Test we prefer first hops over route hints
[rust-lightning] / lightning / src / routing / router.rs
index 6e5c00e7665a4c04ccab6df38de89bef9ad7e5ba..8a7343916d34cacd166762716cdb5ad566ba21fc 100644 (file)
@@ -139,7 +139,7 @@ impl<'a, SP: Sized, Sc: 'a + ScoreLookUp<ScoreParams = SP>, S: Deref<Target = Sc
                        source, target, short_channel_id
                ) {
                        let usage = ChannelUsage {
-                               inflight_htlc_msat: usage.inflight_htlc_msat + used_liquidity,
+                               inflight_htlc_msat: usage.inflight_htlc_msat.saturating_add(used_liquidity),
                                ..usage
                        };
 
@@ -341,7 +341,7 @@ impl Path {
 
 /// 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, Hash, PartialEq, Eq)]
+#[derive(Clone, Debug, Hash, PartialEq, Eq)]
 pub struct Route {
        /// The list of [`Path`]s taken for a single (potentially-)multi-part payment. If no
        /// [`BlindedTail`]s are present, then the pubkey of the last [`RouteHop`] in each path must be
@@ -380,6 +380,12 @@ impl Route {
        }
 }
 
+impl fmt::Display for Route {
+       fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
+               log_route!(self).fmt(f)
+       }
+}
+
 const SERIALIZATION_VERSION: u8 = 1;
 const MIN_SERIALIZATION_VERSION: u8 = 1;
 
@@ -409,6 +415,7 @@ impl Writeable for Route {
                        (1, self.route_params.as_ref().map(|p| &p.payment_params), option),
                        (2, blinded_tails, optional_vec),
                        (3, self.route_params.as_ref().map(|p| p.final_value_msat), option),
+                       (5, self.route_params.as_ref().map(|p| p.max_total_routing_fee_msat), option),
                });
                Ok(())
        }
@@ -436,6 +443,7 @@ impl Readable for Route {
                        (1, payment_params, (option: ReadableArgs, min_final_cltv_expiry_delta)),
                        (2, blinded_tails, optional_vec),
                        (3, final_value_msat, option),
+                       (5, max_total_routing_fee_msat, option)
                });
                let blinded_tails = blinded_tails.unwrap_or(Vec::new());
                if blinded_tails.len() != 0 {
@@ -448,7 +456,7 @@ impl Readable for Route {
                // If we previously wrote the corresponding fields, reconstruct RouteParameters.
                let route_params = match (payment_params, final_value_msat) {
                        (Some(payment_params), Some(final_value_msat)) => {
-                               Some(RouteParameters { payment_params, final_value_msat })
+                               Some(RouteParameters { payment_params, final_value_msat, max_total_routing_fee_msat })
                        }
                        _ => None,
                };
@@ -467,12 +475,22 @@ pub struct RouteParameters {
 
        /// The amount in msats sent on the failed payment path.
        pub final_value_msat: u64,
+
+       /// The maximum total fees, in millisatoshi, that may accrue during route finding.
+       ///
+       /// This limit also applies to the total fees that may arise while retrying failed payment
+       /// paths.
+       ///
+       /// Note that values below a few sats may result in some paths being spuriously ignored.
+       pub max_total_routing_fee_msat: Option<u64>,
 }
 
 impl RouteParameters {
        /// Constructs [`RouteParameters`] from the given [`PaymentParameters`] and a payment amount.
+       ///
+       /// [`Self::max_total_routing_fee_msat`] defaults to 1% of the payment amount + 50 sats
        pub fn from_payment_params_and_value(payment_params: PaymentParameters, final_value_msat: u64) -> Self {
-               Self { payment_params, final_value_msat }
+               Self { payment_params, final_value_msat, max_total_routing_fee_msat: Some(final_value_msat / 100 + 50_000) }
        }
 }
 
@@ -480,6 +498,7 @@ impl Writeable for RouteParameters {
        fn write<W: Writer>(&self, writer: &mut W) -> Result<(), io::Error> {
                write_tlv_fields!(writer, {
                        (0, self.payment_params, required),
+                       (1, self.max_total_routing_fee_msat, option),
                        (2, self.final_value_msat, required),
                        // LDK versions prior to 0.0.114 had the `final_cltv_expiry_delta` parameter in
                        // `RouteParameters` directly. For compatibility, we write it here.
@@ -493,6 +512,7 @@ impl Readable for RouteParameters {
        fn read<R: io::Read>(reader: &mut R) -> Result<Self, DecodeError> {
                _init_and_read_len_prefixed_tlv_fields!(reader, {
                        (0, payment_params, (required: ReadableArgs, 0)),
+                       (1, max_total_routing_fee_msat, option),
                        (2, final_value_msat, required),
                        (4, final_cltv_delta, option),
                });
@@ -505,6 +525,7 @@ impl Readable for RouteParameters {
                Ok(Self {
                        payment_params,
                        final_value_msat: final_value_msat.0.unwrap(),
+                       max_total_routing_fee_msat,
                })
        }
 }
@@ -1244,7 +1265,11 @@ impl<'a> PaymentPath<'a> {
        // Note that this function is not aware of the available_liquidity limit, and thus does not
        // support increasing the value being transferred beyond what was selected during the initial
        // routing passes.
-       fn update_value_and_recompute_fees(&mut self, value_msat: u64) {
+       //
+       // Returns the amount that this path contributes to the total payment value, which may be greater
+       // than `value_msat` if we had to overpay to meet the final node's `htlc_minimum_msat`.
+       fn update_value_and_recompute_fees(&mut self, value_msat: u64) -> u64 {
+               let mut extra_contribution_msat = 0;
                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;
@@ -1259,6 +1284,7 @@ impl<'a> PaymentPath<'a> {
 
                        let cur_hop = &mut self.hops.get_mut(i).unwrap().0;
                        cur_hop.next_hops_fee_msat = total_fee_paid_msat;
+                       cur_hop.path_penalty_msat += extra_contribution_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
@@ -1274,8 +1300,15 @@ impl<'a> PaymentPath<'a> {
                                // 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;
+
+                               // We remember and return the extra fees on the final hop to allow accounting for
+                               // them in the path's value contribution.
+                               if last_hop {
+                                       extra_contribution_msat = extra_fees_msat;
+                               } else {
+                                       total_fee_paid_msat += extra_fees_msat;
+                                       cur_hop_fees_msat += extra_fees_msat;
+                               }
                        }
 
                        if last_hop {
@@ -1303,6 +1336,7 @@ impl<'a> PaymentPath<'a> {
                                }
                        }
                }
+               value_msat + extra_contribution_msat
        }
 }
 
@@ -1468,6 +1502,9 @@ where L::Target: Logger {
        if payee_node_id_opt.map_or(false, |payee| payee == our_node_id) {
                return Err(LightningError{err: "Cannot generate a route to ourselves".to_owned(), action: ErrorAction::IgnoreError});
        }
+       if our_node_id == maybe_dummy_payee_node_id {
+               return Err(LightningError{err: "Invalid origin node id provided, use a different one".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});
@@ -1585,9 +1622,13 @@ where L::Target: Logger {
                        |info| info.features.supports_basic_mpp()))
        } else { false };
 
-       log_trace!(logger, "Searching for a route from payer {} to {} {} MPP and {} first hops {}overriding the network graph", our_node_pubkey,
-               LoggedPayeePubkey(payment_params.payee.node_id()), if allow_mpp { "with" } else { "without" },
-               first_hops.map(|hops| hops.len()).unwrap_or(0), if first_hops.is_some() { "" } else { "not " });
+       let max_total_routing_fee_msat = route_params.max_total_routing_fee_msat.unwrap_or(u64::max_value());
+
+       log_trace!(logger, "Searching for a route from payer {} to {} {} MPP and {} first hops {}overriding the network graph with a fee limit of {} msat",
+               our_node_pubkey, LoggedPayeePubkey(payment_params.payee.node_id()),
+               if allow_mpp { "with" } else { "without" },
+               first_hops.map(|hops| hops.len()).unwrap_or(0), if first_hops.is_some() { "" } else { "not " },
+               max_total_routing_fee_msat);
 
