]> git.bitcoin.ninja Git - rust-lightning/commitdiff
Implement finding paths for MPP
authorGleb Naumenko <naumenko.gs@gmail.com>
Mon, 10 Aug 2020 10:50:29 +0000 (13:50 +0300)
committerGleb Naumenko <naumenko.gs@gmail.com>
Tue, 2 Mar 2021 19:09:49 +0000 (21:09 +0200)
lightning/src/ln/functional_tests.rs
lightning/src/routing/network_graph.rs
lightning/src/routing/router.rs

index 85dae76987dc669424486e2a5d0f03387d469dcf..eef89d1b413cd36704d7ec6a6957f586c00e729e 100644 (file)
@@ -1960,7 +1960,8 @@ fn test_channel_reserve_holding_cell_htlcs() {
 
        // attempt to send amt_msat > their_max_htlc_value_in_flight_msat
        {
 
        // attempt to send amt_msat > their_max_htlc_value_in_flight_msat
        {
-               let (route, our_payment_hash, _) = get_route_and_payment_hash!(recv_value_0 + 1);
+               let (mut route, our_payment_hash, _) = get_route_and_payment_hash!(recv_value_0);
+               route.paths[0].last_mut().unwrap().fee_msat += 1;
                assert!(route.paths[0].iter().rev().skip(1).all(|h| h.fee_msat == feemsat));
                unwrap_send_err!(nodes[0].node.send_payment(&route, our_payment_hash, &None), true, APIError::ChannelUnavailable { ref err },
                        assert!(regex::Regex::new(r"Cannot send value that would put us over the max HTLC value in flight our peer will accept \(\d+\)").unwrap().is_match(err)));
                assert!(route.paths[0].iter().rev().skip(1).all(|h| h.fee_msat == feemsat));
                unwrap_send_err!(nodes[0].node.send_payment(&route, our_payment_hash, &None), true, APIError::ChannelUnavailable { ref err },
                        assert!(regex::Regex::new(r"Cannot send value that would put us over the max HTLC value in flight our peer will accept \(\d+\)").unwrap().is_match(err)));
@@ -6472,7 +6473,7 @@ fn test_update_add_htlc_bolt2_sender_cltv_expiry_too_high() {
        let node_cfgs = create_node_cfgs(2, &chanmon_cfgs);
        let node_chanmgrs = create_node_chanmgrs(2, &node_cfgs, &[None, None]);
        let mut nodes = create_network(2, &node_cfgs, &node_chanmgrs);
        let node_cfgs = create_node_cfgs(2, &chanmon_cfgs);
        let node_chanmgrs = create_node_chanmgrs(2, &node_cfgs, &[None, None]);
        let mut nodes = create_network(2, &node_cfgs, &node_chanmgrs);
-       let _chan = create_announced_chan_between_nodes_with_value(&nodes, 0, 1, 100000, 0, InitFeatures::known(), InitFeatures::known());
+       let _chan = create_announced_chan_between_nodes_with_value(&nodes, 0, 1, 1000000, 0, InitFeatures::known(), InitFeatures::known());
        let logger = test_utils::TestLogger::new();
 
        let (_, our_payment_hash) = get_payment_preimage_hash!(nodes[0]);
        let logger = test_utils::TestLogger::new();
 
        let (_, our_payment_hash) = get_payment_preimage_hash!(nodes[0]);
@@ -6544,9 +6545,13 @@ fn test_update_add_htlc_bolt2_sender_exceed_max_htlc_value_in_flight() {
        send_payment(&nodes[0], &vec!(&nodes[1])[..], max_in_flight, max_in_flight);
 
        let (_, our_payment_hash) = get_payment_preimage_hash!(nodes[0]);
        send_payment(&nodes[0], &vec!(&nodes[1])[..], max_in_flight, max_in_flight);
 
        let (_, our_payment_hash) = get_payment_preimage_hash!(nodes[0]);
-       let net_graph_msg_handler = &nodes[0].net_graph_msg_handler;
-       let logger = test_utils::TestLogger::new();
-       let route = get_route(&nodes[0].node.get_our_node_id(), &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[1].node.get_our_node_id(), None, &[], max_in_flight+1, TEST_FINAL_CLTV, &logger).unwrap();
+       // Manually create a route over our max in flight (which our router normally automatically
+       // limits us to.
+       let route = Route { paths: vec![vec![RouteHop {
+          pubkey: nodes[1].node.get_our_node_id(), node_features: NodeFeatures::known(), channel_features: ChannelFeatures::known(),
+          short_channel_id: nodes[1].node.list_usable_channels()[0].short_channel_id.unwrap(),
+          fee_msat: max_in_flight + 1, cltv_expiry_delta: TEST_FINAL_CLTV
+       }]] };
        unwrap_send_err!(nodes[0].node.send_payment(&route, our_payment_hash, &None), true, APIError::ChannelUnavailable { ref err },
                assert!(regex::Regex::new(r"Cannot send value that would put us over the max HTLC value in flight our peer will accept \(\d+\)").unwrap().is_match(err)));
 
        unwrap_send_err!(nodes[0].node.send_payment(&route, our_payment_hash, &None), true, APIError::ChannelUnavailable { ref err },
                assert!(regex::Regex::new(r"Cannot send value that would put us over the max HTLC value in flight our peer will accept \(\d+\)").unwrap().is_match(err)));
 
index 8075462c938b797d0f8d923d786be9239533317c..6856bb16bcfc4bbb221542d92967f7e32fecfa69 100644 (file)
@@ -98,6 +98,13 @@ impl<C: Deref, L: Deref> NetGraphMsgHandler<C, L> where C::Target: chain::Access
                }
        }
 
                }
        }
 
+       /// Adds a provider used to check new announcements. Does not affect
+       /// existing announcements unless they are updated.
+       /// Add, update or remove the provider would replace the current one.
+       pub fn add_chain_access(&mut self, chain_access: Option<C>) {
+               self.chain_access = chain_access;
+       }
+
        /// Take a read lock on the network_graph and return it in the C-bindings
        /// newtype helper. This is likely only useful when called via the C
        /// bindings as you can call `self.network_graph.read().unwrap()` in Rust
        /// Take a read lock on the network_graph and return it in the C-bindings
        /// newtype helper. This is likely only useful when called via the C
        /// bindings as you can call `self.network_graph.read().unwrap()` in Rust
index 0260aa1fdbd8237eebadb8c88fa4b3d663c6bb09..fedad42cfb2c6468f530931c5c31a623236acb8a 100644 (file)
@@ -22,7 +22,7 @@ use util::ser::{Writeable, Readable};
 use util::logger::Logger;
 
 use std::cmp;
 use util::logger::Logger;
 
 use std::cmp;
-use std::collections::{HashMap,BinaryHeap};
+use std::collections::{HashMap, BinaryHeap};
 use std::ops::Deref;
 
 /// A hop in a route
 use std::ops::Deref;
 
 /// A hop in a route
@@ -38,7 +38,8 @@ pub struct RouteHop {
        /// The channel_announcement features of the channel that should be used from the previous hop
        /// to reach this node.
        pub channel_features: ChannelFeatures,
        /// The channel_announcement features of the channel that should be used from the previous hop
        /// to reach this node.
        pub channel_features: ChannelFeatures,
-       /// The fee taken on this hop. For the last hop, this should be the full value of the payment.
+       /// The fee taken on this hop (for paying for the use of the *next* channel in the path).
+       /// For the last hop, this should be the full value of the payment.
        pub fee_msat: u64,
        /// The CLTV delta added for this hop. For the last hop, this should be the full CLTV value
        /// expected at the destination, in excess of the current block height.
        pub fee_msat: u64,
        /// The CLTV delta added for this hop. For the last hop, this should be the full CLTV value
        /// expected at the destination, in excess of the current block height.
@@ -134,6 +135,12 @@ struct RouteGraphNode {
        pubkey: PublicKey,
        lowest_fee_to_peer_through_node: u64,
        lowest_fee_to_node: u64,
        pubkey: PublicKey,
        lowest_fee_to_peer_through_node: u64,
        lowest_fee_to_node: u64,
+       // The maximum value a yet-to-be-constructed payment path might flow through this node.
+       // This value is upper-bounded by us by:
+       // - how much is needed for a path being constructed
+       // - how much value can channels following this node (up to the destination) can contribute,
+       //   considering their capacity and fees
+       value_contribution_msat: u64
 }
 
 impl cmp::Ord for RouteGraphNode {
 }
 
 impl cmp::Ord for RouteGraphNode {
@@ -156,28 +163,126 @@ struct DummyDirectionalChannelInfo {
        fees: RoutingFees,
 }
 
        fees: RoutingFees,
 }
 
+/// It's useful to keep track of the hops associated with the fees required to use them,
+/// so that we can choose cheaper paths (as per Dijkstra's algorithm).
+/// Fee values should be updated only in the context of the whole path, see update_value_and_recompute_fees.
+/// These fee values are useful to choose hops as we traverse the graph "payee-to-payer".
+#[derive(Clone)]
+struct PathBuildingHop {
+       /// Hop-specific details unrelated to the path during the routing phase,
+       /// but rather relevant to the LN graph.
+       route_hop: RouteHop,
+       /// Minimal fees required to route to the source node of the current hop via any of its inbound channels.
+       src_lowest_inbound_fees: RoutingFees,
+       /// Fees of the channel used in this hop.
+       channel_fees: RoutingFees,
+       /// All the fees paid *after* this channel on the way to the destination
+       next_hops_fee_msat: u64,
+       /// Fee paid for the use of the current channel (see channel_fees).
+       /// The value will be actually deducted from the counterparty balance on the previous link.
+       hop_use_fee_msat: u64,
+       /// Used to compare channels when choosing the for routing.
+       /// Includes paying for the use of a hop and the following hops, as well as
+       /// an estimated cost of reaching this hop.
+       /// Might get stale when fees are recomputed. Primarily for internal use.
+       total_fee_msat: u64,
+}
+
+// Instantiated with a list of hops with correct data in them collected during path finding,
+// an instance of this struct should be further modified only via given methods.
+#[derive(Clone)]
+struct PaymentPath {
+       hops: Vec<PathBuildingHop>,
+}
+
+impl PaymentPath {
+
+       // TODO: Add a value_msat field to PaymentPath and use it instead of this function.
+       fn get_value_msat(&self) -> u64 {
+               self.hops.last().unwrap().route_hop.fee_msat
+       }
+
+       fn get_total_fee_paid_msat(&self) -> u64 {
+               if self.hops.len() < 1 {
+                       return 0;
+               }
+               let mut result = 0;
+               // Can't use next_hops_fee_msat because it gets outdated.
+               for (i, hop) in self.hops.iter().enumerate() {
+                       if i != self.hops.len() - 1 {
+                               result += hop.route_hop.fee_msat;
+                       }
+               }
+               return result;
+       }
+
+       // If an amount transferred by the path is updated, the fees should be adjusted.
+       // Any other way to change fees may result in an inconsistency.
+       // The caller should make sure values don't fall below htlc_minimum_msat of the used channels.
+       fn update_value_and_recompute_fees(&mut self, value_msat: u64) {
+               let mut total_fee_paid_msat = 0 as u64;
+               for i in (1..self.hops.len()).rev() {
+                       let cur_hop_amount_msat = total_fee_paid_msat + value_msat;
+                       let mut cur_hop = self.hops.get_mut(i).unwrap();
+                       cur_hop.next_hops_fee_msat = total_fee_paid_msat;
+                       if let Some(new_fee) = compute_fees(cur_hop_amount_msat, cur_hop.channel_fees) {
+                               cur_hop.hop_use_fee_msat = new_fee;
+                               total_fee_paid_msat += new_fee;
+                       } else {
+                               // It should not be possible because this function is called only to reduce the
+                               // value. In that case, compute_fee was already called with the same fees for
+                               // larger amount and there was no overflow.
+                               unreachable!();
+                       }
+               }
+
+               // Propagate updated fees for the use of the channels to one hop back,
+               // where they will be actually paid (fee_msat).
+               // For the last hop it will represent the value being transferred over this path.
+               for i in 0..self.hops.len() - 1 {
+                       let next_hop_use_fee_msat = self.hops.get(i + 1).unwrap().hop_use_fee_msat;
+                       self.hops.get_mut(i).unwrap().route_hop.fee_msat = next_hop_use_fee_msat;
+               }
+               self.hops.last_mut().unwrap().route_hop.fee_msat = value_msat;
+               self.hops.last_mut().unwrap().hop_use_fee_msat = 0;
+       }
+}
+
+fn compute_fees(amount_msat: u64, channel_fees: RoutingFees) -> Option<u64> {
+       let proportional_fee_millions =
+               amount_msat.checked_mul(channel_fees.proportional_millionths as u64);
+       if let Some(new_fee) = proportional_fee_millions.and_then(|part| {
+                       (channel_fees.base_msat as u64).checked_add(part / 1_000_000) }) {
+
+               Some(new_fee)
+       } else {
+               // This function may be (indirectly) called without any verification,
+               // with channel_fees provided by a caller. We should handle it gracefully.
+               None
+       }
+}
 
