Phoenix Web Module

StarView controllers should use a dedicated :star_view section in your Phoenix web module. Keep it near the existing controller section so controller-style imports stay grouped together.

def star_view do
  quote do
    use Phoenix.Controller, formats: [:html, :json]
    use StarView
    use Phoenix.Component

    use Gettext, backend: MyAppWeb.Gettext

    import Phoenix.Component, except: [assign: 3]
    import Plug.Conn

    alias MyAppWeb.Components.StarView.Layout

    plug :put_root_layout, false

    unquote(verified_routes())
  end
end

The installer also generates MyAppWeb.Components.StarView.Layout. put_root_layout/2 disables Phoenix's root layout for StarView controllers, and Layout.app/1 emits the full document plus the initial Datastar signals for the page.

Then use that section from a controller:

defmodule MyAppWeb.CounterController do
  use MyAppWeb, :star_view

  @impl StarView
  def mount(conn, _params) do
    signal(conn, :count, 0)
  end

  @impl StarView
  def render(assigns) do
    ~H"""
    <Layout.app conn={@conn}>
      <button data-on:click={post("increment")}>+</button>
      <span data-text="$count">{@count}</span>
    </Layout.app>
    """
  end

  @impl StarView
  def handle_event("increment", signals, conn) do
    signal(conn, :count, Map.get(signals, "count", 0) + 1)
  end
end

Router

Add the dispatch route inside your browser pipeline:

pipeline :browser do
  # ...
  plug StarView.Plug.RenameCsrfParam
  plug :protect_from_forgery
  # ...
end

scope "/", MyAppWeb do
  pipe_through :browser

  get "/counter", CounterController, :mount
  post "/ds/:module/:event", StarView.Dispatch, [], alias: false
end

StarView.Dispatch decodes the target controller from the Datastar action, verifies that it used use StarView, starts the SSE response, and calls handle_event/3. The alias: false route option keeps Phoenix from resolving the dispatch plug as MyAppWeb.StarView.Dispatch inside the scoped router block. StarView.Plug.RenameCsrfParam must run before :protect_from_forgery so Datastar's csrf signal is available as Phoenix's _csrf_token parameter.