efekahraman / akka-streams-session-window

Session Window extension for Akka Streams

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Session Window extension for Akka Streams

This library provides session windowing for the Akka Streams.

Session windowing helps to identify periods of activity. This library uses a static idle period and favors the processing time for events to distinguish the periods. More information can be found in the related blog post.

Defines a FlowShape with same input and output types as GraphStage[FlowShape[T, T]]. Requires 3 parameters:

  • gap: Idle time to determine particular activity as a session.
  • maxSize: Max elements to hold in session buffer.
  • overflowStrategy: Strategy to define what happens when new elements arrive and buffer is full. Can be one of:
    • DropOldest: Drops the oldest message in the buffer and adds the new one.
    • DropNewest: Drops the new message.
    • FailStage: Fails the stream with SessionOverflowException.


Current version is built with Akka Streams 2.5.16.

Cross compiled with Scala 2.12 and 2.11.


libraryDependencies += "io.github.efekahraman" %% "akka-stream-session-window" % "0.1.0"


Below snippets show how to create a session window.


import akka.stream._
import akka.stream.scaladsl._

import io.github.efekahraman.akka.stream.DropOldest
import io.github.efekahraman.akka.stream.scaladsl.SessionWindow

import scala.concurrent.duration._

val source: Source[String, NotUsed] = ???
val sessionWindow: GraphStage[FlowShape[String, String]] = SessionWindow(10 second, 5, DropOldest)

val windowedSource = source.via(sessionWindow)
// ...


import akka.stream.*;
import akka.stream.javadsl.*;

import io.github.efekahraman.akka.stream.javadsl.*;

import java.time.Duration;

final Source<String, NotUsed> source = // ...
final GraphStage<FlowShape<String, String>> sessionWindow = SessionWindow.apply(Duration.ofSeconds(10), 5, SessionOverflowStrategy.dropOldest());

final Source<ReadResult, NotUsed> windowedSource = amqpSource.via(window);


Code is available under the Apache 2 license, available at https://opensource.org/licenses/Apache-2.0.