 
-/// Gets a route from us to the given target node.
+/// Gets a route from us (payer) to the given target node (payee).
 ///
 /// Extra routing hops between known nodes and the target will be used if they are included in
 /// last_hops.
 ///
 /// If some channels aren't announced, it may be useful to fill in a first_hops with the
 /// results from a local ChannelManager::list_usable_channels() call. If it is filled in, our
 ///
 /// Extra routing hops between known nodes and the target will be used if they are included in
 /// last_hops.
 ///
 /// If some channels aren't announced, it may be useful to fill in a first_hops with the
 /// results from a local ChannelManager::list_usable_channels() call. If it is filled in, our
-/// view of our local channels (from net_graph_msg_handler) will be ignored, and only those in first_hops
-/// will be used.
+/// view of our local channels (from net_graph_msg_handler) will be ignored, and only those
+/// in first_hops will be used.
 ///
 /// Panics if first_hops contains channels without short_channel_ids
 /// (ChannelManager::list_usable_channels will never include such channels).
 ///
 /// The fees on channels from us to next-hops are ignored (as they are assumed to all be
 ///
 /// Panics if first_hops contains channels without short_channel_ids
 /// (ChannelManager::list_usable_channels will never include such channels).
 ///
 /// The fees on channels from us to next-hops are ignored (as they are assumed to all be
-/// equal), however the enabled/disabled bit on such channels as well as the htlc_minimum_msat
-/// *is* checked as they may change based on the receiving node.
-pub fn get_route<L: Deref>(our_node_id: &PublicKey, network: &NetworkGraph, target: &PublicKey, first_hops: Option<&[&ChannelDetails]>,
+/// equal), however the enabled/disabled bit on such channels as well as the
+/// htlc_minimum_msat/htlc_maximum_msat *are* checked as they may change based on the receiving node.
+pub fn get_route<L: Deref>(our_node_id: &PublicKey, network: &NetworkGraph, payee: &PublicKey, first_hops: Option<&[&ChannelDetails]>,
        last_hops: &[&RouteHint], final_value_msat: u64, final_cltv: u32, logger: L) -> Result<Route, LightningError> where L::Target: Logger {
        // TODO: Obviously *only* using total fee cost sucks. We should consider weighting by
        // uptime/success in using a node in the past.
        last_hops: &[&RouteHint], final_value_msat: u64, final_cltv: u32, logger: L) -> Result<Route, LightningError> where L::Target: Logger {
        // TODO: Obviously *only* using total fee cost sucks. We should consider weighting by
        // uptime/success in using a node in the past.
-       if *target == *our_node_id {
+       if *payee == *our_node_id {
                return Err(LightningError{err: "Cannot generate a route to ourselves".to_owned(), action: ErrorAction::IgnoreError});
        }
 
                return Err(LightningError{err: "Cannot generate a route to ourselves".to_owned(), action: ErrorAction::IgnoreError});
        }
 
@@ -185,7 +290,36 @@ pub fn get_route<L: Deref>(our_node_id: &PublicKey, network: &NetworkGraph, targ
                return Err(LightningError{err: "Cannot generate a route of more value than all existing satoshis".to_owned(), action: ErrorAction::IgnoreError});
        }
 
                return Err(LightningError{err: "Cannot generate a route of more value than all existing satoshis".to_owned(), action: ErrorAction::IgnoreError});
        }
 
-       // We do a dest-to-source Dijkstra's sorting by each node's distance from the destination
+       if final_value_msat == 0 {
+               return Err(LightningError{err: "Cannot send a payment of 0 msat".to_owned(), action: ErrorAction::IgnoreError});
+       }
+
+       for last_hop in last_hops {
+               if last_hop.src_node_id == *payee {
+                       return Err(LightningError{err: "Last hop cannot have a payee as a source.".to_owned(), action: ErrorAction::IgnoreError});
+               }
+       }
+
+       // The general routing idea is the following:
+       // 1. Fill first/last hops communicated by the caller.
+       // 2. Attempt to construct a path from payer to payee for transferring
+       //    any ~sufficient (described later) value.
+       //    If succeed, remember which channels were used and how much liquidity they have available,
+       //    so that future paths don't rely on the same liquidity.
+       // 3. Prooceed to the next step if:
+       //    - we hit the recommended target value;
+       //    - OR if we could not construct a new path. Any next attempt will fail too.
+       //    Otherwise, repeat step 2.
+       // 4. See if we managed to collect paths which aggregately are able to transfer target value
+       //    (not recommended value). If yes, proceed. If not, fail routing.
+       // 5. Randomly combine paths into routes having enough to fulfill the payment. (TODO: knapsack)
+       // 6. Of all the found paths, select only those with the lowest total fee.
+       // 7. The last path in every selected route is likely to be more than we need.
+       //    Reduce its value-to-transfer and recompute fees.
+       // 8. Choose the best route by the lowest total fee.
+
+       // As for the actual search algorithm,
+       // we do a payee-to-payer Dijkstra's sorting by each node's distance from the payee
        // plus the minimum per-HTLC fee to get from it to another node (aka "shitty A*").
        // TODO: There are a few tweaks we could do, including possibly pre-calculating more stuff
        // to use as the A* heuristic beyond just the cost to get one node further than the current
        // plus the minimum per-HTLC fee to get from it to another node (aka "shitty A*").
        // TODO: There are a few tweaks we could do, including possibly pre-calculating more stuff
        // to use as the A* heuristic beyond just the cost to get one node further than the current
@@ -204,11 +338,23 @@ pub fn get_route<L: Deref>(our_node_id: &PublicKey, network: &NetworkGraph, targ
        let mut targets = BinaryHeap::new(); //TODO: Do we care about switching to eg Fibbonaci heap?
        let mut dist = HashMap::with_capacity(network.get_nodes().len());
 
        let mut targets = BinaryHeap::new(); //TODO: Do we care about switching to eg Fibbonaci heap?
        let mut dist = HashMap::with_capacity(network.get_nodes().len());
 
+       // When arranging a route, we select multiple paths so that we can make a multi-path payment.
+       // Don't stop searching for paths when we think they're
+       // sufficient to transfer a given value aggregately.
+       // Search for higher value, so that we collect many more paths,
+       // and then select the best combination among them.
+       const ROUTE_CAPACITY_PROVISION_FACTOR: u64 = 3;
+       let recommended_value_msat = final_value_msat * ROUTE_CAPACITY_PROVISION_FACTOR as u64;
+
+       // Step (1).
+       // Prepare the data we'll use for payee-to-payer search by
+       // inserting first hops suggested by the caller as targets.
+       // Our search will then attempt to reach them while traversing from the payee node.
        let mut first_hop_targets = HashMap::with_capacity(if first_hops.is_some() { first_hops.as_ref().unwrap().len() } else { 0 });
        if let Some(hops) = first_hops {
                for chan in hops {
                        let short_channel_id = chan.short_channel_id.expect("first_hops should be filled in with usable channels, not pending ones");
        let mut first_hop_targets = HashMap::with_capacity(if first_hops.is_some() { first_hops.as_ref().unwrap().len() } else { 0 });
        if let Some(hops) = first_hops {
                for chan in hops {
                        let short_channel_id = chan.short_channel_id.expect("first_hops should be filled in with usable channels, not pending ones");
-                       if chan.remote_network_id == *target {
+                       if chan.remote_network_id == *payee {
                                return Ok(Route {
                                        paths: vec![vec![RouteHop {
                                                pubkey: chan.remote_network_id,
                                return Ok(Route {
                                        paths: vec![vec![RouteHop {
                                                pubkey: chan.remote_network_id,
@@ -219,6 +365,8 @@ pub fn get_route<L: Deref>(our_node_id: &PublicKey, network: &NetworkGraph, targ
                                                cltv_expiry_delta: final_cltv,
                                        }]],
                                });
                                                cltv_expiry_delta: final_cltv,
                                        }]],
                                });
+                       } else if chan.remote_network_id == *our_node_id {
+                               return Err(LightningError{err: "First hop cannot have our_node_id as a destination.".to_owned(), action: ErrorAction::IgnoreError});
                        }
                        first_hop_targets.insert(chan.remote_network_id, (short_channel_id, chan.counterparty_features.clone()));
                }
                        }
                        first_hop_targets.insert(chan.remote_network_id, (short_channel_id, chan.counterparty_features.clone()));
                }
@@ -227,89 +375,209 @@ pub fn get_route<L: Deref>(our_node_id: &PublicKey, network: &NetworkGraph, targ
                }
        }
 
                }
        }
 
+       // We don't want multiple paths (as per MPP) share liquidity of the same channels.
+       // This map allows paths to be aware of the channel use by other paths in the same call.
+       // This would help to make a better path finding decisions and not "overbook" channels.
+       // It is unaware of the directions.
+       // TODO: we could let a caller specify this. Definitely useful when considering our own channels.
+       let mut bookkeeped_channels_liquidity_available_msat = HashMap::new();
+
+       // Keeping track of how much value we already collected across other paths. Helps to decide:
+       // - how much a new path should be transferring (upper bound);
+       // - whether a channel should be disregarded because
+       //   it's available liquidity is too small comparing to how much more we need to collect;
+       // - when we want to stop looking for new paths.
+       let mut already_collected_value_msat = 0;
+
        macro_rules! add_entry {
                // Adds entry which goes from $src_node_id to $dest_node_id
                // over the channel with id $chan_id with fees described in
                // $directional_info.
        macro_rules! add_entry {
                // Adds entry which goes from $src_node_id to $dest_node_id
                // over the channel with id $chan_id with fees described in
                // $directional_info.
-               ( $chan_id: expr, $src_node_id: expr, $dest_node_id: expr, $directional_info: expr, $capacity_sats: expr, $chan_features: expr, $starting_fee_msat: expr ) => {
-                       //TODO: Explore simply adding fee to hit htlc_minimum_msat
-                       if $starting_fee_msat as u64 + final_value_msat >= $directional_info.htlc_minimum_msat {
-                               let proportional_fee_millions = ($starting_fee_msat + final_value_msat).checked_mul($directional_info.fees.proportional_millionths as u64);
-                               if let Some(new_fee) = proportional_fee_millions.and_then(|part| {
-                                               ($directional_info.fees.base_msat as u64).checked_add(part / 1000000) })
-                               {
-                                       let mut total_fee = $starting_fee_msat as u64;
-
-                                       let mut available_msat = $capacity_sats;
+               // $next_hops_fee_msat represents the fees paid for using all the channel *after* this one,
+               // since that value has to be transferred over this channel.
+               ( $chan_id: expr, $src_node_id: expr, $dest_node_id: expr, $directional_info: expr, $capacity_sats: expr, $chan_features: expr, $next_hops_fee_msat: expr,
+                  $next_hops_value_contribution: expr ) => {
+                       // Channels to self should not be used. This is more of belt-and-suspenders, because in
+                       // practice these cases should be caught earlier:
+                       // - for regular channels at channel announcement (TODO)
+                       // - for first and last hops early in get_route
+                       if $src_node_id != $dest_node_id.clone() {
+                               let available_liquidity_msat = bookkeeped_channels_liquidity_available_msat.entry($chan_id.clone()).or_insert_with(|| {
+                                       let mut initial_liquidity_available_msat = None;
+                                       if let Some(capacity_sats) = $capacity_sats {
+                                               initial_liquidity_available_msat = Some(capacity_sats * 1000);
+                                       }
+
                                        if let Some(htlc_maximum_msat) = $directional_info.htlc_maximum_msat {
                                        if let Some(htlc_maximum_msat) = $directional_info.htlc_maximum_msat {
-                                               if let Some(capacity_sats) = $capacity_sats {
-                                                       available_msat = Some(cmp::min(capacity_sats * 1000, htlc_maximum_msat));
+                                               if let Some(available_msat) = initial_liquidity_available_msat {
+                                                       initial_liquidity_available_msat = Some(cmp::min(available_msat, htlc_maximum_msat));
                                                } else {
                                                } else {
-                                                       available_msat = Some(htlc_maximum_msat);
+                                                       initial_liquidity_available_msat = Some(htlc_maximum_msat);
                                                }
                                        }
 
