Method ReadAt

cpp/src/arrow/ipc/reader.cc:2984–3001

Result<int64_t> IoRecordedRandomAccessFile::GetSize() { return file_size_; }

Result<int64_t> IoRecordedRandomAccessFile::ReadAt(int64_t position, int64_t nbytes,
                                                   bool allow_short_read, void* out) {
  auto num_bytes_read = std::min(file_size_, position + nbytes) - position;
  if (!allow_short_read && num_bytes_read != nbytes) {
    return Status::IOError("File too short: expected to be able to read ", nbytes,
                           " bytes, got ", num_bytes_read);
  }

  if (!read_ranges_.empty() &&
      position == read_ranges_.back().offset + read_ranges_.back().length) {
    // merge continuous IOs into one if possible
    read_ranges_.back().length += num_bytes_read;
  } else {
    // no real IO is performed, it is only saved into a vector for replaying later
    read_ranges_.emplace_back(io::ReadRange{position, num_bytes_read});
  }
  return num_bytes_read;
}

Result<std::shared_ptr<Buffer>> IoRecordedRandomAccessFile::ReadAt(
    int64_t position, int64_t nbytes, bool allow_short_read) {