[#131] client: Add GetFullObject helper function

Add helper function which accepts container and object identifiers and
returns object instance read to the memory.

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

client/object_get.go

@@ -342,6 +342,44 @@ func (c *Client) ObjectGetInit(ctx context.Context, prm PrmObjectGet) (*ObjectRe
 	return &r, nil
 }
 
+// GetFullObject reads object header and full payload to the memory and returns
+// the result.
+//
+// Function behavior equivalent to Client.ObjectGetInit, see documentation for details.
+func GetFullObject(ctx context.Context, c *Client, idCnr cid.ID, idObj oid.ID) (*object.Object, error) {
+	var prm PrmObjectGet
+
+	prm.FromContainer(idCnr)
+	prm.ByID(idObj)
+
+	rdr, err := c.ObjectGetInit(ctx, prm)
+	if err != nil {
+		return nil, fmt.Errorf("init object reading: %w", err)
+	}
+
+	var obj object.Object
+
+	if rdr.ReadHeader(&obj) {
+		payload, err := io.ReadAll(rdr)
+		if err != nil {
+			return nil, fmt.Errorf("read payload: %w", err)
+		}
+
+		object.NewRawFrom(&obj).SetPayload(payload)
+	}
+
+	res, err := rdr.Close()
+	if err == nil {
+		err = apistatus.ErrFromStatus(res.Status())
+	}
+
+	if err != nil {
+		return nil, fmt.Errorf("finish object reading: %w", err)
+	}
+
+	return &obj, nil
+}
+
 // PrmObjectHead groups parameters of ObjectHead operation.
 type PrmObjectHead struct {
 	prmObjectRead