                                                }
                                        }
 
-                                       let hm_entry = dist.entry(&$src_node_id);
-                                       let old_entry = hm_entry.or_insert_with(|| {
-                                               let mut fee_base_msat = u32::max_value();
-                                               let mut fee_proportional_millionths = u32::max_value();
-                                               if let Some(fees) = network.get_nodes().get(&$src_node_id).and_then(|node| node.lowest_inbound_channel_fees) {
-                                                       fee_base_msat = fees.base_msat;
-                                                       fee_proportional_millionths = fees.proportional_millionths;
+                                       match initial_liquidity_available_msat {
+                                               Some(available_msat) => available_msat,
+                                               // We assume channels with unknown balance have
+                                               // a capacity of 0.0025 BTC (or 250_000 sats).
+                                               None => 250_000 * 1000
+                                       }
+                               });
+
+                               // It is tricky to substract $next_hops_fee_msat from available liquidity here.
+                               // It may be misleading because we might later choose to reduce the value transferred
+                               // over these channels, and the channel which was insufficient might become sufficient.
+                               // Worst case: we drop a good channel here because it can't cover the high following
+                               // fees caused by one expensive channel, but then this channel could have been used
+                               // if the amount being transferred over this path is lower.
+                               // We do this for now, but this is a subject for removal.
+                               if let Some(available_value_contribution_msat) = available_liquidity_msat.checked_sub($next_hops_fee_msat) {
+
+                                       // Routing Fragmentation Mitigation heuristic:
+                                       //
+                                       // Routing fragmentation across many payment paths increases the overall routing
+                                       // fees as you have irreducible routing fees per-link used (`fee_base_msat`).
+                                       // Taking too many smaller paths also increases the chance of payment failure.
+                                       // Thus to avoid this effect, we require from our collected links to provide
+                                       // at least a minimal contribution to the recommended value yet-to-be-fulfilled.
+                                       //
+                                       // This requirement is currently 5% of the remaining-to-be-collected value.
+                                       // This means as we successfully advance in our collection,
+                                       // the absolute liquidity contribution is lowered,
+                                       // thus increasing the number of potential channels to be selected.
+
+                                       // Derive the minimal liquidity contribution with a ratio of 20 (5%, rounded up).
+                                       let minimal_value_contribution_msat: u64 = (recommended_value_msat - already_collected_value_msat + 19) / 20;
+                                       // Verify the liquidity offered by this channel complies to the minimal contribution.
+                                       let contributes_sufficient_value = available_value_contribution_msat >= minimal_value_contribution_msat;
+
+                                       let value_contribution_msat = cmp::min(available_value_contribution_msat, $next_hops_value_contribution);
+                                       // Includes paying fees for the use of the following channels.
+                                       let amount_to_transfer_over_msat: u64 = match value_contribution_msat.checked_add($next_hops_fee_msat) {
+                                               Some(result) => result,
+                                               // Can't overflow due to how the values were computed right above.
+                                               None => unreachable!(),
+                                       };
+
+                                       // If HTLC minimum is larger than the whole value we're going to transfer, we shouldn't bother
+                                       // even considering this channel, because it won't be useful.
+                                       // TODO: Explore simply adding fee to hit htlc_minimum_msat
+                                       // This is separate from checking amount_to_transfer_over_msat, which also should be
+                                       // lower-bounded by htlc_minimum_msat. Since we're choosing it as maximum possible,
+                                       // this channel should just be skipped if it's not sufficient.
+                                       // amount_to_transfer_over_msat can be both larger and smaller than final_value_msat,
+                                       // so this can't be derived.
+                                       let final_value_satisfies_htlc_minimum_msat = final_value_msat >= $directional_info.htlc_minimum_msat;
+                                       if final_value_satisfies_htlc_minimum_msat &&
+                                               contributes_sufficient_value && amount_to_transfer_over_msat >= $directional_info.htlc_minimum_msat {
+                                               let hm_entry = dist.entry(&$src_node_id);
+                                               let old_entry = hm_entry.or_insert_with(|| {
+                                                       // If there was previously no known way to access
+                                                       // the source node (recall it goes payee-to-payer) of $chan_id, first add
+                                                       // a semi-dummy record just to compute the fees to reach the source node.
+                                                       // This will affect our decision on selecting $chan_id
+                                                       // as a way to reach the $dest_node_id.
+                                                       let mut fee_base_msat = u32::max_value();
+                                                       let mut fee_proportional_millionths = u32::max_value();
+                                                       if let Some(Some(fees)) = network.get_nodes().get(&$src_node_id).map(|node| node.lowest_inbound_channel_fees) {
+                                                               fee_base_msat = fees.base_msat;
+                                                               fee_proportional_millionths = fees.proportional_millionths;
+                                                       }
+                                                       PathBuildingHop {
+                                                               route_hop: RouteHop {
+                                                                       pubkey: $dest_node_id.clone(),
+                                                                       node_features: NodeFeatures::empty(),
+                                                                       short_channel_id: 0,
+                                                                       channel_features: $chan_features.clone(),
+                                                                       fee_msat: 0,
+                                                                       cltv_expiry_delta: 0,
+                                                               },
+                                                               src_lowest_inbound_fees: RoutingFees {
+                                                                       base_msat: fee_base_msat,
+                                                                       proportional_millionths: fee_proportional_millionths,
+                                                               },
+                                                               channel_fees: $directional_info.fees,
+                                                               next_hops_fee_msat: u64::max_value(),
+                                                               hop_use_fee_msat: u64::max_value(),
+                                                               total_fee_msat: u64::max_value(),
+                                                       }
+                                               });
+
+                                               let mut hop_use_fee_msat = 0;
+                                               let mut total_fee_msat = $next_hops_fee_msat;
+
+                                               // Ignore hop_use_fee_msat for channel-from-us as we assume all channels-from-us
+                                               // will have the same effective-fee
+                                               if $src_node_id != *our_node_id {
+                                                       match compute_fees(amount_to_transfer_over_msat, $directional_info.fees) {
+                                                               // max_value means we'll always fail
+                                                               // the old_entry.total_fee_msat > total_fee_msat check
+                                                               None => total_fee_msat = u64::max_value(),
+                                                               Some(fee_msat) => {
+                                                                       hop_use_fee_msat = fee_msat;
+                                                                       total_fee_msat += hop_use_fee_msat;
+                                                                       if let Some(prev_hop_fee_msat) = compute_fees(total_fee_msat + amount_to_transfer_over_msat,
+                                                                                                                                                               old_entry.src_lowest_inbound_fees) {
+                                                                               if let Some(incremented_total_fee_msat) = total_fee_msat.checked_add(prev_hop_fee_msat) {
+                                                                                       total_fee_msat = incremented_total_fee_msat;
+                                                                               }
+                                                                               else {
+                                                                                       // max_value means we'll always fail
+                                                                                       // the old_entry.total_fee_msat > total_fee_msat check
+                                                                                       total_fee_msat = u64::max_value();
+                                                                               }
+                                                                       } else {
+                                                                               // max_value means we'll always fail
+                                                                               // the old_entry.total_fee_msat > total_fee_msat check
+                                                                               total_fee_msat = u64::max_value();
+                                                                       }
+                                                               }
+                                                       }
                                                }
                                                }
-                                               (u64::max_value(),
-                                                       fee_base_msat,
-                                                       fee_proportional_millionths,
-                                                       RouteHop {
+
+                                               let new_graph_node = RouteGraphNode {
+                                                       pubkey: $src_node_id,
+                                                       lowest_fee_to_peer_through_node: total_fee_msat,
+                                                       lowest_fee_to_node: $next_hops_fee_msat as u64 + hop_use_fee_msat,
+                                                       value_contribution_msat: value_contribution_msat,
+                                               };
+
+                                               // Update the way of reaching $src_node_id with the given $chan_id (from $dest_node_id),
+                                               // if this way is cheaper than the already known
+                                               // (considering the cost to "reach" this channel from the route destination,
+                                               // the cost of using this channel,
+                                               // and the cost of routing to the source node of this channel).
+                                               if old_entry.total_fee_msat > total_fee_msat {
+                                                       targets.push(new_graph_node);
+                                                       old_entry.next_hops_fee_msat = $next_hops_fee_msat;
+                                                       old_entry.hop_use_fee_msat = hop_use_fee_msat;
+                                                       old_entry.total_fee_msat = total_fee_msat;
+                                                       old_entry.route_hop = RouteHop {
                                                                pubkey: $dest_node_id.clone(),
                                                                node_features: NodeFeatures::empty(),
                                                                pubkey: $dest_node_id.clone(),
                                                                node_features: NodeFeatures::empty(),
-                                                               short_channel_id: 0,
+                                                               short_channel_id: $chan_id.clone(),
                                                                channel_features: $chan_features.clone(),
                                                                channel_features: $chan_features.clone(),
-                                                               fee_msat: 0,
-                                                               cltv_expiry_delta: 0,
-                                                       },
-                                                       None,
-                                               )
-                                       });
-                                       if $src_node_id != *our_node_id {
-                                               // Ignore new_fee for channel-from-us as we assume all channels-from-us
-                                               // will have the same effective-fee
-                                               total_fee += new_fee;
-                                               if let Some(fee_inc) = final_value_msat.checked_add(total_fee).and_then(|inc| { (old_entry.2 as u64).checked_mul(inc) }) {
-                                                       total_fee += fee_inc / 1000000 + (old_entry.1 as u64);
-                                               } else {
-                                                       // max_value means we'll always fail the old_entry.0 > total_fee check
-                                                       total_fee = u64::max_value();
+                                                               fee_msat: 0, // This value will be later filled with hop_use_fee_msat of the following channel
+                                                               cltv_expiry_delta: $directional_info.cltv_expiry_delta as u32,
+                                                       };
+                                                       old_entry.channel_fees = $directional_info.fees;
                                                }
                                        }
                                                }
                                        }
-                                       let new_graph_node = RouteGraphNode {
-                                               pubkey: $src_node_id,
-                                               lowest_fee_to_peer_through_node: total_fee,
-                                               lowest_fee_to_node: $starting_fee_msat as u64 + new_fee,
-                                       };
-                                       if old_entry.0 > total_fee {
-                                               targets.push(new_graph_node);
-                                               old_entry.0 = total_fee;
-                                               old_entry.3 = RouteHop {
-                                                       pubkey: $dest_node_id.clone(),
-                                                       node_features: NodeFeatures::empty(),
-                                                       short_channel_id: $chan_id.clone(),
-                                                       channel_features: $chan_features.clone(),
-                                                       fee_msat: new_fee, // This field is ignored on the last-hop anyway
-                                                       cltv_expiry_delta: $directional_info.cltv_expiry_delta as u32,
-                                               };
-                                               old_entry.4 = available_msat;
-                                       }
                                }
                        }
                };
        }
 
                                }
                        }
                };
        }
 
+       // Find ways (channels with destination) to reach a given node and store them
+       // in the corresponding data structures (routing graph etc).
+       // $fee_to_target_msat represents how much it costs to reach to this node from the payee,
+       // meaning how much will be paid in fees after this node (to the best of our knowledge).
+       // This data can later be helpful to optimize routing (pay lower fees).
        macro_rules! add_entries_to_cheapest_to_target_node {
        macro_rules! add_entries_to_cheapest_to_target_node {
-               ( $node: expr, $node_id: expr, $fee_to_target_msat: expr ) => {
+               ( $node: expr, $node_id: expr, $fee_to_target_msat: expr, $next_hops_value_contribution: expr ) => {
                        if first_hops.is_some() {
                                if let Some(&(ref first_hop, ref features)) = first_hop_targets.get(&$node_id) {
                        if first_hops.is_some() {
                                if let Some(&(ref first_hop, ref features)) = first_hop_targets.get(&$node_id) {
-                                       add_entry!(first_hop, *our_node_id, $node_id, dummy_directional_info, None::<u64>, features.to_context(), $fee_to_target_msat);
+                                       add_entry!(first_hop, *our_node_id, $node_id, dummy_directional_info, None::<u64>, features.to_context(), $fee_to_target_msat, $next_hops_value_contribution);
                                }
                        }
 
                                }
                        }
 
@@ -329,7 +597,7 @@ pub fn get_route<L: Deref>(our_node_id: &PublicKey, network: &NetworkGraph, targ
                                                        if first_hops.is_none() || chan.node_two != *our_node_id {
                                                                if let Some(two_to_one) = chan.two_to_one.as_ref() {
                                                                        if two_to_one.enabled {
                                                        if first_hops.is_none() || chan.node_two != *our_node_id {
                                                                if let Some(two_to_one) = chan.two_to_one.as_ref() {
                                                                        if two_to_one.enabled {
-                                                                               add_entry!(chan_id, chan.node_two, chan.node_one, two_to_one, chan.capacity_sats, chan.features, $fee_to_target_msat);
+                                                                               add_entry!(chan_id, chan.node_two, chan.node_one, two_to_one, chan.capacity_sats, chan.features, $fee_to_target_msat, $next_hops_value_contribution);
                                                                        }
                                                                }
                                                        }
                                                                        }
                                                                }
                                                        }
@@ -337,7 +605,7 @@ pub fn get_route<L: Deref>(our_node_id: &PublicKey, network: &NetworkGraph, targ
                                                        if first_hops.is_none() || chan.node_one != *our_node_id {
                                                                if let Some(one_to_two) = chan.one_to_two.as_ref() {
                                                                        if one_to_two.enabled {
                                                        if first_hops.is_none() || chan.node_one != *our_node_id {
                                                                if let Some(one_to_two) = chan.one_to_two.as_ref() {
                                                                        if one_to_two.enabled {
-                                                                               add_entry!(chan_id, chan.node_one, chan.node_two, one_to_two, chan.capacity_sats, chan.features, $fee_to_target_msat);
+                                                                               add_entry!(chan_id, chan.node_one, chan.node_two, one_to_two, chan.capacity_sats, chan.features, $fee_to_target_msat, $next_hops_value_contribution);
                                                                        }
                                                                }
 
                                                                        }
                                                                }
 
@@ -349,94 +617,274 @@ pub fn get_route<L: Deref>(our_node_id: &PublicKey, network: &NetworkGraph, targ
                };
        }
 
