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From "Eric Charles (JIRA)" <server-...@james.apache.org>
Subject [jira] [Commented] (JAMES-1436) APPEND IMAP command can result in JAMES IMAP waiting indefinitely for data
Date Mon, 26 Nov 2012 11:23:00 GMT

    [ https://issues.apache.org/jira/browse/JAMES-1436?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13503736#comment-13503736
] 

Eric Charles commented on JAMES-1436:
-------------------------------------

Ok, got it.

The changes is made at a very critical portion of the code.
Before committing your patch, I will run a while to be sure we don't introduce any regression.

Also, is it possible you post here the reasoning that lead you to introduce that SwitchableDelimiterBasedFrameDecoder,
why the synchronization would be needed and the potential effect on the overall performance
of the server.

Thx in advance for your help,

Eric

                
> APPEND IMAP command can result in JAMES IMAP waiting indefinitely for data
> --------------------------------------------------------------------------
>
>                 Key: JAMES-1436
>                 URL: https://issues.apache.org/jira/browse/JAMES-1436
>             Project: James Server
>          Issue Type: Bug
>          Components: IMAPServer
>    Affects Versions: Trunk, 3.0-beta4, 3.0-beta5
>         Environment: Ubuntu 12.04 x86_64
>            Reporter: Samant Maharaj
>         Attachments: JAMES-1436.patch
>
>
> When processing an IMAP APPEND command, the Netty stack in JAMES IMAP can get into a
state where the ImapRequestFrameDecoder will wait for a number message bytes that will never
arrive.
> This has the effect of causing the IMAP client to also block indefinitely waiting for
a response from the server.
> Root Cause:
> This is due to a race condition when the DelimiterBasedFrameDecoder is removed from the
Netty pipeline by the ImapRequestFrameDecoder.
> If the DelimiterBasedFrameDecoder still contains less than one line of data in its buffer,
that data will never be flushed and forwarded down the pipeline. The effect of this is that
a small number of bytes, typically from the early part of the message are omitted and the
final byte count does not match the value calculated from the APPEND command. This results
in the APPEND command never being completely decoded and hence no append actually takes place
nor does a response get sent to the client.
> In order to reliably trigger this bug, JAMES was configured to accept a remote debugging
connection and a conditional breakpoint set at org.jboss.netty.handler.codec.frame.FrameDecoder:439.
The condition was set to 'Thread.sleep(200l); false'. This results in introducing a 200ms
delay on each frame decoding loop without actually hitting the breakpoint. The effect of this
is to allow the threadpool running ImapRequestFrameDecoder time to consume the individual
frames and remove the DelimiterBasedFrameDecoder from the pipeline.

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