when I run
gradlew run

I see the following error in console:

[ERROR] [02/02/2018 13:26:31.219] [Server-akka.actor.default-dispatcher-3] [akka://Server/user/StreamSupervisor-0/flow-3-0-unnamed] Error in stage [akka.http.impl.engine.server.HttpServerBluePrint$ProtocolSwitchStage@7abfcf5d]: The path: 'data' does not exist
java.lang.IllegalArgumentException: The path: 'data' does not exist
        at akka.stream.alpakka.file.javadsl.DirectoryChangesSource.createLogic(DirectoryChangesSource.java:71)

The browser shows:
[13:26:31] WS connection opened [13:26:31] WS connection closed with code: 1006

I see ./build/resources/main/data exists...(data directory did not exist on clone, I created it under ./src/main/resources/data).

What is the correct location for the data directory -- the instructions just say to copy a csv file into it

Looks like this code will materialize the full stream for each new web socket client, meaning duplicates of each processing step.

It can be expensive in real applications.

Is there a way to have just 1 stream and broadcast results to all web socket clients?