[rust-lightning] / lightning / src / routing / router.rs

// This file is Copyright its original authors, visible in version control
// history.
//
// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
// You may not use this file except in accordance with one or both of these
// licenses.

//! The top-level routing/network map tracking logic lives here.
//!
//! You probably want to create a NetGraphMsgHandler and use that as your RoutingMessageHandler and then
//! interrogate it to get routes for your own payments.

use bitcoin::secp256k1::key::PublicKey;

use ln::channelmanager::ChannelDetails;
use ln::features::{ChannelFeatures, InvoiceFeatures, NodeFeatures};
use ln::msgs::{DecodeError, ErrorAction, LightningError, MAX_VALUE_MSAT};
use routing::network_graph::{NetworkGraph, RoutingFees};
use util::ser::{Writeable, Readable};
use util::logger::Logger;

use std::cmp;
use std::collections::{HashMap, BinaryHeap};
use std::ops::Deref;

/// A hop in a route
#[derive(Clone, PartialEq)]
pub struct RouteHop {
        /// The node_id of the node at this hop.
        pub pubkey: PublicKey,
        /// The node_announcement features of the node at this hop. For the last hop, these may be
        /// amended to match the features present in the invoice this node generated.
        pub node_features: NodeFeatures,
        /// The channel that should be used from the previous hop to reach this node.
        pub short_channel_id: u64,
        /// 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 paying for the use of the *next* channel in the path).
        /// For the last hop, this should be the full value of the payment (might be more than
        /// requested if we had to match htlc_minimum_msat).
        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 cltv_expiry_delta: u32,
}

/// (C-not exported)
impl Writeable for Vec<RouteHop> {
        fn write<W: ::util::ser::Writer>(&self, writer: &mut W) -> Result<(), ::std::io::Error> {
                (self.len() as u8).write(writer)?;
                for hop in self.iter() {
                        hop.pubkey.write(writer)?;
                        hop.node_features.write(writer)?;
                        hop.short_channel_id.write(writer)?;
                        hop.channel_features.write(writer)?;
                        hop.fee_msat.write(writer)?;
                        hop.cltv_expiry_delta.write(writer)?;
                }
                Ok(())
        }
}

/// (C-not exported)
impl Readable for Vec<RouteHop> {
        fn read<R: ::std::io::Read>(reader: &mut R) -> Result<Vec<RouteHop>, DecodeError> {
                let hops_count: u8 = Readable::read(reader)?;
                let mut hops = Vec::with_capacity(hops_count as usize);
                for _ in 0..hops_count {
                        hops.push(RouteHop {
                                pubkey: Readable::read(reader)?,
                                node_features: Readable::read(reader)?,
                                short_channel_id: Readable::read(reader)?,
                                channel_features: Readable::read(reader)?,
                                fee_msat: Readable::read(reader)?,
                                cltv_expiry_delta: Readable::read(reader)?,
                        });
                }
                Ok(hops)
        }
}

/// A route directs a payment from the sender (us) to the recipient. If the recipient supports MPP,
/// it can take multiple paths. Each path is composed of one or more hops through the network.
#[derive(Clone, PartialEq)]
pub struct Route {
        /// The list of routes taken for a single (potentially-)multi-part payment. The pubkey of the
        /// last RouteHop in each path must be the same.
        /// Each entry represents a list of hops, NOT INCLUDING our own, where the last hop is the
        /// destination. Thus, this must always be at least length one. While the maximum length of any
        /// given path is variable, keeping the length of any path to less than 20 should currently
        /// ensure it is viable.
        pub paths: Vec<Vec<RouteHop>>,
}

impl Writeable for Route {
        fn write<W: ::util::ser::Writer>(&self, writer: &mut W) -> Result<(), ::std::io::Error> {
                (self.paths.len() as u64).write(writer)?;
                for hops in self.paths.iter() {
                        hops.write(writer)?;
                }
                Ok(())
        }
}

impl Readable for Route {
        fn read<R: ::std::io::Read>(reader: &mut R) -> Result<Route, DecodeError> {
                let path_count: u64 = Readable::read(reader)?;
                let mut paths = Vec::with_capacity(cmp::min(path_count, 128) as usize);
                for _ in 0..path_count {
                        paths.push(Readable::read(reader)?);
                }
                Ok(Route { paths })
        }
}

/// A channel descriptor which provides a last-hop route to get_route
#[derive(Clone)]
pub struct RouteHint {
        /// The node_id of the non-target end of the route
        pub src_node_id: PublicKey,
        /// The short_channel_id of this channel
        pub short_channel_id: u64,
        /// The fees which must be paid to use this channel
        pub fees: RoutingFees,
        /// The difference in CLTV values between this node and the next node.
        pub cltv_expiry_delta: u16,
        /// The minimum value, in msat, which must be relayed to the next hop.
        pub htlc_minimum_msat: Option<u64>,
        /// The maximum value in msat available for routing with a single HTLC.
        pub htlc_maximum_msat: Option<u64>,
}

#[derive(Eq, PartialEq)]
struct RouteGraphNode {
        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,
        /// The effective htlc_minimum_msat at this hop. If a later hop on the path had a higher HTLC
        /// minimum, we use it, plus the fees required at each earlier hop to meet it.
        path_htlc_minimum_msat: u64,
}

impl cmp::Ord for RouteGraphNode {
        fn cmp(&self, other: &RouteGraphNode) -> cmp::Ordering {
                let other_score = cmp::max(other.lowest_fee_to_peer_through_node, other.path_htlc_minimum_msat);
                let self_score = cmp::max(self.lowest_fee_to_peer_through_node, self.path_htlc_minimum_msat);
                other_score.cmp(&self_score).then_with(|| other.pubkey.serialize().cmp(&self.pubkey.serialize()))
        }
}

impl cmp::PartialOrd for RouteGraphNode {
        fn partial_cmp(&self, other: &RouteGraphNode) -> Option<cmp::Ordering> {
                Some(self.cmp(other))
        }
}

struct DummyDirectionalChannelInfo {
        cltv_expiry_delta: u32,
        htlc_minimum_msat: u64,
        htlc_maximum_msat: Option<u64>,
        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<'a> {
        // The RouteHint fields which will eventually be used if this hop is used in a final Route.
        // Note that node_features is calculated separately after our initial graph walk.
        pubkey: PublicKey,
        short_channel_id: u64,
        channel_features: &'a ChannelFeatures,
        fee_msat: u64,
        cltv_expiry_delta: u32,

        /// 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,
        /// This is useful for update_value_and_recompute_fees to make sure
        /// we don't fall below the minimum. Should not be updated manually and
        /// generally should not be accessed.
        htlc_minimum_msat: u64,
        /// A mirror of the same field in RouteGraphNode. Note that this is only used during the graph
        /// walk and may be invalid thereafter.
        path_htlc_minimum_msat: u64,
        /// If we've already processed a node as the best node, we shouldn't process it again. Normally
        /// we'd just ignore it if we did as all channels would have a higher new fee, but because we
        /// may decrease the amounts in use as we walk the graph, the actual calculated fee may
        /// decrease as well. Thus, we have to explicitly track which nodes have been processed and
        /// avoid processing them again.
        was_processed: bool,
        #[cfg(any(test, feature = "fuzztarget"))]
        // In tests, we apply further sanity checks on cases where we skip nodes we already processed
        // to ensure it is specifically in cases where the fee has gone down because of a decrease in
        // value_contribution_msat, which requires tracking it here. See comments below where it is
        // used for more info.
        value_contribution_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<'a> {
        hops: Vec<(PathBuildingHop<'a>, NodeFeatures)>,
}

impl<'a> PaymentPath<'a> {
        // 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().0.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.fee_msat;
                        }
                }
                return result;
        }

        // If the amount transferred by the path is updated, the fees should be adjusted. Any other way
        // to change fees may result in an inconsistency.
        //
        // Sometimes we call this function right after constructing a path which has inconsistent
        // (in terms of reaching htlc_minimum_msat), so that this function puts the fees in order.
        // In that case we call it on the "same" amount we initially allocated for this path, and which
        // could have been reduced on the way. In that case, there is also a risk of exceeding
        // available_liquidity inside this function, because the function is unaware of this bound.
        // In our specific recomputation cases where we never increase the value the risk is pretty low.
        // This function, however, does not support arbitrarily increasing the value being transferred,
        // and the exception will be triggered.
        fn update_value_and_recompute_fees(&mut self, value_msat: u64) {
                assert!(value_msat <= self.hops.last().unwrap().0.fee_msat);

                let mut total_fee_paid_msat = 0 as u64;
                for i in (0..self.hops.len()).rev() {
                        let last_hop = i == self.hops.len() - 1;

                        // For non-last-hop, this value will represent the fees paid on the current hop. It
                        // will consist of the fees for the use of the next hop, and extra fees to match
                        // htlc_minimum_msat of the current channel. Last hop is handled separately.
                        let mut cur_hop_fees_msat = 0;
                        if !last_hop {
                                cur_hop_fees_msat = self.hops.get(i + 1).unwrap().0.hop_use_fee_msat;
                        }

                        let mut cur_hop = &mut self.hops.get_mut(i).unwrap().0;
                        cur_hop.next_hops_fee_msat = total_fee_paid_msat;
                        // Overpay in fees if we can't save these funds due to htlc_minimum_msat.
                        // We try to account for htlc_minimum_msat in scoring (add_entry!), so that nodes don't
                        // set it too high just to maliciously take more fees by exploiting this
                        // match htlc_minimum_msat logic.
                        let mut cur_hop_transferred_amount_msat = total_fee_paid_msat + value_msat;
                        if let Some(extra_fees_msat) = cur_hop.htlc_minimum_msat.checked_sub(cur_hop_transferred_amount_msat) {
                                // Note that there is a risk that *previous hops* (those closer to us, as we go
                                // payee->our_node here) would exceed their htlc_maximum_msat or available balance.
                                //
                                // This might make us end up with a broken route, although this should be super-rare
                                // in practice, both because of how healthy channels look like, and how we pick
                                // channels in add_entry.
                                // Also, this can't be exploited more heavily than *announce a free path and fail
                                // all payments*.
                                cur_hop_transferred_amount_msat += extra_fees_msat;
                                total_fee_paid_msat += extra_fees_msat;
                                cur_hop_fees_msat += extra_fees_msat;
                        }

                        if last_hop {
                                // Final hop is a special case: it usually has just value_msat (by design), but also
                                // it still could overpay for the htlc_minimum_msat.
                                cur_hop.fee_msat = cur_hop_transferred_amount_msat;
                        } else {
                                // Propagate updated fees for the use of the channels to one hop back, where they
                                // will be actually paid (fee_msat). The last hop is handled above separately.
                                cur_hop.fee_msat = cur_hop_fees_msat;
                        }

                        // Fee for the use of the current hop which will be deducted on the previous hop.
                        // Irrelevant for the first hop, as it doesn't have the previous hop, and the use of
                        // this channel is free for us.
                        if i != 0 {
                                if let Some(new_fee) = compute_fees(cur_hop_transferred_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!();
                                }
                        }
                }
        }
}

