explorerd/main: enhance block subscription with retry mechanism when out of sync

This commit enhances subscription initialization to handle scenarios where the explorer database is out of sync with darkfid.

Summary of changes:
- Added "Blockchain not fully synced" error check during block subscription initialization
- Implemented a retry mechanism to resync blocks and reattempt the subscription process

bin/explorer/explorerd/src/main.rs

@@ -189,26 +189,12 @@ async fn realmain(args: Args, ex: Arc<smol::Executor<'static>>) -> Result<()> {
         explorer.connect().await?;
 
         // Sync blocks
-        info!(target: "explorerd", "Syncing blocks from darkfid...");
-        if let Err(e) = explorer.service.sync_blocks(args.reset).await {
-            let error_message = format!("Error syncing blocks: {:?}", e);
-            error!(target: "explorerd", "{error_message}");
-            return Err(Error::DatabaseError(error_message));
-        }
+        sync_blocks(explorer.clone(), args.reset).await?;
 
         // Subscribe blocks
-        info!(target: "explorerd", "Subscribing to new blocks...");
-        match subscribe_sync_blocks(explorer.clone(), config.endpoint.clone(), ex.clone()).await {
-            Ok((sub_task, lst_task)) => {
-                subscriber_task = Some(sub_task);
-                listener_task = Some(lst_task);
-            }
-            Err(e) => {
-                let error_message = format!("Error setting up blocks subscriber: {:?}", e);
-                error!(target: "explorerd", "{error_message}");
-                return Err(Error::DatabaseError(error_message));
-            }
-        };
+        (subscriber_task, listener_task) =
+            subscribe_blocks(explorer.clone(), config.endpoint.clone(), ex.clone(), args.reset)
+                .await?;
     }
 
     log_started_banner(explorer.clone(), &config, &args, &config_path, args.no_sync);
@@ -240,6 +226,49 @@ async fn realmain(args: Args, ex: Arc<smol::Executor<'static>>) -> Result<()> {
     Ok(())
 }
 
+/// Synchronizes blocks from the `darkfid` daemon.
+async fn sync_blocks(explorer: Arc<Explorerd>, reset: bool) -> Result<()> {
+    info!(target: "explorerd", "Syncing blocks from darkfid...");
+    if let Err(e) = explorer.service.sync_blocks(reset).await {
+        let error_message = format!("Error syncing blocks: {:?}", e);
+        error!(target: "explorerd", "{error_message}");
+        return Err(Error::DatabaseError(error_message));
+    }
+    Ok(())
+}
+
+/// Subscribes to new blocks from the `darkfid` daemon, returning optional
+/// stoppable tasks for the subscriber and listener.
+async fn subscribe_blocks(
+    explorer: Arc<Explorerd>,
+    endpoint: Url,
+    executor: Arc<smol::Executor<'static>>,
+    reset: bool,
+) -> Result<(Option<StoppableTaskPtr>, Option<StoppableTaskPtr>)> {
+    info!(target: "explorerd", "Subscribing to new blocks...");
+
+    let result = match subscribe_sync_blocks(explorer.clone(), endpoint.clone(), executor.clone())
+        .await
+    {
+        Ok((subscriber_task, listener_task)) => Ok((subscriber_task, listener_task)),
+        Err(e) => {
+            // If out of sync, sync blocks and retry subscription
+            if e.to_string().contains("Blockchain not fully synced") {
+                sync_blocks(explorer.clone(), reset).await?;
+                subscribe_sync_blocks(explorer.clone(), endpoint.clone(), executor.clone()).await
+            } else {
+                let error_message = format!("Error setting up blocks subscriber: {:?}", e);
+                error!(target: "explorerd", "{error_message}");
+                return Err(Error::DatabaseError(error_message));
+            }
+        }
+    };
+
+    let (subscriber_task, listener_task) = result?;
+    info!(target: "explorerd", "Successfully subscribed to new blocks!");
+    Ok((Some(subscriber_task), Some(listener_task)))
+}
+
 /// Logs a banner displaying the startup details of the DarkFi Explorer Node.
 fn log_started_banner(
     explorer: Arc<Explorerd>,