akka.stream.BufferOverflowException: Buffer overflow (max capacity was: 100)!

[JaroslavTulach]

• Following has appeared in a log that starts with Initializing main module of the Language Server from [2026.1.1-nightly.2026.2.10...
• is there an easy way to configure Akka to not throw this error?

[ERROR] [2026-02-10T09:20:53.004] [akka.actor.ActorSystemImpl] Websocket handler failed with Buffer overflow (max capacity was: 100)!
akka.stream.BufferOverflowException: Buffer overflow (max capacity was: 100)!
	at akka.stream.impl.ActorRefSource$$anon$1.$anonfun$ref$1(ActorRefSource.scala:115)
	at akka.stream.impl.ActorRefSource$$anon$1.$anonfun$ref$1$adapted(ActorRefSource.scala:55)
	at akka.stream.stage.GraphStageLogic$StageActor.internalReceive(GraphStage.scala:240)
	at akka.stream.stage.GraphStageLogic$StageActor.$anonfun$callback$1(GraphStage.scala:201)
	at akka.stream.stage.GraphStageLogic$StageActor.$anonfun$callback$1$adapted(GraphStage.scala:201)
	at akka.stream.impl.fusing.GraphInterpreter.runAsyncInput(GraphInterpreter.scala:467)
	at akka.stream.impl.fusing.GraphInterpreterShell$AsyncInput.execute(ActorGraphInterpreter.scala:517)
	at akka.stream.impl.fusing.GraphInterpreterShell.processEvent(ActorGraphInterpreter.scala:625)
	at akka.stream.impl.fusing.ActorGraphInterpreter.akka$stream$impl$fusing$ActorGraphInterpreter$$processEvent(ActorGraphInterpreter.scala:800)
	at akka.stream.impl.fusing.ActorGraphInterpreter$$anonfun$receive$1.applyOrElse(ActorGraphInterpreter.scala:818)
	at akka.actor.Actor.aroundReceive(Actor.scala:537)
	at akka.actor.Actor.aroundReceive$(Actor.scala:535)
	at akka.stream.impl.fusing.ActorGraphInterpreter.aroundReceive(ActorGraphInterpreter.scala:716)
	at akka.actor.ActorCell.receiveMessage(ActorCell.scala:579)
	at akka.actor.ActorCell.invoke(ActorCell.scala:547)
	at akka.dispatch.Mailbox.processMailbox(Mailbox.scala:270)
	at akka.dispatch.Mailbox.run(Mailbox.scala:231)
	at akka.dispatch.Mailbox.exec(Mailbox.scala:243)
	at java.base@25.0.1/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:511)
	at java.base@25.0.1/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1450)
	at java.base@25.0.1/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:2019)
	at java.base@25.0.1/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:187)
	at org.graalvm.nativeimage.builder/com.oracle.svm.core.thread.PlatformThreads.threadStartRoutine(PlatformThreads.java:832)
	at org.graalvm.nativeimage.builder/com.oracle.svm.core.thread.PlatformThreads.threadStartRoutine(PlatformThreads.java:808)
[ERROR] [2026-02-10T09:20:53.112] [org.enso.languageserver.protocol.binary.BinaryConnectionController] An error occurred during processing web socket connection [127.0.0.1:56741].
akka.http.scaladsl.model.ws.PeerClosedConnectionException: Peer closed connection with code 1011 'internal error'
	at akka.http.impl.engine.ws.WebSocket$PrepareForUserHandler$$anon$1.onPush(WebSocket.scala:116)
	at akka.stream.impl.fusing.GraphInterpreter.processPush(GraphInterpreter.scala:542)
	at akka.stream.impl.fusing.GraphInterpreter.processEvent(GraphInterpreter.scala:496)
	at akka.stream.impl.fusing.GraphInterpreter.execute(GraphInterpreter.scala:390)
	at akka.stream.impl.fusing.GraphInterpreterShell.runBatch(ActorGraphInterpreter.scala:650)
	at akka.stream.impl.fusing.GraphInterpreterShell$AsyncInput.execute(ActorGraphInterpreter.scala:521)
	at akka.stream.impl.fusing.GraphInterpreterShell.processEvent(ActorGraphInterpreter.scala:625)
	at akka.stream.impl.fusing.ActorGraphInterpreter.akka$stream$impl$fusing$ActorGraphInterpreter$$processEvent(ActorGraphInterpreter.scala:800)
	at akka.stream.impl.fusing.ActorGraphInterpreter.akka$stream$impl$fusing$ActorGraphInterpreter$$shortCircuitBatch(ActorGraphInterpreter.scala:787)
	at akka.stream.impl.fusing.ActorGraphInterpreter$$anonfun$receive$1.applyOrElse(ActorGraphInterpreter.scala:819)
	at akka.actor.Actor.aroundReceive(Actor.scala:537)
	at akka.actor.Actor.aroundReceive$(Actor.scala:535)
	at akka.stream.impl.fusing.ActorGraphInterpreter.aroundReceive(ActorGraphInterpreter.scala:716)
	at akka.actor.ActorCell.receiveMessage(ActorCell.scala:579)
	at akka.actor.ActorCell.invoke(ActorCell.scala:547)
	at akka.dispatch.Mailbox.processMailbox(Mailbox.scala:270)
	at akka.dispatch.Mailbox.run(Mailbox.scala:231)
	at akka.dispatch.Mailbox.exec(Mailbox.scala:243)
	at java.base@25.0.1/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:511)
	at java.base@25.0.1/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1450)
	at java.base@25.0.1/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:2019)
	at java.base@25.0.1/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:187)
	at org.graalvm.nativeimage.builder/com.oracle.svm.core.thread.PlatformThreads.threadStartRoutine(PlatformThreads.java:832)
	at org.graalvm.nativeimage.builder/com.oracle.svm.core.thread.PlatformThreads.threadStartRoutine(PlatformThreads.java:808)

