fix(aggregator): avoid epoch service failure when a aggregator start …

…for the first time

Epoch settings for the first "working" epoch were not available at start
since they use the 'signer retrieval offset' of -1 and we handled
discrepencies only starting the current epoch.

Also `handle_discrepancies_at_startup` is modified to register data over
four epochs instead of 3 to take in account the case when between its
call and epoch service 'inform epoch' there's an epoch change.

mithril-aggregator/src/dependency_injection/builder/support/stores.rs

@@ -120,6 +120,12 @@ impl DependenciesBuilder {
                 message: "cannot build aggregator runner: no epoch returned.".to_string(),
                 error: None,
             })?;
+        let retrieval_epoch = current_epoch
+            .offset_to_signer_retrieval_epoch()
+            .map_err(|e| DependenciesBuilderError::Initialization {
+                message: format!("cannot create aggregator runner: failed to offset current epoch '{current_epoch}' to signer retrieval epoch."),
+                error: Some(e.into()),
+            })?;
 
         {
             // Temporary fix, should be removed
@@ -136,11 +142,11 @@ impl DependenciesBuilder {
         let epoch_settings_configuration = self.configuration.get_epoch_settings_configuration();
         debug!(
             logger,
-            "Handle discrepancies at startup of epoch settings store, will record epoch settings from the configuration for epoch {current_epoch}";
+            "Handle discrepancies at startup of epoch settings store, will record epoch settings from the configuration for epoch {retrieval_epoch}";
             "epoch_settings_configuration" => ?epoch_settings_configuration,
         );
         epoch_settings_store
-            .handle_discrepancies_at_startup(current_epoch, &epoch_settings_configuration)
+            .handle_discrepancies_at_startup(retrieval_epoch, &epoch_settings_configuration)
             .await
             .map_err(|e| DependenciesBuilderError::Initialization {
                 message: "can not create aggregator runner".to_string(),

mithril-aggregator/src/store/epoch_settings_storer.rs

@@ -25,15 +25,20 @@ pub trait EpochSettingsStorer: EpochPruningTask + Sync + Send {
     async fn get_epoch_settings(&self, epoch: Epoch) -> StdResult<Option<AggregatorEpochSettings>>;
 
     /// Handle discrepancies at startup in the epoch settings store.
+    ///
     /// In case an aggregator has been launched after some epochs of not being up or at initial startup,
     /// the discrepancies in the epoch settings store needs to be fixed.
-    /// The epoch settings needs to be recorded for the working epoch and the next 2 epochs.
+    ///
+    /// The epoch settings needs to be recorded for the working epoch and the next 3 epochs.
+    /// We need data over four epochs because the epoch service use epoch settings over a window of
+    /// three epochs, and there may be an epoch change between this `handle_discrepancies_at_startup`
+    /// call and the epoch service call.
     async fn handle_discrepancies_at_startup(
         &self,
         current_epoch: Epoch,
         epoch_settings_configuration: &AggregatorEpochSettings,
     ) -> StdResult<()> {
-        for epoch_offset in 0..=2 {
+        for epoch_offset in 0..=3 {
             let epoch = current_epoch + epoch_offset;
             if self.get_epoch_settings(epoch).await?.is_none() {
                 self.save_epoch_settings(epoch, epoch_settings_configuration.clone())
@@ -158,7 +163,7 @@ mod tests {
     }
 
     #[tokio::test]
-    async fn test_handle_discrepancies_at_startup_should_complete_at_least_two_epochs() {
+    async fn test_handle_discrepancies_at_startup_should_complete_at_least_four_epochs() {
         let epoch_settings = AggregatorEpochSettings::dummy();
         let epoch_settings_new = AggregatorEpochSettings {
             protocol_parameters: ProtocolParameters {
@@ -191,6 +196,9 @@ mod tests {
         assert_eq!(Some(epoch_settings_new.clone()), epoch_settings_stored);
 
         let epoch_settings_stored = store.get_epoch_settings(epoch + 3).await.unwrap();
+        assert_eq!(Some(epoch_settings_new.clone()), epoch_settings_stored);
+
+        let epoch_settings_stored = store.get_epoch_settings(epoch + 4).await.unwrap();
         assert!(epoch_settings_stored.is_none());
     }
 }