NIOSSHClient gets stucked

[vladimir-aubrecht]

Problem

When testing NIOSSHClient, I am always getting stucked indefinitely on childChannel wait() method. Could somebody help me understand what is the problem?

Findings

• promise.FutureResult was created successfully, but my guess is, it was never met.
• ExampleExecHandler was never activated and command was never executed.

Setup

• Testing on M1 Macbook Pro with latest MacOS & XCode

[Elektronenhirn108]

@vladimir-aubrecht Same problem here. Did you find a solution?
It appears that createChannel doesn't do anything inside.

[sarensw]

I'm getting an exception exactly there. Do you also get an exception? Or is it just endlessly waiting?

NIOSSHClient/main.swift:97: Fatal error: 'try!' expression unexpectedly raised an error: NIOCore.ChannelError.eof
2022-02-14 11:14:55.954988+0100 NIOSSHClient[89883:1868853] NIOSSHClient/main.swift:97: Fatal error: 'try!' expression unexpectedly raised an error: NIOCore.ChannelError.eof

[Lukasa]

createChannel requires an active SSH connection to be open and running: if it isn't, it won't be able to do anything. Please make sure your connection is created.

@sarensw You seem to have another issue, which is that you're creating a channel when the connection has been torn down already.

[sarensw]

@Lukasa thanks for the info. I'll create another ticket then as I am using the Swift SSH example client without any line changed.

[sarensw]

@Lukasa Now I also stumbled into the same situation as described by the author of this ticket.

The following section is basically taken from the client example, with some prints added.

// Wait for the connection to close
print("closing")
try! childChannel.closeFuture.wait()
print("child channel closed")
let exitStatus = try! exitStatusPromise.futureResult.wait()
print("exist status promise awaited")
try! channel.close().wait()
print("all closed")
print(exitStatus)

closing is printed, but child channel closed is never reached as it gets stuck on try! childChannel.closeFuture.wait().

The command that I provide is executed correctly on the remotely connected system, just as I would expect. So the channel seems to be successfully created.

Do you have any idea? Is there any way that I can analyse this further?

[sarensw]

@Lukasa , so I've been adding print() pretty much everywhere in the code now. It turns out that self.context?.close(...) in GlueHandler never returns

private func partnerWriteEOF() {
    print("func partnerWriteEOF")
    self.context?.close(mode: .output, promise: nil)
    print("func partnerWriteEOF closed")
}

So func partnerWriteEOF is still printed out, but func partnerWriteEOF closed not. This is where the client basically stops working, waiting for close() to return.

[Lukasa]

That is unlikely to be possible: close should be asynchronous, and should not block. Can you use lldb to print the call stack after this point?

[daugust7]

I am having what appears to be the same problem. Any updates @sarensw?

[daugust7]

This also looks related @Lukasa: https://forums.swift.org/t/wrapper-for-niosshclient-swift-nio-ssh-client-example/55741

[sarensw]

@daugust7 no update yet. I want to take some time again next week to "print the call stack after this point" using lldb. As I'm still a Swift beginner, this might take a while 😄 .

You are right with the link in the forum. The question in the forum is actually also from me. So it is related 👍

[JiangYulin]

Any update on this issue?