class ActionDispatch::ShowExceptions

middleware catches the exceptions and returns a failsafe response.
correct status code. If any exception happens inside the exceptions app, this
`“pass”‘, this middleware will send an empty response as a result with the
If the application returns a response with the `X-Cascade` header set to
`config.exceptions_app`, which defaults to ActionDispatch::PublicExceptions.
In Rails applications, the exceptions app can be configured with
`PATH_INFO` to the exception status code, and call the Rack app.
store the exception in `env`, rewrite the
`ShowExceptions`. Every time there is an exception, `ShowExceptions` will
The exceptions app should be passed as a parameter on initialization of
exceptions app that will wrap it in a format for the end user.
This middleware rescues any exception returned by the application and calls an
# Action Dispatch ShowExceptions

def call(env) 

def call(env)
  @app.call(env)
rescue Exception => exception
  request = ActionDispatch::Request.new env
  backtrace_cleaner = request.get_header("action_dispatch.backtrace_cleaner")
  wrapper = ExceptionWrapper.new(backtrace_cleaner, exception)
  request.set_header "action_dispatch.exception", wrapper.unwrapped_exception
  request.set_header "action_dispatch.report_exception", !wrapper.rescue_response?
  if wrapper.show?(request)
    render_exception(request.dup, wrapper)
  else
    raise exception
  end
end

def fallback_to_html_format_if_invalid_mime_type(request) 

def fallback_to_html_format_if_invalid_mime_type(request)
  # If the MIME type for the request is invalid then the @exceptions_app may not
  # be able to handle it. To make it easier to handle, we switch to HTML.
  begin
    request.content_mime_type
  rescue ActionDispatch::Http::MimeNegotiation::InvalidType
    request.set_header "CONTENT_TYPE", "text/html"
  end
  begin
    request.formats
  rescue ActionDispatch::Http::MimeNegotiation::InvalidType
    request.set_header "HTTP_ACCEPT", "text/html"
  end
end

def initialize(app, exceptions_app) 

def initialize(app, exceptions_app)
  @app = app
  @exceptions_app = exceptions_app
end

def pass_response(status) 

def pass_response(status)
  [status, { Rack::CONTENT_TYPE => "text/html; charset=#{Response.default_charset}",
            Rack::CONTENT_LENGTH => "0" }, []]
end

def render_exception(request, wrapper) 

def render_exception(request, wrapper)
  status = wrapper.status_code
  request.set_header "action_dispatch.original_path", request.path_info
  request.set_header "action_dispatch.original_request_method", request.raw_request_method
  fallback_to_html_format_if_invalid_mime_type(request)
  request.path_info = "/#{status}"
  request.request_method = "GET"
  response = @exceptions_app.call(request.env)
  response[1][Constants::X_CASCADE] == "pass" ? pass_response(status) : response
rescue Exception => failsafe_error
  $stderr.puts "Error during failsafe response: #{failsafe_error}\n  #{failsafe_error.backtrace * "\n  "}"
  [500, { Rack::CONTENT_TYPE => "text/plain; charset=utf-8" },
    ["500 Internal Server Error\n" \
    "If you are the administrator of this website, then please read this web " \
    "application's log file and/or the web server's log file to find out what " \
    "went wrong."]]
end