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 (payer) to the given target node (payee).
///
/// If the payee provided features in their invoice, they should be provided via payee_features.
/// Without this, MPP will only be used if the payee's features are available in the network graph.
///
/// 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.
///
/// 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/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, payee_features: Option<InvoiceFeatures>, 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.
        if *payee == *our_node_id {
                return Err(LightningError{err: "Cannot generate a route to ourselves".to_owned(), action: ErrorAction::IgnoreError});
        }

        if final_value_msat > MAX_VALUE_MSAT {
                return Err(LightningError{err: "Cannot generate a route of more value than all existing satoshis".to_owned(), action: ErrorAction::IgnoreError});
        }

        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 pseudo-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 pseudo-A*").
        //
        // We are not a faithful Dijkstra's implementation because we can change values which impact
        // earlier nodes while processing later nodes. Specifically, if we reach a channel with a lower
        // liquidity limit (via htlc_maximum_msat, on-chain capacity or assumed liquidity limits) then
        // the value we are currently attempting to send over a path, we simply reduce the value being
        // sent along the path for any hops after that channel. This may imply that later fees (which
        // we've already tabulated) are lower because a smaller value is passing through the channels
        // (and the proportional fee is thus lower). There isn't a trivial way to recalculate the
        // channels which were selected earlier (and which may still be used for other paths without a
        // lower liquidity limit), so we simply accept that some liquidity-limited paths may be
        // de-preferenced.
        //
        // One potentially problematic case for this algorithm would be if there are many
        // liquidity-limited paths which are liquidity-limited near the destination (ie early in our
        // graph walking), we may never find a path which is not liquidity-limited and has lower
        // proportional fee (and only lower absolute fee when considering the ultimate value sent).
        // Because we only consider paths with at least 5% of the total value being sent, the damage
        // from such a case should be limited, however this could be further reduced in the future by
        // calculating fees on the amount we wish to route over a path, ie ignoring the liquidity
        // limits for the purposes of fee calculation.
        //
        // Alternatively, we could store more detailed path information in the heap (targets, below)
        // and index the best-path map (dist, below) by node *and* HTLC limits, however that would blow
        // up the runtime significantly both algorithmically (as we'd traverse nodes multiple times)
        // and practically (as we would need to store dynamically-allocated path information in heap
        // objects, increasing malloc traffic and indirect memory access significantly). Further, the
        // results of such an algorithm would likely be biased towards lower-value paths.
        //
        // Further, we could return to a faithful Dijkstra's algorithm by rejecting paths with limits
        // outside of our current search value, running a path search more times to gather candidate
        // paths at different values. While this may be acceptable, further path searches may increase
        // runtime for little gain. Specifically, the current algorithm rather efficiently explores the
        // graph for candidate paths, calculating the maximum value which can realistically be sent at
        // the same time, remaining generic across different payment values.
        //
        // 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
        // one.

        let dummy_directional_info = DummyDirectionalChannelInfo { // used for first_hops routes
                cltv_expiry_delta: 0,
                htlc_minimum_msat: 0,
                htlc_maximum_msat: None,
                fees: RoutingFees {
                        base_msat: 0,
                        proportional_millionths: 0,
                }
        };

        // Allow MPP only if we have a features set from somewhere that indicates the payee supports
        // it. If the payee supports it they're supposed to include it in the invoice, so that should
        // work reliably.
        let allow_mpp = if let Some(features) = &payee_features {
                features.supports_basic_mpp()
        } else if let Some(node) = network.get_nodes().get(&payee) {
                if let Some(node_info) = node.announcement_info.as_ref() {
                        node_info.features.supports_basic_mpp()
                } else { false }
        } else { false };

        // 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<_, (_, ChannelFeatures, _, NodeFeatures)> =
                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 == *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.to_context(), chan.outbound_capacity_msat, chan.counterparty_features.to_context()));
                }
                if first_hop_targets.is_empty() {
                        return Err(LightningError{err: "Cannot route when there are no outbound routes away from us".to_owned(), action: ErrorAction::IgnoreError});
                }
        }

        let empty_channel_features = ChannelFeatures::empty();

        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());

        // During routing, if we ignore a path due to an htlc_minimum_msat limit, we set this,
        // indicating that we may wish to try again with a higher value, potentially paying to meet an
        // htlc_minimum with extra fees while still finding a cheaper path.
        let mut hit_minimum_limit;

        // When arranging a route, we select multiple paths so that we can make a multi-path payment.
        // We start with a path_value of the exact amount we want, and if that generates a route we may
        // return it immediately. Otherwise, we don't stop searching for paths until we have 3x the
        // amount we want in total across paths, selecting the best subset at the end.
        const ROUTE_CAPACITY_PROVISION_FACTOR: u64 = 3;
        let recommended_value_msat = final_value_msat * ROUTE_CAPACITY_PROVISION_FACTOR as u64;
        let mut path_value_msat = final_value_msat;

        // 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 (except for `outbound_capacity_msat` in `first_hops`).
        let mut bookkeeped_channels_liquidity_available_msat = HashMap::with_capacity(network.get_nodes().len());

        // 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.
                // $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, $next_hops_path_htlc_minimum_msat: 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(available_msat) = initial_liquidity_available_msat {
                                                        initial_liquidity_available_msat = Some(cmp::min(available_msat, htlc_maximum_msat));
                                                } else {
                                                        initial_liquidity_available_msat = Some(htlc_maximum_msat);
                                                }
                                        }

                                        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)
                                        // or 100% if we're not allowed to do multipath payments.
                                        let minimal_value_contribution_msat: u64 = if allow_mpp {
                                                (recommended_value_msat - already_collected_value_msat + 19) / 20
                                        } else {
                                                final_value_msat
                                        };
                                        // 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!(),
                                        };
                                        #[allow(unused_comparisons)] // $next_hops_path_htlc_minimum_msat is 0 in some calls so rustc complains
                                        let over_path_minimum_msat = amount_to_transfer_over_msat >= $directional_info.htlc_minimum_msat &&
                                                amount_to_transfer_over_msat >= $next_hops_path_htlc_minimum_msat;

                                        // If HTLC minimum is larger than the amount we're going to transfer, we shouldn't
                                        // bother considering this channel.
                                        // Since we're choosing amount_to_transfer_over_msat as maximum possible, it can
                                        // be only reduced later (not increased), so this channel should just be skipped
                                        // as not sufficient.
                                        if !over_path_minimum_msat {
                                                hit_minimum_limit = true;
                                        } else if contributes_sufficient_value {
                                                // Note that low contribution here (limited by available_liquidity_msat)
                                                // might violate htlc_minimum_msat on the hops which are next along the
                                                // payment path (upstream to the payee). To avoid that, we recompute path
                                                // path fees knowing the final path contribution after constructing it.
                                                let path_htlc_minimum_msat = match compute_fees($next_hops_path_htlc_minimum_msat, $directional_info.fees)
                                                                .map(|fee_msat| fee_msat.checked_add($next_hops_path_htlc_minimum_msat)) {
                                                        Some(Some(value_msat)) => cmp::max(value_msat, $directional_info.htlc_minimum_msat),
                                                        _ => u64::max_value()
                                                };
                                                let hm_entry = dist.entry(&$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 {
                                                                pubkey: $dest_node_id.clone(),
                                                                short_channel_id: 0,
                                                                channel_features: $chan_features,
                                                                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(),
                                                                htlc_minimum_msat: $directional_info.htlc_minimum_msat,
                                                                path_htlc_minimum_msat,
                                                                was_processed: false,
                                                                #[cfg(any(test, feature = "fuzztarget"))]
                                                                value_contribution_msat,
                                                        }
                                                });

                                                #[allow(unused_mut)] // We only use the mut in cfg(test)
                                                let mut should_process = !old_entry.was_processed;
                                                #[cfg(any(test, feature = "fuzztarget"))]
                                                {
                                                        // In test/fuzzing builds, we do extra checks to make sure the skipping
                                                        // of already-seen nodes only happens in cases we expect (see below).
                                                        if !should_process { should_process = true; }
                                                }

                                                if should_process {
                                                        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;
                                                                                // When calculating the lowest inbound fees to a node, we
                                                                                // calculate fees here not based on the actual value we think
                                                                                // will flow over this channel, but on the minimum value that
                                                                                // we'll accept flowing over it. The minimum accepted value
                                                                                // is a constant through each path collection run, ensuring
                                                                                // consistent basis. Otherwise we may later find a
                                                                                // different path to the source node that is more expensive,
                                                                                // but which we consider to be cheaper because we are capacity
                                                                                // constrained and the relative fee becomes lower.
                                                                                match compute_fees(minimal_value_contribution_msat, old_entry.src_lowest_inbound_fees)
                                                                                                .map(|a| a.checked_add(total_fee_msat)) {
                                                                                        Some(Some(v)) => {
                                                                                                total_fee_msat = v;
                                                                                        },
                                                                                        _ => {
                                                                                                total_fee_msat = u64::max_value();
                                                                                        }
                                                                                };
                                                                        }
                                                                }
                                                        }

                                                        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,
                                                                path_htlc_minimum_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).
                                                        // Also, consider that htlc_minimum_msat_difference, because we might end up
                                                        // paying it. Consider the following exploit:
                                                        // we use 2 paths to transfer 1.5 BTC. One of them is 0-fee normal 1 BTC path,
                                                        // and for the other one we picked a 1sat-fee path with htlc_minimum_msat of
                                                        // 1 BTC. Now, since the latter is more expensive, we gonna try to cut it
                                                        // by 0.5 BTC, but then match htlc_minimum_msat by paying a fee of 0.5 BTC
                                                        // to this channel.
                                                        // Ideally the scoring could be smarter (e.g. 0.5*htlc_minimum_msat here),
                                                        // but it may require additional tracking - we don't want to double-count
                                                        // the fees included in $next_hops_path_htlc_minimum_msat, but also
                                                        // can't use something that may decrease on future hops.
                                                        let old_cost = cmp::max(old_entry.total_fee_msat, old_entry.path_htlc_minimum_msat);
                                                        let new_cost = cmp::max(total_fee_msat, path_htlc_minimum_msat);

