
 				},
 				_ => panic!("Unexpected event"),
 			}

lightning/src/ln/functional_tests.rs

@@ -4084,6 +4084,34 @@ fn test_no_txn_manager_serialize_deserialize() {
 	send_payment(&nodes[0], &[&nodes[1]], 1000000);
 }
 
+#[test]
+fn mpp_failure() {
+	let chanmon_cfgs = create_chanmon_cfgs(4);
+	let node_cfgs = create_node_cfgs(4, &chanmon_cfgs);
+	let node_chanmgrs = create_node_chanmgrs(4, &node_cfgs, &[None, None, None, None]);
+	let nodes = create_network(4, &node_cfgs, &node_chanmgrs);
+
+	let chan_1_id = create_announced_chan_between_nodes(&nodes, 0, 1, InitFeatures::known(), InitFeatures::known()).0.contents.short_channel_id;
+	let chan_2_id = create_announced_chan_between_nodes(&nodes, 0, 2, InitFeatures::known(), InitFeatures::known()).0.contents.short_channel_id;
+	let chan_3_id = create_announced_chan_between_nodes(&nodes, 1, 3, InitFeatures::known(), InitFeatures::known()).0.contents.short_channel_id;
+	let chan_4_id = create_announced_chan_between_nodes(&nodes, 2, 3, InitFeatures::known(), InitFeatures::known()).0.contents.short_channel_id;
+	let logger = test_utils::TestLogger::new();
+
+	let (_, payment_hash, payment_secret) = get_payment_preimage_hash!(&nodes[3]);
+	let net_graph_msg_handler = &nodes[0].net_graph_msg_handler;
+	let mut route = get_route(&nodes[0].node.get_our_node_id(), &net_graph_msg_handler.network_graph, &nodes[3].node.get_our_node_id(), Some(InvoiceFeatures::known()), None, &[], 100000, TEST_FINAL_CLTV, &logger).unwrap();
+	let path = route.paths[0].clone();
+	route.paths.push(path);
+	route.paths[0][0].pubkey = nodes[1].node.get_our_node_id();
+	route.paths[0][0].short_channel_id = chan_1_id;
+	route.paths[0][1].short_channel_id = chan_3_id;
+	route.paths[1][0].pubkey = nodes[2].node.get_our_node_id();
+	route.paths[1][0].short_channel_id = chan_2_id;
+	route.paths[1][1].short_channel_id = chan_4_id;
+	send_along_route_with_secret(&nodes[0], route, &[&[&nodes[1], &nodes[3]], &[&nodes[2], &nodes[3]]], 200_000, payment_hash, payment_secret);
+	fail_payment_along_route(&nodes[0], &[&[&nodes[1], &nodes[3]], &[&nodes[2], &nodes[3]]], false, payment_hash);
+}
+
 #[test]
 fn test_dup_htlc_onchain_fails_on_reload() {
 	// When a Channel is closed, any outbound HTLCs which were relayed through it are simply
@@ -5914,9 +5942,10 @@ fn test_fail_holding_cell_htlc_upon_free() {
 	let events = nodes[0].node.get_and_clear_pending_events();
 	assert_eq!(events.len(), 1);
 	match &events[0] {
-		&Event::PaymentFailed { ref payment_hash, ref rejected_by_dest, ref network_update, ref error_code, ref error_data } => {
+		&Event::PaymentFailed { ref payment_hash, ref rejected_by_dest, ref network_update, ref error_code, ref error_data, ref all_paths_failed } => {
 			assert_eq!(our_payment_hash.clone(), *payment_hash);
 			assert_eq!(*rejected_by_dest, false);
+			assert_eq!(*all_paths_failed, true);
 			assert_eq!(*network_update, None);
 			assert_eq!(*error_code, None);
 			assert_eq!(*error_data, None);
@@ -6000,9 +6029,10 @@ fn test_free_and_fail_holding_cell_htlcs() {
 	let events = nodes[0].node.get_and_clear_pending_events();
 	assert_eq!(events.len(), 1);
 	match &events[0] {
-		&Event::PaymentFailed { ref payment_hash, ref rejected_by_dest, ref network_update, ref error_code, ref error_data } => {
+		&Event::PaymentFailed { ref payment_hash, ref rejected_by_dest, ref network_update, ref error_code, ref error_data, ref all_paths_failed } => {
 			assert_eq!(payment_hash_2.clone(), *payment_hash);
 			assert_eq!(*rejected_by_dest, false);
+			assert_eq!(*all_paths_failed, true);
 			assert_eq!(*network_update, None);
 			assert_eq!(*error_code, None);
 			assert_eq!(*error_data, None);

