ExecChannel: How to correctly get the exit code

[Nexxurs]

Hey!

I have a question regarding the exitcode for single-command SSH connections.

I am currently using the following piece of code (in Kotlin - abbreviated to focus on the main points)

import com.jcraft.jsch.ChannelExec
import com.jcraft.jsch.JSch
import java.io.BufferedReader
import java.io.InputStreamReader
import com.jcraft.jsch.Session


fun createSession(): Session {
    return JSch().getSession("127.0.0.1")
}

fun run(command: String) {
    val channel = createSession().openChannel("exec") as ChannelExec
    
    try {
        channel.setCommand(command)
        val reader = BufferedReader(InputStreamReader(channel.inputStream))
        channel.connect()

        var lastLine = ""
        while (reader.readLine()?.also { lastLine = it } != null) {
            doStuff(lastLine)
        }
    } finally {
        channel.disconnect()
        while (!channel.isClosed) {
            Thread.sleep(10)
        }
        if (channel.exitStatus != 0) {
            throw Exception("something went wrong")
        }
    }
}

Rarely this fails on commands that I'd expect to run successfully (as the stdout output is correct, in these cases the exitStatus is -1) - I expect some kind of race condition. After checking the code, it looks like isClosed is set before the ChannelClose package is sent, whose response sets the exitStatus.

Is there a way to correctly read the exitStatus after the Channel is closed? AFAIK -1 is a valid exitStatus, which is why I cannot wait until this value changes (and it opens other issues with busy waiting)

If not, please consider this a feature request.

[mwiede]

have you considered the err input stream? see https://stackoverflow.com/a/47554723/2290153 for the explanation