                };
        }
 
-       match network.get_nodes().get(target) {
-               None => {},
-               Some(node) => {
-                       add_entries_to_cheapest_to_target_node!(node, target, 0);
-               },
-       }
+       let mut payment_paths = Vec::<PaymentPath>::new();
+
+       // TODO: diversify by nodes (so that all paths aren't doomed if one node is offline).
+       'paths_collection: loop {
+               // For every new path, start from scratch, except
+               // bookkeeped_channels_liquidity_available_msat, which will improve
+               // the further iterations of path finding. Also don't erase first_hop_targets.
+               targets.clear();
+               dist.clear();
+
+               // Add the payee as a target, so that the payee-to-payer
+               // search algorithm knows what to start with.
+               match network.get_nodes().get(payee) {
+                       // The payee is not in our network graph, so nothing to add here.
+                       // There is still a chance of reaching them via last_hops though,
+                       // so don't yet fail the payment here.
+                       // If not, targets.pop() will not even let us enter the loop in step 2.
+                       None => {},
+                       Some(node) => {
+                               add_entries_to_cheapest_to_target_node!(node, payee, 0, recommended_value_msat);
+                       },
+               }
 
 
-       for hop in last_hops.iter() {
-               let have_hop_src_in_graph =
-                       if let Some(&(ref first_hop, ref features)) = first_hop_targets.get(&hop.src_node_id) {
-                               // If this hop connects to a node with which we have a direct channel, ignore the
-                               // network graph and add both the hop and our direct channel to the candidate set:
-                               //
-                               // Currently there are no channel-context features defined, so we are a
-                               // bit lazy here. In the future, we should pull them out via our
-                               // ChannelManager, but there's no reason to waste the space until we
-                               // need them.
-                               add_entry!(first_hop, *our_node_id , hop.src_node_id, dummy_directional_info, None::<u64>, features.to_context(), 0);
-                               true
-                       } else {
-                               // In any other case, only add the hop if the source is in the regular network
-                               // graph:
-                               network.get_nodes().get(&hop.src_node_id).is_some()
-                       };
-               if have_hop_src_in_graph {
-                       // BOLT 11 doesn't allow inclusion of features for the last hop hints, which
-                       // really sucks, cause we're gonna need that eventually.
-                       let last_hop_htlc_minimum_msat: u64 = match hop.htlc_minimum_msat {
-                               Some(htlc_minimum_msat) => htlc_minimum_msat,
-                               None => 0
-                       };
-                       let directional_info = DummyDirectionalChannelInfo {
-                               cltv_expiry_delta: hop.cltv_expiry_delta as u32,
-                               htlc_minimum_msat: last_hop_htlc_minimum_msat,
-                               htlc_maximum_msat: hop.htlc_maximum_msat,
-                               fees: hop.fees,
-                       };
-                       add_entry!(hop.short_channel_id, hop.src_node_id, target, directional_info, None::<u64>, ChannelFeatures::empty(), 0);
+               // Step (1).
+               // If a caller provided us with last hops, add them to routing targets. Since this happens
+               // earlier than general path finding, they will be somewhat prioritized, although currently
+               // it matters only if the fees are exactly the same.
+               for hop in last_hops.iter() {
+                       let have_hop_src_in_graph =
+                               if let Some(&(ref first_hop, ref features)) = first_hop_targets.get(&hop.src_node_id) {
+                                       // If this hop connects to a node with which we have a direct channel, ignore
+                                       // the network graph and add both the hop and our direct channel to
+                                       // the candidate set.
+                                       //
+                                       // Currently there are no channel-context features defined, so we are a
+                                       // bit lazy here. In the future, we should pull them out via our
+                                       // ChannelManager, but there's no reason to waste the space until we
+                                       // need them.
+                                       add_entry!(first_hop, *our_node_id , hop.src_node_id, dummy_directional_info, None::<u64>, features.to_context(), 0, recommended_value_msat);
+                                       true
+                               } else {
+                                       // In any other case, only add the hop if the source is in the regular network
+                                       // graph:
+                                       network.get_nodes().get(&hop.src_node_id).is_some()
+                               };
+                       if have_hop_src_in_graph {
+                               // BOLT 11 doesn't allow inclusion of features for the last hop hints, which
+                               // really sucks, cause we're gonna need that eventually.
+                               let last_hop_htlc_minimum_msat: u64 = match hop.htlc_minimum_msat {
+                                       Some(htlc_minimum_msat) => htlc_minimum_msat,
+                                       None => 0
+                               };
+                               let directional_info = DummyDirectionalChannelInfo {
+                                       cltv_expiry_delta: hop.cltv_expiry_delta as u32,
+                                       htlc_minimum_msat: last_hop_htlc_minimum_msat,
+                                       htlc_maximum_msat: hop.htlc_maximum_msat,
+                                       fees: hop.fees,
+                               };
+                               add_entry!(hop.short_channel_id, hop.src_node_id, payee, directional_info, None::<u64>, ChannelFeatures::empty(), 0, recommended_value_msat);
+                       }
                }
                }
-       }
 
 
-       while let Some(RouteGraphNode { pubkey, lowest_fee_to_node, .. }) = targets.pop() {
-               if pubkey == *our_node_id {
-                       let mut res = vec!(dist.remove(&our_node_id).unwrap().3);
-                       loop {
-                               if let Some(&(_, ref features)) = first_hop_targets.get(&res.last().unwrap().pubkey) {
-                                       res.last_mut().unwrap().node_features = features.to_context();
-                               } else if let Some(node) = network.get_nodes().get(&res.last().unwrap().pubkey) {
-                                       if let Some(node_info) = node.announcement_info.as_ref() {
-                                               res.last_mut().unwrap().node_features = node_info.features.clone();
+               // At this point, targets are filled with the data from first and
+               // last hops communicated by the caller, and the payment receiver.
+               let mut found_new_path = false;
+
+               // Step (2).
+               // If this loop terminates due the exhaustion of targets, two situations are possible:
+               // - not enough outgoing liquidity:
+               //   0 < already_collected_value_msat < final_value_msat
+               // - enough outgoing liquidity:
+               //   final_value_msat <= already_collected_value_msat < recommended_value_msat
+               // Both these cases (and other cases except reaching recommended_value_msat) mean that
+               // paths_collection will be stopped because found_new_path==false.
+               // This is not necessarily a routing failure.
+               'path_construction: while let Some(RouteGraphNode { pubkey, lowest_fee_to_node, value_contribution_msat, .. }) = targets.pop() {
+
+                       // Since we're going payee-to-payer, hitting our node as a target means we should stop
+                       // traversing the graph and arrange the path out of what we found.
+                       if pubkey == *our_node_id {
+                               let mut new_entry = dist.remove(&our_node_id).unwrap();
+                               let mut ordered_hops = vec!(new_entry.clone());
+
+                               'path_walk: loop {
+                                       if let Some(&(_, ref features)) = first_hop_targets.get(&ordered_hops.last().unwrap().route_hop.pubkey) {
+                                               ordered_hops.last_mut().unwrap().route_hop.node_features = features.to_context();
+                                       } else if let Some(node) = network.get_nodes().get(&ordered_hops.last().unwrap().route_hop.pubkey) {
+                                               if let Some(node_info) = node.announcement_info.as_ref() {
+                                                       ordered_hops.last_mut().unwrap().route_hop.node_features = node_info.features.clone();
+                                               } else {
+                                                       ordered_hops.last_mut().unwrap().route_hop.node_features = NodeFeatures::empty();
+                                               }
                                        } else {
                                        } else {
-                                               res.last_mut().unwrap().node_features = NodeFeatures::empty();
+                                               // We should be able to fill in features for everything except the last
+                                               // hop, if the last hop was provided via a BOLT 11 invoice (though we
+                                               // should be able to extend it further as BOLT 11 does have feature
+                                               // flags for the last hop node itself).
+                                               assert!(ordered_hops.last().unwrap().route_hop.pubkey == *payee);
                                        }
                                        }
-                               } else {
-                                       // We should be able to fill in features for everything except the last
-                                       // hop, if the last hop was provided via a BOLT 11 invoice (though we
-                                       // should be able to extend it further as BOLT 11 does have feature
-                                       // flags for the last hop node itself).
-                                       assert!(res.last().unwrap().pubkey == *target);
+
+                                       // Means we succesfully traversed from the payer to the payee, now
+                                       // save this path for the payment route. Also, update the liquidity
+                                       // remaining on the used hops, so that we take them into account
+                                       // while looking for more paths.
+                                       if ordered_hops.last().unwrap().route_hop.pubkey == *payee {
+                                               break 'path_walk;
+                                       }
+
+                                       new_entry = match dist.remove(&ordered_hops.last().unwrap().route_hop.pubkey) {
+                                               Some(payment_hop) => payment_hop,
+                                               // We can't arrive at None because, if we ever add an entry to targets,
+                                               // we also fill in the entry in dist (see add_entry!).
+                                               None => unreachable!(),
+                                       };
+                                       // We "propagate" the fees one hop backward (topologically) here,
+                                       // so that fees paid for a HTLC forwarding on the current channel are
+                                       // associated with the previous channel (where they will be subtracted).
+                                       ordered_hops.last_mut().unwrap().route_hop.fee_msat = new_entry.hop_use_fee_msat;
+                                       ordered_hops.last_mut().unwrap().route_hop.cltv_expiry_delta = new_entry.route_hop.cltv_expiry_delta;
+                                       ordered_hops.push(new_entry.clone());
                                }
                                }
-                               if res.last().unwrap().pubkey == *target {
-                                       break;
+                               ordered_hops.last_mut().unwrap().route_hop.fee_msat = value_contribution_msat;
+                               ordered_hops.last_mut().unwrap().hop_use_fee_msat = 0;
+                               ordered_hops.last_mut().unwrap().route_hop.cltv_expiry_delta = final_cltv;
+
+                               let payment_path = PaymentPath {hops: ordered_hops};
+                               // Since a path allows to transfer as much value as
+                               // the smallest channel it has ("bottleneck"), we should recompute
+                               // the fees so sender HTLC don't overpay fees when traversing
+                               // larger channels than the bottleneck. This may happen because
+                               // when we were selecting those channels we were not aware how much value
+                               // this path will transfer, and the relative fee for them
+                               // might have been computed considering a larger value.
+                               // Remember that we used these channels so that we don't rely
+                               // on the same liquidity in future paths.
+                               for (i, payment_hop) in payment_path.hops.iter().enumerate() {
+                                       let channel_liquidity_available_msat = bookkeeped_channels_liquidity_available_msat.get_mut(&payment_hop.route_hop.short_channel_id).unwrap();
+                                       let mut spent_on_hop_msat = value_contribution_msat;
+                                       let next_hops_fee_msat = payment_hop.next_hops_fee_msat;
+                                       spent_on_hop_msat += next_hops_fee_msat;
+                                       if *channel_liquidity_available_msat < spent_on_hop_msat {
+                                               // This should not happen because we do recompute fees right before,
+                                               // trying to avoid cases when a hop is not usable due to the fee situation.
+                                               break 'path_construction;
+                                       }
+                                       *channel_liquidity_available_msat -= spent_on_hop_msat;
                                }
                                }
+                               // Track the total amount all our collected paths allow to send so that we:
+                               // - know when to stop looking for more paths
+                               // - know which of the hops are useless considering how much more sats we need
+                               //   (contributes_sufficient_value)
+                               already_collected_value_msat += value_contribution_msat;
+
+                               payment_paths.push(payment_path);
+                               found_new_path = true;
+                               break 'path_construction;
+                       }
 
 
-                               let new_entry = match dist.remove(&res.last().unwrap().pubkey) {
-                                       Some(hop) => hop.3,
-                                       None => return Err(LightningError{err: "Failed to find a non-fee-overflowing path to the given destination".to_owned(), action: ErrorAction::IgnoreError}),
-                               };
-                               res.last_mut().unwrap().fee_msat = new_entry.fee_msat;
-                               res.last_mut().unwrap().cltv_expiry_delta = new_entry.cltv_expiry_delta;
-                               res.push(new_entry);
+                       // Otherwise, since the current target node is not us,
+                       // keep "unrolling" the payment graph from payee to payer by
+                       // finding a way to reach the current target from the payer side.
+                       match network.get_nodes().get(&pubkey) {
+                               None => {},
+                               Some(node) => {
+                                       add_entries_to_cheapest_to_target_node!(node, &pubkey, lowest_fee_to_node, value_contribution_msat);
+                               },
                        }
                        }
-                       res.last_mut().unwrap().fee_msat = final_value_msat;
-                       res.last_mut().unwrap().cltv_expiry_delta = final_cltv;
-                       let route = Route { paths: vec![res] };
-                       log_trace!(logger, "Got route: {}", log_route!(route));
-                       return Ok(route);
                }
 