                                                        if !old_entry.was_processed && new_cost < old_cost {
                                                                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.pubkey = $dest_node_id.clone();
                                                                old_entry.short_channel_id = $chan_id.clone();
                                                                old_entry.channel_features = $chan_features;
                                                                old_entry.fee_msat = 0; // This value will be later filled with hop_use_fee_msat of the following channel
                                                                old_entry.cltv_expiry_delta = $directional_info.cltv_expiry_delta as u32;
                                                                old_entry.channel_fees = $directional_info.fees;
                                                                old_entry.htlc_minimum_msat = $directional_info.htlc_minimum_msat;
                                                                old_entry.path_htlc_minimum_msat = path_htlc_minimum_msat;
                                                                #[cfg(any(test, feature = "fuzztarget"))]
                                                                {
                                                                        old_entry.value_contribution_msat = value_contribution_msat;
                                                                }
                                                        } else if old_entry.was_processed && new_cost < old_cost {
                                                                #[cfg(any(test, feature = "fuzztarget"))]
                                                                {
                                                                        // If we're skipping processing a node which was previously
                                                                        // processed even though we found another path to it with a
                                                                        // cheaper fee, check that it was because the second path we
                                                                        // found (which we are processing now) has a lower value
                                                                        // contribution due to an HTLC minimum limit.
                                                                        //
                                                                        // e.g. take a graph with two paths from node 1 to node 2, one
                                                                        // through channel A, and one through channel B. Channel A and
                                                                        // B are both in the to-process heap, with their scores set by
                                                                        // a higher htlc_minimum than fee.
                                                                        // Channel A is processed first, and the channels onwards from
                                                                        // node 1 are added to the to-process heap. Thereafter, we pop
                                                                        // Channel B off of the heap, note that it has a much more
                                                                        // restrictive htlc_maximum_msat, and recalculate the fees for
                                                                        // all of node 1's channels using the new, reduced, amount.
                                                                        //
                                                                        // This would be bogus - we'd be selecting a higher-fee path
                                                                        // with a lower htlc_maximum_msat instead of the one we'd
                                                                        // already decided to use.
                                                                        debug_assert!(path_htlc_minimum_msat < old_entry.path_htlc_minimum_msat);
                                                                        debug_assert!(value_contribution_msat < old_entry.value_contribution_msat);
                                                                }
                                                        }
                                                }
                                        }
                                }
                        }
                };
        }

        let empty_node_features = NodeFeatures::empty();
        // 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 {
                ( $node: expr, $node_id: expr, $fee_to_target_msat: expr, $next_hops_value_contribution: expr, $next_hops_path_htlc_minimum_msat: expr ) => {
                        let skip_node = if let Some(elem) = dist.get_mut($node_id) {
                                let was_processed = elem.was_processed;
                                elem.was_processed = true;
                                was_processed
                        } else {
                                // Entries are added to dist in add_entry!() when there is a channel from a node.
                                // Because there are no channels from payee, it will not have a dist entry at this point.
                                // If we're processing any other node, it is always be the result of a channel from it.
                                assert_eq!($node_id, payee);
                                false
                        };

                        if !skip_node {
                                if first_hops.is_some() {
                                        if let Some(&(ref first_hop, ref features, ref outbound_capacity_msat, _)) = first_hop_targets.get(&$node_id) {
                                                add_entry!(first_hop, *our_node_id, $node_id, dummy_directional_info, Some(outbound_capacity_msat / 1000), features, $fee_to_target_msat, $next_hops_value_contribution, $next_hops_path_htlc_minimum_msat);
                                        }
                                }

                                let features = if let Some(node_info) = $node.announcement_info.as_ref() {
                                        &node_info.features
                                } else {
                                        &empty_node_features
                                };

                                if !features.requires_unknown_bits() {
                                        for chan_id in $node.channels.iter() {
                                                let chan = network.get_channels().get(chan_id).unwrap();
                                                if !chan.features.requires_unknown_bits() {
                                                        if chan.node_one == *$node_id {
                                                                // ie $node is one, ie next hop in A* is two, via the two_to_one channel
                                                                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, $next_hops_value_contribution, $next_hops_path_htlc_minimum_msat);
                                                                                }
                                                                        }
                                                                }
                                                        } else {
                                                                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, $next_hops_value_contribution, $next_hops_path_htlc_minimum_msat);
                                                                                }
                                                                        }
                                                                }
                                                        }
                                                }
                                        }
                                }
                        }
                };
        }

        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();
                hit_minimum_limit = false;

                // If first hop is a private channel and the only way to reach the payee, this is the only
                // place where it could be added.
                if first_hops.is_some() {
                        if let Some(&(ref first_hop, ref features, ref outbound_capacity_msat, _)) = first_hop_targets.get(&payee) {
                                add_entry!(first_hop, *our_node_id, payee, dummy_directional_info, Some(outbound_capacity_msat / 1000), features, 0, path_value_msat, 0);
                        }
                }

                // 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, path_value_msat, 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, ref outbound_capacity_msat, _)) = 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, Some(outbound_capacity_msat / 1000), features, 0, path_value_msat, 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, payee, directional_info, None::<u64>, &empty_channel_features, 0, path_value_msat, 0);
                        }
                }

                // 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, path_htlc_minimum_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(), NodeFeatures::empty()));

                                'path_walk: loop {
                                        if let Some(&(_, _, _, ref features)) = first_hop_targets.get(&ordered_hops.last().unwrap().0.pubkey) {
                                                ordered_hops.last_mut().unwrap().1 = features.clone();
                                        } else if let Some(node) = network.get_nodes().get(&ordered_hops.last().unwrap().0.pubkey) {
                                                if let Some(node_info) = node.announcement_info.as_ref() {
                                                        ordered_hops.last_mut().unwrap().1 = node_info.features.clone();
                                                } else {
                                                        ordered_hops.last_mut().unwrap().1 = NodeFeatures::empty();
                                                }
                                        } 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!(ordered_hops.last().unwrap().0.pubkey == *payee);
                                        }

                                        // 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().0.pubkey == *payee {
                                                break 'path_walk;
                                        }

                                        new_entry = match dist.remove(&ordered_hops.last().unwrap().0.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().0.fee_msat = new_entry.hop_use_fee_msat;
                                        ordered_hops.last_mut().unwrap().0.cltv_expiry_delta = new_entry.cltv_expiry_delta;
                                        ordered_hops.push((new_entry.clone(), NodeFeatures::empty()));
                                }
                                ordered_hops.last_mut().unwrap().0.fee_msat = value_contribution_msat;
                                ordered_hops.last_mut().unwrap().0.hop_use_fee_msat = 0;
                                ordered_hops.last_mut().unwrap().0.cltv_expiry_delta = final_cltv;

                                let mut payment_path = PaymentPath {hops: ordered_hops};

                                // We could have possibly constructed a slightly inconsistent path: since we reduce
                                // value being transferred along the way, we could have violated htlc_minimum_msat
                                // on some channels we already passed (assuming dest->source direction). Here, we
                                // recompute the fees again, so that if that's the case, we match the currently
                                // underpaid htlc_minimum_msat with fees.
                                payment_path.update_value_and_recompute_fees(cmp::min(value_contribution_msat, final_value_msat));

                                // 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.
                                let mut prevented_redundant_path_selection = false;
                                for (payment_hop, _) in payment_path.hops.iter() {
                                        let channel_liquidity_available_msat = bookkeeped_channels_liquidity_available_msat.get_mut(&payment_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;
                                        }
                                        if spent_on_hop_msat == *channel_liquidity_available_msat {
                                                // If this path used all of this channel's available liquidity, we know
                                                // this path will not be selected again in the next loop iteration.
                                                prevented_redundant_path_selection = true;
                                        }
                                        *channel_liquidity_available_msat -= spent_on_hop_msat;
                                }
                                if !prevented_redundant_path_selection {
                                        // If we weren't capped by hitting a liquidity limit on a channel in the path,
                                        // we'll probably end up picking the same path again on the next iteration.
                                        // Decrease the available liquidity of a hop in the middle of the path.
                                        let victim_liquidity = bookkeeped_channels_liquidity_available_msat.get_mut(
                                                &payment_path.hops[(payment_path.hops.len() - 1) / 2].0.short_channel_id).unwrap();
                                        *victim_liquidity = 0;
                                }

                                // 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;
                        }

                        // If we found a path back to the payee, we shouldn't try to process it again. This is
                        // the equivalent of the `elem.was_processed` check in
                        // add_entries_to_cheapest_to_target_node!() (see comment there for more info).
                        if pubkey == *payee { continue 'path_construction; }

                        // 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, path_htlc_minimum_msat);
                                },
                        }
                }

                if !allow_mpp {
                        // If we don't support MPP, no use trying to gather more value ever.
                        break 'paths_collection;
                }

                // Step (3).
                // Stop either when the recommended value is reached or if no new path was found in this
                // iteration.
                // In the latter case, making another path finding attempt won't help,
                // because we deterministically terminated the search due to low liquidity.
                if already_collected_value_msat >= recommended_value_msat || !found_new_path {
                        break 'paths_collection;
                } else if found_new_path && already_collected_value_msat == final_value_msat && payment_paths.len() == 1 {
                        // Further, if this was our first walk of the graph, and we weren't limited by an
                        // htlc_minimum_msat, return immediately because this path should suffice. If we were
                        // limited by an htlc_minimum_msat value, find another path with a higher value,
                        // potentially allowing us to pay fees to meet the htlc_minimum on the new path while
                        // still keeping a lower total fee than this path.
                        if !hit_minimum_limit {
                                break 'paths_collection;
                        }
                        path_value_msat = recommended_value_msat;
                }
        }

        // 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. And also htlc_minimum_msat.
                                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.
                                // TODO: this could also be optimized by also sorting by feerate_per_sat_routed,
                                // so that the sender pays less fees overall. And also htlc_minimum_msat.
                                cur_route.sort_by_key(|path| { path.hops.iter().map(|hop| hop.0.channel_fees.proportional_millionths as u64).sum::<u64>() });
                                let expensive_payment_path = cur_route.first_mut().unwrap();
                                // We already dropped all the small channels above, meaning all the
                                // remaining channels are larger than remaining overpaid_value_msat.
                                // Thus, this can't be negative.
                                let expensive_path_new_value_msat = expensive_payment_path.get_value_msat() - overpaid_value_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, node_features)| {
                        RouteHop {
                                pubkey: payment_hop.pubkey,
                                node_features: node_features.clone(),
                                short_channel_id: payment_hop.short_channel_id,
                                channel_features: payment_hop.channel_features.clone(),
                                fee_msat: payment_hop.fee_msat,
                                cltv_expiry_delta: payment_hop.cltv_expiry_delta,
                        }
                }).collect());
        }

        if let Some(features) = &payee_features {
                for path in selected_paths.iter_mut() {
                        path.last_mut().unwrap().node_features = features.to_context();
                }
        }

        let route = Route { paths: selected_paths };
        log_trace!(logger, "Got route: {}", log_route!(route));
        Ok(route)
}

#[cfg(test)]
mod tests {
        use routing::router::{get_route, RouteHint, RoutingFees};
        use routing::network_graph::{NetworkGraph, NetGraphMsgHandler};
        use ln::features::{ChannelFeatures, InitFeatures, InvoiceFeatures, NodeFeatures};
        use ln::msgs::{ErrorAction, LightningError, OptionalField, UnsignedChannelAnnouncement, ChannelAnnouncement, RoutingMessageHandler,
           NodeAnnouncement, UnsignedNodeAnnouncement, ChannelUpdate, UnsignedChannelUpdate};
        use ln::channelmanager;
        use util::test_utils;
        use util::ser::Writeable;

        use bitcoin::hashes::sha256d::Hash as Sha256dHash;
        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 bitcoin::secp256k1::key::{PublicKey,SecretKey};
        use bitcoin::secp256k1::{Secp256k1, All};

        use std::sync::Arc;

