https://github.com/rails/rails/pull/25079

4.2.6.rb

begin
  require 'bundler/inline'
rescue LoadError => e
  $stderr.puts 'Bundler version 1.10 or later is required. Please update your Bundler'
  raise e
end

gemfile(true) do
  source 'https://rubygems.org'
  gem 'rails', '4.2.6'
end

require_relative 'app'

app.rb

require 'action_controller/railtie'

class TestApp < Rails::Application
  config.root = File.dirname(__FILE__)
  config.session_store :cookie_store, key: 'cookie_store_key'
  secrets.secret_token    = 'secret_token'
  secrets.secret_key_base = 'secret_key_base'

  config.logger = Logger.new($stdout)
  Rails.logger  = config.logger

  routes.draw do
    get '/' => 'test#halt_and_send_file'
    get '/file' => 'test#file'
    get '/data' => 'test#data'
  end
end

class TestController < ActionController::Base
  include Rails.application.routes.url_helpers

  before_action :halt_and_send_file, only: :file
  before_action :halt_and_send_data, only: :data

  def file
    raise('TestController#file')
  end

  def data
    raise('TestController#data')
  end

  def halt_and_send_file
    send_file Rails.root.join('halt.txt')
  end

  def halt_and_send_data
    send_data "halt!"
  end
end

require 'minitest/autorun'
require 'rack/test'

class BugTest < Minitest::Test
  include Rack::Test::Methods

  def test_send_file_halts_request_cycle
    get '/'
    assert_match 'halt!', last_response.body
  end

  def test_send_file_halts_request_cycle_from_a_before_action
    get '/file'
    assert_match 'halt!', last_response.body
  end

  def test_send_data_halts_request_cycle_from_a_before_action
    get '/data'
    assert_match 'halt!', last_response.body
  end

  private

  def app
    Rails.application
  end
end

edge.rb

begin
  require 'bundler/inline'
rescue LoadError => e
  $stderr.puts 'Bundler version 1.10 or later is required. Please update your Bundler'
  raise e
end

gemfile(true) do
  source 'https://rubygems.org'
  gem 'rails', github: 'rails/rails'
end

require_relative 'app'

halt.txt

halt!

patched.rb

begin
  require 'bundler/inline'
rescue LoadError => e
  $stderr.puts 'Bundler version 1.10 or later is required. Please update your Bundler'
  raise e
end

gemfile(true) do
  source 'https://rubygems.org'
  gem 'rails', github: 'jeffkreeftmeijer/rails', branch: 'send_file-halts-request-cycle'
end

require_relative 'app'