        // Step (1).
        // Prepare the data we'll use for payee-to-payer search by
@@ -1676,22 +1717,25 @@ where L::Target: Logger {
                LoggedPayeePubkey(payment_params.payee.node_id()), our_node_pubkey, final_value_msat);
 
        // Remember how many candidates we ignored to allow for some logging afterwards.
-       let mut num_ignored_value_contribution = 0;
-       let mut num_ignored_path_length_limit = 0;
-       let mut num_ignored_cltv_delta_limit = 0;
-       let mut num_ignored_previously_failed = 0;
+       let mut num_ignored_value_contribution: u32 = 0;
+       let mut num_ignored_path_length_limit: u32 = 0;
+       let mut num_ignored_cltv_delta_limit: u32 = 0;
+       let mut num_ignored_previously_failed: u32 = 0;
+       let mut num_ignored_total_fee_limit: u32 = 0;
+       let mut num_ignored_avoid_overpayment: u32 = 0;
+       let mut num_ignored_htlc_minimum_msat_limit: u32 = 0;
 
        macro_rules! add_entry {
                // Adds entry which goes from $src_node_id to $dest_node_id over the $candidate hop.
                // $next_hops_fee_msat represents the fees paid for using all the channels *after* this one,
                // since that value has to be transferred over this channel.
-               // Returns whether this channel caused an update to `targets`.
+               // Returns the contribution amount of $candidate if the channel caused an update to `targets`.
                ( $candidate: expr, $src_node_id: expr, $dest_node_id: expr, $next_hops_fee_msat: expr,
                        $next_hops_value_contribution: expr, $next_hops_path_htlc_minimum_msat: expr,
                        $next_hops_path_penalty_msat: expr, $next_hops_cltv_delta: expr, $next_hops_path_length: expr ) => { {
                        // We "return" whether we updated the path at the end, and how much we can route via
                        // this channel, via this:
-                       let mut did_add_update_path_to_src_node = None;
+                       let mut hop_contribution_amt_msat = None;
                        // 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)
@@ -1748,9 +1792,9 @@ where L::Target: Logger {
                                        #[allow(unused_comparisons)] // $next_hops_path_htlc_minimum_msat is 0 in some calls so rustc complains
                                        let may_overpay_to_meet_path_minimum_msat =
                                                ((amount_to_transfer_over_msat < $candidate.htlc_minimum_msat() &&
-                                                 recommended_value_msat > $candidate.htlc_minimum_msat()) ||
+                                                 recommended_value_msat >= $candidate.htlc_minimum_msat()) ||
                                                 (amount_to_transfer_over_msat < $next_hops_path_htlc_minimum_msat &&
-                                                 recommended_value_msat > $next_hops_path_htlc_minimum_msat));
+                                                 recommended_value_msat >= $next_hops_path_htlc_minimum_msat));
 
                                        let payment_failed_on_this_channel = scid_opt.map_or(false,
                                                |scid| payment_params.previously_failed_channels.contains(&scid));
@@ -1759,6 +1803,7 @@ where L::Target: Logger {
                                                CandidateRouteHop::FirstHop { .. } => true,
                                                CandidateRouteHop::PrivateHop { .. } => true,
                                                CandidateRouteHop::Blinded { .. } => true,
+                                               CandidateRouteHop::OneHopBlinded { .. } => true,
                                                _ => false,
                                        };
 
@@ -1787,16 +1832,23 @@ where L::Target: Logger {
                                                }
                                                num_ignored_previously_failed += 1;
                                        } else if may_overpay_to_meet_path_minimum_msat {
+                                               if should_log_candidate {
+                                                       log_trace!(logger,
+                                                               "Ignoring {} to avoid overpaying to meet htlc_minimum_msat limit.",
+                                                               LoggedCandidateHop(&$candidate));
+                                               }
+                                               num_ignored_avoid_overpayment += 1;
                                                hit_minimum_limit = true;
                                        } else if over_path_minimum_msat {
                                                // Note that low contribution here (limited by available_liquidity_msat)
                                                // might violate htlc_minimum_msat on the hops which are next along the
                                                // payment path (upstream to the payee). To avoid that, we recompute
                                                // path fees knowing the final path contribution after constructing it.
-                                               let path_htlc_minimum_msat = cmp::max(
-                                                       compute_fees_saturating($next_hops_path_htlc_minimum_msat, $candidate.fees())
-                                                               .saturating_add($next_hops_path_htlc_minimum_msat),
-                                                       $candidate.htlc_minimum_msat());
+                                               let curr_min = cmp::max(
+                                                       $next_hops_path_htlc_minimum_msat, $candidate.htlc_minimum_msat()
+                                               );
+                                               let path_htlc_minimum_msat = compute_fees_saturating(curr_min, $candidate.fees())
+                                                       .saturating_add(curr_min);
                                                let hm_entry = dist.entry($src_node_id);
                                                let old_entry = hm_entry.or_insert_with(|| {
                                                        // If there was previously no known way to access the source node
@@ -1841,96 +1893,111 @@ where L::Target: Logger {
                                                                total_fee_msat = total_fee_msat.saturating_add(hop_use_fee_msat);
                                                        }
 
-                                                       let channel_usage = ChannelUsage {
-                                                               amount_msat: amount_to_transfer_over_msat,
-                                                               inflight_htlc_msat: used_liquidity_msat,
-                                                               effective_capacity,
-                                                       };
-                                                       let channel_penalty_msat = scid_opt.map_or(0,
-                                                               |scid| scorer.channel_penalty_msat(scid, &$src_node_id, &$dest_node_id,
-                                                                       channel_usage, score_params));
-                                                       let path_penalty_msat = $next_hops_path_penalty_msat
-                                                               .saturating_add(channel_penalty_msat);
-                                                       let new_graph_node = RouteGraphNode {
-                                                               node_id: $src_node_id,
-                                                               lowest_fee_to_node: total_fee_msat,
-                                                               total_cltv_delta: hop_total_cltv_delta,
-                                                               value_contribution_msat,
-                                                               path_htlc_minimum_msat,
-                                                               path_penalty_msat,
-                                                               path_length_to_node,
-                                                       };
-
-                                                       // Update the way of reaching $src_node_id with the given short_channel_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)
-                                                               .saturating_add(old_entry.path_penalty_msat);
-                                                       let new_cost = cmp::max(total_fee_msat, path_htlc_minimum_msat)
-                                                               .saturating_add(path_penalty_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.node_id = $dest_node_id.clone();
-                                                               old_entry.candidate = $candidate.clone();
-                                                               old_entry.fee_msat = 0; // This value will be later filled with hop_use_fee_msat of the following channel
-                                                               old_entry.path_htlc_minimum_msat = path_htlc_minimum_msat;
-                                                               old_entry.path_penalty_msat = path_penalty_msat;
-                                                               #[cfg(all(not(ldk_bench), any(test, fuzzing)))]
-                                                               {
-                                                                       old_entry.value_contribution_msat = value_contribution_msat;
+                                                       // Ignore hops if augmenting the current path to them would put us over `max_total_routing_fee_msat`
+                                                       if total_fee_msat > max_total_routing_fee_msat {
+                                                               if should_log_candidate {
+                                                                       log_trace!(logger, "Ignoring {} due to exceeding max total routing fee limit.", LoggedCandidateHop(&$candidate));
                                                                }
-                                                               did_add_update_path_to_src_node = Some(value_contribution_msat);
-                                                       } else if old_entry.was_processed && new_cost < old_cost {
-                                                               #[cfg(all(not(ldk_bench), any(test, fuzzing)))]
-                                                               {
-                                                                       // 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 + path_penalty_msat <
-                                                                               old_entry.value_contribution_msat + old_entry.path_penalty_msat
-                                                                       );
+                                                               num_ignored_total_fee_limit += 1;
+                                                       } else {
+                                                               let channel_usage = ChannelUsage {
+                                                                       amount_msat: amount_to_transfer_over_msat,
+                                                                       inflight_htlc_msat: used_liquidity_msat,
+                                                                       effective_capacity,
+                                                               };
+                                                               let channel_penalty_msat = scid_opt.map_or(0,
+                                                                       |scid| scorer.channel_penalty_msat(scid, &$src_node_id, &$dest_node_id,
+                                                                               channel_usage, score_params));
+                                                               let path_penalty_msat = $next_hops_path_penalty_msat
+                                                                       .saturating_add(channel_penalty_msat);
+                                                               let new_graph_node = RouteGraphNode {
+                                                                       node_id: $src_node_id,
+                                                                       lowest_fee_to_node: total_fee_msat,
+                                                                       total_cltv_delta: hop_total_cltv_delta,
+                                                                       value_contribution_msat,
+                                                                       path_htlc_minimum_msat,
+                                                                       path_penalty_msat,
+                                                                       path_length_to_node,
+                                                               };
+
+                                                               // Update the way of reaching $src_node_id with the given short_channel_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)
+                                                                       .saturating_add(old_entry.path_penalty_msat);
+                                                               let new_cost = cmp::max(total_fee_msat, path_htlc_minimum_msat)
+                                                                       .saturating_add(path_penalty_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.node_id = $dest_node_id.clone();
+                                                                       old_entry.candidate = $candidate.clone();
+                                                                       old_entry.fee_msat = 0; // This value will be later filled with hop_use_fee_msat of the following channel
+                                                                       old_entry.path_htlc_minimum_msat = path_htlc_minimum_msat;
+                                                                       old_entry.path_penalty_msat = path_penalty_msat;
+                                                                       #[cfg(all(not(ldk_bench), any(test, fuzzing)))]
+                                                                       {
+                                                                               old_entry.value_contribution_msat = value_contribution_msat;
+                                                                       }
+                                                                       hop_contribution_amt_msat = Some(value_contribution_msat);
+                                                               } else if old_entry.was_processed && new_cost < old_cost {
+                                                                       #[cfg(all(not(ldk_bench), any(test, fuzzing)))]
+                                                                       {
+                                                                               // 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 + path_penalty_msat <
+                                                                                       old_entry.value_contribution_msat + old_entry.path_penalty_msat
+                                                                               );
+                                                                       }
                                                                }
                                                        }
                                                }
+                                       } else {
+                                               if should_log_candidate {
+                                                       log_trace!(logger,
+                                                               "Ignoring {} due to its htlc_minimum_msat limit.",
+                                                               LoggedCandidateHop(&$candidate));
+                                               }
+                                               num_ignored_htlc_minimum_msat_limit += 1;
                                        }
                                }
                        }
-                       did_add_update_path_to_src_node
+                       hop_contribution_amt_msat
                } }
        }
 
