Implemented get_blob on sampling rocksdb adapter (#732)

* Implemented get_blob on sampling rocksdb adapter

* addressed PR comments

nomos-services/data-availability/sampling/src/storage/adapters/rocksdb.rs

@@ -1,4 +1,8 @@
 use kzgrs_backend::common::ColumnIndex;
+use nomos_da_storage::{
+    fs::load_blob,
+    rocksdb::{key_bytes, DA_VERIFIED_KEY_PREFIX},
+};
 // std
 use serde::{de::DeserializeOwned, Deserialize, Serialize};
 use std::{marker::PhantomData, path::PathBuf};
@@ -19,8 +23,8 @@ pub struct RocksAdapter<B, S>
 where
     S: StorageSerde + Send + Sync + 'static,
 {
-    _settings: RocksAdapterSettings,
-    _storage_relay: OutboundRelay<StorageMsg<RocksBackend<S>>>,
+    settings: RocksAdapterSettings,
+    storage_relay: OutboundRelay<StorageMsg<RocksBackend<S>>>,
     blob: PhantomData<B>,
 }
 
@@ -36,22 +40,43 @@ where
     type Settings = RocksAdapterSettings;
 
     async fn new(
-        _settings: Self::Settings,
-        _storage_relay: OutboundRelay<<StorageService<Self::Backend> as ServiceData>::Message>,
+        settings: Self::Settings,
+        storage_relay: OutboundRelay<<StorageService<Self::Backend> as ServiceData>::Message>,
     ) -> Self {
         Self {
-            _settings,
-            _storage_relay,
+            settings,
+            storage_relay,
             blob: PhantomData,
         }
     }
 
     async fn get_blob(
         &self,
-        _blob_id: <Self::Blob as Blob>::BlobId,
-        _column_idx: ColumnIndex,
+        blob_id: <Self::Blob as Blob>::BlobId,
+        column_idx: ColumnIndex,
     ) -> Result<Option<Self::Blob>, DynError> {
-        todo!()
+        let (reply_tx, reply_rx) = tokio::sync::oneshot::channel();
+        self.storage_relay
+            .send(StorageMsg::Load {
+                key: key_bytes(DA_VERIFIED_KEY_PREFIX, &blob_id),
+                reply_channel: reply_tx,
+            })
+            .await
+            .expect("failed to send Load message to storage relay");
+
+        if reply_rx.await?.is_some() {
+            let blob_bytes = load_blob(
+                self.settings.blob_storage_directory.clone(),
+                blob_id.as_ref(),
+                &column_idx.to_be_bytes(),
+            )
+            .await?;
+            Ok(S::deserialize(blob_bytes)
+                .map(|blob| Some(blob))
+                .unwrap_or_default())
+        } else {
+            Ok(None)
+        }
     }
 }