Question

I’ve written a small program which is able to upload files to a server via ftp. Because of the large size of some files I want to create a progress bar for the user. So during the upload I need to know at certain intervals how many bytes have been sent to the server in order to derive the percentage of the file that has been uploaded. What I have tried so far:

While I call the function FtpPutFile() to upload the file, I spawn a thread with the following code:

hInternet = InternetOpen(NULL,INTERNET_OPEN_TYPE_DIRECT,NULL,NULL,0);
hFtpSession = InternetConnect(hInternet, ftpserver, port, user, pass, INTERNET_SERVICE_FTP, 0,    0); 
int filesize = 0; // 2GB max

hFile = FtpOpenFile(hFtpSession,szFileTitle,GENERIC_READ,FTP_TRANSFER_TYPE_BINARY,0);
filesize = FtpGetFileSize(hFile,0); 
cout << "Size: " << filesize << endl; 

However this doesn’t seem to work as filesize keeps returning a value of -1. I think this is due to the fact that I’m writing to a file (uploading part) and at the same time I’m trying to read it to get the file size. And I think this is not possible (please correct me if I’m wrong).

My main question: is there another way to create a progress bar for ftp uploading? Perhaps counting the bytes before they are uploaded using the function readBytesCount() (not sure if this is possible at all).

Answer 1

You want to:

1. Call InternetSetStatusCallback to set a function that will be called periodically during the transfer.
2. Pass a (non-zero) value the last parameter to FtpOpenFile. This will be passed back to your status callback function during the transfer.

Then, during the FTP operation, your callback function will be invoked periodically with information about the progress of the transfer, which it can then display to the user.

I don’t believe this will let you show actual bytes as they’re being transferred though — if memory serves it mostly shows the discrete steps in a transfer, like opening the handle, resolving names, sending/receiving cookies, and finally closing the handle.

To deal with the actual bytes being written during the transfer of the file itself, you’d typically read a buffer-full of data from the local file, then write that buffer with InternetWriteFile. With that, you can compute the percentage transferred as the number of bytes written so far divided by the total size of the file (and multiply by 100).