class ActionDispatch::ShowExceptions

This middleware rescues any exception returned by the application and calls an exceptions app that will wrap it in a format for the end user.

The exceptions app should be passed as parameter on initialization of ShowExceptions. Every time there is an exception, ShowExceptions will store the exception in env, rewrite the PATH_INFO to the exception status code and call the Rack app.

If the application returns a “X-Cascade” pass response, this middleware will send an empty response as result with the correct status code. If any exception happens inside the exceptions app, this middleware catches the exceptions and returns a failsafe response.

Public Class Methods

new(app, exceptions_app) click to toggle source
# File lib/action_dispatch/middleware/show_exceptions.rb, line 18
def initialize(app, exceptions_app)
  @app = app
  @exceptions_app = exceptions_app
end

Public Instance Methods

call(env) click to toggle source
# File lib/action_dispatch/middleware/show_exceptions.rb, line 23
def call(env)
  request = ActionDispatch::Request.new env
  @app.call(env)
rescue Exception => exception
  if request.show_exceptions?
    render_exception(request, exception)
  else
    raise exception
  end
end

Private Instance Methods

fallback_to_html_format_if_invalid_mime_type(request) click to toggle source
# File lib/action_dispatch/middleware/show_exceptions.rb, line 57
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.
  request.formats
rescue ActionDispatch::Http::MimeNegotiation::InvalidType
  request.set_header "HTTP_ACCEPT", "text/html"
end
pass_response(status) click to toggle source
# File lib/action_dispatch/middleware/show_exceptions.rb, line 66
def pass_response(status)
  [status, { "Content-Type" => "text/html; charset=#{Response.default_charset}", "Content-Length" => "0" }, []]
end
render_exception(request, exception) click to toggle source
# File lib/action_dispatch/middleware/show_exceptions.rb, line 35
def render_exception(request, exception)
  backtrace_cleaner = request.get_header "action_dispatch.backtrace_cleaner"
  wrapper = ExceptionWrapper.new(backtrace_cleaner, exception)
  status  = wrapper.status_code
  request.set_header "action_dispatch.exception", wrapper.unwrapped_exception
  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]["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, { "Content-Type" => "text/plain" },
    ["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