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https://issues.apache.org/jira/browse/SSHD-85?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16055905#comment-16055905
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Bill Kuker commented on SSHD-85:
--------------------------------
I have a "NOT A FIX" fix....
The following change to the server makes every single test I run pass every
single time:
https://github.com/bkuker/mina-sshd/commit/2e1ae7bdd93420039d0b06317b3377a03707a839
*My opinion on what that means:*
There is a race on the SSHD server between the final writes to the client and
the connection closing. Delaying the close by an arbitrary amount of time means
the write() call always wins the race.
*Why this "fix" is no good:*
Obviously a 500ms sleep is a silly way to fix the problem, and is still a race
condition, just one with a nearly certain outcome.
*What I need to do:*
Delay the close() call until the final write() call is done. At that point all
of the data have been passed on to the OS and TCP will do it's best to finish
sending the data.
> Port Forward closes connection before all bytes are sent
> --------------------------------------------------------
>
> Key: SSHD-85
> URL: https://issues.apache.org/jira/browse/SSHD-85
> Project: MINA SSHD
> Issue Type: Bug
> Affects Versions: 0.2.0, 1.4.0, 1.6.0
> Environment: Windows or Linux, JSCH Client
> Reporter: Bill Kuker
> Assignee: Guillaume Nodet
> Attachments: MINA-Port-Forward.txt, SSHD-85_testcase.txt
>
>
> When I am forwarding connections from a Client to a port on the SSH Server
> through the SSH Client to a Remote Server on the SSH Client network:
> Client --(a)---> SSH Server <===[ssh]===> SSH Client --(b)--> Remote Server
> if the Remote Server sends some bytes and immediately closes the connection
> (b) to the SSH Client the SSH Server will close the connection (a) to the
> client before all of those bytes are sent to the SSH Client.
> This is probably a race condition. If I run one connection at a time it works
> 99% of the time, but if I use a load generator (a completely separate
> process) to max out all 4 cores I can make it fail (I do not get all the
> bytes from Remote Server at Client) 99% of the time. Also by running about
> 100 simultaneous requests I get maybe a 20% failure rate.
> If the Remote Server is something like Telnet (Open for a while, user closes
> connection) everything seems fine, but the the Remote Server is a web server
> with keep alive disabled, and many small requests are made, many images,
> htmls, css are truncated.
> Sorry I can't be more precise with this, but I hope anyone else having a
> similar trouble can help fill out this bug with details.
> *Update in 2017*
> I have provided a maven project with a unit test that has a 100% failure rate
> on my desktop without resorting to creating artificial load. It is a lot
> simpler:
> https://github.com/bkuker/sshd-85
> https://github.com/bkuker/sshd-85/blob/master/src/main/java/com/billkuker/sshd/sshd85/TheTest.java
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