[JaroslavTulach]

• the exception is throw from here:
• https://github.com/akka/akka-core/blob/e1b50a23547c6946d8f4c860333b3c6b575f277d/akka-stream/src/main/scala/akka/stream/impl/g.scala#L115

                  case s: Fail =>
                    log.log(
                      s.logLevel,
                      "Failing because buffer is full and overflowStrategy is: [Fail] in stream [{}]",
                      name)
                    val bufferOverflowException =
                      BufferOverflowException(s"Buffer overflow (max capacity was: $maxBuffer)!")
                    failStage(bufferOverflowException)

• there is a configuration option maxBuffer
  • increasing it might mitigate this problem
• the current size is 100 as set by Increase Binary WebSocket Buffer #1923 changing it should be easy
• the config seems to be set at

"main"
	at org.enso.languageserver.http.server.BinaryWebSocketServer.<init>(BinaryWebSocketServer.scala:51)
	at org.enso.languageserver.boot.MainModule.<init>(MainModule.scala:529)
	at org.enso.languageserver.boot.LanguageServerComponent.start(LanguageServerComponent.scala:44)
	at org.enso.languageserver.boot.LanguageServerApp$.run(LanguageServerApp.scala:33)
	at org.enso.languageserver.boot.LanguageServerApp.run(LanguageServerApp.scala)
	at org.enso.languageserver.boot.LanguageServerRunner.runLanguageServer(LanguageServerRunner.java:25)
	at org.enso.runner.common.LanguageServerApi.launchLanguageServer(LanguageServerApi.java:34)
	at org.enso.runner.Main.handleLaunch(Main.java:1718)
	at org.enso.runner.Main.launch(Main.java:1654)
	at org.enso.runner.Main.main(Main.java:1145)

• https://github.com/enso-org/enso/blame/eb374645d260debecbceeea4e687f98eda623760/engine/language-server/src/main/scala/org/enso/languageserver/boot/MainModule.scala#L524

[hubertp]

Increased as part of #14740. GUI should probably redesign communication so that it doesn't flood LS with requests on startup, or LS could pick a different strategy with buffer.