SCP user friendly exceptions

[fioan89]

Version

2.10.0

Bug description

When using the SCP client to upload a file to a remote location that does not exist a WindowClosedException is raised instead of a more user friendly SCP exception detailing the reason of why the upload/download failed.

The snippet of code below raises a WindowClosedException exception when /remote/path/that/does/not/exist doesn't exist.

val session = sshClient.connect(
    username,
    hostname,
    port
).verify(5000).session
session.auth().await(5000)

scpClient = ScpClientCreator.instance().createScpClient(session)
scpClient.upload("/local/path/file_name",  "/remote/path/that/does/not/exist/file_name", options)

Actual behavior

e = {WindowClosedException@37364} "org.apache.sshd.common.channel.WindowClosedException: Already closed: RemoteWindow[client](ChannelExec[id=0, recipient=0]-ClientSessionImpl[ifaur@localhost/127.0.0.1:2222])"
 disconnectCode = 0
 backtrace = {Object[6]@37368} 
 detailMessage = "Already closed: RemoteWindow[client](ChannelExec[id=0, recipient=0]-ClientSessionImpl[ifaur@localhost/127.0.0.1:2222])"
 cause = {WindowClosedException@37364} "org.apache.sshd.common.channel.WindowClosedException: Already closed: RemoteWindow[client](ChannelExec[id=0, recipient=0]-ClientSessionImpl[ifaur@localhost/127.0.0.1:2222])"
 stackTrace = {StackTraceElement[39]@37373} 
  0 = {StackTraceElement@41979} "org.apache.sshd.common.channel.RemoteWindow.waitForCondition(RemoteWindow.java:230)"
  1 = {StackTraceElement@41980} "org.apache.sshd.common.channel.RemoteWindow.waitForSpace(RemoteWindow.java:187)"
  2 = {StackTraceElement@41981} "org.apache.sshd.common.channel.ChannelOutputStream.flush(ChannelOutputStream.java:278)"
  3 = {StackTraceElement@41982} "org.apache.sshd.scp.common.helpers.ScpIoUtils.writeLine(ScpIoUtils.java:82)"
  4 = {StackTraceElement@41983} "org.apache.sshd.scp.common.helpers.ScpIoUtils.sendAcknowledgedCommand(ScpIoUtils.java:94)"
  5 = {StackTraceElement@41984} "org.apache.sshd.scp.common.ScpHelper.sendAcknowledgedCommand(ScpHelper.java:724)"
  6 = {StackTraceElement@41985} "org.apache.sshd.scp.common.ScpHelper.sendDir(ScpHelper.java:686)"
  7 = {StackTraceElement@41986} "org.apache.sshd.scp.common.ScpHelper.send(ScpHelper.java:484)"
  8 = {StackTraceElement@41987} "org.apache.sshd.scp.common.ScpHelper.send(ScpHelper.java:454)"
  9 = {StackTraceElement@41988} "org.apache.sshd.scp.client.AbstractScpClient.lambda$upload$0(AbstractScpClient.java:143)"
  10 = {StackTraceElement@41989} "org.apache.sshd.scp.client.DefaultScpClient.runUpload(DefaultScpClient.java:149)"
  11 = {StackTraceElement@41990} "org.apache.sshd.scp.client.AbstractScpClient.upload(AbstractScpClient.java:143)"
  12 = {StackTraceElement@41991} "org.apache.sshd.scp.client.ScpClient.upload(ScpClient.java:106)"

Expected behavior

a SCPException or even a basic IOException with a more relevant message:

• destination "/remote/path/that/does/not/exist/file_name" does not exist or could not be created
• "/remote/path/that/does/not/exist/file_name" no such file or directory

Relevant log output

No response

Other information

No response

[lgoldstein]

Actually, this is does not seem to a MINA SSHD issue but rather a specific server issue - see especially PR#428 where a missing remote file is actuall signalled as a WARNING by the OpenSSH server rather than an ERROR. Furthermore, the SCP protocol does not really provide a good mechansim for specific errors - at most, some text after the ERROR stats - which most clients (jncluding us) ignore.

[fioan89]

If remember correctly when I played with this, I also tested the SCP client shipped with Windows MinGW. That was working better with more specific/user friendly erros. I can try to reproduce the issue again and post the logs from that client.

[fioan89]

Here is an example of an error from a different scp client:

$ scp log.txt [email protected]:/home/ifaur/some_remote_path/
[email protected]'s password:
scp: dest open "/home/ifaur/some_remote_path/": Failure
scp: failed to upload file log.txt to /home/ifaur/some_remote_path/

Something more verbose:

$ scp -v log.txt [email protected]:/home/ifaur/some_remote_path/
Executing: program /usr/bin/ssh host 192.168.0.68, user ifaur, command sftp
OpenSSH_9.4p1, OpenSSL 3.1.2 1 Aug 2023
debug1: Reading configuration data /c/Users/Fauri/.ssh/config
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Connecting to 192.168.0.68 [192.168.0.68] port 22.
debug1: Connection established.
........................................................................................................................
scp: debug1: stat remote: No such file or directory
scp: dest open "/home/ifaur/some_remote_path/": Failure
scp: failed to upload file log.txt to /home/ifaur/some_remote_path/
debug1: client_input_channel_req: channel 0 rtype exit-status reply 0
debug1: channel 0: free: client-session, nchannels 1
Transferred: sent 3776, received 3920 bytes, in 0.4 seconds
Bytes per second: sent 9221.3, received 9572.9
debug1: Exit status 0

I've removed the key handshake bits for brevity.

[lgoldstein]

This log does not reveal what is being transmitted at the low-level SCP protocol