@@ -2048,7 +2115,7 @@ where L::Target: Logger {
                                // in the regular network graph.
                                first_hop_targets.get(&intro_node_id).is_some() ||
                                network_nodes.get(&intro_node_id).is_some();
-                       if !have_intro_node_in_graph { continue }
+                       if !have_intro_node_in_graph || our_node_id == intro_node_id { continue }
                        let candidate = if hint.1.blinded_hops.len() == 1 {
                                CandidateRouteHop::OneHopBlinded { hint, hint_idx }
                        } else { CandidateRouteHop::Blinded { hint, hint_idx } };
@@ -2067,9 +2134,10 @@ where L::Target: Logger {
                                                Some(fee) => fee,
                                                None => continue
                                        };
+                                       let path_min = candidate.htlc_minimum_msat().saturating_add(
+                                               compute_fees_saturating(candidate.htlc_minimum_msat(), candidate.fees()));
                                        add_entry!(first_hop_candidate, our_node_id, intro_node_id, blinded_path_fee,
-                                               path_contribution_msat, candidate.htlc_minimum_msat(), 0_u64,
-                                               candidate.cltv_expiry_delta(),
+                                               path_contribution_msat, path_min, 0_u64, candidate.cltv_expiry_delta(),
                                                candidate.blinded_path().map_or(1, |bp| bp.blinded_hops.len() as u8));
                                }
                        }
@@ -2077,14 +2145,15 @@ where L::Target: Logger {
                for route in payment_params.payee.unblinded_route_hints().iter()
                        .filter(|route| !route.0.is_empty())
                {
-                       let first_hop_in_route = &(route.0)[0];
-                       let have_hop_src_in_graph =
-                               // Only add the hops in this route to our candidate set if either
-                               // we have a direct channel to the first hop or the first hop is
-                               // in the regular network graph.
-                               first_hop_targets.get(&NodeId::from_pubkey(&first_hop_in_route.src_node_id)).is_some() ||
-                               network_nodes.get(&NodeId::from_pubkey(&first_hop_in_route.src_node_id)).is_some();
-                       if have_hop_src_in_graph {
+                       let first_hop_src_id = NodeId::from_pubkey(&route.0.first().unwrap().src_node_id);
+                       let first_hop_src_is_reachable =
+                               // Only add the hops in this route to our candidate set if either we are part of
+                               // the first hop, we have a direct channel to the first hop, or the first hop is in
+                               // the regular network graph.
+                               our_node_id == first_hop_src_id ||
+                               first_hop_targets.get(&first_hop_src_id).is_some() ||
+                               network_nodes.get(&first_hop_src_id).is_some();
+                       if first_hop_src_is_reachable {
                                // We start building the path from reverse, i.e., from payee
                                // to the first RouteHintHop in the path.
                                let hop_iter = route.0.iter().rev();
@@ -2101,6 +2170,15 @@ where L::Target: Logger {
                                for (idx, (hop, prev_hop_id)) in hop_iter.zip(prev_hop_iter).enumerate() {
                                        let source = NodeId::from_pubkey(&hop.src_node_id);
                                        let target = NodeId::from_pubkey(&prev_hop_id);
+
+                                       if let Some(first_channels) = first_hop_targets.get(&target) {
+                                               if first_channels.iter().any(|d| d.outbound_scid_alias == Some(hop.short_channel_id)) {
+                                                       log_trace!(logger, "Ignoring route hint with SCID {} (and any previous) due to it being a direct channel of ours.",
+                                                               hop.short_channel_id);
+                                                       break;
+                                               }
+                                       }
+
                                        let candidate = network_channels
                                                .get(&hop.short_channel_id)
                                                .and_then(|channel| channel.as_directed_to(&target))
@@ -2144,12 +2222,12 @@ where L::Target: Logger {
                                                .saturating_add(1);
 
                                        // Searching for a direct channel between last checked hop and first_hop_targets
-                                       if let Some(first_channels) = first_hop_targets.get_mut(&NodeId::from_pubkey(&prev_hop_id)) {
+                                       if let Some(first_channels) = first_hop_targets.get_mut(&target) {
                                                sort_first_hop_channels(first_channels, &used_liquidities,
                                                        recommended_value_msat, our_node_pubkey);
                                                for details in first_channels {
                                                        let first_hop_candidate = CandidateRouteHop::FirstHop { details };
-                                                       add_entry!(first_hop_candidate, our_node_id, NodeId::from_pubkey(&prev_hop_id),
+                                                       add_entry!(first_hop_candidate, our_node_id, target,
                                                                aggregate_next_hops_fee_msat, aggregate_path_contribution_msat,
                                                                aggregate_next_hops_path_htlc_minimum_msat, aggregate_next_hops_path_penalty_msat,
                                                                aggregate_next_hops_cltv_delta, aggregate_next_hops_path_length);
@@ -2169,11 +2247,15 @@ where L::Target: Logger {
                                                .map_or(None, |inc| inc.checked_add(aggregate_next_hops_fee_msat));
                                        aggregate_next_hops_fee_msat = if let Some(val) = hops_fee { val } else { break; };
 
-                                       let hop_htlc_minimum_msat = candidate.htlc_minimum_msat();
-                                       let hop_htlc_minimum_msat_inc = if let Some(val) = compute_fees(aggregate_next_hops_path_htlc_minimum_msat, hop.fees) { val } else { break; };
-                                       let hops_path_htlc_minimum = aggregate_next_hops_path_htlc_minimum_msat
-                                               .checked_add(hop_htlc_minimum_msat_inc);
-                                       aggregate_next_hops_path_htlc_minimum_msat = if let Some(val) = hops_path_htlc_minimum { cmp::max(hop_htlc_minimum_msat, val) } else { break; };
+                                       // The next channel will need to relay this channel's min_htlc *plus* the fees taken by
+                                       // this route hint's source node to forward said min over this channel.
+                                       aggregate_next_hops_path_htlc_minimum_msat = {
+                                               let curr_htlc_min = cmp::max(
+                                                       candidate.htlc_minimum_msat(), aggregate_next_hops_path_htlc_minimum_msat
+                                               );
+                                               let curr_htlc_min_fee = if let Some(val) = compute_fees(curr_htlc_min, hop.fees) { val } else { break };
+                                               if let Some(min) = curr_htlc_min.checked_add(curr_htlc_min_fee) { min } else { break }
+                                       };
 
