SftpFileStream also sends SSH_FXP_FSTAT upon init when mode is not Append

[waynebrantley]

Using your library I cannot connect to a particular SFTP server.
I attempted to connect to this server using WinSCP and it fails also, unless I set the SFTP protocol to version 3 or 4 (instead of the default version 6).

How can I set the version of the SFTP protocol that SSH.NET uses?

[drieseng]

We're using version 3.
Can you share more information on the the server and the error that you get?

[waynebrantley]

Here is the code I am using
using (var stfp = new SftpClient(_hostName.Option, port, _userName.Option, _password.Option)) { stfp.Connect(); stfp.WriteAllBytes(fileName, ms.ToArray()); stfp.Disconnect(); }
Here is the error where I call WriteAllBytes.

Renci.SshNet.Common.SshException: Cannot find message [/testfile3343.01232017]
   at Renci.SshNet.Sftp.SftpSession.RequestFStat(Byte[] handle)
   at Renci.SshNet.Sftp.SftpFileStream..ctor(ISftpSession session, String path, FileMode mode, FileAccess access, Int32 bufferSize, Boolean useAsync)
   at Renci.SshNet.Sftp.SftpFileStream..ctor(ISftpSession session, String path, FileMode mode, FileAccess access, Int32 bufferSize)
   at Renci.SshNet.SftpClient.WriteAllBytes(String path, Byte[] bytes)

I found a similar issue here: http://sshnet3.rssing.com/chan-6841276/all_p70.html
This person said

It seems my customer has disabled the shell to let only the sftp with SSH2 1024 key connection.

I found a reference to this issue about an IBM Proxy Server not supporting anything but protocol 3. That is what led me to try that. I then contacted the vendor and in fact they WERE using an IBM proxy server and indicated it must be version 3 or 4.

Potentially there is another way to send the data other than WriteAllBytes that would result in different protocol commands that might work?

[waynebrantley]

@drieseng Sent you an email to your github email profile. I can give you access to the server where you can reproduce this issue if interested.

[waynebrantley]

@drieseng So I figured out what this issue is. The issue is permissions are denied to set the attributes of files on the SFTP server. So, I commented out the following line and everything worked fine:

https://github.com/sshnet/SSH.NET/blob/develop/src/Renci.SshNet/Sftp/SftpFileStream.cs#L272

• It occurs to me this code is getting the attributes of a file even when the FileMode is not append. So if this code only tried to get the attributes when mode was Append that would solve this bug.
• Additionally, it appears it is possible that anytime you are dealing with attributes you may be denied permission - so that should probably be accounted for somehow.

Any chance the suggested change above can be implemented and a new package pushed?

If it helps, for example when uploading with WinSCP, the UI shows this error.

Permission denied.
Error code: 3
Error message from server: This server does not support operations to modify file attributes.

[drieseng]

Wayne, in this case we're not setting attributes but getting the attributes.
If possible, I'd still like to be able to reproduce this issue myself.
Can you get me the correct credentials?

[waynebrantley]

I agree with your premise! I will attempt to get credentials for you to reproduce it.

[waynebrantley]

I sent you credentials to reproduce the error.

[drieseng]

I was able to reproduce the error. There are actually a few strange things I noticed with that SSH server:

• It reports a generate failure when you use SSH_FXP_FSTAT to obtain the file attributes for a SSH_FXF_WRITE handle of a file that did not exist when the handle was created. If a failure is to be reported, I would at least expect a SSH_FX_NO_SUCH_FILE. Note that OpenSSH does not report a failure in this case, but - as always - the SSH specification is not clear on this.
• A given filename can exist multiple times (at one point, I had at least five distinct files with the same absolute file name).

I agree with your conclusion that we should only obtain the file attributes if we want to append.
I'll fix this asap.

[waynebrantley]

Thanks for doing this.
Do you have a timeframe for this milestone to be completed? It is the 2016.1 milestone, so a little worried.
😄

(I already forked it, it builds except one test fails - so I can always run off my own clone if it is going to be several months - but rather wait if just a few weeks)