[#186] localstorage: Implement utility functions over StorageEngine

Implement Put/Get/GetRange/Select/SelectAll functions over storage
engine. These functions are going to be used by Object service.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/local_object_storage/engine/get.go

@@ -97,3 +97,28 @@ func (e *StorageEngine) Get(prm *GetPrm) (*GetRes, error) {
 		obj: obj,
 	}, nil
 }
+
+// Get reads object from local storage by provided address.
+func Get(storage *StorageEngine, addr *objectSDK.Address) (*object.Object, error) {
+	res, err := storage.Get(new(GetPrm).
+		WithAddress(addr),
+	)
+	if err != nil {
+		return nil, err
+	}
+
+	return res.Object(), nil
+}
+
+// GetRange reads object payload range from local storage by provided address.
+func GetRange(storage *StorageEngine, addr *objectSDK.Address, rng *objectSDK.Range) ([]byte, error) {
+	res, err := storage.Get(new(GetPrm).
+		WithAddress(addr).
+		WithPayloadRange(rng.GetOffset(), rng.GetLength()),
+	)
+	if err != nil {
+		return nil, err
+	}
+
+	return res.Object().Payload(), nil
+}

pkg/local_object_storage/engine/head.go

@@ -73,3 +73,15 @@ func (e *StorageEngine) Head(prm *HeadPrm) (*HeadRes, error) {
 		head: head,
 	}, nil
 }
+
+// Head reads object header from local storage by provided address.
+func Head(storage *StorageEngine, addr *objectSDK.Address) (*object.Object, error) {
+	res, err := storage.Head(new(HeadPrm).
+		WithAddress(addr),
+	)
+	if err != nil {
+		return nil, err
+	}
+
+	return res.Header(), nil
+}

pkg/local_object_storage/engine/put.go

@@ -89,3 +89,12 @@ func (e *StorageEngine) objectExists(obj *object.Object, shards []*shard.Shard)
 
 	return exists
 }
+
+// Put writes provided object to local storage.
+func Put(storage *StorageEngine, obj *object.Object) error {
+	_, err := storage.Put(new(PutPrm).
+		WithObject(obj),
+	)
+
+	return err
+}

pkg/local_object_storage/engine/select.go

@@ -58,3 +58,20 @@ func (e *StorageEngine) Select(prm *SelectPrm) (*SelectRes, error) {
 		addrList: addrList,
 	}, nil
 }
+
+// Select selects objects from local storage using provided filters.
+func Select(storage *StorageEngine, fs object.SearchFilters) ([]*object.Address, error) {
+	res, err := storage.Select(new(SelectPrm).
+		WithFilters(fs),
+	)
+	if err != nil {
+		return nil, err
+	}
+
+	return res.AddressList(), nil
+}
+
+// SelectAll selects all objects from local storage.
+func SelectAll(storage *StorageEngine) ([]*object.Address, error) {
+	return Select(storage, object.SearchFilters{})
+}