[JSch-users] SFTP RFCs

Jung, Volker

2014-12-12 08:56:36 UTC

Hello Flavio,

to my knowledge SFTP is not covered by the mentioned RFC 1350 (TFTP) and there is no RFC which does. As of today there are only a number of drafts specifying the SFTP protocol.

The FileZilla-Project wiki has a page [1] with links to most or all relevant RFCs and SFTP specification drafts (English Wikipedia entry for 'SSH File Transfer Protocol' is also a good starting point). Please see for yourself whether SFTP does specify the ominous final packet.

Cheers
Volker

[1] https://wiki.filezilla-project.org/SFTP_specifications

Von: Flavio Orfano [mailto:***@hotmail.com]
Gesendet: Freitag, 12. Dezember 2014 01:49
An: jsch-***@lists.sourceforge.net
Betreff: [JSch-users] SFTP RFCs

Hello Lads,

I do use JSCH(version 1.0.50) for SFTP on my application .
Running our component against a Sterling Integrator(IBM) to do a SFTP pooling is failing due to the following:

According to them when the SFTP is done with a file, their Sterling Integrator (IBM) sends a final packet and waits for a ACK from my component (which uses JSCH) but as it never get the ACK from us saying all is fine then their Sterling Integrator resend the file again and again (infinite loop).

They mention that this is according to an RFC (have to confirm with them). Doing a quick search in google I could find the RFC 1350 https://tools.ietf.org/html/rfc1350. in this RFC it mention about normal termination:
Normal Termination

The end of a transfer is marked by a DATA packet that contains

between 0 and 511 bytes of data (i.e., Datagram length < 516). This

packet is acknowledged by an ACK packet like all other DATA packets.

The host acknowledging the final DATA packet may terminate its side

of the connection on sending the final ACK. On the other hand,

dallying is encouraged. This means that the host sending the final

ACK will wait for a while before terminating in order to retransmit

the final ACK if it has been lost. The acknowledger will know that

the ACK has been lost if it receives the final DATA packet again.

The host sending the last DATA must retransmit it until the packet is

acknowledged or the sending host times out. If the response is an

ACK, the transmission was completed successfully. If the sender of

the data times out and is not prepared to retransmit any more, the

transfer may still have been completed successfully, after which the

acknowledger or network may have experienced a problem. It is also

possible in this case that the transfer was unsuccessful. In any

case, the connection has been closed.

My QUESTION IS: Do JSCH follow any RFC related to TFTP, FTP etc? Or would it only follow the SSH RFCs? Also would any RFC for SSH have similar normal termination as described above?

So I am trying to understand if their comment makes any sense or not. I would appreciate any input here.

Cheers!

Flavio