Improve database type safety

The database is now bound to a type eg. alice::State or bob::State.
The caller cannot expect to retrieve a type that is different to
the type that was stored.

xmr-btc/src/alice.rs

@@ -82,7 +82,7 @@ pub async fn next_state<
 }
 
 #[allow(clippy::large_enum_variant)]
-#[derive(Debug)]
+#[derive(Debug, Deserialize, Serialize)]
 pub enum State {
     State0(State0),
     State1(State1),

xmr-btc/src/bob.rs

@@ -82,7 +82,7 @@ pub async fn next_state<
     }
 }
 
-#[derive(Debug)]
+#[derive(Debug, Deserialize, Serialize)]
 pub enum State {
     State0(State0),
     State1(State1),

xmr-btc/tests/e2e.rs

@@ -18,6 +18,7 @@ mod tests {
     use monero_harness::Monero;
     use rand::rngs::OsRng;
 
+    use crate::harness::storage::Database;
     use std::{convert::TryInto, path::Path};
     use testcontainers::clients::Cli;
     use tracing_subscriber::util::SubscriberInitExt;
@@ -251,8 +252,10 @@ mod tests {
         let cli = Cli::default();
         let (monero, _container) = Monero::new(&cli);
         let bitcoind = init_bitcoind(&cli).await;
-        let alice_db = harness::storage::Database::open(Path::new(ALICE_TEST_DB_FOLDER)).unwrap();
+        let alice_db: Database<alice::State> =
-        let bob_db = harness::storage::Database::open(Path::new(BOB_TEST_DB_FOLDER)).unwrap();
+            harness::storage::Database::open(Path::new(ALICE_TEST_DB_FOLDER)).unwrap();
+        let bob_db: Database<bob::State> =
+            harness::storage::Database::open(Path::new(BOB_TEST_DB_FOLDER)).unwrap();
 
         let (
             alice_state0,
@@ -281,29 +284,26 @@ mod tests {
             .await
             .unwrap();
 
-            let alice_state5: alice::State5 = alice_state.try_into().unwrap();
-            let bob_state3: bob::State3 = bob_state.try_into().unwrap();
-
             // save state to db
-            alice_db.insert_latest_state(&alice_state5).await.unwrap();
+            alice_db.insert_latest_state(&alice_state).await.unwrap();
-            bob_db.insert_latest_state(&bob_state3).await.unwrap();
+            bob_db.insert_latest_state(&bob_state).await.unwrap();
         };
 
         let (alice_state6, bob_state5) = {
             // recover state from db
-            let alice_state5: alice::State5 = alice_db.get_latest_state().unwrap();
+            let alice_state = alice_db.get_latest_state().unwrap();
-            let bob_state3: bob::State3 = bob_db.get_latest_state().unwrap();
+            let bob_state = bob_db.get_latest_state().unwrap();
 
             let (alice_state, bob_state) = future::try_join(
                 run_alice_until(
                     &mut alice_node,
-                    alice_state5.into(),
+                    alice_state,
                     harness::alice::is_state6,
                     &mut OsRng,
                 ),
                 run_bob_until(
                     &mut bob_node,
-                    bob_state3.into(),
+                    bob_state,
                     harness::bob::is_state5,
                     &mut OsRng,
                 ),

xmr-btc/tests/harness/storage.rs

@@ -2,24 +2,31 @@ use anyhow::{anyhow, Context, Result};
 use serde::{de::DeserializeOwned, Deserialize, Serialize};
 use std::path::Path;
 
-pub struct Database {
+pub struct Database<T>
+where
+    T: Serialize + DeserializeOwned,
+{
     db: sled::Db,
+    _marker: std::marker::PhantomData<T>,
 }
 
-impl Database {
+impl<T> Database<T>
+where
+    T: Serialize + DeserializeOwned,
+{
     const LAST_STATE_KEY: &'static str = "latest_state";
 
     pub fn open(path: &Path) -> Result<Self> {
         let db =
             sled::open(path).with_context(|| format!("Could not open the DB at {:?}", path))?;
 
-        Ok(Database { db })
+        Ok(Database {
+            db,
+            _marker: Default::default(),
+        })
     }
 
-    pub async fn insert_latest_state<T>(&self, state: &T) -> Result<()>
+    pub async fn insert_latest_state(&self, state: &T) -> Result<()> {
-    where
-        T: Serialize + DeserializeOwned,
-    {
         let key = serialize(&Self::LAST_STATE_KEY)?;
         let new_value = serialize(&state).context("Could not serialize new state value")?;
 
@@ -37,10 +44,7 @@ impl Database {
             .context("Could not flush db")
     }
 
-    pub fn get_latest_state<T>(&self) -> anyhow::Result<T>
+    pub fn get_latest_state(&self) -> anyhow::Result<T> {
-    where
-        T: DeserializeOwned,
-    {
         let key = serialize(&Self::LAST_STATE_KEY)?;
 
         let encoded = self