question: public static byte [ ] packHeader ( byte cmd , long pkg_len , byte errno ) throws UnsupportedEncodingException { byte [ ] header ; byte [ ] hex_len ; header = new byte [ FDFS_PROTO_PKG_LEN_SIZE + 2 ] ; Arrays . fill ( header , ( byte ) 0 ) ; hex_len = ProtoCommon . long2buff ( pkg_len ) ; System . arraycopy ( hex_len , 0 , header , 0 , hex_len . length ) ; header [ PROTO_HEADER_CMD_INDEX ] = cmd ; header [ PROTO_HEADER_STATUS_INDEX ] = errno ; return header ; }
target:  pack header by FastDFS transfer protocol