                                        if idx == route.0.len() - 1 {
                                                // The last hop in this iterator is the first hop in
@@ -2289,8 +2371,8 @@ where L::Target: Logger {
                                // recompute the fees again, so that if that's the case, we match the currently
                                // underpaid htlc_minimum_msat with fees.
                                debug_assert_eq!(payment_path.get_value_msat(), value_contribution_msat);
-                               value_contribution_msat = cmp::min(value_contribution_msat, final_value_msat);
-                               payment_path.update_value_and_recompute_fees(value_contribution_msat);
+                               let desired_value_contribution = cmp::min(value_contribution_msat, final_value_msat);
+                               value_contribution_msat = payment_path.update_value_and_recompute_fees(desired_value_contribution);
 
                                // Since a path allows to transfer as much value as
                                // the smallest channel it has ("bottleneck"), we should recompute
@@ -2375,6 +2457,9 @@ where L::Target: Logger {
                // because we deterministically terminated the search due to low liquidity.
                if !found_new_path && channel_saturation_pow_half != 0 {
                        channel_saturation_pow_half = 0;
+               } else if !found_new_path && hit_minimum_limit && already_collected_value_msat < final_value_msat && path_value_msat != recommended_value_msat {
+                       log_trace!(logger, "Failed to collect enough value, but running again to collect extra paths with a potentially higher limit.");
+                       path_value_msat = recommended_value_msat;
                } else if already_collected_value_msat >= recommended_value_msat || !found_new_path {
                        log_trace!(logger, "Have now collected {} msat (seeking {} msat) in paths. Last path loop {} a new path.",
                                already_collected_value_msat, recommended_value_msat, if found_new_path { "found" } else { "did not find" });
@@ -2389,15 +2474,22 @@ where L::Target: Logger {
                                log_trace!(logger, "Collected exactly our payment amount on the first pass, without hitting an htlc_minimum_msat limit, exiting.");
                                break 'paths_collection;
                        }
-                       log_trace!(logger, "Collected our payment amount on the first pass, but running again to collect extra paths with a potentially higher limit.");
+                       log_trace!(logger, "Collected our payment amount on the first pass, but running again to collect extra paths with a potentially higher value to meet htlc_minimum_msat limit.");
                        path_value_msat = recommended_value_msat;
                }
        }
 
        let num_ignored_total = num_ignored_value_contribution + num_ignored_path_length_limit +
-               num_ignored_cltv_delta_limit + num_ignored_previously_failed;
+               num_ignored_cltv_delta_limit + num_ignored_previously_failed +
+               num_ignored_avoid_overpayment + num_ignored_htlc_minimum_msat_limit +
+               num_ignored_total_fee_limit;
        if num_ignored_total > 0 {
-               log_trace!(logger, "Ignored {} candidate hops due to insufficient value contribution, {} due to path length limit, {} due to CLTV delta limit, {} due to previous payment failure. Total: {} ignored candidates.", num_ignored_value_contribution, num_ignored_path_length_limit, num_ignored_cltv_delta_limit, num_ignored_previously_failed, num_ignored_total);
+               log_trace!(logger,
+                       "Ignored {} candidate hops due to insufficient value contribution, {} due to path length limit, {} due to CLTV delta limit, {} due to previous payment failure, {} due to htlc_minimum_msat limit, {} to avoid overpaying, {} due to maximum total fee limit. Total: {} ignored candidates.",
+                       num_ignored_value_contribution, num_ignored_path_length_limit,
+                       num_ignored_cltv_delta_limit, num_ignored_previously_failed,
+                       num_ignored_htlc_minimum_msat_limit, num_ignored_avoid_overpayment,
+                       num_ignored_total_fee_limit, num_ignored_total);
        }
 
        // Step (5).
@@ -2546,6 +2638,15 @@ where L::Target: Logger {
        }
 
        let route = Route { paths, route_params: Some(route_params.clone()) };
+
+       // Make sure we would never create a route whose total fees exceed max_total_routing_fee_msat.
+       if let Some(max_total_routing_fee_msat) = route_params.max_total_routing_fee_msat {
+               if route.get_total_fees() > max_total_routing_fee_msat {
+                       return Err(LightningError{err: format!("Failed to find route that adheres to the maximum total fee limit of {}msat",
+                               max_total_routing_fee_msat), action: ErrorAction::IgnoreError});
+               }
+       }
+
        log_info!(logger, "Got route: {}", log_route!(route));
        Ok(route)
 }
@@ -2845,7 +2946,7 @@ mod tests {
                        Arc::clone(&logger), &scorer, &Default::default(), &random_seed_bytes) {
                                assert_eq!(err, "First hop cannot have our_node_pubkey as a destination.");
                } else { panic!(); }
+
                let route = get_route(&our_id, &route_params, &network_graph.read_only(), None,
                        Arc::clone(&logger), &scorer, &Default::default(), &random_seed_bytes).unwrap();
                assert_eq!(route.paths[0].hops.len(), 2);
@@ -3061,8 +3162,9 @@ mod tests {
                        excess_data: Vec::new()
                });
 
-               let route_params = RouteParameters::from_payment_params_and_value(
+               let mut route_params = RouteParameters::from_payment_params_and_value(
                        payment_params.clone(), 60_000);
+               route_params.max_total_routing_fee_msat = Some(15_000);
                let route = get_route(&our_id, &route_params, &network_graph.read_only(), None,
                        Arc::clone(&logger), &scorer, &Default::default(), &random_seed_bytes).unwrap();
                // Overpay fees to hit htlc_minimum_msat.
@@ -3128,6 +3230,67 @@ mod tests {
                assert_eq!(fees, 5_000);
        }
 
+       #[test]
+       fn htlc_minimum_recipient_overpay_test() {
+               let (secp_ctx, network_graph, gossip_sync, _, logger) = build_graph();
+               let (_, our_id, privkeys, nodes) = get_nodes(&secp_ctx);
+               let config = UserConfig::default();
+               let payment_params = PaymentParameters::from_node_id(nodes[2], 42).with_bolt11_features(channelmanager::provided_invoice_features(&config)).unwrap();
+               let scorer = ln_test_utils::TestScorer::new();
+               let keys_manager = ln_test_utils::TestKeysInterface::new(&[0u8; 32], Network::Testnet);
+               let random_seed_bytes = keys_manager.get_secure_random_bytes();
+
+               // Route to node2 over a single path which requires overpaying the recipient themselves.
+
+               // First disable all paths except the us -> node1 -> node2 path
+               update_channel(&gossip_sync, &secp_ctx, &privkeys[2], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 13,
+                       timestamp: 2,
+                       flags: 3,
+                       cltv_expiry_delta: 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: 0,
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               // Set channel 4 to free but with a high htlc_minimum_msat
+               update_channel(&gossip_sync, &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: 15_000,
+                       htlc_maximum_msat: MAX_VALUE_MSAT,
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               // Now check that we'll fail to find a path if we fail to find a path if the htlc_minimum
+               // is overrun. Note that the fees are actually calculated on 3*payment amount as that's
+               // what we try to find a route for, so this test only just happens to work out to exactly
+               // the fee limit.
+               let mut route_params = RouteParameters::from_payment_params_and_value(
+                       payment_params.clone(), 5_000);
+               route_params.max_total_routing_fee_msat = Some(9_999);
+               if let Err(LightningError{err, action: ErrorAction::IgnoreError}) = get_route(&our_id,
+                       &route_params, &network_graph.read_only(), None, Arc::clone(&logger), &scorer,
+                       &Default::default(), &random_seed_bytes) {
+                               assert_eq!(err, "Failed to find route that adheres to the maximum total fee limit of 9999msat");
+               } else { panic!(); }
+
+               let mut route_params = RouteParameters::from_payment_params_and_value(
+                       payment_params.clone(), 5_000);
+               route_params.max_total_routing_fee_msat = Some(10_000);
+               let route = get_route(&our_id, &route_params, &network_graph.read_only(), None,
+                       Arc::clone(&logger), &scorer, &Default::default(), &random_seed_bytes).unwrap();
+               assert_eq!(route.get_total_fees(), 10_000);
+       }
+
        #[test]
        fn disable_channels_test() {
                let (secp_ctx, network_graph, gossip_sync, _, logger) = build_graph();
@@ -5239,9 +5402,21 @@ mod tests {
                        } else { panic!(); }
                }
 
