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https://issues.apache.org/jira/browse/SSHD-1147?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17308212#comment-17308212
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Thomas Wolf commented on SSHD-1147:
-----------------------------------
Created [PR 187|https://github.com/apache/mina-sshd/pull/187]. [~alex_dkhn], do
you have a possibility to test that patch against a real IBM Sterling B2B SFTP
server?
But I find that implementation in this IBM Sterling B2B SFTP Gateway --
according to the description you linked -- simply buggy. Their server should be
smart enough to distinguish between repeated file reading attempts, and other
operations like stat'ing the file.
Googling around one finds that this behavior has caused similar troubles with
other SFTP clients, too. Oh well. IBM's the mountain, it won't move...
Perhaps that team that is trying to use Apache MINA sshd in that IBM Sterling
B2B thing (instead of the "commercial library" used until now) can change that
implementation to something better.
> SftpClient is not able to download file from proprietory SFTP servers (IBM)
> with a one time download policy
> -----------------------------------------------------------------------------------------------------------
>
> Key: SSHD-1147
> URL: https://issues.apache.org/jira/browse/SSHD-1147
> Project: MINA SSHD
> Issue Type: Wish
> Affects Versions: 2.5.1
> Reporter: Alex D
> Priority: Major
> Time Spent: 10m
> Remaining Estimate: 0h
>
> Some propretory SFTP servers support a so-called "one time download" policy
> also known as Extractability Count.
> Current implementation of the input stream based read ofile operation
> org.apache.sshd.client.subsystem.sftp.SftpClient::read(String path) uses
> org.apache.sshd.client.subsystem.sftp.impl.SftpInputStreamAsync
> which performs 2 operations in its constructor:
> 1) Open remote file (SftpClient::open)
> 2) Calculate remote file size using file's handle obtained in 1)
> As a result the following error is produced on attempt to download a file
> from IBMs SFTP:
> SFTP error (SSH_FX_FAILURE): The message [remote file path] is not
> extractable!
> IBM specifically states that it's not their problem at all, and they are not
> going to fix it.
> According to their flow described here:
> https://www.ibm.com/support/pages/node/1121475?lang=en
> "Any attempt from client to issue other SFTP operations like SSH_FXP_STAT
> (reading attributes) makes server to validate extractability_count > 0.
> If found 0, download would be reported as "not extractable".
> Most likely it's possible to use SftpClient::openRemoteFileChannel and work
> with the obtained FileChannel manually without any additional requests to
> stat remote file size.
> Though it would be a cumbersome approach, as reading remote file in chunks
> not knowing its size in this case will be far from optimal.
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