de5@ornl.gov (Dave Sill) (12/05/90)
Where can I find detailed information about what conversions FTP will perform in different modes and between different systems? E.g., does it do byte order swaps in binary mode between a VMS VAX and SPARCstation? What conversions does ASCII mode imply? Etc. The man page doesn't have it, and the RFC index doesn't show anything promising. Thanks in advance. Please reply by e-mail. -- Dave Sill (de5@ornl.gov) Martin Marietta Energy Systems Workstation Support
romkey@ASYLUM.SF.CA.US (John Romkey) (12/07/90)
In FTP ASCII mode, posit the existence of a newline convention for the two systems doing the FTP. I'm not sure what VMS does; suppose it indicates newline by storing a carriage return line feed sequence (CR LF). Suppose the other end is a UNIX system, indicating newline with just linefeeds. [There have been other systems, like Symbolics lisp machines, that would indicate line feed with a character > 128 decimal] As the server picks up the file it's going to send, it maps every instance of the newline indicator (CR LF in this case) to CR LF over the TCP connection. So in this example, no work is done. It also maps any lone CR to CR NUL. The client, receiving the file, maps every instance of CR LF to its local newline format, in this instance, LF. And it umaps CR NUL to just CR. Basically, FTP has its own representation of newlines for the file while the file is in transit. The transmitter must encode the file from its own format into that representation; the receiver must decode it from FTP's representation into its own format. In image (binary) mode, FTP doesn't know anything about byte swaps or file formats. It picks up a pile of bytes off the disk, sends them, and the receiver writes what it receives. If you're moving a binary database between processors with different word sizes and byte orders, there's no way for FTP to know how to convert those. You've got to do that conversion either before or after you move the file. There's also a mode called "local n" for dealing with non-8 bit word systems, like TOPS-20 or lisp machines, which doesn't really matter here. - john romkey Epilogue Technology USENET/UUCP/Internet: romkey@asylum.sf.ca.us FAX: 415 594-1141