Add safe_epoch_retention_limit to Configuration

In order to ensure that if a retention limit is set it's not lower than
a minimum value in order to not prune data that will be used at later
epochs.

mithril-aggregator/src/configuration.rs

@@ -193,6 +193,16 @@ impl Configuration {
 
         self.data_stores_directory.clone()
     }
+
+    /// Same as the [store retention limit][Configuration::store_retention_limit] but will never
+    /// yield a value lower than 3.
+    ///
+    /// This is in order to avoid pruning data that will be used in future epochs (like the protocol
+    /// parameters).
+    pub fn safe_epoch_retention_limit(&self) -> Option<u64> {
+        self.store_retention_limit
+            .map(|limit| if limit > 3 { limit as u64 } else { 3 })
+    }
 }
 
 /// Default configuration with all the default values for configurations.
@@ -323,3 +333,39 @@ impl Source for DefaultConfiguration {
         Ok(result)
     }
 }
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn safe_epoch_retention_limit_wont_change_a_value_higher_than_three() {
+        for limit in 4..=10u64 {
+            let configuration = Configuration {
+                store_retention_limit: Some(limit as usize),
+                ..Configuration::new_sample()
+            };
+            assert_eq!(configuration.safe_epoch_retention_limit(), Some(limit));
+        }
+    }
+
+    #[test]
+    fn safe_epoch_retention_limit_wont_change_a_none_value() {
+        let configuration = Configuration {
+            store_retention_limit: None,
+            ..Configuration::new_sample()
+        };
+        assert_eq!(configuration.safe_epoch_retention_limit(), None);
+    }
+
+    #[test]
+    fn safe_epoch_retention_limit_wont_yield_a_value_lower_than_three() {
+        for limit in 0..=3 {
+            let configuration = Configuration {
+                store_retention_limit: Some(limit),
+                ..Configuration::new_sample()
+            };
+            assert_eq!(configuration.safe_epoch_retention_limit(), Some(3));
+        }
+    }
+}

mithril-aggregator/src/dependency_injection/builder.rs

@@ -275,7 +275,7 @@ impl DependenciesBuilder {
     async fn build_stake_store(&mut self) -> Result<Arc<StakePoolStore>> {
         let stake_pool_store = Arc::new(StakePoolStore::new(
             self.get_sqlite_connection().await?,
-            self.configuration.store_retention_limit.map(|l| l as u64),
+            self.configuration.safe_epoch_retention_limit(),
         ));
 
         Ok(stake_pool_store)
@@ -422,7 +422,7 @@ impl DependenciesBuilder {
     ) -> Result<Arc<dyn ProtocolParametersStorer>> {
         Ok(Arc::new(EpochSettingStore::new(
             self.get_sqlite_connection().await?,
-            self.configuration.store_retention_limit.map(|l| l as u64),
+            self.configuration.safe_epoch_retention_limit(),
         )))
     }
 
@@ -648,7 +648,7 @@ impl DependenciesBuilder {
             self.get_chain_observer().await?,
             self.get_verification_key_store().await?,
             self.get_signer_recorder().await?,
-            self.configuration.store_retention_limit.map(|l| l as u64),
+            self.configuration.safe_epoch_retention_limit(),
         );
 
         Ok(Arc::new(registerer))