PRB: ITC Cannot Perform ASCII-type FTP Transfer

• Microsoft Visual Basic Professional and Enterprise Editions for Windows, version 5.0

SYMPTOMS

When you use the Microsoft Internet Transfer Control (ITC) to transfer text files to or from certain servers, the resulting file appears corrupted. It might appear to have extra or missing characters, or consist of completely meaningless garbage data.

CAUSE

The Microsoft Internet Transfer Control does not offer the option of an ASCII-type FTP file transfer. This can make it impossible to transfer text files to or from certain servers using this control.

RESOLUTION

Because the control does not offer this functionality, it cannot be used in situations where an ASCII-type transfer is required. One possible workaround is to call the Win32 Internet (WinInet) FTP APIs directly. These APIs are used by the ITC, and offer the option of either a binary or ASCII transfer, even though an ASCII-type transfer option is not exposed in the ITC.

For an example of how to call the WinInet FTP APIs directly from Visual Basic, see the following article(s) in the Microsoft Knowledge Base:

Q175179 : FILE: VBFTP.EXE: Implementing FTP Using WinInet API from VB

STATUS

This behavior is by design. The Internet Transfer Control is not a complete implementation of the FTP protocol.

MORE INFORMATION

The FTP protocol offers two types of transfers: binary and ASCII. In a binary download (which is always used by the ITC), the FTP server sends to the client the exact contents of a file. In a binary upload, the FTP server stores exactly what the client sends. This is desirable behavior for most types of files, such as executable programs, images, word processor documents, and so on.

In contrast, during an ASCII transfer, the FTP server converts between standard ASCII (which is being sent to or received from the client), and the internal representation of text used on the server. The differences may be conventions for marking the end of a line with carriage-return and linefeed characters, or the server may use an entirely different text encoding method (usually EBCDIC, commonly used on IBM mainframe and midrange systems). If a server stores text files in a format other than standard ASCII, transferring it with the binary transfer type results in what appears to be "corrupt" data in the destination file, since the character set translation does not take place.

Additional query words: kbVBp500 kbDSupport kbdsi

Keywords          : 
Version           : WINDOWS:5.0
Platform          : WINDOWS 
Issue type        : kbprb 

Last Reviewed: May 14, 1999