Implement withRunningKafkaOnFoundPort (#76)

* Make withRunningKafka generic

* Factor out withTempDir helper method

* Factor out withRunningZooKeeper helper method

* Implement withRunningKafkaOnFoundPort

This is useful for writing tests that configure kafka/zookeeper to
listen on port 0, i.e. listen on an arbitrary available port.

README.md

@@ -78,6 +78,27 @@ class MySpec extends WordSpec with EmbeddedKafka {
 }
 ```
 
+If you want to run ZooKeeper and Kafka on arbitrary available ports, you can
+use the `withRunningKafkaOnFoundPort` method. This is useful to make tests more
+reliable, especially when running tests in parallel or on machines where other
+tests or services may be running with port numbers you can't control.
+
+```scala
+class MySpec extends WordSpec with EmbeddedKafka {
+
+"runs with embedded kafka on arbitrary available ports" should {
+
+    val userDefinedConfig = EmbeddedKafkaConfig(kafkaPort = 0, zooKeeperPort = 0)
+
+    withRunningKafkaOnFoundPort(userDefinedConfig) { implicit actualConfig =>
+      // now a kafka broker is listening on actualConfig.kafkaPort
+      publishStringMessageToKafka("topic", "message")
+      consumeFirstStringMessageFrom("topic") shouldBe "message"
+    }
+
+}
+```
+
 The same implicit `EmbeddedKafkaConfig` is used to define custom consumer or producer properties
 
