[SPARK-22836][ui] Show driver logs in UI when available.

Port code from the old executors listener to the new one, so that
the driver logs present in the application start event are kept.

Author: Marcelo Vanzin

core/src/main/scala/org/apache/spark/status/AppStatusListener.scala

@@ -114,6 +114,17 @@ private[spark] class AppStatusListener(
 
     kvstore.write(new ApplicationInfoWrapper(appInfo))
     kvstore.write(appSummary)
+
+    // Update the driver block manager with logs from this event. The SparkContext initialization
+    // code registers the driver before this event is sent.
+    event.driverLogs.foreach { logs =>
+      val driver = liveExecutors.get(SparkContext.DRIVER_IDENTIFIER)
+        .orElse(liveExecutors.get(SparkContext.LEGACY_DRIVER_IDENTIFIER))
+      driver.foreach { d =>
+        d.executorLogs = logs.toMap
+        update(d, System.nanoTime())
+      }
+    }
   }
 
   override def onEnvironmentUpdate(event: SparkListenerEnvironmentUpdate): Unit = {

core/src/test/scala/org/apache/spark/status/AppStatusListenerSuite.scala

@@ -939,6 +939,24 @@ class AppStatusListenerSuite extends SparkFunSuite with BeforeAndAfter {
     }
   }
 
+  test("driver logs") {
+    val listener = new AppStatusListener(store, conf, true)
+
+    val driver = BlockManagerId(SparkContext.DRIVER_IDENTIFIER, "localhost", 42)
+    listener.onBlockManagerAdded(SparkListenerBlockManagerAdded(time, driver, 42L))
+    listener.onApplicationStart(SparkListenerApplicationStart(
+      "name",
+      Some("id"),
+      time,
+      "user",
+      Some("attempt"),
+      Some(Map("stdout" -> "file.txt"))))
+
+    check[ExecutorSummaryWrapper](SparkContext.DRIVER_IDENTIFIER) { d =>
+      assert(d.info.executorLogs("stdout") === "file.txt")
+    }
+  }
+
   private def key(stage: StageInfo): Array[Int] = Array(stage.stageId, stage.attemptId)
 
   private def check[T: ClassTag](key: Any)(fn: T => Unit): Unit = {