Log warn when Entity with name=null is created / if dispatching entities fails (#475)kamon-0.6.x

An application that creates a metric while passing `null` as metrics name
will not receive the expected `TickMetricSnapshot` (if it subscribes for
metrics).

As log level _warn_ (instead of error) is chosen, because from an application
perspective the app's functionality is not affected, i.e. there's no _immediate_
action required, but it's ok if this gets solved eventually.

2 files changed, 18 insertions, 3 deletions

diff --git a/kamon-core/src/main/scala/kamon/metric/Entity.scala b/kamon-core/src/main/scala/kamon/metric/Entity.scala
index 91249af0..17b728fd 100644
--- a/kamon-core/src/main/scala/kamon/metric/Entity.scala
+++ b/kamon-core/src/main/scala/kamon/metric/Entity.scala
@@ -16,6 +16,8 @@
 
 package kamon.metric
 
+import org.slf4j.LoggerFactory
+
 /**
  *  Identify a `thing` that is being monitored by Kamon. A [[kamon.metric.Entity]] is used to identify tracked `things`
  *  in both the metrics recording and reporting sides. Only the name and category fields are used with determining
@@ -23,9 +25,14 @@ package kamon.metric
  *
  *  // TODO: Find a better word for `thing`.
  */
-case class Entity(name: String, category: String, tags: Map[String, String])
+case class Entity(name: String, category: String, tags: Map[String, String]) {
+  if(name == null) Entity.log.warn("Entity with name=null created (category: {}), your monitoring will not work as expected!", category)
+}
 
 object Entity {
+
+  private lazy val log = LoggerFactory.getLogger(classOf[Entity])
+
   def apply(name: String, category: String): Entity =
     apply(name, category, Map.empty)
 
diff --git a/kamon-core/src/main/scala/kamon/metric/SubscriptionsDispatcher.scala b/kamon-core/src/main/scala/kamon/metric/SubscriptionsDispatcher.scala
index 09bf58ad..ab25173a 100644
--- a/kamon-core/src/main/scala/kamon/metric/SubscriptionsDispatcher.scala
+++ b/kamon-core/src/main/scala/kamon/metric/SubscriptionsDispatcher.scala
@@ -20,11 +20,12 @@ import akka.actor._
 import kamon.metric.SubscriptionsDispatcher._
 import kamon.util.{MilliTimestamp, GlobPathFilter}
 import scala.concurrent.duration.FiniteDuration
+import scala.util.control.NonFatal
 
 /**
  *  Manages subscriptions to metrics and dispatch snapshots on every tick to all subscribers.
  */
-private[kamon] class SubscriptionsDispatcher(interval: FiniteDuration, metricsExtension: MetricsModuleImpl) extends Actor {
+private[kamon] class SubscriptionsDispatcher(interval: FiniteDuration, metricsExtension: MetricsModuleImpl) extends Actor with ActorLogging {
   var lastTick = MilliTimestamp.now
   var oneShotSubscriptions = Map.empty[ActorRef, SubscriptionFilter]
   var permanentSubscriptions = Map.empty[ActorRef, SubscriptionFilter]
@@ -72,7 +73,14 @@ private[kamon] class SubscriptionsDispatcher(interval: FiniteDuration, metricsEx
     snapshots: Map[Entity, EntitySnapshot]): Unit = {
 
     for ((subscriber, filter) ← subscriptions) {
-      val selection = snapshots.filter(group ⇒ filter.accept(group._1))
+      val selection = snapshots.filter(group ⇒
+        try filter.accept(group._1)
+        catch {
+          case NonFatal(e) =>
+            log.warning("Checking if filter {} accepts snapshot {} failed: {}", filter, group._1, e)
+            false
+        }
+      )
       val tickMetrics = TickMetricSnapshot(lastTick, currentTick, selection)
 
       subscriber ! tickMetrics