Rajeev Pentyala – Microsoft Power Platform

    /// <summary>
    /// Downloads a file
    /// </summary>
    /// <param name="service">The service</param>
    /// <param name="entityReference">A reference to the record with the file column</param>
    /// <param name="fileAttributeName">The name of the file column</param>
    /// <returns></returns>
    private static byte[] DownloadFile(
                IOrganizationService service,
                EntityReference entityReference,
                string fileAttributeName)
    {
        InitializeFileBlocksDownloadRequest initializeFileBlocksDownloadRequest = new InitializeFileBlocksDownloadRequest()
        {
            Target = entityReference,
            FileAttributeName = fileAttributeName
        };

        var initializeFileBlocksDownloadResponse =
              (InitializeFileBlocksDownloadResponse)service.Execute(initializeFileBlocksDownloadRequest);

        string fileContinuationToken = initializeFileBlocksDownloadResponse.FileContinuationToken;
        long fileSizeInBytes = initializeFileBlocksDownloadResponse.FileSizeInBytes;

        List<byte> fileBytes = new List<byte>();

        long offset = 0;
        long blockSizeDownload = 4 * 1024 * 1024; // 4 MB

        // File size may be smaller than defined block size
        if (fileSizeInBytes < blockSizeDownload)
        {
            blockSizeDownload = fileSizeInBytes;
        }

        while (fileSizeInBytes > 0)
        {
            // Prepare the request
            DownloadBlockRequest downLoadBlockRequest = new()
            {
                BlockLength = blockSizeDownload,
                FileContinuationToken = fileContinuationToken,
                Offset = offset
            };

            // Send the request
            var downloadBlockResponse =
                     (DownloadBlockResponse)service.Execute(downLoadBlockRequest);

            // Add the block returned to the list
            fileBytes.AddRange(downloadBlockResponse.Data);

            // Subtract the amount downloaded,
            // which may make fileSizeInBytes < 0 and indicate
            // no further blocks to download
            fileSizeInBytes -= (int)blockSizeDownload;
            // Increment the offset to start at the beginning of the next block.
            offset += blockSizeDownload;
        }

        return fileBytes.ToArray();
    }