`extract_back(bytes)` and return the starting address, guaranteeing it's a continuous buffer, possiblily by memcpying to a internal allocated new buff

try to extract `bytes` bytes from front elemnt (iov[0]) return the pointer if succeeded, or nullptr otherwise (alloc failed, or not enough data, etc.)

move to next, return 0 for success, -1 for failure

move to next, return 0 for success, -1 for failure

convert oss last modified time in listobjects, e.g. "2023-10-12T02:03:53.000Z"