Halt!

halt! sets the current context body, plain-text content type, and status code. It is most useful in a before filter, where setting context content prevents the controller action from running.

File: src/controllers/admin_controller.cr — place the filter and action inside AdminController.

class AdminController < ApplicationController
  before_action do
    only :index do
      halt!(403, "Forbidden") unless session[:admin_id]?
    end
  end

  def index
    render("index.ecr")
  end
end

halt! marks the request context; it does not raise an exception that escapes ordinary Crystal control flow. Inside an action, return an explicit response when later expressions must not run.

File: the controller that owns show, for example src/controllers/admin_controller.cr — replace that action body.

def show
  unless authorized?
    return set_response(
      body: "Forbidden",
      status_code: 403,
      content_type: "text/plain"
    )
  end

  render("show.ecr")
end

Amber's redirect helper sets the Location header and uses the same context response mechanism.

File: a controller action under src/controllers/ — return this expression at the point where request processing should redirect.

redirect_to location: "/login", status: 302

The V1 Slang example and its claim that halt! interrupts any action like an exception are not copied into V2.