+               {
+                       // Attempt to route while setting max_total_routing_fee_msat to 149_999 results in a failure.
+                       let route_params = RouteParameters { payment_params: payment_params.clone(), final_value_msat: 200_000,
+                               max_total_routing_fee_msat: Some(149_999) };
+                       if let Err(LightningError{err, action: ErrorAction::IgnoreError}) = get_route(
+                               &our_id, &route_params, &network_graph.read_only(), None, Arc::clone(&logger),
+                               &scorer, &(), &random_seed_bytes) {
+                                       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_params = RouteParameters::from_payment_params_and_value(payment_params, 200_000);
+                       let route_params = RouteParameters { payment_params: payment_params.clone(), final_value_msat: 200_000,
+                               max_total_routing_fee_msat: Some(150_000) };
                        let route = get_route(&our_id, &route_params, &network_graph.read_only(), None,
                                Arc::clone(&logger), &scorer, &Default::default(), &random_seed_bytes).unwrap();
                        assert_eq!(route.paths.len(), 2);
@@ -5708,8 +5883,9 @@ mod tests {
                {
                        // 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_params = RouteParameters::from_payment_params_and_value(
+                       let mut route_params = RouteParameters::from_payment_params_and_value(
                                payment_params, 90_000);
+                       route_params.max_total_routing_fee_msat = Some(90_000*2);
                        let route = get_route(&our_id, &route_params, &network_graph.read_only(), None,
                                Arc::clone(&logger), &scorer, &Default::default(), &random_seed_bytes).unwrap();
                        assert_eq!(route.paths.len(), 1);
@@ -5777,8 +5953,9 @@ mod tests {
                        // 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_params = RouteParameters::from_payment_params_and_value(
+                       let mut route_params = RouteParameters::from_payment_params_and_value(
                                payment_params, 90_000);
+                       route_params.max_total_routing_fee_msat = Some(90_000*2);
                        let route = get_route(&our_id, &route_params, &network_graph.read_only(), None,
                                Arc::clone(&logger), &scorer, &Default::default(), &random_seed_bytes).unwrap();
                        assert_eq!(route.paths.len(), 1);
@@ -6483,8 +6660,9 @@ mod tests {
 
                // Make sure we'll error if our route hints don't have enough liquidity according to their
                // htlc_maximum_msat.
-               let route_params = RouteParameters::from_payment_params_and_value(
+               let mut route_params = RouteParameters::from_payment_params_and_value(
                        payment_params, max_htlc_msat + 1);
+               route_params.max_total_routing_fee_msat = None;
                if let Err(LightningError{err, action: ErrorAction::IgnoreError}) = get_route(&our_id,
                        &route_params, &netgraph, None, Arc::clone(&logger), &scorer, &Default::default(),
                        &random_seed_bytes)
@@ -6498,8 +6676,9 @@ mod tests {
                let payment_params = PaymentParameters::from_node_id(dest_node_id, 42)
                        .with_route_hints(vec![route_hint_1, route_hint_2]).unwrap()
                        .with_bolt11_features(channelmanager::provided_invoice_features(&config)).unwrap();
-               let route_params = RouteParameters::from_payment_params_and_value(
+               let mut route_params = RouteParameters::from_payment_params_and_value(
                        payment_params, max_htlc_msat + 1);
+               route_params.max_total_routing_fee_msat = Some(max_htlc_msat * 2);
                let route = get_route(&our_id, &route_params, &netgraph, None, Arc::clone(&logger),
                        &scorer, &Default::default(), &random_seed_bytes).unwrap();
                assert_eq!(route.paths.len(), 2);
@@ -6934,7 +7113,8 @@ mod tests {
                let payment_params = PaymentParameters::blinded(blinded_hints.clone())
                        .with_bolt12_features(bolt12_features.clone()).unwrap();
 