        // Using the same keys for LN and BTC ids
        fn add_channel(net_graph_msg_handler: &NetGraphMsgHandler<Arc<test_utils::TestChainSource>, Arc<test_utils::TestLogger>>, secp_ctx: &Secp256k1<All>, node_1_privkey: &SecretKey,
           node_2_privkey: &SecretKey, features: ChannelFeatures, short_channel_id: u64) {
                let node_id_1 = PublicKey::from_secret_key(&secp_ctx, node_1_privkey);
                let node_id_2 = PublicKey::from_secret_key(&secp_ctx, node_2_privkey);

                let unsigned_announcement = UnsignedChannelAnnouncement {
                        features,
                        chain_hash: genesis_block(Network::Testnet).header.block_hash(),
                        short_channel_id,
                        node_id_1,
                        node_id_2,
                        bitcoin_key_1: node_id_1,
                        bitcoin_key_2: node_id_2,
                        excess_data: Vec::new(),
                };

                let msghash = hash_to_message!(&Sha256dHash::hash(&unsigned_announcement.encode()[..])[..]);
                let valid_announcement = ChannelAnnouncement {
                        node_signature_1: secp_ctx.sign(&msghash, node_1_privkey),
                        node_signature_2: secp_ctx.sign(&msghash, node_2_privkey),
                        bitcoin_signature_1: secp_ctx.sign(&msghash, node_1_privkey),
                        bitcoin_signature_2: secp_ctx.sign(&msghash, node_2_privkey),
                        contents: unsigned_announcement.clone(),
                };
                match net_graph_msg_handler.handle_channel_announcement(&valid_announcement) {
                        Ok(res) => assert!(res),
                        _ => panic!()
                };
        }

        fn update_channel(net_graph_msg_handler: &NetGraphMsgHandler<Arc<test_utils::TestChainSource>, Arc<test_utils::TestLogger>>, secp_ctx: &Secp256k1<All>, node_privkey: &SecretKey, update: UnsignedChannelUpdate) {
                let msghash = hash_to_message!(&Sha256dHash::hash(&update.encode()[..])[..]);
                let valid_channel_update = ChannelUpdate {
                        signature: secp_ctx.sign(&msghash, node_privkey),
                        contents: update.clone()
                };

                match net_graph_msg_handler.handle_channel_update(&valid_channel_update) {
                        Ok(res) => assert!(res),
                        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);
                let unsigned_announcement = UnsignedNodeAnnouncement {
                        features,
                        timestamp,
                        node_id,
                        rgb: [0; 3],
                        alias: [0; 32],
                        addresses: Vec::new(),
                        excess_address_data: Vec::new(),
                        excess_data: Vec::new(),
                };
                let msghash = hash_to_message!(&Sha256dHash::hash(&unsigned_announcement.encode()[..])[..]);
                let valid_announcement = NodeAnnouncement {
                        signature: secp_ctx.sign(&msghash, node_privkey),
                        contents: unsigned_announcement.clone()
                };

                match net_graph_msg_handler.handle_node_announcement(&valid_announcement) {
                        Ok(_) => (),
                        Err(_) => panic!()
                };
        }

        fn get_nodes(secp_ctx: &Secp256k1<All>) -> (SecretKey, PublicKey, Vec<SecretKey>, Vec<PublicKey>) {
                let privkeys: Vec<SecretKey> = (2..10).map(|i| {
                        SecretKey::from_slice(&hex::decode(format!("{:02}", i).repeat(32)).unwrap()[..]).unwrap()
                }).collect();

                let pubkeys = privkeys.iter().map(|secret| PublicKey::from_secret_key(&secp_ctx, secret)).collect();

                let our_privkey = SecretKey::from_slice(&hex::decode("01".repeat(32)).unwrap()[..]).unwrap();
                let our_id = PublicKey::from_secret_key(&secp_ctx, &our_privkey);

                (our_privkey, our_id, privkeys, pubkeys)
        }

        fn id_to_feature_flags(id: u8) -> Vec<u8> {
                // Set the feature flags to the id'th odd (ie non-required) feature bit so that we can
                // test for it later.
                let idx = (id - 1) * 2 + 1;
                if idx > 8*3 {
                        vec![1 << (idx - 8*3), 0, 0, 0]
                } else if idx > 8*2 {
                        vec![1 << (idx - 8*2), 0, 0]
                } else if idx > 8*1 {
                        vec![1 << (idx - 8*1), 0]
                } else {
                        vec![1 << idx]
                }
        }

        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 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:
                //
                //        -1(1)2-  node0  -1(3)2-
                //       /                       \
                // our_id -1(12)2- node7 -1(13)2--- node2
                //       \                       /
                //        -1(2)2-  node1  -1(4)2-
                //
                //
                // chan1  1-to-2: disabled
                // chan1  2-to-1: enabled, 0 fee
                //
                // chan2  1-to-2: enabled, ignored fee
                // chan2  2-to-1: enabled, 0 fee
                //
                // chan3  1-to-2: enabled, 0 fee
                // chan3  2-to-1: enabled, 100 msat fee
                //
                // chan4  1-to-2: enabled, 100% fee
                // chan4  2-to-1: enabled, 0 fee
                //
                // chan12 1-to-2: enabled, ignored fee
                // chan12 2-to-1: enabled, 0 fee
                //
                // chan13 1-to-2: enabled, 200% fee
                // chan13 2-to-1: enabled, 0 fee
                //
                //
                //       -1(5)2- node3 -1(8)2--
                //       |         2          |
                //       |       (11)         |
                //      /          1           \
                // node2--1(6)2- node4 -1(9)2--- node6 (not in global route map)
                //      \                      /
                //       -1(7)2- node5 -1(10)2-
                //
                // chan5  1-to-2: enabled, 100 msat fee
                // chan5  2-to-1: enabled, 0 fee
                //
                // chan6  1-to-2: enabled, 0 fee
                // chan6  2-to-1: enabled, 0 fee
                //
                // chan7  1-to-2: enabled, 100% fee
                // chan7  2-to-1: enabled, 0 fee
                //
                // chan8  1-to-2: enabled, variable fee (0 then 1000 msat)
                // chan8  2-to-1: enabled, 0 fee
                //
                // chan9  1-to-2: enabled, 1001 msat fee
                // chan9  2-to-1: enabled, 0 fee
                //
                // chan10 1-to-2: enabled, 0 fee
                // chan10 2-to-1: enabled, 0 fee
                //
                // chan11 1-to-2: enabled, 0 fee
                // chan11 2-to-1: enabled, 0 fee

                let (our_privkey, _, privkeys, _) = get_nodes(&secp_ctx);

                add_channel(&net_graph_msg_handler, &secp_ctx, &our_privkey, &privkeys[0], ChannelFeatures::from_le_bytes(id_to_feature_flags(1)), 1);
                update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[0], UnsignedChannelUpdate {
                        chain_hash: genesis_block(Network::Testnet).header.block_hash(),
                        short_channel_id: 1,
                        timestamp: 1,
                        flags: 1,
                        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()
                });

                add_or_update_node(&net_graph_msg_handler, &secp_ctx, &privkeys[0], NodeFeatures::from_le_bytes(id_to_feature_flags(1)), 0);

                add_channel(&net_graph_msg_handler, &secp_ctx, &our_privkey, &privkeys[1], ChannelFeatures::from_le_bytes(id_to_feature_flags(2)), 2);
                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: 1,
                        flags: 0,
                        cltv_expiry_delta: u16::max_value(),
                        htlc_minimum_msat: 0,
                        htlc_maximum_msat: OptionalField::Absent,
                        fee_base_msat: u32::max_value(),
                        fee_proportional_millionths: u32::max_value(),
                        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: 2,
                        timestamp: 1,
                        flags: 1,
                        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()
                });

                add_or_update_node(&net_graph_msg_handler, &secp_ctx, &privkeys[1], NodeFeatures::from_le_bytes(id_to_feature_flags(2)), 0);

                add_channel(&net_graph_msg_handler, &secp_ctx, &our_privkey, &privkeys[7], ChannelFeatures::from_le_bytes(id_to_feature_flags(12)), 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,
                        timestamp: 1,
                        flags: 0,
                        cltv_expiry_delta: u16::max_value(),
                        htlc_minimum_msat: 0,
                        htlc_maximum_msat: OptionalField::Absent,
                        fee_base_msat: u32::max_value(),
                        fee_proportional_millionths: u32::max_value(),
                        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: 12,
                        timestamp: 1,
                        flags: 1,
                        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()
                });

                add_or_update_node(&net_graph_msg_handler, &secp_ctx, &privkeys[7], NodeFeatures::from_le_bytes(id_to_feature_flags(8)), 0);

                add_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[0], &privkeys[2], ChannelFeatures::from_le_bytes(id_to_feature_flags(3)), 3);
                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: 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: 3,
                        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()
                });

                add_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[1], &privkeys[2], ChannelFeatures::from_le_bytes(id_to_feature_flags(4)), 4);
                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: 1,
                        flags: 0,
                        cltv_expiry_delta: (4 << 8) | 1,
                        htlc_minimum_msat: 0,
                        htlc_maximum_msat: OptionalField::Absent,
                        fee_base_msat: 0,
                        fee_proportional_millionths: 1000000,
                        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: 4,
                        timestamp: 1,
                        flags: 1,
                        cltv_expiry_delta: (4 << 8) | 2,
                        htlc_minimum_msat: 0,
                        htlc_maximum_msat: OptionalField::Absent,
                        fee_base_msat: 0,
                        fee_proportional_millionths: 0,
                        excess_data: Vec::new()
                });

                add_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[7], &privkeys[2], ChannelFeatures::from_le_bytes(id_to_feature_flags(13)), 13);
                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: 1,
                        flags: 0,
                        cltv_expiry_delta: (13 << 8) | 1,
                        htlc_minimum_msat: 0,
                        htlc_maximum_msat: OptionalField::Absent,
                        fee_base_msat: 0,
                        fee_proportional_millionths: 2000000,
                        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: 13,
                        timestamp: 1,
                        flags: 1,
                        cltv_expiry_delta: (13 << 8) | 2,
                        htlc_minimum_msat: 0,
                        htlc_maximum_msat: OptionalField::Absent,
                        fee_base_msat: 0,
                        fee_proportional_millionths: 0,
                        excess_data: Vec::new()
                });

                add_or_update_node(&net_graph_msg_handler, &secp_ctx, &privkeys[2], NodeFeatures::from_le_bytes(id_to_feature_flags(3)), 0);

