Cancellation support interceptor

cancellationTest.kt

class JobCancellationInterceptor(val originalInterceptor: ContinuationInterceptor?) :
        AbstractCoroutineContextElement(ContinuationInterceptor),
        ContinuationInterceptor {

    override fun <T> interceptContinuation(continuation: Continuation<T>): Continuation<T> =
        CancellableCheckContinuation(continuation).let {
            originalInterceptor?.interceptContinuation(it) ?: it
        }

    class CancellableCheckContinuation<T>(val continuation: Continuation<T>) : Continuation<T> {
        override val context: CoroutineContext get() = continuation.context

        override fun resume(value: T) {
            val job = context[Job]
            if (job?.isCompleted == true) {
                println("Cancelling continuation, because job is already completed")
                continuation.resumeWithException(job.getCompletionException())
            } else {
                continuation.resume(value)
            }
        }

        override fun resumeWithException(exception: Throwable) =
                continuation.resumeWithException(exception)
    }
}

fun CoroutineContext.addCancellationInterceptor(): CoroutineContext = this + JobCancellationInterceptor(this[ContinuationInterceptor])