-               let route_params = RouteParameters::from_payment_params_and_value(payment_params, 100_000);
+               let mut route_params = RouteParameters::from_payment_params_and_value(payment_params, 100_000);
+               route_params.max_total_routing_fee_msat = Some(100_000);
                let route = get_route(&our_id, &route_params, &network_graph, None, Arc::clone(&logger),
                        &scorer, &Default::default(), &random_seed_bytes).unwrap();
                assert_eq!(route.paths.len(), 2);
@@ -7109,6 +7289,558 @@ mod tests {
                assert_eq!(route.get_total_fees(), blinded_payinfo.fee_base_msat as u64);
                assert_eq!(route.get_total_amount(), amt_msat);
        }
+
+       #[test]
+       fn we_are_intro_node_candidate_hops() {
+               // This previously led to a panic in the router because we'd generate a Path with only a
+               // BlindedTail and 0 unblinded hops, due to the only candidate hops being blinded route hints
+               // where the origin node is the intro node. We now fully disallow considering candidate hops
+               // where the origin node is the intro node.
+               let (secp_ctx, network_graph, _, _, logger) = build_graph();
+               let (_, our_id, _, nodes) = get_nodes(&secp_ctx);
+               let scorer = ln_test_utils::TestScorer::new();
+               let keys_manager = ln_test_utils::TestKeysInterface::new(&[0u8; 32], Network::Testnet);
+               let random_seed_bytes = keys_manager.get_secure_random_bytes();
+               let config = UserConfig::default();
+
+               // Values are taken from the fuzz input that uncovered this panic.
+               let amt_msat = 21_7020_5185_1423_0019;
+
+               let blinded_path = BlindedPath {
+                       introduction_node_id: our_id,
+                       blinding_point: ln_test_utils::pubkey(42),
+                       blinded_hops: vec![
+                               BlindedHop { blinded_node_id: ln_test_utils::pubkey(42 as u8), encrypted_payload: Vec::new() },
+                               BlindedHop { blinded_node_id: ln_test_utils::pubkey(42 as u8), encrypted_payload: Vec::new() }
+                       ],
+               };
+               let blinded_payinfo = BlindedPayInfo {
+                       fee_base_msat: 5052_9027,
+                       fee_proportional_millionths: 0,
+                       htlc_minimum_msat: 21_7020_5185_1423_0019,
+                       htlc_maximum_msat: 1844_6744_0737_0955_1615,
+                       cltv_expiry_delta: 0,
+                       features: BlindedHopFeatures::empty(),
+               };
+               let mut blinded_hints = vec![
+                       (blinded_payinfo.clone(), blinded_path.clone()),
+                       (blinded_payinfo.clone(), blinded_path.clone()),
+               ];
+               blinded_hints[1].1.introduction_node_id = nodes[6];
+
+               let bolt12_features: Bolt12InvoiceFeatures = channelmanager::provided_invoice_features(&config).to_context();
+               let payment_params = PaymentParameters::blinded(blinded_hints.clone())
+                       .with_bolt12_features(bolt12_features.clone()).unwrap();
+
+               let netgraph = network_graph.read_only();
+               let route_params = RouteParameters::from_payment_params_and_value(
+                       payment_params, amt_msat);
+               if let Err(LightningError { err, .. }) = get_route(
+                       &our_id, &route_params, &netgraph, None, Arc::clone(&logger), &scorer, &(), &random_seed_bytes
+               ) {
+                       assert_eq!(err, "Failed to find a path to the given destination");
+               } else { panic!() }
+       }
+
+       #[test]
+       fn we_are_intro_node_bp_in_final_path_fee_calc() {
+               // This previously led to a debug panic in the router because we'd find an invalid Path with
+               // 0 unblinded hops and a blinded tail, leading to the generation of a final
+               // PaymentPathHop::fee_msat that included both the blinded path fees and the final value of
+               // the payment, when it was intended to only include the final value of the payment.
+               let (secp_ctx, network_graph, _, _, logger) = build_graph();
+               let (_, our_id, _, nodes) = get_nodes(&secp_ctx);
+               let scorer = ln_test_utils::TestScorer::new();
+               let keys_manager = ln_test_utils::TestKeysInterface::new(&[0u8; 32], Network::Testnet);
+               let random_seed_bytes = keys_manager.get_secure_random_bytes();
+               let config = UserConfig::default();
+
+               // Values are taken from the fuzz input that uncovered this panic.
+               let amt_msat = 21_7020_5185_1423_0019;
+
+               let blinded_path = BlindedPath {
+                       introduction_node_id: our_id,
+                       blinding_point: ln_test_utils::pubkey(42),
+                       blinded_hops: vec![
+                               BlindedHop { blinded_node_id: ln_test_utils::pubkey(42 as u8), encrypted_payload: Vec::new() },
+                               BlindedHop { blinded_node_id: ln_test_utils::pubkey(42 as u8), encrypted_payload: Vec::new() }
+                       ],
+               };
+               let blinded_payinfo = BlindedPayInfo {
+                       fee_base_msat: 10_4425_1395,
+                       fee_proportional_millionths: 0,
+                       htlc_minimum_msat: 21_7301_9934_9094_0931,
+                       htlc_maximum_msat: 1844_6744_0737_0955_1615,
+                       cltv_expiry_delta: 0,
+                       features: BlindedHopFeatures::empty(),
+               };
+               let mut blinded_hints = vec![
+                       (blinded_payinfo.clone(), blinded_path.clone()),
+                       (blinded_payinfo.clone(), blinded_path.clone()),
+                       (blinded_payinfo.clone(), blinded_path.clone()),
+               ];
+               blinded_hints[1].0.fee_base_msat = 5052_9027;
+               blinded_hints[1].0.htlc_minimum_msat = 21_7020_5185_1423_0019;
+               blinded_hints[1].0.htlc_maximum_msat = 1844_6744_0737_0955_1615;
+
+               blinded_hints[2].1.introduction_node_id = nodes[6];
+
+               let bolt12_features: Bolt12InvoiceFeatures = channelmanager::provided_invoice_features(&config).to_context();
+               let payment_params = PaymentParameters::blinded(blinded_hints.clone())
+                       .with_bolt12_features(bolt12_features.clone()).unwrap();
+
+               let netgraph = network_graph.read_only();
+               let route_params = RouteParameters::from_payment_params_and_value(
+                       payment_params, amt_msat);
+               if let Err(LightningError { err, .. }) = get_route(
+                       &our_id, &route_params, &netgraph, None, Arc::clone(&logger), &scorer, &(), &random_seed_bytes
+               ) {
+                       assert_eq!(err, "Failed to find a path to the given destination");
+               } else { panic!() }
+       }
+
+       #[test]
+       fn min_htlc_overpay_violates_max_htlc() {
+               do_min_htlc_overpay_violates_max_htlc(true);
+               do_min_htlc_overpay_violates_max_htlc(false);
+       }
+       fn do_min_htlc_overpay_violates_max_htlc(blinded_payee: bool) {
+               // Test that if overpaying to meet a later hop's min_htlc and causes us to violate an earlier
+               // hop's max_htlc, we don't consider that candidate hop valid. Previously we would add this hop
+               // to `targets` and build an invalid path with it, and subsquently hit a debug panic asserting
+               // that the used liquidity for a hop was less than its available liquidity limit.
+               let secp_ctx = Secp256k1::new();
+               let logger = Arc::new(ln_test_utils::TestLogger::new());
+               let network_graph = Arc::new(NetworkGraph::new(Network::Testnet, Arc::clone(&logger)));
+               let scorer = ln_test_utils::TestScorer::new();
+               let keys_manager = ln_test_utils::TestKeysInterface::new(&[0u8; 32], Network::Testnet);
+               let random_seed_bytes = keys_manager.get_secure_random_bytes();
+               let config = UserConfig::default();
+
+               // Values are taken from the fuzz input that uncovered this panic.
+               let amt_msat = 7_4009_8048;
+               let (_, our_id, _, nodes) = get_nodes(&secp_ctx);
+               let first_hop_outbound_capacity = 2_7345_2000;
+               let first_hops = vec![get_channel_details(
+                       Some(200), nodes[0], channelmanager::provided_init_features(&config),
+                       first_hop_outbound_capacity
+               )];
+
+               let base_fee = 1_6778_3453;
+               let htlc_min = 2_5165_8240;
+               let payment_params = if blinded_payee {
+                       let blinded_path = BlindedPath {
+                               introduction_node_id: nodes[0],
+                               blinding_point: ln_test_utils::pubkey(42),
+                               blinded_hops: vec![
+                                       BlindedHop { blinded_node_id: ln_test_utils::pubkey(42 as u8), encrypted_payload: Vec::new() },
+                                       BlindedHop { blinded_node_id: ln_test_utils::pubkey(42 as u8), encrypted_payload: Vec::new() }
+                               ],
+                       };
+                       let blinded_payinfo = BlindedPayInfo {
+                               fee_base_msat: base_fee,
+                               fee_proportional_millionths: 0,
+                               htlc_minimum_msat: htlc_min,
+                               htlc_maximum_msat: htlc_min * 1000,
+                               cltv_expiry_delta: 0,
+                               features: BlindedHopFeatures::empty(),
+                       };
+                       let bolt12_features: Bolt12InvoiceFeatures = channelmanager::provided_invoice_features(&config).to_context();
+                       PaymentParameters::blinded(vec![(blinded_payinfo, blinded_path)])
+                               .with_bolt12_features(bolt12_features.clone()).unwrap()
+               } else {
+                       let route_hint = RouteHint(vec![RouteHintHop {
+                               src_node_id: nodes[0],
+                               short_channel_id: 42,
+                               fees: RoutingFees {
+                                       base_msat: base_fee,
+                                       proportional_millionths: 0,
+                               },
+                               cltv_expiry_delta: 10,
+                               htlc_minimum_msat: Some(htlc_min),
