class Rack::ShowExceptions

def call(env)
  @app.call(env)
rescue StandardError, LoadError, SyntaxError => e
  exception_string = dump_exception(e)
  env[RACK_ERRORS].puts(exception_string)
  env[RACK_ERRORS].flush
  if accepts_html?(env)
    content_type = "text/html"
    body = pretty(env, e)
  else
    content_type = "text/plain"
    body = exception_string
  end
  [
    500,
    {
      CONTENT_TYPE => content_type,
      CONTENT_LENGTH => body.bytesize.to_s,
    },
    [body],
  ]
end