                add_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[2], &privkeys[4], ChannelFeatures::from_le_bytes(id_to_feature_flags(6)), 6);
                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: 1,
                        flags: 0,
                        cltv_expiry_delta: (6 << 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[4], UnsignedChannelUpdate {
                        chain_hash: genesis_block(Network::Testnet).header.block_hash(),
                        short_channel_id: 6,
                        timestamp: 1,
                        flags: 1,
                        cltv_expiry_delta: (6 << 8) | 2,
                        htlc_minimum_msat: 0,
                        htlc_maximum_msat: OptionalField::Absent,
                        fee_base_msat: 0,
                        fee_proportional_millionths: 0,
                        excess_data: Vec::new(),
                });

                add_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[4], &privkeys[3], ChannelFeatures::from_le_bytes(id_to_feature_flags(11)), 11);
                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: 1,
                        flags: 0,
                        cltv_expiry_delta: (11 << 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[3], UnsignedChannelUpdate {
                        chain_hash: genesis_block(Network::Testnet).header.block_hash(),
                        short_channel_id: 11,
                        timestamp: 1,
                        flags: 1,
                        cltv_expiry_delta: (11 << 8) | 2,
                        htlc_minimum_msat: 0,
                        htlc_maximum_msat: OptionalField::Absent,
                        fee_base_msat: 0,
                        fee_proportional_millionths: 0,
                        excess_data: Vec::new()
                });

                add_or_update_node(&net_graph_msg_handler, &secp_ctx, &privkeys[4], NodeFeatures::from_le_bytes(id_to_feature_flags(5)), 0);

                add_or_update_node(&net_graph_msg_handler, &secp_ctx, &privkeys[3], NodeFeatures::from_le_bytes(id_to_feature_flags(4)), 0);

                add_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[2], &privkeys[5], ChannelFeatures::from_le_bytes(id_to_feature_flags(7)), 7);
                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: 1,
                        flags: 0,
                        cltv_expiry_delta: (7 << 8) | 1,
                        htlc_minimum_msat: 0,
                        htlc_maximum_msat: OptionalField::Absent,
                        fee_base_msat: 0,
                        fee_proportional_millionths: 1000000,
                        excess_data: Vec::new()
                });
                update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[5], UnsignedChannelUpdate {
                        chain_hash: genesis_block(Network::Testnet).header.block_hash(),
                        short_channel_id: 7,
                        timestamp: 1,
                        flags: 1,
                        cltv_expiry_delta: (7 << 8) | 2,
                        htlc_minimum_msat: 0,
                        htlc_maximum_msat: OptionalField::Absent,
                        fee_base_msat: 0,
                        fee_proportional_millionths: 0,
                        excess_data: Vec::new()
                });

                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, chain_monitor, logger)
        }

        #[test]
        fn simple_route_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

                if let Err(LightningError{err, action: ErrorAction::IgnoreError}) = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, 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, None, &Vec::new(), 100, 42, Arc::clone(&logger)).unwrap();
                assert_eq!(route.paths[0].len(), 2);

                assert_eq!(route.paths[0][0].pubkey, nodes[1]);
                assert_eq!(route.paths[0][0].short_channel_id, 2);
                assert_eq!(route.paths[0][0].fee_msat, 100);
                assert_eq!(route.paths[0][0].cltv_expiry_delta, (4 << 8) | 1);
                assert_eq!(route.paths[0][0].node_features.le_flags(), &id_to_feature_flags(2));
                assert_eq!(route.paths[0][0].channel_features.le_flags(), &id_to_feature_flags(2));

                assert_eq!(route.paths[0][1].pubkey, nodes[2]);
                assert_eq!(route.paths[0][1].short_channel_id, 4);
                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(4));
        }

        #[test]
        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,
                        counterparty_forwarding_info: None,
                }];

                if let Err(LightningError{err, action: ErrorAction::IgnoreError}) = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, 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, 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);

                // Simple route to 2 via 1

                // 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,
                        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[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()
                });

                // 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()
                });

                // 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()
                });

                // 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, None, &Vec::new(), 199_999_999, 42, Arc::clone(&logger)) {
                        assert_eq!(err, "Failed to find a path to the given destination");
                } else { panic!(); }

                // 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, None, &Vec::new(), 199_999_999, 42, Arc::clone(&logger)).unwrap();
                assert_eq!(route.paths[0].len(), 2);
        }

        #[test]
        fn htlc_minimum_overpay_test() {
                let (secp_ctx, net_graph_msg_handler, _, logger) = build_graph();
                let (our_privkey, our_id, privkeys, nodes) = get_nodes(&secp_ctx);

                // A route to node#2 via two paths.
                // One path allows transferring 35-40 sats, another one also allows 35-40 sats.
                // Thus, they can't send 60 without overpaying.
                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: 35_000,
                        htlc_maximum_msat: OptionalField::Present(40_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: 3,
                        flags: 0,
                        cltv_expiry_delta: 0,
                        htlc_minimum_msat: 35_000,
                        htlc_maximum_msat: OptionalField::Present(40_000),
                        fee_base_msat: 0,
                        fee_proportional_millionths: 0,
                        excess_data: Vec::new()
                });

                // Make 0 fee.
                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[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::Absent,
                        fee_base_msat: 0,
                        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: 1,
                        timestamp: 3,
                        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()
                });

                let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2],
                        Some(InvoiceFeatures::known()), None, &Vec::new(), 60_000, 42, Arc::clone(&logger)).unwrap();
                // Overpay fees to hit htlc_minimum_msat.
                let overpaid_fees = route.paths[0][0].fee_msat + route.paths[1][0].fee_msat;
                // TODO: this could be better balanced to overpay 10k and not 15k.
                assert_eq!(overpaid_fees, 15_000);

                // Now, test that if there are 2 paths, a "cheaper" by fee path wouldn't be prioritized
                // while taking even more fee to match htlc_minimum_msat.
                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: 4,
                        flags: 0,
                        cltv_expiry_delta: 0,
                        htlc_minimum_msat: 65_000,
                        htlc_maximum_msat: OptionalField::Present(80_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: 2,
                        timestamp: 3,
                        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[1], UnsignedChannelUpdate {
                        chain_hash: genesis_block(Network::Testnet).header.block_hash(),
                        short_channel_id: 4,
                        timestamp: 4,
                        flags: 0,
                        cltv_expiry_delta: 0,
                        htlc_minimum_msat: 0,
                        htlc_maximum_msat: OptionalField::Absent,
                        fee_base_msat: 0,
                        fee_proportional_millionths: 100_000,
                        excess_data: Vec::new()
                });

                let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2],
                        Some(InvoiceFeatures::known()), None, &Vec::new(), 60_000, 42, Arc::clone(&logger)).unwrap();
                // Fine to overpay for htlc_minimum_msat if it allows us to save fee.
                assert_eq!(route.paths.len(), 1);
                assert_eq!(route.paths[0][0].short_channel_id, 12);
                let fees = route.paths[0][0].fee_msat;
                assert_eq!(fees, 5_000);

                let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2],
                        Some(InvoiceFeatures::known()), None, &Vec::new(), 50_000, 42, Arc::clone(&logger)).unwrap();
                // Not fine to overpay for htlc_minimum_msat if it requires paying more than fee on
                // the other channel.
                assert_eq!(route.paths.len(), 1);
                assert_eq!(route.paths[0][0].short_channel_id, 2);
                let fees = route.paths[0][0].fee_msat;
                assert_eq!(fees, 5_000);
        }

        #[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, 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: 250_000_000,
                        inbound_capacity_msat: 0,
                        is_live: true,
                        counterparty_forwarding_info: None,
                }];
                let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, 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, 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: 250_000_000,
                        inbound_capacity_msat: 0,
                        is_live: true,
                        counterparty_forwarding_info: None,
                }];
                let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, 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));

                // Note that we don't test disabling node 3 and failing to route to it, as we (somewhat
                // naively) assume that the user checked the feature bits on the invoice, which override
                // the node_announcement.
        }

        #[test]
        fn our_chans_test() {
                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 route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[0], None, None, &Vec::new(), 100, 42, Arc::clone(&logger)).unwrap();
                assert_eq!(route.paths[0].len(), 3);

                assert_eq!(route.paths[0][0].pubkey, nodes[1]);
                assert_eq!(route.paths[0][0].short_channel_id, 2);
                assert_eq!(route.paths[0][0].fee_msat, 200);
                assert_eq!(route.paths[0][0].cltv_expiry_delta, (4 << 8) | 1);
                assert_eq!(route.paths[0][0].node_features.le_flags(), &id_to_feature_flags(2));
                assert_eq!(route.paths[0][0].channel_features.le_flags(), &id_to_feature_flags(2));

                assert_eq!(route.paths[0][1].pubkey, nodes[2]);
                assert_eq!(route.paths[0][1].short_channel_id, 4);
                assert_eq!(route.paths[0][1].fee_msat, 100);
                assert_eq!(route.paths[0][1].cltv_expiry_delta, (3 << 8) | 2);
                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(4));

                assert_eq!(route.paths[0][2].pubkey, nodes[0]);
                assert_eq!(route.paths[0][2].short_channel_id, 3);
                assert_eq!(route.paths[0][2].fee_msat, 100);
                assert_eq!(route.paths[0][2].cltv_expiry_delta, 42);
                assert_eq!(route.paths[0][2].node_features.le_flags(), &id_to_feature_flags(1));
                assert_eq!(route.paths[0][2].channel_features.le_flags(), &id_to_feature_flags(3));

                // 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: 250_000_000,
                        inbound_capacity_msat: 0,
                        is_live: true,
                        counterparty_forwarding_info: None,
                }];
                let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, 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]);
                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));
        }

        fn last_hops(nodes: &Vec<PublicKey>) -> Vec<RouteHint> {
                let zero_fees = RoutingFees {
                        base_msat: 0,
                        proportional_millionths: 0,
                };
                vec!(RouteHint {
                        src_node_id: nodes[3].clone(),
                        short_channel_id: 8,
                        fees: zero_fees,
                        cltv_expiry_delta: (8 << 8) | 1,
                        htlc_minimum_msat: None,
                        htlc_maximum_msat: None,
                }, RouteHint {
                        src_node_id: nodes[4].clone(),
                        short_channel_id: 9,
                        fees: RoutingFees {
                                base_msat: 1001,
                                proportional_millionths: 0,
                        },
                        cltv_expiry_delta: (9 << 8) | 1,
                        htlc_minimum_msat: None,
                        htlc_maximum_msat: None,
                }, RouteHint {
                        src_node_id: nodes[5].clone(),
                        short_channel_id: 10,
                        fees: zero_fees,
                        cltv_expiry_delta: (10 << 8) | 1,
                        htlc_minimum_msat: None,
                        htlc_maximum_msat: None,
                })
        }

        #[test]
        fn last_hops_test() {
                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

