Fix a panic in Route's new fee-calculation methods and clean up

This addresses Val's feedback on the new Route fee- and
amount-calculation methods, including fixing the panic she
identified and cleaning up various docs and comments.

diff --git a/lightning/src/routing/router.rs b/lightning/src/routing/router.rs
index 98b3d8f52453b939d129426d32117bbb6cedb1cb..e60fd1ee1b3f63b72c733491496cda6926028be3 100644 (file)
--- a/lightning/src/routing/router.rs
+++ b/lightning/src/routing/router.rs
@@ -72,21 +72,22 @@ pub struct Route {
 }
 
 impl Route {
-       /// Returns the total amount of fees paid on this Route.
-       /// This doesn't include any extra payment made to the recipient,
-       /// which can happen in excess of the amount passed to `get_route`'s `final_value_msat`.
+       /// Returns the total amount of fees paid on this [`Route`].
+       ///
+       /// This doesn't include any extra payment made to the recipient, which can happen in excess of
+       /// the amount passed to [`get_route`]'s `final_value_msat`.
        pub fn get_total_fees(&self) -> u64 {
                // Do not count last hop of each path since that's the full value of the payment
                return self.paths.iter()
-                       .flat_map(|path| path.split_last().unwrap().1)
+                       .flat_map(|path| path.split_last().map(|(_, path_prefix)| path_prefix).unwrap_or(&[]))
                        .map(|hop| &hop.fee_msat)
                        .sum();
        }
-       /// Returns the total amount paid on this Route, excluding the fees.
+
+       /// Returns the total amount paid on this [`Route`], excluding the fees.
        pub fn get_total_amount(&self) -> u64 {
                return self.paths.iter()
-                       .map(|path| path.split_last().unwrap().0)
-                       .map(|hop| &hop.fee_msat)
+                       .map(|path| path.split_last().map(|(hop, _)| hop.fee_msat).unwrap_or(0))
                        .sum();
        }
 }
@@ -4226,17 +4227,17 @@ mod tests {
                                RouteHop {
                                        pubkey: PublicKey::from_slice(&hex::decode("02eec7245d6b7d2ccb30380bfbe2a3648cd7a942653f5aa340edcea1f283686619").unwrap()[..]).unwrap(),
                                        channel_features: ChannelFeatures::empty(), node_features: NodeFeatures::empty(),
-                                       short_channel_id: 0, fee_msat: 100, cltv_expiry_delta: 0 // Test vectors are garbage and not generateble from a RouteHop, we fill in payloads manually
+                                       short_channel_id: 0, fee_msat: 100, cltv_expiry_delta: 0
                                },
                                RouteHop {
                                        pubkey: PublicKey::from_slice(&hex::decode("0324653eac434488002cc06bbfb7f10fe18991e35f9fe4302dbea6d2353dc0ab1c").unwrap()[..]).unwrap(),
                                        channel_features: ChannelFeatures::empty(), node_features: NodeFeatures::empty(),
-                                       short_channel_id: 0, fee_msat: 150, cltv_expiry_delta: 0 // Test vectors are garbage and not generateble from a RouteHop, we fill in payloads manually
+                                       short_channel_id: 0, fee_msat: 150, cltv_expiry_delta: 0
                                },
                                RouteHop {
                                        pubkey: PublicKey::from_slice(&hex::decode("027f31ebc5462c1fdce1b737ecff52d37d75dea43ce11c74d25aa297165faa2007").unwrap()[..]).unwrap(),
                                        channel_features: ChannelFeatures::empty(), node_features: NodeFeatures::empty(),
-                                       short_channel_id: 0, fee_msat: 225, cltv_expiry_delta: 0 // Test vectors are garbage and not generateble from a RouteHop, we fill in payloads manually
+                                       short_channel_id: 0, fee_msat: 225, cltv_expiry_delta: 0
                                },
                        ]],
                };
@@ -4252,23 +4253,23 @@ mod tests {
                                RouteHop {
                                        pubkey: PublicKey::from_slice(&hex::decode("02eec7245d6b7d2ccb30380bfbe2a3648cd7a942653f5aa340edcea1f283686619").unwrap()[..]).unwrap(),
                                        channel_features: ChannelFeatures::empty(), node_features: NodeFeatures::empty(),
-                                       short_channel_id: 0, fee_msat: 100, cltv_expiry_delta: 0 // Test vectors are garbage and not generateble from a RouteHop, we fill in payloads manually
+                                       short_channel_id: 0, fee_msat: 100, cltv_expiry_delta: 0
                                },
                                RouteHop {
                                        pubkey: PublicKey::from_slice(&hex::decode("0324653eac434488002cc06bbfb7f10fe18991e35f9fe4302dbea6d2353dc0ab1c").unwrap()[..]).unwrap(),
                                        channel_features: ChannelFeatures::empty(), node_features: NodeFeatures::empty(),
-                                       short_channel_id: 0, fee_msat: 150, cltv_expiry_delta: 0 // Test vectors are garbage and not generateble from a RouteHop, we fill in payloads manually
+                                       short_channel_id: 0, fee_msat: 150, cltv_expiry_delta: 0
                                },
                        ],vec![
                                RouteHop {
                                        pubkey: PublicKey::from_slice(&hex::decode("02eec7245d6b7d2ccb30380bfbe2a3648cd7a942653f5aa340edcea1f283686619").unwrap()[..]).unwrap(),
                                        channel_features: ChannelFeatures::empty(), node_features: NodeFeatures::empty(),
-                                       short_channel_id: 0, fee_msat: 100, cltv_expiry_delta: 0 // Test vectors are garbage and not generateble from a RouteHop, we fill in payloads manually
+                                       short_channel_id: 0, fee_msat: 100, cltv_expiry_delta: 0
                                },
                                RouteHop {
                                        pubkey: PublicKey::from_slice(&hex::decode("0324653eac434488002cc06bbfb7f10fe18991e35f9fe4302dbea6d2353dc0ab1c").unwrap()[..]).unwrap(),
                                        channel_features: ChannelFeatures::empty(), node_features: NodeFeatures::empty(),
-                                       short_channel_id: 0, fee_msat: 150, cltv_expiry_delta: 0 // Test vectors are garbage and not generateble from a RouteHop, we fill in payloads manually
+                                       short_channel_id: 0, fee_msat: 150, cltv_expiry_delta: 0
                                },
                        ]],
                };
@@ -4277,6 +4278,17 @@ mod tests {
                assert_eq!(route.get_total_amount(), 300);
        }
 
+       #[test]
+       fn total_empty_route_no_panic() {
+               // In an earlier version of `Route::get_total_fees` and `Route::get_total_amount`, they
+               // would both panic if the route was completely empty. We test to ensure they return 0
+               // here, even though its somewhat nonsensical as a route.
+               let route = Route { paths: Vec::new() };
+
+               assert_eq!(route.get_total_fees(), 0);
+               assert_eq!(route.get_total_amount(), 0);
+       }
+
        #[cfg(not(feature = "no-std"))]
        pub(super) fn random_init_seed() -> u64 {
                // Because the default HashMap in std pulls OS randomness, we can use it as a (bad) RNG.