lightning/src/ln/onion_route_tests.rs

@@ -163,8 +163,9 @@ fn run_onion_failure_test_with_fail_intercept<F1,F2,F3>(_name: &str, test_case:
 
 	let events = nodes[0].node.get_and_clear_pending_events();
 	assert_eq!(events.len(), 1);
-	if let &Event::PaymentFailed { payment_hash:_, ref rejected_by_dest, ref network_update, ref error_code, error_data: _ } = &events[0] {
+	if let &Event::PaymentFailed { payment_hash:_, ref rejected_by_dest, ref network_update, ref error_code, error_data: _, ref all_paths_failed } = &events[0] {
 		assert_eq!(*rejected_by_dest, !expected_retryable);
+		assert_eq!(*all_paths_failed, true);
 		assert_eq!(*error_code, expected_error_code);
 		if expected_channel_update.is_some() {
 			match network_update {

lightning/src/routing/network_graph.rs

@@ -1728,6 +1728,7 @@ mod tests {
 			net_graph_msg_handler.handle_event(&Event::PaymentFailed {
 				payment_hash: PaymentHash([0; 32]),
 				rejected_by_dest: false,
+				all_paths_failed: true,
 				network_update: Some(NetworkUpdate::ChannelUpdateMessage {
 					msg: valid_channel_update,
 				}),
@@ -1750,6 +1751,7 @@ mod tests {
 			net_graph_msg_handler.handle_event(&Event::PaymentFailed {
 				payment_hash: PaymentHash([0; 32]),
 				rejected_by_dest: false,
+				all_paths_failed: true,
 				network_update: Some(NetworkUpdate::ChannelClosed {
 					short_channel_id,
 					is_permanent: false,
@@ -1771,6 +1773,7 @@ mod tests {
 			net_graph_msg_handler.handle_event(&Event::PaymentFailed {
 				payment_hash: PaymentHash([0; 32]),
 				rejected_by_dest: false,
+				all_paths_failed: true,
 				network_update: Some(NetworkUpdate::ChannelClosed {
 					short_channel_id,
 					is_permanent: true,

lightning/src/util/events.rs

@@ -141,6 +141,10 @@ pub enum Event {
 		/// [`NetworkGraph`]: crate::routing::network_graph::NetworkGraph
 		/// [`NetGraphMsgHandler`]: crate::routing::network_graph::NetGraphMsgHandler
 		network_update: Option<NetworkUpdate>,
+		/// For both single-path and multi-path payments, this is set if all paths of the payment have
+		/// failed. This will be set to false if (1) this is an MPP payment and (2) other parts of the
+		/// larger MPP payment were still in flight when this event was generated.
+		all_paths_failed: bool,
 #[cfg(test)]
 		error_code: Option<u16>,
 #[cfg(test)]
@@ -224,7 +228,7 @@ impl Writeable for Event {
 					(0, payment_preimage, required),
 				});
 			},
-			&Event::PaymentFailed { ref payment_hash, ref rejected_by_dest, ref network_update,
+			&Event::PaymentFailed { ref payment_hash, ref rejected_by_dest, ref network_update, ref all_paths_failed,
 				#[cfg(test)]
 				ref error_code,
 				#[cfg(test)]
@@ -239,6 +243,7 @@ impl Writeable for Event {
 					(0, payment_hash, required),
 					(1, network_update, option),
 					(2, rejected_by_dest, required),
+					(3, all_paths_failed, required),
 				});
 			},
 			&Event::PendingHTLCsForwardable { time_forwardable: _ } => {
@@ -322,15 +327,18 @@ impl MaybeReadable for Event {
 					let mut payment_hash = PaymentHash([0; 32]);
 					let mut rejected_by_dest = false;
 					let mut network_update = None;
+					let mut all_paths_failed = Some(true);
 					read_tlv_fields!(reader, {
 						(0, payment_hash, required),
 						(1, network_update, ignorable),
 						(2, rejected_by_dest, required),
+						(3, all_paths_failed, option),
 					});
 					Ok(Some(Event::PaymentFailed {
 						payment_hash,
 						rejected_by_dest,
 						network_update,
+						all_paths_failed: all_paths_failed.unwrap(),
 						#[cfg(test)]
 						error_code,
 						#[cfg(test)]