                }
 
-               match network.get_nodes().get(&pubkey) {
-                       None => {},
-                       Some(node) => {
-                               add_entries_to_cheapest_to_target_node!(node, &pubkey, lowest_fee_to_node);
-                       },
+               // Step (3).
+               // Stop either when recommended value is reached,
+               // or if during last iteration no new path was found.
+               // In the latter case, making another path finding attempt could not help,
+               // because we deterministically terminate the search due to low liquidity.
+               if already_collected_value_msat >= recommended_value_msat || !found_new_path {
+                       break 'paths_collection;
+               }
+       }
+
+       // Step (4).
+       if payment_paths.len() == 0 {
+               return Err(LightningError{err: "Failed to find a path to the given destination".to_owned(), action: ErrorAction::IgnoreError});
+       }
+
+       if already_collected_value_msat < final_value_msat {
+               return Err(LightningError{err: "Failed to find a sufficient route to the given destination".to_owned(), action: ErrorAction::IgnoreError});
+       }
+
+       // Sort by total fees and take the best paths.
+       payment_paths.sort_by_key(|path| path.get_total_fee_paid_msat());
+       if payment_paths.len() > 50 {
+               payment_paths.truncate(50);
+       }
+
+       // Draw multiple sufficient routes by randomly combining the selected paths.
+       let mut drawn_routes = Vec::new();
+       for i in 0..payment_paths.len() {
+               let mut cur_route = Vec::<PaymentPath>::new();
+               let mut aggregate_route_value_msat = 0;
+
+               // Step (5).
+               // TODO: real random shuffle
+               // Currently just starts with i_th and goes up to i-1_th in a looped way.
+               let cur_payment_paths = [&payment_paths[i..], &payment_paths[..i]].concat();
+
+               // Step (6).
+               for payment_path in cur_payment_paths {
+                       cur_route.push(payment_path.clone());
+                       aggregate_route_value_msat += payment_path.get_value_msat();
+                       if aggregate_route_value_msat > final_value_msat {
+                               // Last path likely overpaid. Substract it from the most expensive
+                               // (in terms of proportional fee) path in this route and recompute fees.
+                               // This might be not the most economically efficient way, but fewer paths
+                               // also makes routing more reliable.
+                               let mut overpaid_value_msat = aggregate_route_value_msat - final_value_msat;
+
+                               // First, drop some expensive low-value paths entirely if possible.
+                               // Sort by value so that we drop many really-low values first, since
+                               // fewer paths is better: the payment is less likely to fail.
+                               // TODO: this could also be optimized by also sorting by feerate_per_sat_routed,
+                               // so that the sender pays less fees overall.
+                               cur_route.sort_by_key(|path| path.get_value_msat());
+                               // We should make sure that at least 1 path left.
+                               let mut paths_left = cur_route.len();
+                               cur_route.retain(|path| {
+                                       if paths_left == 1 {
+                                               return true
+                                       }
+                                       let mut keep = true;
+                                       let path_value_msat = path.get_value_msat();
+                                       if path_value_msat <= overpaid_value_msat {
+                                               keep = false;
+                                               overpaid_value_msat -= path_value_msat;
+                                               paths_left -= 1;
+                                       }
+                                       keep
+                               });
+
+                               if overpaid_value_msat == 0 {
+                                       break;
+                               }
+
+                               assert!(cur_route.len() > 0);
+
+                               // Step (7).
+                               // Now, substract the overpaid value from the most-expensive path.
+                               cur_route.sort_by_key(|path| { path.hops.iter().map(|hop| hop.channel_fees.proportional_millionths as u64).sum::<u64>() });
+                               let expensive_payment_path = cur_route.last_mut().unwrap();
+                               let expensive_path_new_value_msat = expensive_payment_path.get_value_msat() - overpaid_value_msat;
+                               // TODO: make sure expensive_path_new_value_msat doesn't cause to fall behind htlc_minimum_msat.
+                               expensive_payment_path.update_value_and_recompute_fees(expensive_path_new_value_msat);
+                               break;
+                       }
                }
                }
+               drawn_routes.push(cur_route);
+       }
+
+       // Step (8).
+       // Select the best route by lowest total fee.
+       drawn_routes.sort_by_key(|paths| paths.iter().map(|path| path.get_total_fee_paid_msat()).sum::<u64>());
+       let mut selected_paths = Vec::<Vec::<RouteHop>>::new();
+       for payment_path in drawn_routes.first().unwrap() {
+               selected_paths.push(payment_path.hops.iter().map(|payment_hop| payment_hop.route_hop.clone()).collect());
        }
 
        }
 
-       Err(LightningError{err: "Failed to find a path to the given destination".to_owned(), action: ErrorAction::IgnoreError})
+       let route = Route { paths: selected_paths };
+       log_trace!(logger, "Got route: {}", log_route!(route));
+       return Ok(route);
 }
 
 #[cfg(test)]
 }
 
 #[cfg(test)]
@@ -454,6 +902,9 @@ mod tests {
        use bitcoin::hashes::Hash;
        use bitcoin::network::constants::Network;
        use bitcoin::blockdata::constants::genesis_block;
        use bitcoin::hashes::Hash;
        use bitcoin::network::constants::Network;
        use bitcoin::blockdata::constants::genesis_block;
+       use bitcoin::blockdata::script::Builder;
+       use bitcoin::blockdata::opcodes;
+       use bitcoin::blockdata::transaction::TxOut;
 
        use hex;
 
 
        use hex;
 
@@ -502,12 +953,10 @@ mod tests {
 
                match net_graph_msg_handler.handle_channel_update(&valid_channel_update) {
                        Ok(res) => assert!(res),
 
                match net_graph_msg_handler.handle_channel_update(&valid_channel_update) {
                        Ok(res) => assert!(res),
-                       // Err(_) => panic!()
-                       Err(e) => println!("{:?}", e.err)
+                       Err(_) => panic!()
                };
        }
 
                };
        }
 
-
        fn add_or_update_node(net_graph_msg_handler: &NetGraphMsgHandler<Arc<test_utils::TestChainSource>, Arc<test_utils::TestLogger>>, secp_ctx: &Secp256k1<All>, node_privkey: &SecretKey,
           features: NodeFeatures, timestamp: u32) {
                let node_id = PublicKey::from_secret_key(&secp_ctx, node_privkey);
        fn add_or_update_node(net_graph_msg_handler: &NetGraphMsgHandler<Arc<test_utils::TestChainSource>, Arc<test_utils::TestLogger>>, secp_ctx: &Secp256k1<All>, node_privkey: &SecretKey,
           features: NodeFeatures, timestamp: u32) {
                let node_id = PublicKey::from_secret_key(&secp_ctx, node_privkey);
@@ -561,9 +1010,10 @@ mod tests {
                }
        }
 
                }
        }
 
-       fn build_graph() -> (Secp256k1<All>, NetGraphMsgHandler<std::sync::Arc<crate::util::test_utils::TestChainSource>, std::sync::Arc<crate::util::test_utils::TestLogger>>, std::sync::Arc<test_utils::TestLogger>) {
+       fn build_graph() -> (Secp256k1<All>, NetGraphMsgHandler<std::sync::Arc<test_utils::TestChainSource>, std::sync::Arc<crate::util::test_utils::TestLogger>>, std::sync::Arc<test_utils::TestChainSource>, std::sync::Arc<test_utils::TestLogger>) {
                let secp_ctx = Secp256k1::new();
                let logger = Arc::new(test_utils::TestLogger::new());
                let secp_ctx = Secp256k1::new();
                let logger = Arc::new(test_utils::TestLogger::new());
+               let chain_monitor = Arc::new(test_utils::TestChainSource::new(Network::Testnet));
                let net_graph_msg_handler = NetGraphMsgHandler::new(genesis_block(Network::Testnet).header.block_hash(), None, Arc::clone(&logger));
                // Build network from our_id to node7:
                //
                let net_graph_msg_handler = NetGraphMsgHandler::new(genesis_block(Network::Testnet).header.block_hash(), None, Arc::clone(&logger));
                // Build network from our_id to node7:
                //
@@ -860,15 +1310,20 @@ mod tests {
 
                add_or_update_node(&net_graph_msg_handler, &secp_ctx, &privkeys[5], NodeFeatures::from_le_bytes(id_to_feature_flags(6)), 0);
 
 
                add_or_update_node(&net_graph_msg_handler, &secp_ctx, &privkeys[5], NodeFeatures::from_le_bytes(id_to_feature_flags(6)), 0);
 
-               (secp_ctx, net_graph_msg_handler, logger)
+               (secp_ctx, net_graph_msg_handler, chain_monitor, logger)
        }
 
        #[test]
        fn simple_route_test() {
        }
 
        #[test]
        fn simple_route_test() {
-               let (secp_ctx, net_graph_msg_handler, logger) = build_graph();
+               let (secp_ctx, net_graph_msg_handler, _, logger) = build_graph();
                let (_, our_id, _, nodes) = get_nodes(&secp_ctx);
 
                let (_, our_id, _, nodes) = get_nodes(&secp_ctx);
 
-               // Simple route to 3 via 2
+               // Simple route to 2 via 1
+
+               if let Err(LightningError{err, action: ErrorAction::IgnoreError}) = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, &Vec::new(), 0, 42, Arc::clone(&logger)) {
+                       assert_eq!(err, "Cannot send a payment of 0 msat");
+               } else { panic!(); }
+
                let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, &Vec::new(), 100, 42, Arc::clone(&logger)).unwrap();
                assert_eq!(route.paths[0].len(), 2);
 
                let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, &Vec::new(), 100, 42, Arc::clone(&logger)).unwrap();
                assert_eq!(route.paths[0].len(), 2);
 
@@ -888,16 +1343,58 @@ mod tests {
        }
 
        #[test]
        }
 
        #[test]
-       fn disable_channels_test() {
-               let (secp_ctx, net_graph_msg_handler, logger) = build_graph();
+       fn invalid_first_hop_test() {
+               let (secp_ctx, net_graph_msg_handler, _, logger) = build_graph();
+               let (_, our_id, _, nodes) = get_nodes(&secp_ctx);
+
+               // Simple route to 2 via 1
+
+               let our_chans = vec![channelmanager::ChannelDetails {
+                       channel_id: [0; 32],
+                       short_channel_id: Some(2),
+                       remote_network_id: our_id,
+                       counterparty_features: InitFeatures::from_le_bytes(vec![0b11]),
+                       channel_value_satoshis: 100000,
+                       user_id: 0,
+                       outbound_capacity_msat: 100000,
+                       inbound_capacity_msat: 100000,
+                       is_live: true,
+               }];
+
+               if let Err(LightningError{err, action: ErrorAction::IgnoreError}) = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], Some(&our_chans.iter().collect::<Vec<_>>()), &Vec::new(), 100, 42, Arc::clone(&logger)) {
+                       assert_eq!(err, "First hop cannot have our_node_id as a destination.");
+               } else { panic!(); }
+
+               let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, &Vec::new(), 100, 42, Arc::clone(&logger)).unwrap();
+               assert_eq!(route.paths[0].len(), 2);
+       }
+
+       #[test]
+       fn htlc_minimum_test() {
+               let (secp_ctx, net_graph_msg_handler, _, logger) = build_graph();
                let (our_privkey, our_id, privkeys, nodes) = get_nodes(&secp_ctx);
 
                let (our_privkey, our_id, privkeys, nodes) = get_nodes(&secp_ctx);
 
-               // // Disable channels 4 and 12 by flags=2
+               // Simple route to 2 via 1
+               // Should fail if htlc_minimum can't be reached
+
+               update_channel(&net_graph_msg_handler, &secp_ctx, &our_privkey, UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 2,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 50_000,
+                       htlc_maximum_msat: OptionalField::Absent,
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+               // Make 0 fee.
                update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[1], UnsignedChannelUpdate {
                        chain_hash: genesis_block(Network::Testnet).header.block_hash(),
                        short_channel_id: 4,
                        timestamp: 2,
                update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[1], UnsignedChannelUpdate {
                        chain_hash: genesis_block(Network::Testnet).header.block_hash(),
                        short_channel_id: 4,
                        timestamp: 2,
-                       flags: 2, // to disable
+                       flags: 0,
                        cltv_expiry_delta: 0,
                        htlc_minimum_msat: 0,
                        htlc_maximum_msat: OptionalField::Absent,
                        cltv_expiry_delta: 0,
                        htlc_minimum_msat: 0,
                        htlc_maximum_msat: OptionalField::Absent,
@@ -905,6 +1402,8 @@ mod tests {
                        fee_proportional_millionths: 0,
                        excess_data: Vec::new()
                });
                        fee_proportional_millionths: 0,
                        excess_data: Vec::new()
                });
+
+               // Disable other paths
                update_channel(&net_graph_msg_handler, &secp_ctx, &our_privkey, UnsignedChannelUpdate {
                        chain_hash: genesis_block(Network::Testnet).header.block_hash(),
                        short_channel_id: 12,
                update_channel(&net_graph_msg_handler, &secp_ctx, &our_privkey, UnsignedChannelUpdate {
                        chain_hash: genesis_block(Network::Testnet).header.block_hash(),
                        short_channel_id: 12,
@@ -917,64 +1416,206 @@ mod tests {
                        fee_proportional_millionths: 0,
                        excess_data: Vec::new()
                });
                        fee_proportional_millionths: 0,
                        excess_data: Vec::new()
                });
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[0], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 3,
+                       timestamp: 2,
+                       flags: 2, // to disable
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Absent,
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[7], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 13,
+                       timestamp: 2,
+                       flags: 2, // to disable
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Absent,
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[2], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 6,
+                       timestamp: 2,
+                       flags: 2, // to disable
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Absent,
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[2], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 7,
+                       timestamp: 2,
+                       flags: 2, // to disable
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Absent,
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
 