                // 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, 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, None, &last_hops(&nodes).iter().collect::<Vec<_>>(), 100, 42, Arc::clone(&logger)).unwrap();
                assert_eq!(route.paths[0].len(), 5);

                assert_eq!(route.paths[0][0].pubkey, nodes[1]);
                assert_eq!(route.paths[0][0].short_channel_id, 2);
                assert_eq!(route.paths[0][0].fee_msat, 100);
                assert_eq!(route.paths[0][0].cltv_expiry_delta, (4 << 8) | 1);
                assert_eq!(route.paths[0][0].node_features.le_flags(), &id_to_feature_flags(2));
                assert_eq!(route.paths[0][0].channel_features.le_flags(), &id_to_feature_flags(2));

                assert_eq!(route.paths[0][1].pubkey, nodes[2]);
                assert_eq!(route.paths[0][1].short_channel_id, 4);
                assert_eq!(route.paths[0][1].fee_msat, 0);
                assert_eq!(route.paths[0][1].cltv_expiry_delta, (6 << 8) | 1);
                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(4));

                assert_eq!(route.paths[0][2].pubkey, nodes[4]);
                assert_eq!(route.paths[0][2].short_channel_id, 6);
                assert_eq!(route.paths[0][2].fee_msat, 0);
                assert_eq!(route.paths[0][2].cltv_expiry_delta, (11 << 8) | 1);
                assert_eq!(route.paths[0][2].node_features.le_flags(), &id_to_feature_flags(5));
                assert_eq!(route.paths[0][2].channel_features.le_flags(), &id_to_feature_flags(6));

                assert_eq!(route.paths[0][3].pubkey, nodes[3]);
                assert_eq!(route.paths[0][3].short_channel_id, 11);
                assert_eq!(route.paths[0][3].fee_msat, 0);
                assert_eq!(route.paths[0][3].cltv_expiry_delta, (8 << 8) | 1);
                // If we have a peer in the node map, we'll use their features here since we don't have
                // a way of figuring out their features from the invoice:
                assert_eq!(route.paths[0][3].node_features.le_flags(), &id_to_feature_flags(4));
                assert_eq!(route.paths[0][3].channel_features.le_flags(), &id_to_feature_flags(11));

                assert_eq!(route.paths[0][4].pubkey, nodes[6]);
                assert_eq!(route.paths[0][4].short_channel_id, 8);
                assert_eq!(route.paths[0][4].fee_msat, 100);
                assert_eq!(route.paths[0][4].cltv_expiry_delta, 42);
                assert_eq!(route.paths[0][4].node_features.le_flags(), &Vec::<u8>::new()); // We dont pass flags in from invoices yet
                assert_eq!(route.paths[0][4].channel_features.le_flags(), &Vec::<u8>::new()); // We can't learn any flags from invoices, sadly
        }

        #[test]
        fn our_chans_last_hop_connect_test() {
                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_chans = vec![channelmanager::ChannelDetails {
                        channel_id: [0; 32],
                        short_channel_id: Some(42),
                        remote_network_id: nodes[3].clone(),
                        counterparty_features: InitFeatures::from_le_bytes(vec![0b11]),
                        channel_value_satoshis: 0,
                        user_id: 0,
                        outbound_capacity_msat: 250_000_000,
                        inbound_capacity_msat: 0,
                        is_live: true,
                        counterparty_forwarding_info: None,
                }];
                let mut last_hops = last_hops(&nodes);
                let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[6], None, Some(&our_chans.iter().collect::<Vec<_>>()), &last_hops.iter().collect::<Vec<_>>(), 100, 42, Arc::clone(&logger)).unwrap();
                assert_eq!(route.paths[0].len(), 2);

                assert_eq!(route.paths[0][0].pubkey, nodes[3]);
                assert_eq!(route.paths[0][0].short_channel_id, 42);
                assert_eq!(route.paths[0][0].fee_msat, 0);
                assert_eq!(route.paths[0][0].cltv_expiry_delta, (8 << 8) | 1);
                assert_eq!(route.paths[0][0].node_features.le_flags(), &vec![0b11]);
                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[6]);
                assert_eq!(route.paths[0][1].short_channel_id, 8);
                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(), &Vec::<u8>::new()); // We dont pass flags in from invoices yet
                assert_eq!(route.paths[0][1].channel_features.le_flags(), &Vec::<u8>::new()); // We can't learn any flags from invoices, sadly

                last_hops[0].fees.base_msat = 1000;

                // Revert to via 6 as the fee on 8 goes up
                let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[6], None, None, &last_hops.iter().collect::<Vec<_>>(), 100, 42, Arc::clone(&logger)).unwrap();
                assert_eq!(route.paths[0].len(), 4);

                assert_eq!(route.paths[0][0].pubkey, nodes[1]);
                assert_eq!(route.paths[0][0].short_channel_id, 2);
                assert_eq!(route.paths[0][0].fee_msat, 200); // fee increased as its % of value transferred across node
                assert_eq!(route.paths[0][0].cltv_expiry_delta, (4 << 8) | 1);
                assert_eq!(route.paths[0][0].node_features.le_flags(), &id_to_feature_flags(2));
                assert_eq!(route.paths[0][0].channel_features.le_flags(), &id_to_feature_flags(2));

                assert_eq!(route.paths[0][1].pubkey, nodes[2]);
                assert_eq!(route.paths[0][1].short_channel_id, 4);
                assert_eq!(route.paths[0][1].fee_msat, 100);
                assert_eq!(route.paths[0][1].cltv_expiry_delta, (7 << 8) | 1);
                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(4));

                assert_eq!(route.paths[0][2].pubkey, nodes[5]);
                assert_eq!(route.paths[0][2].short_channel_id, 7);
                assert_eq!(route.paths[0][2].fee_msat, 0);
                assert_eq!(route.paths[0][2].cltv_expiry_delta, (10 << 8) | 1);
                // If we have a peer in the node map, we'll use their features here since we don't have
                // a way of figuring out their features from the invoice:
                assert_eq!(route.paths[0][2].node_features.le_flags(), &id_to_feature_flags(6));
                assert_eq!(route.paths[0][2].channel_features.le_flags(), &id_to_feature_flags(7));

                assert_eq!(route.paths[0][3].pubkey, nodes[6]);
                assert_eq!(route.paths[0][3].short_channel_id, 10);
                assert_eq!(route.paths[0][3].fee_msat, 100);
                assert_eq!(route.paths[0][3].cltv_expiry_delta, 42);
                assert_eq!(route.paths[0][3].node_features.le_flags(), &Vec::<u8>::new()); // We dont pass flags in from invoices yet
                assert_eq!(route.paths[0][3].channel_features.le_flags(), &Vec::<u8>::new()); // We can't learn any flags from invoices, sadly

                // ...but still use 8 for larger payments as 6 has a variable feerate
                let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[6], None, None, &last_hops.iter().collect::<Vec<_>>(), 2000, 42, Arc::clone(&logger)).unwrap();
                assert_eq!(route.paths[0].len(), 5);

                assert_eq!(route.paths[0][0].pubkey, nodes[1]);
                assert_eq!(route.paths[0][0].short_channel_id, 2);
                assert_eq!(route.paths[0][0].fee_msat, 3000);
                assert_eq!(route.paths[0][0].cltv_expiry_delta, (4 << 8) | 1);
                assert_eq!(route.paths[0][0].node_features.le_flags(), &id_to_feature_flags(2));
                assert_eq!(route.paths[0][0].channel_features.le_flags(), &id_to_feature_flags(2));

                assert_eq!(route.paths[0][1].pubkey, nodes[2]);
                assert_eq!(route.paths[0][1].short_channel_id, 4);
                assert_eq!(route.paths[0][1].fee_msat, 0);
                assert_eq!(route.paths[0][1].cltv_expiry_delta, (6 << 8) | 1);
                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(4));

                assert_eq!(route.paths[0][2].pubkey, nodes[4]);
                assert_eq!(route.paths[0][2].short_channel_id, 6);
                assert_eq!(route.paths[0][2].fee_msat, 0);
                assert_eq!(route.paths[0][2].cltv_expiry_delta, (11 << 8) | 1);
                assert_eq!(route.paths[0][2].node_features.le_flags(), &id_to_feature_flags(5));
                assert_eq!(route.paths[0][2].channel_features.le_flags(), &id_to_feature_flags(6));

                assert_eq!(route.paths[0][3].pubkey, nodes[3]);
                assert_eq!(route.paths[0][3].short_channel_id, 11);
                assert_eq!(route.paths[0][3].fee_msat, 1000);
                assert_eq!(route.paths[0][3].cltv_expiry_delta, (8 << 8) | 1);
                // If we have a peer in the node map, we'll use their features here since we don't have
                // a way of figuring out their features from the invoice:
                assert_eq!(route.paths[0][3].node_features.le_flags(), &id_to_feature_flags(4));
                assert_eq!(route.paths[0][3].channel_features.le_flags(), &id_to_feature_flags(11));

                assert_eq!(route.paths[0][4].pubkey, nodes[6]);
                assert_eq!(route.paths[0][4].short_channel_id, 8);
                assert_eq!(route.paths[0][4].fee_msat, 2000);
                assert_eq!(route.paths[0][4].cltv_expiry_delta, 42);
                assert_eq!(route.paths[0][4].node_features.le_flags(), &Vec::<u8>::new()); // We dont pass flags in from invoices yet
                assert_eq!(route.paths[0][4].channel_features.le_flags(), &Vec::<u8>::new()); // We can't learn any flags from invoices, sadly
        }

        #[test]
        fn unannounced_path_test() {
                // We should be able to send a payment to a destination without any help of a routing graph
                // if we have a channel with a common counterparty that appears in the first and last hop
                // hints.
                let source_node_id = PublicKey::from_secret_key(&Secp256k1::new(), &SecretKey::from_slice(&hex::decode(format!("{:02}", 41).repeat(32)).unwrap()[..]).unwrap());
                let middle_node_id = PublicKey::from_secret_key(&Secp256k1::new(), &SecretKey::from_slice(&hex::decode(format!("{:02}", 42).repeat(32)).unwrap()[..]).unwrap());
                let target_node_id = PublicKey::from_secret_key(&Secp256k1::new(), &SecretKey::from_slice(&hex::decode(format!("{:02}", 43).repeat(32)).unwrap()[..]).unwrap());

                // If we specify a channel to a middle hop, that overrides our local channel view and that gets used
                let last_hops = vec![RouteHint {
                        src_node_id: middle_node_id,
                        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 our_chans = vec![channelmanager::ChannelDetails {
                        channel_id: [0; 32],
                        short_channel_id: Some(42),
                        remote_network_id: middle_node_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,
                        counterparty_forwarding_info: None,
                }];
                let route = get_route(&source_node_id, &NetworkGraph::new(genesis_block(Network::Testnet).header.block_hash()), &target_node_id, None, Some(&our_chans.iter().collect::<Vec<_>>()), &last_hops.iter().collect::<Vec<_>>(), 100, 42, Arc::new(test_utils::TestLogger::new())).unwrap();

                assert_eq!(route.paths[0].len(), 2);

                assert_eq!(route.paths[0][0].pubkey, middle_node_id);
                assert_eq!(route.paths[0][0].short_channel_id, 42);
                assert_eq!(route.paths[0][0].fee_msat, 1000);
                assert_eq!(route.paths[0][0].cltv_expiry_delta, (8 << 8) | 1);
                assert_eq!(route.paths[0][0].node_features.le_flags(), &[0b11]);
                assert_eq!(route.paths[0][0].channel_features.le_flags(), &[0; 0]); // We can't learn any flags from invoices, sadly

                assert_eq!(route.paths[0][1].pubkey, target_node_id);
                assert_eq!(route.paths[0][1].short_channel_id, 8);
                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(), &[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],
                                        Some(InvoiceFeatures::known()), 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],
                                Some(InvoiceFeatures::known()), 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);
                }

