sven-lange-last commented on a change in pull request #2878: Streamingly read 
user-logs.
URL: 
https://github.com/apache/incubator-openwhisk/pull/2878#discussion_r152211268
 
 

 ##########
 File path: 
core/invoker/src/main/scala/whisk/core/containerpool/docker/DockerContainer.scala
 ##########
 @@ -224,31 +230,73 @@ class DockerContainer(protected val id: ContainerId,
    *
    * @return a vector of Strings with log lines in our own JSON format
    */
-  def logs(limit: ByteSize, waitForSentinel: Boolean)(implicit transid: 
TransactionId): Future[Vector[String]] = {
-
-    def readLogs(retries: Int): Future[Vector[String]] = {
-      docker
-        .rawContainerLogs(id, logFileOffset)
-        .flatMap { rawLogBytes =>
-          val rawLog =
-            new String(rawLogBytes.array, rawLogBytes.arrayOffset, 
rawLogBytes.position, StandardCharsets.UTF_8)
-          val (isComplete, isTruncated, formattedLogs) = 
processJsonDriverLogContents(rawLog, waitForSentinel, limit)
-
-          if (retries > 0 && !isComplete && !isTruncated) {
-            logging.info(this, s"log cursor advanced but missing sentinel, 
trying $retries more times")
-            akka.pattern.after(filePollInterval, 
as.scheduler)(readLogs(retries - 1))
-          } else {
-            logFileOffset += rawLogBytes.position - rawLogBytes.arrayOffset
-            Future.successful(formattedLogs)
-          }
-        }
-        .andThen {
-          case Failure(e) =>
-            logging.error(this, s"Failed to obtain logs of ${id.asString}: 
${e.getClass} - ${e.getMessage}")
-        }
+  def logs(limit: ByteSize, waitForSentinel: Boolean)(implicit transid: 
TransactionId): Source[ByteString, Any] = {
+    val source = docker
+      .rawContainerLogs(id, logFileOffset.get(), if (waitForSentinel) 
Some(filePollInterval) else None)
+      .via(Framing.delimiter(delimiter, Int.MaxValue))
+      .limitWeighted(limit.toBytes) { obj =>
+        val size = obj.size + 1
+        logFileOffset.addAndGet(size)
+        size
+      }
+      .recover {
+        case _: StreamLimitReachedException =>
+          ByteString(LogLine(Instant.now.toString, "stderr", 
Messages.truncateLogs(limit)).toJson.compactPrint)
+      }
+
+    // Only apply sentinel counting if it is needed
+    val specializedSource = if (waitForSentinel) {
+      source.via(new 
WaitForOccurances(_.containsSlice(DockerContainer.ActivationSentinel), 2))
+    } else {
+      source
     }
 
-    readLogs((waitForLogs / filePollInterval).toInt)
+    specializedSource.takeWithin(waitForLogs)
   }
 
+  /* Delimiter used to split logs */
+  private val delimiter = ByteString("\n")
+}
+
+/**
+ * Completes the stream once the given predicate is fulfilled by N events in 
the stream.
+ *
+ * '''Emits when''' an upstream element arrives and does not fulfill the 
predicate
+ *
+ * '''Backpressures when''' downstream backpressures
+ *
+ * '''Completes when''' upstream completes or predicate is fulfilled N times
+ *
+ * '''Cancels when''' downstream cancels
+ */
+class WaitForOccurances[T](isInEvent: T => Boolean, neededOccurances: Int) 
extends GraphStage[FlowShape[T, T]] {
+  val in = Inlet[T]("WaitForOccurances.in")
+  val out = Outlet[T]("WaitForOccurances.out")
+  override val shape = FlowShape.of(in, out)
+
+  override def createLogic(inheritedAttributes: Attributes): GraphStageLogic =
+    new GraphStageLogic(shape) with InHandler with OutHandler {
+      private var occurancesFound = 0
+
+      override def onPull(): Unit = pull(in)
+
+      override def onPush(): Unit = {
+        val event = grab(in)
 
 Review comment:
   I suggest `element` instead of `event`.

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