Issue about FileTransfer() download in Phonegap

Issue about FileTransfer() download in Phonegap


I have been develop Phonegap's App for android and iOS. And i try to
download file(.pdf) from server use FileTransfer() download, all
performing normal. But when i use fileTransfer.onprogress then it seem
download more size of file( my file 20Mb and it download 40Mb more than
2x).
fileTransfer.onprogress = function(progressEvent) {
if (progressEvent.lengthComputable) {
var percent = progressEvent.loaded/progressEvent.total;
//percent allways equal 2, than more 2x size of real file
console.log(percent);
}
};
Else FileTransfer() upload working well.
I don't known why? Can anyone help and explain for me. Thank you so much.