                // Check that setting outbound_capacity_msat in first_hops limits the channels.
                // Disable channel #1 and use another 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: 1,
                        timestamp: 3,
                        flags: 2,
                        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()
                });

                // Now, limit the first_hop by the outbound_capacity_msat of 200_000 sats.
                let our_chans = vec![channelmanager::ChannelDetails {
                        channel_id: [0; 32],
                        short_channel_id: Some(42),
                        remote_network_id: nodes[0].clone(),
                        counterparty_features: InitFeatures::from_le_bytes(vec![0b11]),
                        channel_value_satoshis: 0,
                        user_id: 0,
                        outbound_capacity_msat: 200_000_000,
                        inbound_capacity_msat: 0,
                        is_live: true,
                        counterparty_forwarding_info: None,
                }];

                {
                        // 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],
                                        Some(InvoiceFeatures::known()), Some(&our_chans.iter().collect::<Vec<_>>()), &Vec::new(), 200_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],
                                Some(InvoiceFeatures::known()), Some(&our_chans.iter().collect::<Vec<_>>()), &Vec::new(), 200_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, 200_000_000);
                }

                // Enable channel #1 back.
                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: 4,
                        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()
                });


                // 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],
                                        Some(InvoiceFeatures::known()), 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],
                                Some(InvoiceFeatures::known()), 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],
                                        Some(InvoiceFeatures::known()), 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],
                                Some(InvoiceFeatures::known()), 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],
                                        Some(InvoiceFeatures::known()), 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],
                                Some(InvoiceFeatures::known()), 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],
                                        Some(InvoiceFeatures::known()), 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],
                                Some(InvoiceFeatures::known()), 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],
                                Some(InvoiceFeatures::known()), 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, 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], Some(InvoiceFeatures::known()), 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],
                                Some(InvoiceFeatures::known()), 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],
                                Some(InvoiceFeatures::known()), 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],
                                        Some(InvoiceFeatures::known()), 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],
                                Some(InvoiceFeatures::known()), 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],
                                Some(InvoiceFeatures::known()), 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],
                                        Some(InvoiceFeatures::known()), 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],
                                Some(InvoiceFeatures::known()), 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],
                                        Some(InvoiceFeatures::known()), 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],
                                Some(InvoiceFeatures::known()), 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],
                                Some(InvoiceFeatures::known()), 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);
                }
        }

        #[test]
        fn min_criteria_consistency() {
                // Test that we don't use an inconsistent metric between updating and walking nodes during
                // our Dijkstra's pass. In the initial version of MPP, the "best source" for a given node
                // was updated with a different criterion from the heap sorting, resulting in loops in
                // calculated paths. We test for that specific case here.

                // We construct a network that looks like this:
                //
                //            node2 -1(3)2- node3
                //              2          2
                //               (2)     (4)
                //                  1   1
                //    node1 -1(5)2- node4 -1(1)2- node6
                //    2
                //   (6)
                //        1
                // our_node
                //
                // We create a loop on the side of our real path - our destination is node 6, with a
                // previous hop of node 4. From 4, the cheapest previous path is channel 2 from node 2,
                // followed by node 3 over channel 3. Thereafter, the cheapest next-hop is back to node 4
                // (this time over channel 4). Channel 4 has 0 htlc_minimum_msat whereas channel 1 (the
                // other channel with a previous-hop of node 4) has a high (but irrelevant to the overall
                // payment) htlc_minimum_msat. In the original algorithm, this resulted in node4's
                // "previous hop" being set to node 3, creating a loop in the path.
                let secp_ctx = Secp256k1::new();
                let logger = Arc::new(test_utils::TestLogger::new());
                let net_graph_msg_handler = NetGraphMsgHandler::new(genesis_block(Network::Testnet).header.block_hash(), None, Arc::clone(&logger));
                let (our_privkey, our_id, privkeys, nodes) = get_nodes(&secp_ctx);

                add_channel(&net_graph_msg_handler, &secp_ctx, &our_privkey, &privkeys[1], ChannelFeatures::from_le_bytes(id_to_feature_flags(6)), 6);
                update_channel(&net_graph_msg_handler, &secp_ctx, &our_privkey, UnsignedChannelUpdate {
                        chain_hash: genesis_block(Network::Testnet).header.block_hash(),
                        short_channel_id: 6,
                        timestamp: 1,
                        flags: 0,
                        cltv_expiry_delta: (6 << 8) | 0,
                        htlc_minimum_msat: 0,
                        htlc_maximum_msat: OptionalField::Absent,
                        fee_base_msat: 0,
                        fee_proportional_millionths: 0,
                        excess_data: Vec::new()
                });
                add_or_update_node(&net_graph_msg_handler, &secp_ctx, &privkeys[1], NodeFeatures::from_le_bytes(id_to_feature_flags(1)), 0);

                add_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[1], &privkeys[4], ChannelFeatures::from_le_bytes(id_to_feature_flags(5)), 5);
                update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[1], UnsignedChannelUpdate {
                        chain_hash: genesis_block(Network::Testnet).header.block_hash(),
                        short_channel_id: 5,
                        timestamp: 1,
                        flags: 0,
                        cltv_expiry_delta: (5 << 8) | 0,
                        htlc_minimum_msat: 0,
                        htlc_maximum_msat: OptionalField::Absent,
                        fee_base_msat: 100,
                        fee_proportional_millionths: 0,
                        excess_data: Vec::new()
                });
                add_or_update_node(&net_graph_msg_handler, &secp_ctx, &privkeys[4], NodeFeatures::from_le_bytes(id_to_feature_flags(4)), 0);

                add_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[4], &privkeys[3], ChannelFeatures::from_le_bytes(id_to_feature_flags(4)), 4);
                update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[4], UnsignedChannelUpdate {
                        chain_hash: genesis_block(Network::Testnet).header.block_hash(),
                        short_channel_id: 4,
                        timestamp: 1,
                        flags: 0,
                        cltv_expiry_delta: (4 << 8) | 0,
                        htlc_minimum_msat: 0,
                        htlc_maximum_msat: OptionalField::Absent,
                        fee_base_msat: 0,
                        fee_proportional_millionths: 0,
                        excess_data: Vec::new()
                });
                add_or_update_node(&net_graph_msg_handler, &secp_ctx, &privkeys[3], NodeFeatures::from_le_bytes(id_to_feature_flags(3)), 0);

                add_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[3], &privkeys[2], ChannelFeatures::from_le_bytes(id_to_feature_flags(3)), 3);
                update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[3], UnsignedChannelUpdate {
                        chain_hash: genesis_block(Network::Testnet).header.block_hash(),
                        short_channel_id: 3,
                        timestamp: 1,
                        flags: 0,
                        cltv_expiry_delta: (3 << 8) | 0,
                        htlc_minimum_msat: 0,
                        htlc_maximum_msat: OptionalField::Absent,
                        fee_base_msat: 0,
                        fee_proportional_millionths: 0,
                        excess_data: Vec::new()
                });
                add_or_update_node(&net_graph_msg_handler, &secp_ctx, &privkeys[2], NodeFeatures::from_le_bytes(id_to_feature_flags(2)), 0);

                add_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[2], &privkeys[4], ChannelFeatures::from_le_bytes(id_to_feature_flags(2)), 2);
                update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[2], UnsignedChannelUpdate {
                        chain_hash: genesis_block(Network::Testnet).header.block_hash(),
                        short_channel_id: 2,
                        timestamp: 1,
                        flags: 0,
                        cltv_expiry_delta: (2 << 8) | 0,
                        htlc_minimum_msat: 0,
                        htlc_maximum_msat: OptionalField::Absent,
                        fee_base_msat: 0,
                        fee_proportional_millionths: 0,
                        excess_data: Vec::new()
                });

                add_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[4], &privkeys[6], ChannelFeatures::from_le_bytes(id_to_feature_flags(1)), 1);
                update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[4], UnsignedChannelUpdate {
                        chain_hash: genesis_block(Network::Testnet).header.block_hash(),
                        short_channel_id: 1,
                        timestamp: 1,
                        flags: 0,
                        cltv_expiry_delta: (1 << 8) | 0,
                        htlc_minimum_msat: 100,
                        htlc_maximum_msat: OptionalField::Absent,
                        fee_base_msat: 0,
                        fee_proportional_millionths: 0,
                        excess_data: Vec::new()
                });
                add_or_update_node(&net_graph_msg_handler, &secp_ctx, &privkeys[6], NodeFeatures::from_le_bytes(id_to_feature_flags(6)), 0);

                {
                        // Now ensure the route flows simply over nodes 1 and 4 to 6.
                        let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[6], None, None, &Vec::new(), 10_000, 42, Arc::clone(&logger)).unwrap();
                        assert_eq!(route.paths.len(), 1);
                        assert_eq!(route.paths[0].len(), 3);

                        assert_eq!(route.paths[0][0].pubkey, nodes[1]);
                        assert_eq!(route.paths[0][0].short_channel_id, 6);
                        assert_eq!(route.paths[0][0].fee_msat, 100);
                        assert_eq!(route.paths[0][0].cltv_expiry_delta, (5 << 8) | 0);
                        assert_eq!(route.paths[0][0].node_features.le_flags(), &id_to_feature_flags(1));
                        assert_eq!(route.paths[0][0].channel_features.le_flags(), &id_to_feature_flags(6));

                        assert_eq!(route.paths[0][1].pubkey, nodes[4]);
                        assert_eq!(route.paths[0][1].short_channel_id, 5);
                        assert_eq!(route.paths[0][1].fee_msat, 0);
                        assert_eq!(route.paths[0][1].cltv_expiry_delta, (1 << 8) | 0);
                        assert_eq!(route.paths[0][1].node_features.le_flags(), &id_to_feature_flags(4));
                        assert_eq!(route.paths[0][1].channel_features.le_flags(), &id_to_feature_flags(5));

                        assert_eq!(route.paths[0][2].pubkey, nodes[6]);
                        assert_eq!(route.paths[0][2].short_channel_id, 1);
                        assert_eq!(route.paths[0][2].fee_msat, 10_000);
                        assert_eq!(route.paths[0][2].cltv_expiry_delta, 42);
                        assert_eq!(route.paths[0][2].node_features.le_flags(), &id_to_feature_flags(6));
                        assert_eq!(route.paths[0][2].channel_features.le_flags(), &id_to_feature_flags(1));
                }
        }


