Method ReadBufferAt

cpp/src/arrow/io/file.cc:237–248

  }

  Result<std::shared_ptr<Buffer>> ReadBufferAt(int64_t position, int64_t nbytes) {
    ARROW_ASSIGN_OR_RAISE(auto buffer, AllocateResizableBuffer(nbytes, pool_));

    ARROW_ASSIGN_OR_RAISE(int64_t bytes_read,
                          ReadAt(position, nbytes, buffer->mutable_data()));
    if (bytes_read < nbytes) {
      RETURN_NOT_OK(buffer->Resize(bytes_read));
      buffer->ZeroPadding();
    }
    // R build with openSUSE155 requires an explicit shared_ptr construction
    return std::shared_ptr<Buffer>(std::move(buffer));
  }

  Status WillNeed(const std::vector<ReadRange>& ranges) {
    auto report_error = [](int errnum, const char* msg) -> Status {