Limit OnionMessenger outbound buffer size

Drop OMs if they push us over the max OnionMessenger outbound buffer size

Author: valentinewallace

lightning/src/onion_message/functional_tests.rs

@@ -170,3 +170,13 @@ fn reply_path() {
 		"lightning::onion_message::messenger".to_string(),
 		format!("Received an onion message with path_id: None and reply_path").to_string(), 2);
 }
+
+#[test]
+fn peer_buffer_full() {
+	let nodes = create_nodes(2);
+	for _ in 0..188 {
+		nodes[0].messenger.send_onion_message(&[], Destination::Node(nodes[1].get_node_pk()), None).unwrap();
+	}
+	let err = nodes[0].messenger.send_onion_message(&[], Destination::Node(nodes[1].get_node_pk()), None).unwrap_err();
+	assert_eq!(err, SendError::PeerBufferFull);
+}

lightning/src/onion_message/messenger.rs

@@ -23,6 +23,7 @@ use super::packet::{BIG_PACKET_HOP_DATA_LEN, ForwardControlTlvs, Packet, Payload
 use super::utils;
 use util::events::OnionMessageProvider;
 use util::logger::Logger;
+use util::ser::Writeable;
 
 use core::ops::Deref;
 use sync::{Arc, Mutex};
@@ -122,6 +123,8 @@ pub enum SendError {
 	TooFewBlindedHops,
 	/// Our next-hop peer was offline or does not support onion message forwarding.
 	InvalidFirstHop,
+	/// Our next-hop peer's buffer was full.
+	PeerBufferFull,
 }
 
 impl<Signer: Sign, K: Deref, L: Deref> OnionMessenger<Signer, K, L>
@@ -172,6 +175,7 @@ impl<Signer: Sign, K: Deref, L: Deref> OnionMessenger<Signer, K, L>
 		match pending_per_peer_msgs.entry(introduction_node_id) {
 			hash_map::Entry::Vacant(_) => Err(SendError::InvalidFirstHop),
 			hash_map::Entry::Occupied(mut e) => {
+				if peer_buffer_full(e.get()) { return Err(SendError::PeerBufferFull) }
 				e.get_mut().push_back(msgs::OnionMessage { blinding_point, onion_routing_packet });
 				Ok(())
 			}
@@ -192,6 +196,18 @@ impl<Signer: Sign, K: Deref, L: Deref> OnionMessenger<Signer, K, L>
 	}
 }
 
+fn peer_buffer_full(peer_buf: &VecDeque<msgs::OnionMessage>) -> bool {
+	const MAX_BUFFER_SIZE: usize = 1024 * 256;
+	let mut buffered_bytes = 0;
+	for om in peer_buf {
+		buffered_bytes += om.serialized_length();
+		if buffered_bytes >= MAX_BUFFER_SIZE {
+			return true
+		}
+	}
+	false
+}
+
 impl<Signer: Sign, K: Deref, L: Deref> OnionMessageHandler for OnionMessenger<Signer, K, L>
 	where K::Target: KeysInterface<Signer = Signer>,
 	      L::Target: Logger,