Does raise with Plug.Exception still generate stack traces?

Questions / Help
1

In a newly generated phoenix project every resource is fetched with a “bang”

def show(conn, %{"id" => resource_id}) do
  resource = Resource.get!(resource_id)
  render(conn, "show.html", resource: resource)
end

where the Ecto.NoResultsError exception is then dealt with by Plug.Exception or something like that.

What I want to know is whether any other relatively expensive operation gets executed (like getting the stack trace) in the “not found” scenario.

2

And whether (if it does generate the stack trace) this controller would be any faster when lots of requests to non-existent resources are being made

def show(conn, %{"id" => resource_id}) do
  case Resource.get(resource_id) do
    nil -> render(conn, MyApp.ErrorView, "404.html")
    resource -> render(conn, "show.html", resource: resource)
  end
end

I guess I can just test it …

3

It seems like every controller is being called inside a try block? And then __catch__ seems to be calling System.stacktrace?

Is that correct? Does phoenix also use this error handler module? Or only during dev?

4

Phoenix seems to be using

which does almost the same thing. So the stack trace is still being generated, even though not used (in the case of ecto errors)?

5

Finally, I wonder if an authorization library based on exceptions would be much slower than something like https://github.com/schrockwell/bodyguard, because I want to do this

# in controller
def create(conn, %{"resource" => resource_params}, current_user) do
  case Resource.create(resource_params, user: current_user) do
    {:ok, resource} -> redirect(conn, to: resource_path(conn, :show, resource))
    {:error, changeset} -> render(conn, "new.html", changeset: changeset)
  end
end

# in resource context
def create(params, user: user) do
  # raises an exception that has a Plug.Exception implementation
  authorize!(:create, user) 
  
  %Resource{owner_id: user.id}
  |> Resource.changeset(params)
  |> Repo.insert()
end

and move auth logic into the context like it’s done in http://trailblazer.to/ …