Function FileRead

cpp/src/arrow/util/io_util.cc:1648–1687

}

Result<int64_t> FileRead(int fd, uint8_t* buffer, int64_t nbytes) {
#if defined(_WIN32)
  HANDLE handle = reinterpret_cast<HANDLE>(_get_osfhandle(fd));
#endif
  int64_t total_bytes_read = 0;

  while (total_bytes_read < nbytes) {
    const int64_t chunksize =
        std::min(static_cast<int64_t>(ARROW_MAX_IO_CHUNKSIZE), nbytes - total_bytes_read);
    int64_t bytes_read = 0;
#if defined(_WIN32)
    DWORD dwBytesRead = 0;
    if (!ReadFile(handle, buffer, static_cast<uint32_t>(chunksize), &dwBytesRead,
                  nullptr)) {
      auto errnum = GetLastError();
      // Return a normal EOF when the write end of a pipe was closed
      if (errnum != ERROR_HANDLE_EOF && errnum != ERROR_BROKEN_PIPE) {
        return IOErrorFromWinError(GetLastError(), "Error reading bytes from file");
      }
    }
    bytes_read = dwBytesRead;
#else
    bytes_read = static_cast<int64_t>(read(fd, buffer, static_cast<size_t>(chunksize)));
    if (bytes_read == -1) {
      if (errno == EINTR) {
        continue;
      }
      return IOErrorFromErrno(errno, "Error reading bytes from file");
    }
#endif

    if (bytes_read == 0) {
      // EOF
      break;
    }
    buffer += bytes_read;
    total_bytes_read += bytes_read;
  }
  return total_bytes_read;
}

Result<int64_t> FileReadAt(int fd, uint8_t* buffer, int64_t position, int64_t nbytes) {
  int64_t bytes_read = 0;