Re: avoiding reinventing the wheel on file transfer.

[Simon Tatham <anakin%pobox.com@localhost>]

Bill Sommerfeld  <sommerfeld%east.sun.com@localhost> wrote:
> file transfer involves a bunch of really ugly issues (newline
> conventions, binary/ascii/... modes, i18n of filenames, etc., etc.).
> Many of these problems have already been tackled by FTP.

I'd applaud any efforts to use existing solutions to these ugly
issues, but I for one do like SFTP as a concept. It has useful
things that FTP doesn't and probably couldn't without serious
effort:

 - a well-defined, portable and securable chmod (SITE EXEC doesn't
   cut it, not least because it's hard to vet carefully at the
   server end and so most FTP servers simply don't bother to support
   it AFAICT).

 - a well-defined machine readable format for directory listings, so
   you can write automated clients that do complex manipulation of
   the remote fs, because they can look at a dir listing and
   reliably get things like file sizes back out. Also you can
   sensibly write a GUI client which displays sizes in a separate
   Windows-like column, without having to parse the size data out of
   an ASCII listing which you're _assuming_ has the format you
   expect.

 - no reliance on command line details at the server end. In FTP, if
   you want a long listing, or a short listing, or a listing in
   columns, or a listing sorted by this or that, you have to know
   what command line options the server's `ls' binary happens to
   take - and in general, the server doesn't even tell you this!
   Whereas in SFTP, you can process command line options (or
   whatever local equivalent you like) locally, which means you can
   _document_ them carefully and fully for your users. Then you
   retrieve raw dir listing data from the server, and you format and
   sort it exactly as you like.

 - SFTP has the extensibility philosophy of SSH2 in general; I can
   define an extension, publish documentation of it, and rely on
   nobody else's extension clashing with it or interoperating badly
   with it.

I know I have no official clout with the WG, but if I did, I would
strongly oppose any move to abandon SFTP in favour of a thinly
modified FTP. By all means look at FTP to see how it solves problems
SFTP still needs to solve, but _please_ don't throw the baby out
with the bathwater. SFTP is a massive improvement on FTP in many
areas, and really we want a protocol with the best features of
_both_.

Cheers,
Simon
-- 
Simon Tatham         "Imagine what the world would be like if
<anakin%pobox.com@localhost>    there were no hypothetical situations..."