Duplicate post on stackoverflow.com:
https://stackoverflow.com/q/32560472/850848

See also https://winscp.net/tracker/1358

I were using winscpnet for file downloading. now i needed to support file resume funtionality. For that what i have done is
var options = new TransferOptions();
options.ResumeSupport.State = TransferResumeSupportState.On;

And in my code for downloading I have done

TransferOperationResult transferResult = session.GetFiles(
_appSettings["SFTP_IncomingFileFolder"] + file.Folder + @"/" + file.FileName,
_appSettings["Local_IncomingFileFolder"] + file.Folder + @"\" + file.FileName +".filepart", false, options);
transferResult.Check();

Now to check if file resume work I disconnect while downloading. Problem is that every time I now download it starts from zero instead of the place where it left. Like for 100 mb file if local downloaded length is 30 mb. when i try to reconnect it starts from zero length.