        #[test]
        fn exact_fee_liquidity_limit() {
                // Test that if, while walking the graph, we find a hop that has exactly enough liquidity
                // for us, including later hop fees, we take it. In the first version of our MPP algorithm
                // we calculated fees on a higher value, resulting in us ignoring such paths.
                let (secp_ctx, net_graph_msg_handler, _, logger) = build_graph();
                let (our_privkey, our_id, _, nodes) = get_nodes(&secp_ctx);

                // We modify the graph to set the htlc_maximum of channel 2 to below the value we wish to
                // send.
                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(85_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: 0,
                        cltv_expiry_delta: (4 << 8) | 1,
                        htlc_minimum_msat: 0,
                        htlc_maximum_msat: OptionalField::Present(270_000),
                        fee_base_msat: 0,
                        fee_proportional_millionths: 1000000,
                        excess_data: Vec::new()
                });

                {
                        // Now, attempt to route 90 sats, which is exactly 90 sats at the last hop, plus the
                        // 200% fee charged channel 13 in the 1-to-2 direction.
                        let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, None, &Vec::new(), 90_000, 42, Arc::clone(&logger)).unwrap();
                        assert_eq!(route.paths.len(), 1);
                        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, 12);
                        assert_eq!(route.paths[0][0].fee_msat, 90_000*2);
                        assert_eq!(route.paths[0][0].cltv_expiry_delta, (13 << 8) | 1);
                        assert_eq!(route.paths[0][0].node_features.le_flags(), &id_to_feature_flags(8));
                        assert_eq!(route.paths[0][0].channel_features.le_flags(), &id_to_feature_flags(12));

                        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, 90_000);
                        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 htlc_max_reduction_below_min() {
                // Test that if, while walking the graph, we reduce the value being sent to meet an
                // htlc_maximum_msat, we don't end up undershooting a later htlc_minimum_msat. In the
                // initial version of MPP we'd accept such routes but reject them while recalculating fees,
                // resulting in us thinking there is no possible path, even if other paths exist.
                let (secp_ctx, net_graph_msg_handler, _, logger) = build_graph();
                let (our_privkey, our_id, privkeys, nodes) = get_nodes(&secp_ctx);

                // We modify the graph to set the htlc_minimum of channel 2 and 4 as needed - channel 2
                // gets an htlc_maximum_msat of 80_000 and channel 4 an htlc_minimum_msat of 90_000. We
                // then try to send 90_000.
                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(80_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: (4 << 8) | 1,
                        htlc_minimum_msat: 90_000,
                        htlc_maximum_msat: OptionalField::Absent,
                        fee_base_msat: 0,
                        fee_proportional_millionths: 0,
                        excess_data: Vec::new()
                });

                {
                        // Now, attempt to route 90 sats, hitting the htlc_minimum on channel 4, but
                        // overshooting the htlc_maximum on channel 2. Thus, we should pick the (absurdly
                        // expensive) channels 12-13 path.
                        let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], Some(InvoiceFeatures::known()), None, &Vec::new(), 90_000, 42, Arc::clone(&logger)).unwrap();
                        assert_eq!(route.paths.len(), 1);
                        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, 12);
                        assert_eq!(route.paths[0][0].fee_msat, 90_000*2);
                        assert_eq!(route.paths[0][0].cltv_expiry_delta, (13 << 8) | 1);
                        assert_eq!(route.paths[0][0].node_features.le_flags(), &id_to_feature_flags(8));
                        assert_eq!(route.paths[0][0].channel_features.le_flags(), &id_to_feature_flags(12));

                        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, 90_000);
                        assert_eq!(route.paths[0][1].cltv_expiry_delta, 42);
                        assert_eq!(route.paths[0][1].node_features.le_flags(), InvoiceFeatures::known().le_flags());
                        assert_eq!(route.paths[0][1].channel_features.le_flags(), &id_to_feature_flags(13));
                }
        }

        use std::fs::File;
        use util::ser::Readable;
        /// Tries to open a network graph file, or panics with a URL to fetch it.
        pub(super) fn get_route_file() -> Result<std::fs::File, std::io::Error> {
                let res = File::open("net_graph-2021-02-12.bin") // By default we're run in RL/lightning
                        .or_else(|_| File::open("lightning/net_graph-2021-02-12.bin")) // We may be run manually in RL/
                        .or_else(|_| { // Fall back to guessing based on the binary location
                                // path is likely something like .../rust-lightning/target/debug/deps/lightning-...
                                let mut path = std::env::current_exe().unwrap();
                                path.pop(); // lightning-...
                                path.pop(); // deps
                                path.pop(); // debug
                                path.pop(); // target
                                path.push("lightning");
                                path.push("net_graph-2021-02-12.bin");
                                eprintln!("{}", path.to_str().unwrap());
                                File::open(path)
                        });
                #[cfg(require_route_graph_test)]
                return Ok(res.expect("Didn't have route graph and was configured to require it"));
                res
        }

        pub(super) fn random_init_seed() -> u64 {
                // Because the default HashMap in std pulls OS randomness, we can use it as a (bad) RNG.
                use std::hash::{BuildHasher, Hasher};
                let seed = std::collections::hash_map::RandomState::new().build_hasher().finish();
                println!("Using seed of {}", seed);
                seed
        }

        #[test]
        fn generate_routes() {
                let mut d = match get_route_file() {
                        Ok(f) => f,
                        Err(_) => {
                                eprintln!("Please fetch https://bitcoin.ninja/ldk-net_graph-879e309c128-2020-02-12.bin and place it at lightning/net_graph-2021-02-12.bin");
                                return;
                        },
                };
                let graph = NetworkGraph::read(&mut d).unwrap();

                // First, get 100 (source, destination) pairs for which route-getting actually succeeds...
                let mut seed = random_init_seed() as usize;
                'load_endpoints: for _ in 0..10 {
                        loop {
                                seed = seed.overflowing_mul(0xdeadbeef).0;
                                let src = graph.get_nodes().keys().skip(seed % graph.get_nodes().len()).next().unwrap();
                                seed = seed.overflowing_mul(0xdeadbeef).0;
                                let dst = graph.get_nodes().keys().skip(seed % graph.get_nodes().len()).next().unwrap();
                                let amt = seed as u64 % 200_000_000;
                                if get_route(src, &graph, dst, None, None, &[], amt, 42, &test_utils::TestLogger::new()).is_ok() {
                                        continue 'load_endpoints;
                                }
                        }
                }
        }

        #[test]
        fn generate_routes_mpp() {
                let mut d = match get_route_file() {
                        Ok(f) => f,
                        Err(_) => {
                                eprintln!("Please fetch https://bitcoin.ninja/ldk-net_graph-879e309c128-2020-02-12.bin and place it at lightning/net_graph-2021-02-12.bin");
                                return;
                        },
                };
                let graph = NetworkGraph::read(&mut d).unwrap();

                // First, get 100 (source, destination) pairs for which route-getting actually succeeds...
                let mut seed = random_init_seed() as usize;
                'load_endpoints: for _ in 0..10 {
                        loop {
                                seed = seed.overflowing_mul(0xdeadbeef).0;
                                let src = graph.get_nodes().keys().skip(seed % graph.get_nodes().len()).next().unwrap();
                                seed = seed.overflowing_mul(0xdeadbeef).0;
                                let dst = graph.get_nodes().keys().skip(seed % graph.get_nodes().len()).next().unwrap();
                                let amt = seed as u64 % 200_000_000;
                                if get_route(src, &graph, dst, Some(InvoiceFeatures::known()), None, &[], amt, 42, &test_utils::TestLogger::new()).is_ok() {
                                        continue 'load_endpoints;
                                }
                        }
                }
        }
}

#[cfg(all(test, feature = "unstable"))]
mod benches {
        use super::*;
        use util::logger::{Logger, Record};

        use std::fs::File;
        use test::Bencher;

        struct DummyLogger {}
        impl Logger for DummyLogger {
                fn log(&self, _record: &Record) {}
        }

        #[bench]
        fn generate_routes(bench: &mut Bencher) {
                let mut d = tests::get_route_file()
                        .expect("Please fetch https://bitcoin.ninja/ldk-net_graph-879e309c128-2020-02-12.bin and place it at lightning/net_graph-2021-02-12.bin");
                let graph = NetworkGraph::read(&mut d).unwrap();

                // First, get 100 (source, destination) pairs for which route-getting actually succeeds...
                let mut path_endpoints = Vec::new();
                let mut seed: usize = 0xdeadbeef;
                'load_endpoints: for _ in 0..100 {
                        loop {
                                seed *= 0xdeadbeef;
                                let src = graph.get_nodes().keys().skip(seed % graph.get_nodes().len()).next().unwrap();
                                seed *= 0xdeadbeef;
                                let dst = graph.get_nodes().keys().skip(seed % graph.get_nodes().len()).next().unwrap();
                                let amt = seed as u64 % 1_000_000;
                                if get_route(src, &graph, dst, None, None, &[], amt, 42, &DummyLogger{}).is_ok() {
                                        path_endpoints.push((src, dst, amt));
                                        continue 'load_endpoints;
                                }
                        }
                }

                // ...then benchmark finding paths between the nodes we learned.
                let mut idx = 0;
                bench.iter(|| {
                        let (src, dst, amt) = path_endpoints[idx % path_endpoints.len()];
                        assert!(get_route(src, &graph, dst, None, None, &[], amt, 42, &DummyLogger{}).is_ok());
                        idx += 1;
                });
        }

        #[bench]
        fn generate_mpp_routes(bench: &mut Bencher) {
                let mut d = tests::get_route_file()
                        .expect("Please fetch https://bitcoin.ninja/ldk-net_graph-879e309c128-2020-02-12.bin and place it at lightning/net_graph-2021-02-12.bin");
                let graph = NetworkGraph::read(&mut d).unwrap();

                // First, get 100 (source, destination) pairs for which route-getting actually succeeds...
                let mut path_endpoints = Vec::new();
                let mut seed: usize = 0xdeadbeef;
                'load_endpoints: for _ in 0..100 {
                        loop {
                                seed *= 0xdeadbeef;
                                let src = graph.get_nodes().keys().skip(seed % graph.get_nodes().len()).next().unwrap();
                                seed *= 0xdeadbeef;
                                let dst = graph.get_nodes().keys().skip(seed % graph.get_nodes().len()).next().unwrap();
                                let amt = seed as u64 % 1_000_000;
                                if get_route(src, &graph, dst, Some(InvoiceFeatures::known()), None, &[], amt, 42, &DummyLogger{}).is_ok() {
                                        path_endpoints.push((src, dst, amt));
                                        continue 'load_endpoints;
                                }
                        }
                }

                // ...then benchmark finding paths between the nodes we learned.
                let mut idx = 0;
                bench.iter(|| {
                        let (src, dst, amt) = path_endpoints[idx % path_endpoints.len()];
                        assert!(get_route(src, &graph, dst, Some(InvoiceFeatures::known()), None, &[], amt, 42, &DummyLogger{}).is_ok());
                        idx += 1;
                });
        }
}