 
-               // If all the channels require some features we don't understand, route should fail
-               if let Err(LightningError{err, action: ErrorAction::IgnoreError}) = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, &Vec::new(), 100, 42, Arc::clone(&logger)) {
+               if let Err(LightningError{err, action: ErrorAction::IgnoreError}) = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, &Vec::new(), 49_999, 42, Arc::clone(&logger)) {
                        assert_eq!(err, "Failed to find a path to the given destination");
                } else { panic!(); }
 
                        assert_eq!(err, "Failed to find a path to the given destination");
                } else { panic!(); }
 
-               // If we specify a channel to node7, that overrides our local channel view and that gets used
-               let our_chans = vec![channelmanager::ChannelDetails {
-                       channel_id: [0; 32],
-                       short_channel_id: Some(42),
-                       remote_network_id: nodes[7].clone(),
-                       counterparty_features: InitFeatures::from_le_bytes(vec![0b11]),
-                       channel_value_satoshis: 0,
-                       user_id: 0,
-                       outbound_capacity_msat: 0,
-                       inbound_capacity_msat: 0,
-                       is_live: true,
-               }];
-               let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], Some(&our_chans.iter().collect::<Vec<_>>()),  &Vec::new(), 100, 42, Arc::clone(&logger)).unwrap();
+               // A payment above the minimum should pass
+               let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, &Vec::new(), 50_000, 42, Arc::clone(&logger)).unwrap();
                assert_eq!(route.paths[0].len(), 2);
 
                assert_eq!(route.paths[0].len(), 2);
 
-               assert_eq!(route.paths[0][0].pubkey, nodes[7]);
-               assert_eq!(route.paths[0][0].short_channel_id, 42);
-               assert_eq!(route.paths[0][0].fee_msat, 200);
-               assert_eq!(route.paths[0][0].cltv_expiry_delta, (13 << 8) | 1);
-               assert_eq!(route.paths[0][0].node_features.le_flags(), &vec![0b11]); // it should also override our view of their features
-               assert_eq!(route.paths[0][0].channel_features.le_flags(), &Vec::<u8>::new()); // No feature flags will meet the relevant-to-channel conversion
-
-               assert_eq!(route.paths[0][1].pubkey, nodes[2]);
-               assert_eq!(route.paths[0][1].short_channel_id, 13);
-               assert_eq!(route.paths[0][1].fee_msat, 100);
-               assert_eq!(route.paths[0][1].cltv_expiry_delta, 42);
-               assert_eq!(route.paths[0][1].node_features.le_flags(), &id_to_feature_flags(3));
-               assert_eq!(route.paths[0][1].channel_features.le_flags(), &id_to_feature_flags(13));
-       }
-
-       #[test]
-       fn disable_node_test() {
-               let (secp_ctx, net_graph_msg_handler, logger) = build_graph();
-               let (_, our_id, privkeys, nodes) = get_nodes(&secp_ctx);
+               // This was a check against final_value_msat.
+               // Now let's check against amount_to_transfer_over_msat.
+               // Set minimal HTLC of 200_000_000 msat.
+               update_channel(&net_graph_msg_handler, &secp_ctx, &our_privkey, UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 2,
+                       timestamp: 3,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 200_000_000,
+                       htlc_maximum_msat: OptionalField::Absent,
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
 
 
-               // Disable nodes 1, 2, and 8 by requiring unknown feature bits
-               let mut unknown_features = NodeFeatures::known();
-               unknown_features.set_required_unknown_bits();
-               add_or_update_node(&net_graph_msg_handler, &secp_ctx, &privkeys[0], unknown_features.clone(), 1);
-               add_or_update_node(&net_graph_msg_handler, &secp_ctx, &privkeys[1], unknown_features.clone(), 1);
-               add_or_update_node(&net_graph_msg_handler, &secp_ctx, &privkeys[7], unknown_features.clone(), 1);
+               // Second hop only allows to forward 199_999_999 at most, thus not allowing the first hop to
+               // be used.
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[1], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 4,
+                       timestamp: 3,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(199_999_999),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
 
 
-               // If all nodes require some features we don't understand, route should fail
-               if let Err(LightningError{err, action: ErrorAction::IgnoreError}) = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, &Vec::new(), 100, 42, Arc::clone(&logger)) {
+               // Not possible to send 199_999_999, because the minimum on channel=2 is 200_000_000.
+               if let Err(LightningError{err, action: ErrorAction::IgnoreError}) = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, &Vec::new(), 199_999_999, 42, Arc::clone(&logger)) {
                        assert_eq!(err, "Failed to find a path to the given destination");
                } else { panic!(); }
 
                        assert_eq!(err, "Failed to find a path to the given destination");
                } else { panic!(); }
 
-               // If we specify a channel to node7, that overrides our local channel view and that gets used
-               let our_chans = vec![channelmanager::ChannelDetails {
-                       channel_id: [0; 32],
-                       short_channel_id: Some(42),
-                       remote_network_id: nodes[7].clone(),
+               // Lift the restriction on the first hop.
+               update_channel(&net_graph_msg_handler, &secp_ctx, &our_privkey, UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 2,
+                       timestamp: 4,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Absent,
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               // A payment above the minimum should pass
+               let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, &Vec::new(), 199_999_999, 42, Arc::clone(&logger)).unwrap();
+               assert_eq!(route.paths[0].len(), 2);
+       }
+
+       #[test]
+       fn disable_channels_test() {
+               let (secp_ctx, net_graph_msg_handler, _, logger) = build_graph();
+               let (our_privkey, our_id, privkeys, nodes) = get_nodes(&secp_ctx);
+
+               // // Disable channels 4 and 12 by flags=2
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[1], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 4,
+                       timestamp: 2,
+                       flags: 2, // to disable
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Absent,
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+               update_channel(&net_graph_msg_handler, &secp_ctx, &our_privkey, UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 12,
+                       timestamp: 2,
+                       flags: 2, // to disable
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Absent,
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               // If all the channels require some features we don't understand, route should fail
+               if let Err(LightningError{err, action: ErrorAction::IgnoreError}) = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, &Vec::new(), 100, 42, Arc::clone(&logger)) {
+                       assert_eq!(err, "Failed to find a path to the given destination");
+               } else { panic!(); }
+
+               // If we specify a channel to node7, that overrides our local channel view and that gets used
+               let our_chans = vec![channelmanager::ChannelDetails {
+                       channel_id: [0; 32],
+                       short_channel_id: Some(42),
+                       remote_network_id: nodes[7].clone(),
+                       counterparty_features: InitFeatures::from_le_bytes(vec![0b11]),
+                       channel_value_satoshis: 0,
+                       user_id: 0,
+                       outbound_capacity_msat: 0,
+                       inbound_capacity_msat: 0,
+                       is_live: true,
+               }];
+               let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], Some(&our_chans.iter().collect::<Vec<_>>()),  &Vec::new(), 100, 42, Arc::clone(&logger)).unwrap();
+               assert_eq!(route.paths[0].len(), 2);
+
+               assert_eq!(route.paths[0][0].pubkey, nodes[7]);
+               assert_eq!(route.paths[0][0].short_channel_id, 42);
+               assert_eq!(route.paths[0][0].fee_msat, 200);
+               assert_eq!(route.paths[0][0].cltv_expiry_delta, (13 << 8) | 1);
+               assert_eq!(route.paths[0][0].node_features.le_flags(), &vec![0b11]); // it should also override our view of their features
+               assert_eq!(route.paths[0][0].channel_features.le_flags(), &Vec::<u8>::new()); // No feature flags will meet the relevant-to-channel conversion
+
+               assert_eq!(route.paths[0][1].pubkey, nodes[2]);
+               assert_eq!(route.paths[0][1].short_channel_id, 13);
+               assert_eq!(route.paths[0][1].fee_msat, 100);
+               assert_eq!(route.paths[0][1].cltv_expiry_delta, 42);
+               assert_eq!(route.paths[0][1].node_features.le_flags(), &id_to_feature_flags(3));
+               assert_eq!(route.paths[0][1].channel_features.le_flags(), &id_to_feature_flags(13));
+       }
+
+       #[test]
+       fn disable_node_test() {
+               let (secp_ctx, net_graph_msg_handler, _, logger) = build_graph();
+               let (_, our_id, privkeys, nodes) = get_nodes(&secp_ctx);
+
+               // Disable nodes 1, 2, and 8 by requiring unknown feature bits
+               let mut unknown_features = NodeFeatures::known();
+               unknown_features.set_required_unknown_bits();
+               add_or_update_node(&net_graph_msg_handler, &secp_ctx, &privkeys[0], unknown_features.clone(), 1);
+               add_or_update_node(&net_graph_msg_handler, &secp_ctx, &privkeys[1], unknown_features.clone(), 1);
+               add_or_update_node(&net_graph_msg_handler, &secp_ctx, &privkeys[7], unknown_features.clone(), 1);
+
+               // If all nodes require some features we don't understand, route should fail
+               if let Err(LightningError{err, action: ErrorAction::IgnoreError}) = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, &Vec::new(), 100, 42, Arc::clone(&logger)) {
+                       assert_eq!(err, "Failed to find a path to the given destination");
+               } else { panic!(); }
+
+               // If we specify a channel to node7, that overrides our local channel view and that gets used
+               let our_chans = vec![channelmanager::ChannelDetails {
+                       channel_id: [0; 32],
+                       short_channel_id: Some(42),
+                       remote_network_id: nodes[7].clone(),
                        counterparty_features: InitFeatures::from_le_bytes(vec![0b11]),
                        channel_value_satoshis: 0,
                        user_id: 0,
                        counterparty_features: InitFeatures::from_le_bytes(vec![0b11]),
                        channel_value_satoshis: 0,
                        user_id: 0,
@@ -1006,7 +1647,7 @@ mod tests {
 
        #[test]
        fn our_chans_test() {
 
        #[test]
        fn our_chans_test() {
-               let (secp_ctx, net_graph_msg_handler, logger) = build_graph();
+               let (secp_ctx, net_graph_msg_handler, _, logger) = build_graph();
                let (_, our_id, _, nodes) = get_nodes(&secp_ctx);
 
                // Route to 1 via 2 and 3 because our channel to 1 is disabled
                let (_, our_id, _, nodes) = get_nodes(&secp_ctx);
 
                // Route to 1 via 2 and 3 because our channel to 1 is disabled
@@ -1098,10 +1739,32 @@ mod tests {
 
        #[test]
        fn last_hops_test() {
 
        #[test]
        fn last_hops_test() {
-               let (secp_ctx, net_graph_msg_handler, logger) = build_graph();
+               let (secp_ctx, net_graph_msg_handler, _, logger) = build_graph();
                let (_, our_id, _, nodes) = get_nodes(&secp_ctx);
 
                // Simple test across 2, 3, 5, and 4 via a last_hop channel
                let (_, our_id, _, nodes) = get_nodes(&secp_ctx);
 
                // Simple test across 2, 3, 5, and 4 via a last_hop channel
+
+               // First check that lst hop can't have its source as the payee.
+               let invalid_last_hop = RouteHint {
+                       src_node_id: nodes[6],
+                       short_channel_id: 8,
+                       fees: RoutingFees {
+                               base_msat: 1000,
+                               proportional_millionths: 0,
+                       },
+                       cltv_expiry_delta: (8 << 8) | 1,
+                       htlc_minimum_msat: None,
+                       htlc_maximum_msat: None,
+               };
+
+               let mut invalid_last_hops = last_hops(&nodes);
+               invalid_last_hops.push(invalid_last_hop);
+               {
+                       if let Err(LightningError{err, action: ErrorAction::IgnoreError}) = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[6], None, &invalid_last_hops.iter().collect::<Vec<_>>(), 100, 42, Arc::clone(&logger)) {
+                               assert_eq!(err, "Last hop cannot have a payee as a source.");
+                       } else { panic!(); }
+               }
+
                let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[6], None, &last_hops(&nodes).iter().collect::<Vec<_>>(), 100, 42, Arc::clone(&logger)).unwrap();
                assert_eq!(route.paths[0].len(), 5);
 
                let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[6], None, &last_hops(&nodes).iter().collect::<Vec<_>>(), 100, 42, Arc::clone(&logger)).unwrap();
                assert_eq!(route.paths[0].len(), 5);
 
@@ -1145,7 +1808,7 @@ mod tests {
 
        #[test]
        fn our_chans_last_hop_connect_test() {
 
        #[test]
        fn our_chans_last_hop_connect_test() {
-               let (secp_ctx, net_graph_msg_handler, logger) = build_graph();
+               let (secp_ctx, net_graph_msg_handler, _, logger) = build_graph();
                let (_, our_id, _, nodes) = get_nodes(&secp_ctx);
 
