How do you implement a responding shell script in a Kotlin web service coroutines request? - kotlin

Question

I created a web service with spring boot 2 and Kotlin to access same unix scripts and other programs of a certain server via a process builder. The response messages shall contain the stdout of the shell script I use. But I have problems with the coroutines in Kotlin. When I use process.waitFor() this is a blocking function. How can you use a dedicated thread(-pool) to track the external processes and suspend the coroutines for that time?
In the following code snippet you see how I get the return code of a shell script and the stdout information of it:
val process = ProcessBuilder(cmd)
.redirectErrorStream(true)
.start()
val exitCode = process.waitFor()
return CmdResult(
exitCode,
process.inputStream
)
I failed with the following trial, because I did not get the stdout information and did not know how to get the result out of the scope to use it as a return type:
val dispatcher = newFixedThreadPoolContext(4, "myPool")
launch(dispatcher) {
val process = ProcessBuilder(listOf(cmdScript))
.redirectErrorStream(true)
.start()
val exitCode = process.waitFor()
CmdResult(
exitCode,
process.inputStream
)
}.join()

Answer 1

You can use top level function withContext to return from a coroutine:
val dispatcher = newFixedThreadPoolContext(4, "myPool")
val result = withContext(dispatcher) {
val process = ProcessBuilder(listOf(cmdScript))
.redirectErrorStream(true)
.start()
val exitCode = process.waitFor()
CmdResult(
exitCode,
process.inputStream
)
}