How to overcome 4Gb limitation on file download in virtual drive based on Cloud Sync Engine?

Question

I am implementing a virtual drive using Cloud Files API and this project . However, the download is stuck on files larger than 4Gb. The progress stops and the TransferDataAsync() is never called again, even though there are more bytes left in the file.

Answer 1

You need to add optional length to the segment length:

public async Task TransferDataAsync(long offset, long length,
    ITransferDataOperationContext operationContext, ITransferDataResultContext resultContext)
{
    if (operationContext.FileSize > 0x100000000)
    {
        length += operationContext.OptionalLength;
    }
    …
}

From my experience, this will somewhat slow down the download for small files. So it makes sense to do this only for files over 4Gb.