Add awaitShutdown utils

Author: debuglevel

src/main/kotlin/de/debuglevel/microservices/utils/spark/SparkTestUtils.kt

@@ -0,0 +1,60 @@
+package de.debuglevel.microservices.utils.spark
+
+import de.debuglevel.microservices.utils.configuration.MicroserviceConfiguration
+import spark.Service
+import spark.Spark
+import java.io.IOException
+import java.net.ServerSocket
+
+object SparkTestUtils {
+    /**
+     * Shutdown spark server and wait until Spark is finally shut down.
+     *
+     * This is actually a rather nasty workaround to close Spark after test and ensure that it's down when we exit this method (the actual stopping is done in a separate Thread; so we have no notification about that).
+     * But even this does not necessarily catch all race conditions.
+     */
+    fun awaitShutdown() {
+        Spark.stop()
+
+        while (isLocalPortInUse(MicroserviceConfiguration.port)) {
+            Thread.sleep(100)
+        }
+
+        while (isSparkInitialized()) {
+            Thread.sleep(100)
+        }
+    }
+
+    /**
+     * Access the internals of Spark to check if the "initialized" flag is already set to false.
+     */
+    private fun isSparkInitialized(): Boolean {
+
+        val sparkClass = Spark::class.java
+        val getInstanceMethod = sparkClass.getDeclaredMethod("getInstance")
+        getInstanceMethod.isAccessible = true
+        val service = getInstanceMethod.invoke(null) as Service
+
+        val serviceClass = service::class.java
+        val initializedField = serviceClass.getDeclaredField("initialized")
+        initializedField.isAccessible = true
+        val initialized = initializedField.getBoolean(service)
+
+        return initialized
+    }
+
+    /**
+     * Check if the Spark port could again be opened; if not, it is still in use by Spark.
+     */
+    private fun isLocalPortInUse(port: Int): Boolean {
+        return try {
+            // ServerSocket try to open a LOCAL port
+            ServerSocket(port).close()
+            // local port can be opened, it's available
+            false
+        } catch (e: IOException) {
+            // local port cannot be opened, it's in use
+            true
+        }
+    }
+}