WebSocket server in http4s that forwards messages from each client to the others

ws.scala

//> using dep org.http4s::http4s-ember-server::0.23.28
import cats.effect.IO
import cats.effect.IOApp
import cats.effect.std.UUIDGen
import cats.syntax.all.*
import fs2.concurrent.Topic
import org.http4s.HttpApp
import org.http4s.ember.server.EmberServerBuilder
import org.http4s.websocket.WebSocketFrame

import java.util.UUID

object ws extends IOApp.Simple:
  def run: IO[Unit] =
    val srv =
      for
        messages <- Topic[IO, (UUID, WebSocketFrame)].toResource
        _ <- EmberServerBuilder
          .default[IO]
          .withHttpWebSocketApp: builder =>
            HttpApp.liftF[IO]:
              builder.build: input =>
                fs2.Stream
                  .eval(UUIDGen[IO].randomUUID)
                  .flatMap { myId =>
                    input
                      .tupleLeft(myId)
                      .through(messages.publish)
                      .mergeHaltBoth(
                        messages.subscribeUnbounded
                          .filterNot(_._1 == myId)
                          .map(_._2)
                      )
                  }
          .build
      yield ()
    srv.useForever