On remote weaves [SFTP]

Robey Pointer robey at lag.net
Mon Aug 8 23:55:12 BST 2005

Hash: SHA1

I keep getting distracted when I'm about to reply to this, so I'm  
going to jot this off quick before I get pulled away again. :)

On 2 Aug 2005, at 9:55, John A Meinel wrote:

> Aaron Bentley wrote:
>> I don't see what's lacking in the sftp protocol.  Locking and  
>> pipelining
>> are both explicitly supported, as well as lstat.  It's just that by
>> using the commandline sftp client you limit yourself to what it
>> supports, and you aren't able to take full advantage of the protocol.
> I have no problem with a more advanced use of the SFTP protocol. I
> haven't ever really seen anywhere where it was fully defined. If it  
> has
> explicit locking, pipelining, appending and lstat, it seems to provide
> everything we need. Is there an official SFTP definition, or is it  
> just
> whatever happens to be implemented by the OpenSSH people? (I realize
> some portion of it has to be official, but are locking, etc  
> official, or
> just common extensions?)

It has all those things, but explicit file locking was only added in  
version 5 of the protocol.  Most SFTP implementations only speak v3  
protocol because that was the latest stable version for a long time.   
(OpenSSH is in this camp.)  Versions 4-6 have been creations of the  
IETF working group, and I think they've been discouraging  
implementations until they -- ya know -- finish. :)  (My  
understanding is that they keep bumping the version number because  
people prematurely implement one of the drafts and then the IETF WG  
wants to change it later.)

So the short version is: I would not count on byte-level explicit  
file locking in SFTP today.  The O_EXCL flag in open() should be  
pretty safe, though.

Paramiko doesn't do pipelining, but it's on my to-do list, primarily  
because you all got me excited about it. :)


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