-void compressZlib(SharedBuffer<u8> data, std::ostream &os);
-void compressZlib(const std::string &data, std::ostream &os);
+void compressZlib(SharedBuffer<u8> data, std::ostream &os, int level = -1);
+void compressZlib(const std::string &data, std::ostream &os, int level = -1);