Datastar HTTP

ascent-datastar-http makes a zio-http server "an ascent client": render a UI with ascent-html, push patch-elements / patch-signals through the official datastar SDK. Keep the SDK's events { handler { … } } idiom; swap templates for ascent views.

patchSignal

Handler-level assert: the SSE body carries a datastar-patch-signals frame with the named value.

{
  val handler0: Handler[Datastar, Nothing, Any, Unit] = Handler.fromZIO {
    AscentDatastar.patchSignal("count", 42)
  }
  val sse = events(handler0)
  for
    response <- sse(())
    body     <- response.body.asString.orDie
  yield (
    response.status == Status.Ok,
    body.contains("event: datastar-patch-signals"),
    body.contains("\"count\":42"),
  )
}

(true,true,true)

Live counter server

End-to-end against an in-process server (ephemeral port, scoped to the example): POST /increment succeeds while the server is live, then the Scope closes and the port is released.

{
  case class State(count: Ref[Int], pulse: Hub[Unit])

  def pushCount(state: State): ZIO[Datastar, Nothing, Unit] =
    state.count.get.flatMap(c => AscentDatastar.patchSignal("count", c)(using JsonEncoder.int))

  def routes(state: State): Routes[Any, Nothing] =
    Routes(
      Method.GET / "sse" -> events {
        handler { (_: Request) =>
          for
            _      <- pushCount(state)
            stream <- state.pulse.subscribe.map(zio.stream.ZStream.fromQueue(_))
            _      <- stream.mapZIO(_ => pushCount(state)).runDrain
          yield ()
        }
      },
      Method.POST / "increment" -> handler { (_: Request) =>
        (state.count.update(_ + 1) *> state.pulse.publish(()).unit).as(Response.ok)
      },
    ).sandbox

  (for
    count <- Ref.make(0)
    pulse <- Hub.unbounded[Unit]
    state = State(count, pulse)
    port <- Server.install(routes(state))
    base = s"http://localhost:$port"
    st <- Client.batched(Request.post(s"$base/increment", Body.empty)).map(_.status)
  yield st)
    .provideSomeLayer(Server.defaultWith(_.port(0)) ++ Client.default)
    .orDie
}

Ok