+                               htlc_maximum_msat: None,
+                       }]);
+
+                       PaymentParameters::from_node_id(nodes[1], 42)
+                               .with_route_hints(vec![route_hint]).unwrap()
+                               .with_bolt11_features(channelmanager::provided_invoice_features(&config)).unwrap()
+               };
+
+               let netgraph = network_graph.read_only();
+               let route_params = RouteParameters::from_payment_params_and_value(
+                       payment_params, amt_msat);
+               if let Err(LightningError { err, .. }) = get_route(
+                       &our_id, &route_params, &netgraph, Some(&first_hops.iter().collect::<Vec<_>>()),
+                       Arc::clone(&logger), &scorer, &(), &random_seed_bytes
+               ) {
+                       assert_eq!(err, "Failed to find a path to the given destination");
+               } else { panic!() }
+       }
+
+       #[test]
+       fn previously_used_liquidity_violates_max_htlc() {
+               do_previously_used_liquidity_violates_max_htlc(true);
+               do_previously_used_liquidity_violates_max_htlc(false);
+
+       }
+       fn do_previously_used_liquidity_violates_max_htlc(blinded_payee: bool) {
+               // Test that if a candidate first_hop<>route_hint_src_node channel does not have enough
+               // contribution amount to cover the next hop's min_htlc plus fees, we will not consider that
+               // candidate. In this case, the candidate does not have enough due to a previous path taking up
+               // some of its liquidity. Previously we would construct an invalid path and hit a debug panic
+               // asserting that the used liquidity for a hop was less than its available liquidity limit.
+               let secp_ctx = Secp256k1::new();
+               let logger = Arc::new(ln_test_utils::TestLogger::new());
+               let network_graph = Arc::new(NetworkGraph::new(Network::Testnet, Arc::clone(&logger)));
+               let scorer = ln_test_utils::TestScorer::new();
+               let keys_manager = ln_test_utils::TestKeysInterface::new(&[0u8; 32], Network::Testnet);
+               let random_seed_bytes = keys_manager.get_secure_random_bytes();
+               let config = UserConfig::default();
+
+               // Values are taken from the fuzz input that uncovered this panic.
+               let amt_msat = 52_4288;
+               let (_, our_id, _, nodes) = get_nodes(&secp_ctx);
+               let first_hops = vec![get_channel_details(
+                       Some(161), nodes[0], channelmanager::provided_init_features(&config), 486_4000
+               ), get_channel_details(
+                       Some(122), nodes[0], channelmanager::provided_init_features(&config), 179_5000
+               )];
+
+               let base_fees = [0, 425_9840, 0, 0];
+               let htlc_mins = [1_4392, 19_7401, 1027, 6_5535];
+               let payment_params = if blinded_payee {
+                       let blinded_path = BlindedPath {
+                               introduction_node_id: nodes[0],
+                               blinding_point: ln_test_utils::pubkey(42),
+                               blinded_hops: vec![
+                                       BlindedHop { blinded_node_id: ln_test_utils::pubkey(42 as u8), encrypted_payload: Vec::new() },
+                                       BlindedHop { blinded_node_id: ln_test_utils::pubkey(42 as u8), encrypted_payload: Vec::new() }
+                               ],
+                       };
+                       let mut blinded_hints = Vec::new();
+                       for (base_fee, htlc_min) in base_fees.iter().zip(htlc_mins.iter()) {
+                               blinded_hints.push((BlindedPayInfo {
+                                       fee_base_msat: *base_fee,
+                                       fee_proportional_millionths: 0,
+                                       htlc_minimum_msat: *htlc_min,
+                                       htlc_maximum_msat: htlc_min * 100,
+                                       cltv_expiry_delta: 10,
+                                       features: BlindedHopFeatures::empty(),
+                               }, blinded_path.clone()));
+                       }
+                       let bolt12_features: Bolt12InvoiceFeatures = channelmanager::provided_invoice_features(&config).to_context();
+                       PaymentParameters::blinded(blinded_hints.clone())
+                               .with_bolt12_features(bolt12_features.clone()).unwrap()
+               } else {
+                       let mut route_hints = Vec::new();
+                       for (idx, (base_fee, htlc_min)) in base_fees.iter().zip(htlc_mins.iter()).enumerate() {
+                               route_hints.push(RouteHint(vec![RouteHintHop {
+                                       src_node_id: nodes[0],
+                                       short_channel_id: 42 + idx as u64,
+                                       fees: RoutingFees {
+                                               base_msat: *base_fee,
+                                               proportional_millionths: 0,
+                                       },
+                                       cltv_expiry_delta: 10,
+                                       htlc_minimum_msat: Some(*htlc_min),
+                                       htlc_maximum_msat: Some(htlc_min * 100),
+                               }]));
+                       }
+                       PaymentParameters::from_node_id(nodes[1], 42)
+                               .with_route_hints(route_hints).unwrap()
+                               .with_bolt11_features(channelmanager::provided_invoice_features(&config)).unwrap()
+               };
+
+               let netgraph = network_graph.read_only();
+               let route_params = RouteParameters::from_payment_params_and_value(
+                       payment_params, amt_msat);
+
+               let route = get_route(
+                       &our_id, &route_params, &netgraph, Some(&first_hops.iter().collect::<Vec<_>>()),
+                       Arc::clone(&logger), &scorer, &(), &random_seed_bytes
+               ).unwrap();
+               assert_eq!(route.paths.len(), 1);
+               assert_eq!(route.get_total_amount(), amt_msat);
+       }
+
+       #[test]
+       fn candidate_path_min() {
+               // Test that if a candidate first_hop<>network_node channel does not have enough contribution
+               // amount to cover the next channel's min htlc plus fees, we will not consider that candidate.
+               // Previously, we were storing RouteGraphNodes with a path_min that did not include fees, and
+               // would add a connecting first_hop node that did not have enough contribution amount, leading
+               // to a debug panic upon invalid path construction.
+               let secp_ctx = Secp256k1::new();
+               let logger = Arc::new(ln_test_utils::TestLogger::new());
+               let network_graph = Arc::new(NetworkGraph::new(Network::Testnet, Arc::clone(&logger)));
+               let gossip_sync = P2PGossipSync::new(network_graph.clone(), None, logger.clone());
+               let scorer = ProbabilisticScorer::new(ProbabilisticScoringDecayParameters::default(), network_graph.clone(), logger.clone());
+               let keys_manager = ln_test_utils::TestKeysInterface::new(&[0u8; 32], Network::Testnet);
+               let random_seed_bytes = keys_manager.get_secure_random_bytes();
+               let config = UserConfig::default();
+
+               // Values are taken from the fuzz input that uncovered this panic.
+               let amt_msat = 7_4009_8048;
+               let (_, our_id, privkeys, nodes) = get_nodes(&secp_ctx);
+               let first_hops = vec![get_channel_details(
+                       Some(200), nodes[0], channelmanager::provided_init_features(&config), 2_7345_2000
+               )];
+
+               add_channel(&gossip_sync, &secp_ctx, &privkeys[0], &privkeys[6], ChannelFeatures::from_le_bytes(id_to_feature_flags(6)), 6);
+               update_channel(&gossip_sync, &secp_ctx, &privkeys[0], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 6,
+                       timestamp: 1,
+                       flags: 0,
+                       cltv_expiry_delta: (6 << 4) | 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: MAX_VALUE_MSAT,
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+               add_or_update_node(&gossip_sync, &secp_ctx, &privkeys[0], NodeFeatures::from_le_bytes(id_to_feature_flags(1)), 0);
+
+               let htlc_min = 2_5165_8240;
+               let blinded_hints = vec![
+                       (BlindedPayInfo {
+                               fee_base_msat: 1_6778_3453,
+                               fee_proportional_millionths: 0,
+                               htlc_minimum_msat: htlc_min,
+                               htlc_maximum_msat: htlc_min * 100,
+                               cltv_expiry_delta: 10,
+                               features: BlindedHopFeatures::empty(),
+                       }, BlindedPath {
+                               introduction_node_id: nodes[0],
+                               blinding_point: ln_test_utils::pubkey(42),
+                               blinded_hops: vec![
+                                       BlindedHop { blinded_node_id: ln_test_utils::pubkey(42 as u8), encrypted_payload: Vec::new() },
+                                       BlindedHop { blinded_node_id: ln_test_utils::pubkey(42 as u8), encrypted_payload: Vec::new() }
+                               ],
+                       })
+               ];
+               let bolt12_features: Bolt12InvoiceFeatures = channelmanager::provided_invoice_features(&config).to_context();
+               let payment_params = PaymentParameters::blinded(blinded_hints.clone())
+                       .with_bolt12_features(bolt12_features.clone()).unwrap();
+               let route_params = RouteParameters::from_payment_params_and_value(
+                       payment_params, amt_msat);
+               let netgraph = network_graph.read_only();
+
+               if let Err(LightningError { err, .. }) = get_route(
+                       &our_id, &route_params, &netgraph, Some(&first_hops.iter().collect::<Vec<_>>()),
+                       Arc::clone(&logger), &scorer, &ProbabilisticScoringFeeParameters::default(),
+                       &random_seed_bytes
+               ) {
+                       assert_eq!(err, "Failed to find a path to the given destination");
+               } else { panic!() }
+       }
+
+       #[test]
+       fn path_contribution_includes_min_htlc_overpay() {
+               // Previously, the fuzzer hit a debug panic because we wouldn't include the amount overpaid to
