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https://issues.apache.org/jira/browse/SSHD-1078?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17197061#comment-17197061
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min yun law commented on SSHD-1078:
-----------------------------------
{code:java}
I think you should be able to share a session and create multiple channels,
provided that one channel is used by a single thread{code}
As I described for this bug, if the shared session is being used for big file
upload( size > 4G), the channel by SCP/SFTP will break or get stuck.
in our environment, there are two threads that share the same session to a
remote node. one thread (A) for file uploading, one thread (B) implements the
remote lock checking loop which make sure only A is the JVM that was doing the
file uploading, not other JVM. When using Mina SSHD, execute channel for B
will get stuck after few remote command calls, and scp/sftp channel for A get
closed in the middle of file uploading.
Jsch work without any problem in above two thread.
> SCP/SFTP failed for big file upload
> -----------------------------------
>
> Key: SSHD-1078
> URL: https://issues.apache.org/jira/browse/SSHD-1078
> Project: MINA SSHD
> Issue Type: Bug
> Affects Versions: 2.5.1
> Reporter: min yun law
> Priority: Major
>
> Trying to merge product from jsch to mina sshd that keep the same SSH
> architecture (lets call SessionPool) which for each remote node, there is
> only one session object and limited channels (<=8) for executing commands and
> file operations. The SessionPool manages the session/channels for nodes and
> make sure only 8 threads(ssh channels) per node that can be run concurrently.
> This architecture works for Jsch for many years, but when using mina sshd,
> this architecture wont work when with upload big file, we always see
> following exception:
> {code:java}
> java.io.EOFException: Channel is being closed
> at
> org.apache.sshd.common.channel.AbstractChannel$2.<init>(AbstractChannel.java:794)
> at
> org.apache.sshd.common.channel.AbstractChannel.writePacket(AbstractChannel.java:792)
> at
> org.apache.sshd.common.channel.ChannelAsyncOutputStream.doWriteIfPossible(ChannelAsyncOutputStream.java:168)
> at
> org.apache.sshd.common.channel.ChannelAsyncOutputStream.writePacket(ChannelAsyncOutputStream.java:70)
> at
> org.apache.sshd.client.subsystem.sftp.impl.DefaultSftpClient.send(DefaultSftpClient.java:292)
> at
> org.apache.sshd.client.subsystem.sftp.impl.SftpOutputStreamAsync.flush(SftpOutputStreamAsync.java:210)
> at
> org.apache.sshd.client.subsystem.sftp.impl.SftpOutputStreamAsync.write(SftpOutputStreamAsync.java:141)
> {code}
> From SSH server log, we see follow error:
> {code:java}
> Aug 19 15:56:38 xxxx sftp-server[202217]: error: Unknown message 0
> Aug 19 15:56:38 xxxx sftp-server[202217]: error: msg_len 0 < consumed 1
> {code}
> other client side exceptions by mina sshd as:
> org.apache.sshd.common.channel.WindowClosedException: Already closed:
> Window[client/remote](ChannelExec[id=79, recipient=1]-ClientSessionImp
>
> ----
> After many tries, finally I found that for big file upload/download, I have
> to give its own SshClient/ClientSession objects and then there will no such
> channel closing exception during file upload.
> That means we cannot share the same SshClient and ClientSession object per
> remote node to execute commands and file operations, and there may has bug in
> ClientSession when handle channels in this situation.
> the reason that we like to share the same SshClient/ClientSession for the
> same remote node is to manage the session/channels and close them when no
> usage, also to reduce the cost to allocate those objects.
>
>
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