                // Simple test with outbound channel to 4 to test that last_hops and first_hops connect
                let (_, our_id, _, nodes) = get_nodes(&secp_ctx);
 
                // Simple test with outbound channel to 4 to test that last_hops and first_hops connect
@@ -1306,4 +1969,1130 @@ mod tests {
                assert_eq!(route.paths[0][1].node_features.le_flags(), &[0; 0]); // We dont pass flags in from invoices yet
                assert_eq!(route.paths[0][1].channel_features.le_flags(), &[0; 0]); // We can't learn any flags from invoices, sadly
        }
                assert_eq!(route.paths[0][1].node_features.le_flags(), &[0; 0]); // We dont pass flags in from invoices yet
                assert_eq!(route.paths[0][1].channel_features.le_flags(), &[0; 0]); // We can't learn any flags from invoices, sadly
        }
+
+       #[test]
+       fn available_amount_while_routing_test() {
+               // Tests whether we choose the correct available channel amount while routing.
+
+               let (secp_ctx, mut net_graph_msg_handler, chain_monitor, logger) = build_graph();
+               let (our_privkey, our_id, privkeys, nodes) = get_nodes(&secp_ctx);
+
+               // We will use a simple single-path route from
+               // our node to node2 via node0: channels {1, 3}.
+
+               // First disable all other paths.
+               update_channel(&net_graph_msg_handler, &secp_ctx, &our_privkey, UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 2,
+                       timestamp: 2,
+                       flags: 2,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(100_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+               update_channel(&net_graph_msg_handler, &secp_ctx, &our_privkey, UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 12,
+                       timestamp: 2,
+                       flags: 2,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(100_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               // Make the first channel (#1) very permissive,
+               // and we will be testing all limits on the second channel.
+               update_channel(&net_graph_msg_handler, &secp_ctx, &our_privkey, UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 1,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(1_000_000_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               // First, let's see if routing works if we have absolutely no idea about the available amount.
+               // In this case, it should be set to 250_000 sats.
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[0], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 3,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Absent,
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               {
+                       // Attempt to route more than available results in a failure.
+                       if let Err(LightningError{err, action: ErrorAction::IgnoreError}) = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, &Vec::new(), 250_000_001, 42, Arc::clone(&logger)) {
+                               assert_eq!(err, "Failed to find a sufficient route to the given destination");
+                       } else { panic!(); }
+               }
+
+               {
+                       // Now, attempt to route an exact amount we have should be fine.
+                       let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, &Vec::new(), 250_000_000, 42, Arc::clone(&logger)).unwrap();
+                       assert_eq!(route.paths.len(), 1);
+                       let path = route.paths.last().unwrap();
+                       assert_eq!(path.len(), 2);
+                       assert_eq!(path.last().unwrap().pubkey, nodes[2]);
+                       assert_eq!(path.last().unwrap().fee_msat, 250_000_000);
+               }
+
+               // Now let's see if routing works if we know only htlc_maximum_msat.
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[0], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 3,
+                       timestamp: 3,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(15_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               {
+                       // Attempt to route more than available results in a failure.
+                       if let Err(LightningError{err, action: ErrorAction::IgnoreError}) = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, &Vec::new(), 15_001, 42, Arc::clone(&logger)) {
+                               assert_eq!(err, "Failed to find a sufficient route to the given destination");
+                       } else { panic!(); }
+               }
+
+               {
+                       // Now, attempt to route an exact amount we have should be fine.
+                       let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, &Vec::new(), 15_000, 42, Arc::clone(&logger)).unwrap();
+                       assert_eq!(route.paths.len(), 1);
+                       let path = route.paths.last().unwrap();
+                       assert_eq!(path.len(), 2);
+                       assert_eq!(path.last().unwrap().pubkey, nodes[2]);
+                       assert_eq!(path.last().unwrap().fee_msat, 15_000);
+               }
+
+               // Now let's see if routing works if we know only capacity from the UTXO.
+
+               // We can't change UTXO capacity on the fly, so we'll disable
+               // the existing channel and add another one with the capacity we need.
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[0], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 3,
+                       timestamp: 4,
+                       flags: 2,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Absent,
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               let good_script = Builder::new().push_opcode(opcodes::all::OP_PUSHNUM_2)
+               .push_slice(&PublicKey::from_secret_key(&secp_ctx, &privkeys[0]).serialize())
+               .push_slice(&PublicKey::from_secret_key(&secp_ctx, &privkeys[2]).serialize())
+               .push_opcode(opcodes::all::OP_PUSHNUM_2)
+               .push_opcode(opcodes::all::OP_CHECKMULTISIG).into_script().to_v0_p2wsh();
+
+               *chain_monitor.utxo_ret.lock().unwrap() = Ok(TxOut { value: 15, script_pubkey: good_script.clone() });
+               net_graph_msg_handler.add_chain_access(Some(chain_monitor));
+
+               add_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[0], &privkeys[2], ChannelFeatures::from_le_bytes(id_to_feature_flags(3)), 333);
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[0], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 333,
+                       timestamp: 1,
+                       flags: 0,
+                       cltv_expiry_delta: (3 << 8) | 1,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Absent,
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[2], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 333,
+                       timestamp: 1,
+                       flags: 1,
+                       cltv_expiry_delta: (3 << 8) | 2,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Absent,
+                       fee_base_msat: 100,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               {
+                       // Attempt to route more than available results in a failure.
+                       if let Err(LightningError{err, action: ErrorAction::IgnoreError}) = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, &Vec::new(), 15_001, 42, Arc::clone(&logger)) {
+                               assert_eq!(err, "Failed to find a sufficient route to the given destination");
+                       } else { panic!(); }
+               }
+
+               {
+                       // Now, attempt to route an exact amount we have should be fine.
+                       let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, &Vec::new(), 15_000, 42, Arc::clone(&logger)).unwrap();
+                       assert_eq!(route.paths.len(), 1);
+                       let path = route.paths.last().unwrap();
+                       assert_eq!(path.len(), 2);
+                       assert_eq!(path.last().unwrap().pubkey, nodes[2]);
+                       assert_eq!(path.last().unwrap().fee_msat, 15_000);
+               }
+
+               // Now let's see if routing chooses htlc_maximum_msat over UTXO capacity.
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[0], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 333,
+                       timestamp: 6,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(10_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               {
+                       // Attempt to route more than available results in a failure.
+                       if let Err(LightningError{err, action: ErrorAction::IgnoreError}) = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, &Vec::new(), 10_001, 42, Arc::clone(&logger)) {
+                               assert_eq!(err, "Failed to find a sufficient route to the given destination");
+                       } else { panic!(); }
+               }
+
+               {
+                       // Now, attempt to route an exact amount we have should be fine.
+                       let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, &Vec::new(), 10_000, 42, Arc::clone(&logger)).unwrap();
+                       assert_eq!(route.paths.len(), 1);
+                       let path = route.paths.last().unwrap();
+                       assert_eq!(path.len(), 2);
+                       assert_eq!(path.last().unwrap().pubkey, nodes[2]);
+                       assert_eq!(path.last().unwrap().fee_msat, 10_000);
+               }
+       }
+
+       #[test]
+       fn available_liquidity_last_hop_test() {
+               // Check that available liquidity properly limits the path even when only
+               // one of the latter hops is limited.
+               let (secp_ctx, net_graph_msg_handler, _, logger) = build_graph();
+               let (our_privkey, our_id, privkeys, nodes) = get_nodes(&secp_ctx);
+
+               // Path via {node7, node2, node4} is channels {12, 13, 6, 11}.
+               // {12, 13, 11} have the capacities of 100, {6} has a capacity of 50.
+               // Total capacity: 50 sats.
+
+               // Disable other potential paths.
+               update_channel(&net_graph_msg_handler, &secp_ctx, &our_privkey, UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 2,
+                       timestamp: 2,
+                       flags: 2,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(100_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[2], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 7,
+                       timestamp: 2,
+                       flags: 2,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(100_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               // Limit capacities
+
+               update_channel(&net_graph_msg_handler, &secp_ctx, &our_privkey, UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 12,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(100_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[7], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 13,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(100_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[2], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 6,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(50_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[4], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 11,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(100_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+               {
+                       // Attempt to route more than available results in a failure.
+                       if let Err(LightningError{err, action: ErrorAction::IgnoreError}) = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[3], None, &Vec::new(), 60_000, 42, Arc::clone(&logger)) {
+                               assert_eq!(err, "Failed to find a sufficient route to the given destination");
+                       } else { panic!(); }
+               }
+
+               {
+                       // Now, attempt to route 49 sats (just a bit below the capacity).
+                       let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[3], None, &Vec::new(), 49_000, 42, Arc::clone(&logger)).unwrap();
+                       assert_eq!(route.paths.len(), 1);
+                       let mut total_amount_paid_msat = 0;
+                       for path in &route.paths {
+                               assert_eq!(path.len(), 4);
+                               assert_eq!(path.last().unwrap().pubkey, nodes[3]);
+                               total_amount_paid_msat += path.last().unwrap().fee_msat;
+                       }
+                       assert_eq!(total_amount_paid_msat, 49_000);
+               }
+
+               {
+                       // Attempt to route an exact amount is also fine
+                       let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[3], None, &Vec::new(), 50_000, 42, Arc::clone(&logger)).unwrap();
+                       assert_eq!(route.paths.len(), 1);
+                       let mut total_amount_paid_msat = 0;
+                       for path in &route.paths {
+                               assert_eq!(path.len(), 4);
+                               assert_eq!(path.last().unwrap().pubkey, nodes[3]);
+                               total_amount_paid_msat += path.last().unwrap().fee_msat;
+                       }
+                       assert_eq!(total_amount_paid_msat, 50_000);
+               }
+       }
+
+       #[test]
+       fn ignore_fee_first_hop_test() {
+               let (secp_ctx, net_graph_msg_handler, _, logger) = build_graph();
+               let (our_privkey, our_id, privkeys, nodes) = get_nodes(&secp_ctx);
+
+               // Path via node0 is channels {1, 3}. Limit them to 100 and 50 sats (total limit 50).
+               update_channel(&net_graph_msg_handler, &secp_ctx, &our_privkey, UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 1,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(100_000),
+                       fee_base_msat: 1_000_000,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[0], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 3,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(50_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               {
+                       let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, &Vec::new(), 50_000, 42, Arc::clone(&logger)).unwrap();
+                       assert_eq!(route.paths.len(), 1);
+                       let mut total_amount_paid_msat = 0;
+                       for path in &route.paths {
+                               assert_eq!(path.len(), 2);
+                               assert_eq!(path.last().unwrap().pubkey, nodes[2]);
+                               total_amount_paid_msat += path.last().unwrap().fee_msat;
+                       }
+                       assert_eq!(total_amount_paid_msat, 50_000);
+               }
+       }
+
+       #[test]
+       fn simple_mpp_route_test() {
+               let (secp_ctx, net_graph_msg_handler, _, logger) = build_graph();
+               let (our_privkey, our_id, privkeys, nodes) = get_nodes(&secp_ctx);
+
+               // We need a route consisting of 3 paths:
+               // From our node to node2 via node0, node7, node1 (three paths one hop each).
+               // To achieve this, the amount being transferred should be around
+               // the total capacity of these 3 paths.
+
+               // First, we set limits on these (previously unlimited) channels.
+               // Their aggregate capacity will be 50 + 60 + 180 = 290 sats.
+
+               // Path via node0 is channels {1, 3}. Limit them to 100 and 50 sats (total limit 50).
+               update_channel(&net_graph_msg_handler, &secp_ctx, &our_privkey, UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 1,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(100_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[0], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 3,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(50_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               // Path via node7 is channels {12, 13}. Limit them to 60 and 60 sats
+               // (total limit 60).
+               update_channel(&net_graph_msg_handler, &secp_ctx, &our_privkey, UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 12,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(60_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[7], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 13,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(60_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               // Path via node1 is channels {2, 4}. Limit them to 200 and 180 sats
+               // (total capacity 180 sats).
+               update_channel(&net_graph_msg_handler, &secp_ctx, &our_privkey, UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 2,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(200_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[1], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 4,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(180_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               {
+                       // Attempt to route more than available results in a failure.
+                       if let Err(LightningError{err, action: ErrorAction::IgnoreError}) = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, &Vec::new(), 300_000, 42, Arc::clone(&logger)) {
+                               assert_eq!(err, "Failed to find a sufficient route to the given destination");
+                       } else { panic!(); }
+               }
+
+               {
+                       // Now, attempt to route 250 sats (just a bit below the capacity).
+                       // Our algorithm should provide us with these 3 paths.
+                       let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, &Vec::new(), 250_000, 42, Arc::clone(&logger)).unwrap();
+                       assert_eq!(route.paths.len(), 3);
+                       let mut total_amount_paid_msat = 0;
+                       for path in &route.paths {
+                               assert_eq!(path.len(), 2);
+                               assert_eq!(path.last().unwrap().pubkey, nodes[2]);
+                               total_amount_paid_msat += path.last().unwrap().fee_msat;
+                       }
+                       assert_eq!(total_amount_paid_msat, 250_000);
+               }
+
+               {
+                       // Attempt to route an exact amount is also fine
+                       let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, &Vec::new(), 290_000, 42, Arc::clone(&logger)).unwrap();
+                       assert_eq!(route.paths.len(), 3);
+                       let mut total_amount_paid_msat = 0;
+                       for path in &route.paths {
+                               assert_eq!(path.len(), 2);
+                               assert_eq!(path.last().unwrap().pubkey, nodes[2]);
+                               total_amount_paid_msat += path.last().unwrap().fee_msat;
+                       }
+                       assert_eq!(total_amount_paid_msat, 290_000);
+               }
+       }
+
+       #[test]
