Subject: Ftp-WG: SIZE

From: Dave Cridland <[email-masked]>
Date: Tue, 4 Jan 2000 12:40:32 -0500

I'd humbly suggest a 4XX series error code be generated - since retrying
might work, depending on the mechanism chosen to block it in the first
place. (Current server load, for instance, or simply a minute's wait).

That should prevent older, possibly incorrect clients from deciding that the
file does not exist, which is an additional advantage. Who knows what
they'll think about a 4XX, but hopefully they'll just worry the user about
it, or else not use a progress bar.

-----Original Message-----
From: Alun Jones [mailto:[email-masked]]
Sent: Monday, January 03, 2000 5:09 PM
To: FTPEXT Working Group
Subject: Ftp-WG: SIZE

At 09:48 AM 1/3/2000 , Stephen Tihor wrote:
[ Snipped ]

One might also note that there are several other existing behaviours that 
can induce this kind of drain on resources.  How many large servers, for 
instance, allow "LIST -R" from their root directory, and sort the output as 
they go?  Or "STAT -R" for the same effect?  Then there's the servers that 
allow in-line compression into ZIP/ZOO/GZIP/whatever format.  Each of these 
produces a processor drain on the server that is relatively large compared 
to the drain on the client's resources.  But then we start getting into 
wondering whether we should note that a fast client connecting to a slower 
server might also provide for an effective denial-of-service attack. :-)

There is a limit to what an RFC can cover in terms of such decisions as to 
what is worth implementing, and what is likely to be abused; my own 
suggestion would be to update the "Error responses" paragraph to note "too 
expensive to compute" as another allowed reason for generating 550 (or 
perhaps another code could be used?  how would that affect existing clients 
that use SIZE?)

Needless to say, if the 550 code is used, the presence of a 550 return from 
SIZE must not be treated as an assertion that the file does not exist, as I 
have seen some clients believe.

Are there any systems that might find it difficult to calculate transfer 
size in modes other than ASCII?

Alun.
~~~~

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