Rails middleware to provide information about errors during requests

application.rb

module MyApp
  class Application < Rails::Application
    if Rails.env == 'test'
      require 'diagnostic'
      config.middleware.use(MyApp::DiagnosticMiddleware)
    end
  end
end

diagnostic.rb

module MyApp
  class DiagnosticMiddleware
    FILENAME = 'diagnostic.txt'

    def initialize(app)
      @app = app
    end

    def call(env)
      return @app.call(env)
    rescue StandardError => e
      trace = e.backtrace.select{ |l|l.start_with?(Rails.root.to_s) }.join("\n    ")
      msg = "#{e.class}\n#{e.message}\n#{trace}\n"
      File.open(FILENAME, 'a') { |f| f.write msg }
      raise e
    end
  end
end

Thanks, very useful. I just print to stdout:

module MyApp
  class DiagnosticMiddleware

    def initialize(app)
      @app = app
    end

    def call(env)
      return @app.call(env)
    rescue StandardError => error
      puts error.message
      puts error.backtrace
      raise error
    end
  end
end

Proved helpful in a case of "Internal server error" while running a spec which did not provide much detail either on the page or in the test log file.

Thanks a bunch !

the same here, i would also like to have it as a spec, so it does not work for me.

It didn't work for me until I changed it to rescue Exception instead of StandardError.

application.rb should be:

if Rails.env == 'test'
  require File.expand_path('../diagnostic', __FILE__)
  config.middleware.use(MyApp::DiagnosticMiddleware)
end

I happened to handle this a little bit differently -- by detecting RoutingErrors on image paths: https://gist.github.com/mcmire/68cd9c74ba765a2d5dfb14abf58409aa