+       fn long_mpp_route_test() {
+               let (secp_ctx, net_graph_msg_handler, _, logger) = build_graph();
+               let (our_privkey, our_id, privkeys, nodes) = get_nodes(&secp_ctx);
+
+               // We need a route consisting of 3 paths:
+               // From our node to node3 via {node0, node2}, {node7, node2, node4} and {node7, node2}.
+               // Note that these paths overlap (channels 5, 12, 13).
+               // We will route 300 sats.
+               // Each path will have 100 sats capacity, those channels which
+               // are used twice will have 200 sats capacity.
+
+               // Disable other potential paths.
+               update_channel(&net_graph_msg_handler, &secp_ctx, &our_privkey, UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 2,
+                       timestamp: 2,
+                       flags: 2,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(100_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[2], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 7,
+                       timestamp: 2,
+                       flags: 2,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(100_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               // Path via {node0, node2} is channels {1, 3, 5}.
+               update_channel(&net_graph_msg_handler, &secp_ctx, &our_privkey, UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 1,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(100_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[0], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 3,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(100_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               // Capacity of 200 sats because this channel will be used by 3rd path as well.
+               add_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[2], &privkeys[3], ChannelFeatures::from_le_bytes(id_to_feature_flags(5)), 5);
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[2], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 5,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(200_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               // Path via {node7, node2, node4} is channels {12, 13, 6, 11}.
+               // Add 100 sats to the capacities of {12, 13}, because these channels
+               // are also used for 3rd path. 100 sats for the rest. Total capacity: 100 sats.
+               update_channel(&net_graph_msg_handler, &secp_ctx, &our_privkey, UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 12,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(200_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[7], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 13,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(200_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[2], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 6,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(100_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[4], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 11,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(100_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               // Path via {node7, node2} is channels {12, 13, 5}.
+               // We already limited them to 200 sats (they are used twice for 100 sats).
+               // Nothing to do here.
+
+               {
+                       // Attempt to route more than available results in a failure.
+                       if let Err(LightningError{err, action: ErrorAction::IgnoreError}) = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[3], None, &Vec::new(), 350_000, 42, Arc::clone(&logger)) {
+                               assert_eq!(err, "Failed to find a sufficient route to the given destination");
+                       } else { panic!(); }
+               }
+
+               {
+                       // Now, attempt to route 300 sats (exact amount we can route).
+                       // Our algorithm should provide us with these 3 paths, 100 sats each.
+                       let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[3], None, &Vec::new(), 300_000, 42, Arc::clone(&logger)).unwrap();
+                       assert_eq!(route.paths.len(), 3);
+
+                       let mut total_amount_paid_msat = 0;
+                       for path in &route.paths {
+                               assert_eq!(path.last().unwrap().pubkey, nodes[3]);
+                               total_amount_paid_msat += path.last().unwrap().fee_msat;
+                       }
+                       assert_eq!(total_amount_paid_msat, 300_000);
+               }
+
+       }
+
+       #[test]
+       fn mpp_cheaper_route_test() {
+               let (secp_ctx, net_graph_msg_handler, _, logger) = build_graph();
+               let (our_privkey, our_id, privkeys, nodes) = get_nodes(&secp_ctx);
+
+               // This test checks that if we have two cheaper paths and one more expensive path,
+               // so that liquidity-wise any 2 of 3 combination is sufficient,
+               // two cheaper paths will be taken.
+               // These paths have equal available liquidity.
+
+               // We need a combination of 3 paths:
+               // From our node to node3 via {node0, node2}, {node7, node2, node4} and {node7, node2}.
+               // Note that these paths overlap (channels 5, 12, 13).
+               // Each path will have 100 sats capacity, those channels which
+               // are used twice will have 200 sats capacity.
+
+               // Disable other potential paths.
+               update_channel(&net_graph_msg_handler, &secp_ctx, &our_privkey, UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 2,
+                       timestamp: 2,
+                       flags: 2,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(100_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[2], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 7,
+                       timestamp: 2,
+                       flags: 2,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(100_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               // Path via {node0, node2} is channels {1, 3, 5}.
+               update_channel(&net_graph_msg_handler, &secp_ctx, &our_privkey, UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 1,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(100_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[0], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 3,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(100_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               // Capacity of 200 sats because this channel will be used by 3rd path as well.
+               add_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[2], &privkeys[3], ChannelFeatures::from_le_bytes(id_to_feature_flags(5)), 5);
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[2], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 5,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(200_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               // Path via {node7, node2, node4} is channels {12, 13, 6, 11}.
+               // Add 100 sats to the capacities of {12, 13}, because these channels
+               // are also used for 3rd path. 100 sats for the rest. Total capacity: 100 sats.
+               update_channel(&net_graph_msg_handler, &secp_ctx, &our_privkey, UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 12,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(200_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[7], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 13,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(200_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[2], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 6,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(100_000),
+                       fee_base_msat: 1_000,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[4], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 11,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(100_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               // Path via {node7, node2} is channels {12, 13, 5}.
+               // We already limited them to 200 sats (they are used twice for 100 sats).
+               // Nothing to do here.
+
+               {
+                       // Now, attempt to route 180 sats.
+                       // Our algorithm should provide us with these 2 paths.
+                       let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[3], None, &Vec::new(), 180_000, 42, Arc::clone(&logger)).unwrap();
+                       assert_eq!(route.paths.len(), 2);
+
+                       let mut total_value_transferred_msat = 0;
+                       let mut total_paid_msat = 0;
+                       for path in &route.paths {
+                               assert_eq!(path.last().unwrap().pubkey, nodes[3]);
+                               total_value_transferred_msat += path.last().unwrap().fee_msat;
+                               for hop in path {
+                                       total_paid_msat += hop.fee_msat;
+                               }
+                       }
+                       // If we paid fee, this would be higher.
+                       assert_eq!(total_value_transferred_msat, 180_000);
+                       let total_fees_paid = total_paid_msat - total_value_transferred_msat;
+                       assert_eq!(total_fees_paid, 0);
+               }
+       }
+
+       #[test]
+       fn fees_on_mpp_route_test() {
+               // This test makes sure that MPP algorithm properly takes into account
+               // fees charged on the channels, by making the fees impactful:
+               // if the fee is not properly accounted for, the behavior is different.
+               let (secp_ctx, net_graph_msg_handler, _, logger) = build_graph();
+               let (our_privkey, our_id, privkeys, nodes) = get_nodes(&secp_ctx);
+
+               // We need a route consisting of 2 paths:
+               // From our node to node3 via {node0, node2} and {node7, node2, node4}.
+               // We will route 200 sats, Each path will have 100 sats capacity.
+
+               // This test is not particularly stable: e.g.,
+               // there's a way to route via {node0, node2, node4}.
+               // It works while pathfinding is deterministic, but can be broken otherwise.
+               // It's fine to ignore this concern for now.
+
+               // Disable other potential paths.
+               update_channel(&net_graph_msg_handler, &secp_ctx, &our_privkey, UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 2,
+                       timestamp: 2,
+                       flags: 2,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(100_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[2], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 7,
+                       timestamp: 2,
+                       flags: 2,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(100_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               // Path via {node0, node2} is channels {1, 3, 5}.
+               update_channel(&net_graph_msg_handler, &secp_ctx, &our_privkey, UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 1,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(100_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[0], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 3,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(100_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               add_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[2], &privkeys[3], ChannelFeatures::from_le_bytes(id_to_feature_flags(5)), 5);
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[2], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 5,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(100_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               // Path via {node7, node2, node4} is channels {12, 13, 6, 11}.
+               // All channels should be 100 sats capacity. But for the fee experiment,
+               // we'll add absolute fee of 150 sats paid for the use channel 6 (paid to node2 on channel 13).
+               // Since channel 12 allows to deliver only 250 sats to channel 13, channel 13 can transfer only
+               // 100 sats (and pay 150 sats in fees for the use of channel 6),
+               // so no matter how large are other channels,
+               // the whole path will be limited by 100 sats with just these 2 conditions:
+               // - channel 12 capacity is 250 sats
+               // - fee for channel 6 is 150 sats
+               // Let's test this by enforcing these 2 conditions and removing other limits.
+               update_channel(&net_graph_msg_handler, &secp_ctx, &our_privkey, UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 12,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(250_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[7], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 13,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Absent,
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[2], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 6,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Absent,
+                       fee_base_msat: 150_000,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[4], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 11,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Absent,
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               {
+                       // Attempt to route more than available results in a failure.
+                       if let Err(LightningError{err, action: ErrorAction::IgnoreError}) = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[3], None, &Vec::new(), 210_000, 42, Arc::clone(&logger)) {
+                               assert_eq!(err, "Failed to find a sufficient route to the given destination");
+                       } else { panic!(); }
+               }
+
+               {
+                       // Now, attempt to route 200 sats (exact amount we can route).
+                       let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[3], None, &Vec::new(), 200_000, 42, Arc::clone(&logger)).unwrap();
+                       assert_eq!(route.paths.len(), 2);
+
+                       let mut total_amount_paid_msat = 0;
+                       for path in &route.paths {
+                               assert_eq!(path.last().unwrap().pubkey, nodes[3]);
+                               total_amount_paid_msat += path.last().unwrap().fee_msat;
+                       }
+                       assert_eq!(total_amount_paid_msat, 200_000);
+               }
+
+       }
+
+       #[test]
+       fn drop_lowest_channel_mpp_route_test() {
+               // This test checks that low-capacity channel is dropped when after
+               // path finding we realize that we found more capacity than we need.
+               let (secp_ctx, net_graph_msg_handler, _, logger) = build_graph();
+               let (our_privkey, our_id, privkeys, nodes) = get_nodes(&secp_ctx);
+
+               // We need a route consisting of 3 paths:
+               // From our node to node2 via node0, node7, node1 (three paths one hop each).
+
+               // The first and the second paths should be sufficient, but the third should be
+               // cheaper, so that we select it but drop later.
+
+               // First, we set limits on these (previously unlimited) channels.
+               // Their aggregate capacity will be 50 + 60 + 20 = 130 sats.
+
+               // Path via node0 is channels {1, 3}. Limit them to 100 and 50 sats (total limit 50);
+               update_channel(&net_graph_msg_handler, &secp_ctx, &our_privkey, UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 1,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(100_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[0], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 3,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(50_000),
+                       fee_base_msat: 100,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               // Path via node7 is channels {12, 13}. Limit them to 60 and 60 sats (total limit 60);
+               update_channel(&net_graph_msg_handler, &secp_ctx, &our_privkey, UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 12,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(60_000),
+                       fee_base_msat: 100,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[7], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 13,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(60_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               // Path via node1 is channels {2, 4}. Limit them to 20 and 20 sats (total capacity 20 sats).
+               update_channel(&net_graph_msg_handler, &secp_ctx, &our_privkey, UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 2,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(20_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+               update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[1], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 4,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(20_000),
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               {
+                       // Attempt to route more than available results in a failure.
+                       if let Err(LightningError{err, action: ErrorAction::IgnoreError}) = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, &Vec::new(), 150_000, 42, Arc::clone(&logger)) {
+                               assert_eq!(err, "Failed to find a sufficient route to the given destination");
+                       } else { panic!(); }
+               }
+
+               {
+                       // Now, attempt to route 125 sats (just a bit below the capacity of 3 channels).
+                       // Our algorithm should provide us with these 3 paths.
+                       let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, &Vec::new(), 125_000, 42, Arc::clone(&logger)).unwrap();
+                       assert_eq!(route.paths.len(), 3);
+                       let mut total_amount_paid_msat = 0;
+                       for path in &route.paths {
+                               assert_eq!(path.len(), 2);
+                               assert_eq!(path.last().unwrap().pubkey, nodes[2]);
+                               total_amount_paid_msat += path.last().unwrap().fee_msat;
+                       }
+                       assert_eq!(total_amount_paid_msat, 125_000);
+               }
+
+               {
+                       // Attempt to route without the last small cheap channel
+                       let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, &Vec::new(), 90_000, 42, Arc::clone(&logger)).unwrap();
+                       assert_eq!(route.paths.len(), 2);
+                       let mut total_amount_paid_msat = 0;
+                       for path in &route.paths {
+                               assert_eq!(path.len(), 2);
+                               assert_eq!(path.last().unwrap().pubkey, nodes[2]);
+                               total_amount_paid_msat += path.last().unwrap().fee_msat;
+                       }
+                       assert_eq!(total_amount_paid_msat, 90_000);
+               }
+       }
+
 }
 }