feat(rln): close db connection before dropping rln object (#187)

utils/src/merkle_tree/full_merkle_tree.rs

@@ -101,6 +101,10 @@ where
         })
     }
 
+    fn close_db_connection(&mut self) -> Result<()> {
+        Ok(())
+    }
+
     // Returns the depth of the tree
     fn depth(&self) -> usize {
         self.depth

utils/src/merkle_tree/merkle_tree.rs

@@ -65,6 +65,7 @@ pub trait ZerokitMerkleTree {
     fn verify(&self, leaf: &FrOf<Self::Hasher>, witness: &Self::Proof) -> Result<bool>;
     fn set_metadata(&mut self, metadata: &[u8]) -> Result<()>;
     fn metadata(&self) -> Result<Vec<u8>>;
+    fn close_db_connection(&mut self) -> Result<()>;
 }
 
 pub trait ZerokitMerkleProof {

utils/src/merkle_tree/optimal_merkle_tree.rs

@@ -83,6 +83,10 @@ where
         })
     }
 
+    fn close_db_connection(&mut self) -> Result<()> {
+        Ok(())
+    }
+
     // Returns the depth of the tree
     fn depth(&self) -> usize {
         self.depth

utils/src/pm_tree/sled_adapter.rs

@@ -45,6 +45,15 @@ impl Database for SledDB {
         Ok(SledDB(db))
     }
 
+    fn close(&mut self) -> PmtreeResult<()> {
+        let _ = self.0.flush().map_err(|_| {
+            PmtreeErrorKind::DatabaseError(DatabaseErrorKind::CustomError(
+                "Cannot flush database".to_string(),
+            ))
+        })?;
+        Ok(())
+    }
+
     fn get(&self, key: DBKey) -> PmtreeResult<Option<Value>> {
         match self.0.get(key) {
             Ok(value) => Ok(value.map(|val| val.to_vec())),