eval: add counter for unknown messages

This will get inremented when we get messages from the
LWC API service and do not recognize the id.

atlas-eval/src/main/scala/com/netflix/atlas/eval/stream/LwcToAggrDatapoint.scala

@@ -37,6 +37,8 @@ import com.netflix.atlas.eval.model.LwcSubscription
 private[stream] class LwcToAggrDatapoint(context: StreamContext)
     extends GraphStage[FlowShape[List[AnyRef], List[AggrDatapoint]]] {
 
+  private val unknown = context.registry.counter("atlas.eval.unknownMessages")
+
   private val in = Inlet[List[AnyRef]]("LwcToAggrDatapoint.in")
   private val out = Outlet[List[AggrDatapoint]]("LwcToAggrDatapoint.out")
 
@@ -75,18 +77,23 @@ private[stream] class LwcToAggrDatapoint(context: StreamContext)
       }
 
       private def pushDatapoint(dp: LwcDatapoint): Option[AggrDatapoint] = {
-        state.get(dp.id).map { sub =>
-          // TODO, put in source, for now make it random to avoid dedup
-          nextSource += 1
-          val expr = sub.expr
-          val step = sub.step
-          AggrDatapoint(dp.timestamp, step, expr, nextSource.toString, dp.tags, dp.value)
+        state.get(dp.id) match {
+          case Some(sub) =>
+            // TODO, put in source, for now make it random to avoid dedup
+            nextSource += 1
+            val expr = sub.expr
+            val step = sub.step
+            Some(AggrDatapoint(dp.timestamp, step, expr, nextSource.toString, dp.tags, dp.value))
+          case None =>
+            unknown.increment()
+            None
         }
       }
 
       private def pushDiagnosticMessage(diagMsg: LwcDiagnosticMessage): Unit = {
-        state.get(diagMsg.id).foreach { sub =>
-          context.log(sub.expr, diagMsg.message)
+        state.get(diagMsg.id) match {
+          case Some(sub) => context.log(sub.expr, diagMsg.message)
+          case None      => unknown.increment()
         }
       }