 ```scala
@@ -102,7 +123,7 @@ class MySpec extends WordSpec with EmbeddedKafka {
 }
 ```
 
-This works for both `withRunningKafka` and `EmbeddedKafka.start()`
+This works for `withRunningKafka`, `withRunningKafkaOnFoundPort`, and `EmbeddedKafka.start()`
 
 Also, it is now possible to provide custom properties to the broker while starting Kafka. `EmbeddedKafkaConfig` has a 
 `customBrokerProperties` field which can be used to provide extra properties contained in a `Map[String, String]`.

embedded-kafka/src/main/scala/net/manub/embeddedkafka/EmbeddedKafka.scala

@@ -129,26 +129,64 @@ sealed trait EmbeddedKafkaSupport {
     * @param body   the function to execute
     * @param config an implicit [[EmbeddedKafkaConfig]]
     */
-  def withRunningKafka(body: => Any)(
-      implicit config: EmbeddedKafkaConfig): Any = {
-
-    def cleanLogs(directories: Directory*): Unit = {
-      directories.foreach(_.deleteRecursively())
+  def withRunningKafka[T](body: => T)(
+      implicit config: EmbeddedKafkaConfig): T = {
+    withRunningZooKeeper(config.zooKeeperPort) { zkPort =>
+      withTempDir("kafka") { kafkaLogsDir =>
+        val broker = startKafka(config.copy(zooKeeperPort = zkPort), kafkaLogsDir)
+        try {
+          body
+        } finally {
+          broker.shutdown()
+          broker.awaitShutdown()
+        }
+      }
     }
+  }
 
-    val zkLogsDir = Directory.makeTemp("zookeeper-logs")
-    val kafkaLogsDir = Directory.makeTemp("kafka")
+  /**
+    * Starts a ZooKeeper instance and a Kafka broker, then executes the body passed as a parameter.
+    * The actual ZooKeeper and Kafka ports will be detected and inserted into a copied version of
+    * the EmbeddedKafkaConfig that gets passed to body. This is useful if you set either or both
+    * port to 0, which will listen on an arbitrary available port.
+    *
+    * @param config the user-defined [[EmbeddedKafkaConfig]]
+    * @param body   the function to execute, given an [[EmbeddedKafkaConfig]] with the actual
+    *               ports Kafka and ZooKeeper are running on
+    */
+  def withRunningKafkaOnFoundPort[T](config: EmbeddedKafkaConfig)(body: EmbeddedKafkaConfig => T): T = {
+    withRunningZooKeeper(config.zooKeeperPort) { zkPort =>
+      withTempDir("kafka") { kafkaLogsDir =>
+        val broker: KafkaServer = startKafka(config.copy(zooKeeperPort = zkPort), kafkaLogsDir)
+        val kafkaPort = broker.boundPort(broker.config.listeners.head.listenerName)
+        val actualConfig = config.copy(kafkaPort = kafkaPort, zooKeeperPort = zkPort)
+        try {
+          body(actualConfig)
+        } finally {
+          broker.shutdown()
+          broker.awaitShutdown()
+        }
+      }
+    }
+  }
 
-    val factory = startZooKeeper(config.zooKeeperPort, zkLogsDir)
-    val broker = startKafka(config, kafkaLogsDir)
+  private def withRunningZooKeeper[T](port: Int)(body: Int => T): T = {
+    withTempDir("zookeeper-logs") { zkLogsDir =>
+      val factory = startZooKeeper(port, zkLogsDir)
+      try {
+        body(factory.getLocalPort)
+      } finally {
+        factory.shutdown()
+      }
+    }
+  }
 
+  private def withTempDir[T](prefix: String)(body: Directory => T): T = {
+    val dir = Directory.makeTemp(prefix)
     try {
-      body
+      body(dir)
     } finally {
-      broker.shutdown()
-      broker.awaitShutdown()
-      factory.shutdown()
-      cleanLogs(zkLogsDir, kafkaLogsDir)
+      dir.deleteRecursively()
     }
   }
 

embedded-kafka/src/test/scala/net/manub/embeddedkafka/EmbeddedKafkaWithRunningKafkaOnFoundPortSpec.scala

@@ -0,0 +1,59 @@
+package net.manub.embeddedkafka
+
+class EmbeddedKafkaWithRunningKafkaOnFoundPortSpec
+    extends EmbeddedKafkaSpecSupport
+    with EmbeddedKafka {
+
+  "the withRunningKafkaOnFoundPort method" should {
+    "start and stop Kafka and Zookeeper successfully on non-zero ports" in {
+      val userDefinedConfig = EmbeddedKafkaConfig(kafkaPort = 12345, zooKeeperPort = 12346)
+      val actualConfig = withRunningKafkaOnFoundPort(userDefinedConfig) { actualConfig =>
+        actualConfig shouldBe userDefinedConfig
+        bothKafkaAndZkAreAvailable(actualConfig)
+        actualConfig
+      }
+      bothKafkaAndZkAreNotAvailable(actualConfig)
+    }
+
+    "start and stop multiple Kafka and Zookeeper successfully on arbitrary available ports" in {
+      val userDefinedConfig = EmbeddedKafkaConfig(kafkaPort = 0, zooKeeperPort = 0)
+      val actualConfig1 = withRunningKafkaOnFoundPort(userDefinedConfig) { actualConfig1 =>
+        bothKafkaAndZkAreAvailable(actualConfig1)
+        publishStringMessageToKafka("topic", "message1")(actualConfig1)
+        consumeFirstStringMessageFrom("topic")(actualConfig1) shouldBe "message1"
+        val actualConfig2 = withRunningKafkaOnFoundPort(userDefinedConfig) { actualConfig2 =>
+          bothKafkaAndZkAreAvailable(actualConfig2)
+          publishStringMessageToKafka("topic", "message2")(actualConfig2)
+          consumeFirstStringMessageFrom("topic")(actualConfig2) shouldBe "message2"
+          val allConfigs = Seq(userDefinedConfig, actualConfig1, actualConfig2)
+          // Confirm both actual configs are running on separate non-zero ports, but otherwise equal
+          allConfigs.map(_.kafkaPort).distinct should have size 3
+          allConfigs.map(_.zooKeeperPort).distinct should have size 3
+          allConfigs.map(_.copy(kafkaPort = 0, zooKeeperPort = 0)).distinct should have size 1
+          actualConfig2
+        }
+        bothKafkaAndZkAreNotAvailable(actualConfig2)
+        actualConfig1
+      }
+      bothKafkaAndZkAreNotAvailable(actualConfig1)
+    }
+
+    "work with a simple example using implicits" in {
+      val userDefinedConfig = EmbeddedKafkaConfig(kafkaPort = 0, zooKeeperPort = 0)
+      withRunningKafkaOnFoundPort(userDefinedConfig) { implicit actualConfig =>
+        publishStringMessageToKafka("topic", "message")
+        consumeFirstStringMessageFrom("topic") shouldBe "message"
+      }
+    }
+  }
+
+  private def bothKafkaAndZkAreAvailable(config: EmbeddedKafkaConfig): Unit = {
+    kafkaIsAvailable(config.kafkaPort)
+    zookeeperIsAvailable(config.zooKeeperPort)
+  }
+
+  private def bothKafkaAndZkAreNotAvailable(config: EmbeddedKafkaConfig): Unit = {
+    kafkaIsNotAvailable(config.kafkaPort)
+    zookeeperIsNotAvailable(config.zooKeeperPort)
+  }
+}

embedded-kafka/src/test/scala/net/manub/embeddedkafka/embeddedKafkaSpecSupport.scala

@@ -60,15 +60,15 @@ abstract class EmbeddedKafkaSpecSupport
     expectMsg(1 second, ConnectionSuccessful)
   }
 
-  def kafkaIsNotAvailable(): Unit = {
+  def kafkaIsNotAvailable(kafkaPort: Int = 6001): Unit = {
     system.actorOf(
-      TcpClient.props(new InetSocketAddress("localhost", 6001), testActor))
+      TcpClient.props(new InetSocketAddress("localhost", kafkaPort), testActor))
     expectMsg(1 second, ConnectionFailed)
   }
 
-  def zookeeperIsNotAvailable(): Unit = {
+  def zookeeperIsNotAvailable(zookeeperPort: Int = 6000): Unit = {
     system.actorOf(
-      TcpClient.props(new InetSocketAddress("localhost", 6000), testActor))
+      TcpClient.props(new InetSocketAddress("localhost", zookeeperPort), testActor))
     expectMsg(1 second, ConnectionFailed)
   }
 }