feat(engine): Add LeftoversStore trait to store any amounts pending to be settled

Author: gakonst

crates/interledger-settlement-engines/src/stores/mod.rs

@@ -1,6 +1,7 @@
 use bytes::Bytes;
 use futures::future::Future;
 use http::StatusCode;
+use num_bigint::BigUint;
 
 pub mod redis_ethereum_ledger;
 pub mod redis_store_common;
@@ -28,3 +29,12 @@ pub trait IdempotentEngineStore {
         data: Bytes,
     ) -> Box<dyn Future<Item = (), Error = ()> + Send>;
 }
+
+pub trait LeftoversStore {
+    /// Saves the leftover data
+    fn save_leftovers(
+        &self,
+        account_id: String,
+        leftovers: BigUint,
+    ) -> Box<dyn Future<Item = (), Error = ()> + Send>;
+}

crates/interledger-settlement-engines/src/stores/redis_ethereum_ledger/store.rs

@@ -13,6 +13,8 @@ use redis::{self, cmd, r#async::SharedConnection, ConnectionInfo, PipelineComman
 use log::{error, trace};
 
 use crate::stores::redis_store_common::{EngineRedisStore, EngineRedisStoreBuilder};
+use crate::stores::LeftoversStore;
+use num_bigint::BigUint;
 
 // Key for the latest observed block and balance. The data is stored in order to
 // avoid double crediting transactions which have already been processed, and in
@@ -105,6 +107,12 @@ impl EthereumLedgerRedisStore {
     }
 }
 
+impl LeftoversStore for EthereumLedgerRedisStore {
+    fn save_leftovers(&self, account_id: String, leftovers: BigUint) -> Box<dyn Future<Item = (), Error = ()> + Send> {
+        Box::new(ok(()))
+    }
+}
+
 impl EthereumStore for EthereumLedgerRedisStore {
     type Account = Account;