+               // meet a last hop's min_htlc in the total collected paths value. We now include this value and
+               // also penalize hops along the overpaying path to ensure that it gets deprioritized in path
+               // selection, both tested here.
+               let secp_ctx = Secp256k1::new();
+               let logger = Arc::new(ln_test_utils::TestLogger::new());
+               let network_graph = Arc::new(NetworkGraph::new(Network::Testnet, Arc::clone(&logger)));
+               let scorer = ProbabilisticScorer::new(ProbabilisticScoringDecayParameters::default(), network_graph.clone(), logger.clone());
+               let keys_manager = ln_test_utils::TestKeysInterface::new(&[0u8; 32], Network::Testnet);
+               let random_seed_bytes = keys_manager.get_secure_random_bytes();
+               let config = UserConfig::default();
+
+               // Values are taken from the fuzz input that uncovered this panic.
+               let amt_msat = 562_0000;
+               let (_, our_id, _, nodes) = get_nodes(&secp_ctx);
+               let first_hops = vec![
+                       get_channel_details(
+                               Some(83), nodes[0], channelmanager::provided_init_features(&config), 2199_0000,
+                       ),
+               ];
+
+               let htlc_mins = [49_0000, 1125_0000];
+               let payment_params = {
+                       let blinded_path = BlindedPath {
+                               introduction_node_id: nodes[0],
+                               blinding_point: ln_test_utils::pubkey(42),
+                               blinded_hops: vec![
+                                       BlindedHop { blinded_node_id: ln_test_utils::pubkey(42 as u8), encrypted_payload: Vec::new() },
+                                       BlindedHop { blinded_node_id: ln_test_utils::pubkey(42 as u8), encrypted_payload: Vec::new() }
+                               ],
+                       };
+                       let mut blinded_hints = Vec::new();
+                       for htlc_min in htlc_mins.iter() {
+                               blinded_hints.push((BlindedPayInfo {
+                                       fee_base_msat: 0,
+                                       fee_proportional_millionths: 0,
+                                       htlc_minimum_msat: *htlc_min,
+                                       htlc_maximum_msat: *htlc_min * 100,
+                                       cltv_expiry_delta: 10,
+                                       features: BlindedHopFeatures::empty(),
+                               }, blinded_path.clone()));
+                       }
+                       let bolt12_features: Bolt12InvoiceFeatures = channelmanager::provided_invoice_features(&config).to_context();
+                       PaymentParameters::blinded(blinded_hints.clone())
+                               .with_bolt12_features(bolt12_features.clone()).unwrap()
+               };
+
+               let netgraph = network_graph.read_only();
+               let route_params = RouteParameters::from_payment_params_and_value(
+                       payment_params, amt_msat);
+               let route = get_route(
+                       &our_id, &route_params, &netgraph, Some(&first_hops.iter().collect::<Vec<_>>()),
+                       Arc::clone(&logger), &scorer, &ProbabilisticScoringFeeParameters::default(),
+                       &random_seed_bytes
+               ).unwrap();
+               assert_eq!(route.paths.len(), 1);
+               assert_eq!(route.get_total_amount(), amt_msat);
+       }
+
+       #[test]
+       fn first_hop_preferred_over_hint() {
+               // Check that if we have a first hop to a peer we'd always prefer that over a route hint
+               // they gave us, but we'd still consider all subsequent hints if they are more attractive.
+               let secp_ctx = Secp256k1::new();
+               let logger = Arc::new(ln_test_utils::TestLogger::new());
+               let network_graph = Arc::new(NetworkGraph::new(Network::Testnet, Arc::clone(&logger)));
+               let gossip_sync = P2PGossipSync::new(Arc::clone(&network_graph), None, Arc::clone(&logger));
+               let scorer = ln_test_utils::TestScorer::new();
+               let keys_manager = ln_test_utils::TestKeysInterface::new(&[0u8; 32], Network::Testnet);
+               let random_seed_bytes = keys_manager.get_secure_random_bytes();
+               let config = UserConfig::default();
+
+               let amt_msat = 1_000_000;
+               let (our_privkey, our_node_id, privkeys, nodes) = get_nodes(&secp_ctx);
+
+               add_channel(&gossip_sync, &secp_ctx, &our_privkey, &privkeys[0],
+                       ChannelFeatures::from_le_bytes(id_to_feature_flags(1)), 1);
+               update_channel(&gossip_sync, &secp_ctx, &our_privkey, UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 1,
+                       timestamp: 1,
+                       flags: 0,
+                       cltv_expiry_delta: 42,
+                       htlc_minimum_msat: 1_000,
+                       htlc_maximum_msat: 10_000_000,
+                       fee_base_msat: 800,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+               update_channel(&gossip_sync, &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: 42,
+                       htlc_minimum_msat: 1_000,
+                       htlc_maximum_msat: 10_000_000,
+                       fee_base_msat: 800,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               add_channel(&gossip_sync, &secp_ctx, &privkeys[0], &privkeys[1],
+                       ChannelFeatures::from_le_bytes(id_to_feature_flags(1)), 2);
+               update_channel(&gossip_sync, &secp_ctx, &privkeys[0], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 2,
+                       timestamp: 2,
+                       flags: 0,
+                       cltv_expiry_delta: 42,
+                       htlc_minimum_msat: 1_000,
+                       htlc_maximum_msat: 10_000_000,
+                       fee_base_msat: 800,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+               update_channel(&gossip_sync, &secp_ctx, &privkeys[1], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 2,
+                       timestamp: 2,
+                       flags: 1,
+                       cltv_expiry_delta: 42,
+                       htlc_minimum_msat: 1_000,
+                       htlc_maximum_msat: 10_000_000,
+                       fee_base_msat: 800,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+
+               let dest_node_id = nodes[2];
+
+               let route_hint = RouteHint(vec![RouteHintHop {
+                       src_node_id: our_node_id,
+                       short_channel_id: 44,
+                       fees: RoutingFees {
+                               base_msat: 234,
+                               proportional_millionths: 0,
+                       },
+                       cltv_expiry_delta: 10,
+                       htlc_minimum_msat: None,
+                       htlc_maximum_msat: Some(5_000_000),
+               },
+               RouteHintHop {
+                       src_node_id: nodes[0],
+                       short_channel_id: 45,
+                       fees: RoutingFees {
+                               base_msat: 123,
+                               proportional_millionths: 0,
+                       },
+                       cltv_expiry_delta: 10,
+                       htlc_minimum_msat: None,
+                       htlc_maximum_msat: None,
+               }]);
+
+               let payment_params = PaymentParameters::from_node_id(dest_node_id, 42)
+                       .with_route_hints(vec![route_hint]).unwrap()
+                       .with_bolt11_features(channelmanager::provided_invoice_features(&config)).unwrap();
+               let route_params = RouteParameters::from_payment_params_and_value(
+                       payment_params, amt_msat);
+
+               // First create an insufficient first hop for channel with SCID 1 and check we'd use the
+               // route hint.
+               let first_hop = get_channel_details(Some(1), nodes[0],
+                       channelmanager::provided_init_features(&config), 999_999);
+               let first_hops = vec![first_hop];
+
+               let route = get_route(&our_node_id, &route_params.clone(), &network_graph.read_only(),
+                       Some(&first_hops.iter().collect::<Vec<_>>()), Arc::clone(&logger), &scorer,
+                       &Default::default(), &random_seed_bytes).unwrap();
+               assert_eq!(route.paths.len(), 1);
+               assert_eq!(route.get_total_amount(), amt_msat);
+               assert_eq!(route.paths[0].hops.len(), 2);
+               assert_eq!(route.paths[0].hops[0].short_channel_id, 44);
+               assert_eq!(route.paths[0].hops[1].short_channel_id, 45);
+               assert_eq!(route.get_total_fees(), 123);
+
+               // Now check we would trust our first hop info, i.e., fail if we detect the route hint is
+               // for a first hop channel.
+               let mut first_hop = get_channel_details(Some(1), nodes[0], channelmanager::provided_init_features(&config), 999_999);
+               first_hop.outbound_scid_alias = Some(44);
+               let first_hops = vec![first_hop];
+
+               let route_res = get_route(&our_node_id, &route_params.clone(), &network_graph.read_only(),
+                       Some(&first_hops.iter().collect::<Vec<_>>()), Arc::clone(&logger), &scorer,
+                       &Default::default(), &random_seed_bytes);
+               assert!(route_res.is_err());
+
+               // Finally check we'd use the first hop if has sufficient outbound capacity. But we'd stil
+               // use the cheaper second hop of the route hint.
+               let mut first_hop = get_channel_details(Some(1), nodes[0],
+                       channelmanager::provided_init_features(&config), 10_000_000);
+               first_hop.outbound_scid_alias = Some(44);
+               let first_hops = vec![first_hop];
+
+               let route = get_route(&our_node_id, &route_params.clone(), &network_graph.read_only(),
+                       Some(&first_hops.iter().collect::<Vec<_>>()), Arc::clone(&logger), &scorer,
+                       &Default::default(), &random_seed_bytes).unwrap();
+               assert_eq!(route.paths.len(), 1);
+               assert_eq!(route.get_total_amount(), amt_msat);
+               assert_eq!(route.paths[0].hops.len(), 2);
+               assert_eq!(route.paths[0].hops[0].short_channel_id, 1);
+               assert_eq!(route.paths[0].hops[1].short_channel_id, 45);
+               assert_eq!(route.get_total_fees(), 123);
+       }
 }
 
 #[cfg(all(any(test, ldk_bench), not(feature = "no-std")))]