Details
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Question
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Status: Resolved
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Major
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Resolution: Not A Problem
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2.8.0
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None
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None
Description
Hi Thomas,
I have connection problems with a Microsoft SFTP server called Rebex SFTP Server (https://www.rebex.net/buru-sftp-server/).
This is a NEW connection setup for our SFTP client/server product.
I have SFTP client based on Apache SSHD 2.8.0. The client is configured for pushing files to the Rebex SFTP server.
Description of the problem :
Sometimes the SFTP client is unable to push files on this remote SFTP Server, the SSH handshake fails during SSH handshake for an authentication timeout set to 60 secs that expires.
The exception is the following :
Caused by: org.apache.sshd.common.SshException: DefaultAuthFuture[ssh-connection]: Failed to get operation result within specified timeout: 60000
at org.apache.sshd.common.future.AbstractSshFuture$$Lambda$284/0000000000000000.apply(Unknown Source)
at org.apache.sshd.common.future.AbstractSshFuture.formatExceptionMessage(AbstractSshFuture.java:185)
at org.apache.sshd.common.future.AbstractSshFuture.verifyResult(AbstractSshFuture.java:111)
at org.apache.sshd.client.future.DefaultAuthFuture.verify(DefaultAuthFuture.java:39)
at org.apache.sshd.client.future.DefaultAuthFuture.verify(DefaultAuthFuture.java:32)
at org.apache.sshd.common.future.VerifiableFuture.verify(VerifiableFuture.java:56)
at com.primeur.sshd.client.SSHDClient.connect(SSHDClient.java:157)
When the connection fails, looking through the verbose logs of the client I sometimes found :
[8/23/22 6:35:52:064 EDT] 0000bfcb id=00000000 org.apache.sshd.common.channel.ChannelAsyncOutputStream 1 doWriteIfPossible doWriteIfPossible([SftpChannelSubsystem[id=0, recipient=0]-ClientSessionImpl[StateStreet@/127.0.0.1:40787][sftp]] cmd=SSH_MSG_CHANNEL_DATA) delaying write until space is available in the remote window
This trace seems to evidence some issues writing data on socket according to SSH protocol....
I've managed to handle this warning "delaying write until space is available in the remote window" setting the system property -Dorg.apache.sshd.config.sftp-chunk-if-window-less-than-packet=true without any improvement.
The authentication timeout expires because the SSH messages related to client authentication are not sent and received between client and server.
Q. What do you think about this log ?
[8/23/22 6:35:52:285 EDT] 0000bfcf id=00000000 common.session.helpers.ReservedSessionMessagesHandlerAdapter 1 handleIgnoreMessage handleIgnoreMessage(ClientSessionImpl[StateStreet@/127.0.0.1:40787]) SSH_MSG_IGNORE
The receiving of some SSH_MSG_IGNORE messages from SFTP remote server could mean that the socket connection is in idle state and no data flow on the socket.
Q. Can you confirm ?
Q. Do you think that this issue is caused by external factor (i.e network latency/load, firewalls, balancers etc..... or is caused by some tricky SSH implementation details or interoperability issues with this SFTP server (less likely...) ?
Thank you in advance for your cooperation.
Regards, Roberto.