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From "Goldstein Lyor (JIRA)" <j...@apache.org>
Subject [jira] [Resolved] (SSHD-903) SFTP version negotiation does not work
Date Fri, 01 Mar 2019 04:55:00 GMT

     [ https://issues.apache.org/jira/browse/SSHD-903?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Goldstein Lyor resolved SSHD-903.
       Resolution: Fixed
    Fix Version/s: 2.3.0

Tested it with _WinSCP_ and forced version on the server side. BTW, I have thought about the
initial issue that caused you to detect this problem (the file corruption). Can it be related
to the {{fsync}} issue ?

Here is what {{fysnc}} issue is (in a nutshell...) - when one creates/updates a file via the
Java API the file contents are not immediately sync-ed with the file system. This means that
if another process attempts to access the file within a short time (how short I cannot tell)
from when it was updated it may still get old data. In other words, unless one explicitly
cause the {{fsync}} (there are several ways to do this in java) the file will *eventually*
be sync-ed (maybe a few seconds) - but until then, external processes need to wait enough
time before accessing the updated/created file.

> SFTP version negotiation does not work  
> ----------------------------------------
>                 Key: SSHD-903
>                 URL: https://issues.apache.org/jira/browse/SSHD-903
>             Project: MINA SSHD
>          Issue Type: Bug
>    Affects Versions: 2.2.0
>            Reporter: Mark Ebbers
>            Assignee: Goldstein Lyor
>            Priority: Major
>             Fix For: 2.3.0
>         Attachments: screenshot-winscp-sftp-version.png, sftp-version-1.png, sftp-version-2.png,
winscp-info.png, winscp.png
>          Time Spent: 20m
>  Remaining Estimate: 0h
> I have some problems with uploading files to our MINA SSHD based SFTP server when using
,different version, of WinSCP as SFTP client. WinSCP is configured to use version 6 of the
SFTP protocol if possible. 
> Uploading a file of ~ 45KB sometimes result in a file of 32711 bytes where in the data
is not appended (from the second SFTP packet) but overwritten. (But did not pin point the
exact bug)
> As a temporary solution I found, in issue SSHD-874, a comment which suggest to force
the server to use sftp-protocol version 3. If I do this I expect the server to negotiate
with the client that version 3 should be used instead of version 6. But what happens is that
the server sends a not supported message.
> I think that the AbstractSftpSubsystemHelper::checkVersionCompatibility() is the problem.
> See my screenshots. As you can see the version proposed by WinSCP is version 6. I forced
the server on version 3.

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