Code Quality Rank: L5
Monthly Downloads: 17,743
Programming language: Ruby
License: MIT License
Tags: Error Handling     Projects    
Latest version: v0.8.0.0

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[Exception Handler](readme/title.jpg "Exception Handler Logo")

<!-- Intro --> ExceptionHandler is presently the MOST POPULAR exceptions gem for CUSTOM Rails error pages. With 290,000+ downloads, it is the only gem to provide custom 400/500 exception pages for Rails 5 & 6 Current (August 2018)

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<!-- Navigation --> ๐Ÿ“ Introduction - โš ๏ธ Installation - ๐Ÿ”ง Configuration - โ˜Ž๏ธ Support - โญ Changelog

<!-- Introduction --> ๐Ÿ“ Introduction

ExceptionHandler replaces Rails' default error pages with dynamic views. It does this by injecting config.exceptions_app with our controller - allowing us to populate erroneous responses with our own HTML. To understand how this works, you need to appreciate how Rails handles errors: Rails uses ActionDispatch::ShowExceptions (above) to generate error responses. Because web browsers (Rails is a web framework) can only interpret HTTP responses, Ruby/Rails exceptions have to be translated into something a browser can read. This is done by calling the above middleware. -- As highlighted, an HTTP response is built independent of the Rails stack. This includes assigning an HTTP status code and HTML response body. It's the response body which ExceptionHandler is designed to override.

<!-- Sep -->

<!-- Installation --> โš ๏ธ Installation

๐Ÿ’Ž RubyGems (Code) | ๐Ÿ’ป Medium (Tutorial) # Gemfile gem 'exception_handler', '~>' Because ExceptionHandler is built around a Rails engine, there is nothing to be done to get it working in production. Installing the Gem should translate your production 4xx/5xx error pages into dynamic views. Environments other than production (development/staging) required the dev variable to be true.

<!-- Sep -->

<!-- configuration --> ๐Ÿ”ง Configuration

๐Ÿ“ Config    ๐Ÿ’ป Dev    ๐Ÿ’พ Database    โœ‰๏ธ Email    ๐Ÿ‘“ Views    ๐Ÿ’ฌ Locales    ๐Ÿ“‹ Layouts    โ›”๏ธ Custom Exceptions

<!-- Config -->

The ONLY thing you need to manage ExceptionHandler is its config settings.

Whilst the gem works out of the box (without any configuration), if you want to manage the layouts, email, dev or the database, you'll need to set the appropriate values in the config hash.

This is done in config/application.rb or config/environments/[env].rb โ†ด

# config/application.rb

module YourApp
  class Application < Rails::Application

    # => This is an example of ALL available config options
    # => You're able to see exactly how it works here:
    # => https://github.com/richpeck/exception_handler/blob/master/lib/exception_handler/config.rb

    # => Config hash (no initializer required)
    config.exception_handler = {
      dev:        nil, # allows you to turn ExceptionHandler "on" in development
      db:         nil, # allocates a "table name" into which exceptions are saved (defaults to nil)
      email:      nil, # sends exception emails to a listed email (string // "[email protected]")

      # Custom Exceptions
      custom_exceptions: {
        #'ActionController::RoutingError' => :not_found # => example

      # On default 5xx error page, social media links included
      social: {        
        facebook: nil, # Facebook page name   
        twitter:  nil, # Twitter handle  
        youtube:  nil, # Youtube channel name / ID
        linkedin: nil, # LinkedIn name
        fusion:   nil  # FL Fusion handle

      # This is an entirely NEW structure for the "layouts" area
      # You're able to define layouts, notifications etc โ†ด

      # All keys interpolated as strings, so you can use symbols, strings or integers where necessary
      exceptions: {

        :all => {
          layout: "exception", # define layout
          notification: true, # (false by default)
          deliver: #something here to control the type of response
        :4xx => {
          layout: nil, # define layout
          notification: true, # (false by default)
          deliver: #something here to control the type of response    
        :5xx => {
          layout: "exception", # define layout
          notification: true, # (false by default)
          deliver: #something here to control the type of response    
        500 => {
          layout: "exception", # define layout
          notification: true, # (false by default)
          deliver: #something here to control the type of response    

        # This is the old structure
        # Still works but will be deprecated in future versions

        501 => "exception",
        502 => "exception",
        503 => "exception",
        504 => "exception",
        505 => "exception",
        507 => "exception",
        510 => "exception"


For a full retinue of the available options, you'll be best looking at the config file itself.


If using an engine, you DON'T need an initializer:

# lib/engine.rb
module YourModule
  class Engine < Rails::Engine

    # => ExceptionHandler
    # => Works in and out of an initializer
    config.exception_handler = {
      dev: nil, # => this will not load the gem in development
      db:  true # => this will use the :errors table to store exceptions

The best thing about using a config options block is that you are able to only define the options that you require.

If you have particular options you only wish to run in staging, or have single options for production etc, this setup gives you the ability to manage it properly...

<!-- Dev --> ๐Ÿ’ป Dev

As explained, ExceptionHandler does not work in development by default.

This is because it overrides the exceptions_app middleware hook - which is only invoked in production or staging.

To get it working in development, you need to override the config.consider_all_requests_local setting (a standard component of Rails) - setting it to "false" โ†ด

This is normally done by changing the setting in your Rails config files. However, to make the process simpler for ExceptionHandler- we've added a dev option which allows you to override the hook through the context of the gem...

# config/application.rb
config.exception_handler = { dev: true }

This disables config.consider_all_requests_local, making Rails behave as it would in production.

Whilst simple, it's not recommended for extended use. Very good for testing new ideas etc.

<!-- DB --> ๐Ÿ’พ DB

To save exceptions to your database, you're able to set the db option.

Because we use a controller to manage the underlying way the system works, we're able to invoke the likes of a model with other functionality.

Ths is done automatically with the latest version of ExceptionHandler.

To do this, once you've populated the option with either true or a string, run rails db:migrate from your console.

Our new migration system will automatically run the migration.

# config/application.rb
config.exception_handler = { db: true }

This enables ActiveRecord::Base on the [Exception](app/models/exception_handler/exception.rb) class, allowing us to save to the database.

In order for this to work, your db needs the correct table.

<!-- Email --> โœ‰๏ธ Email

ExceptionHandler also sends email notifications.

If you want to receive emails whenever your application raises an error, you can do so by adding your email to the config:

# config/application.rb
config.exception_handler = {
  email: "[email protected]"

Please Note this requires ActionMailer. If you don't have any outbound SMTP server, SendGrid is free.

From version, you're able to define whether email notifications are sent on a per-error basis:

# config/application.rb
config.exception_handlder = {

  # This has to be present for any "notification" declarations to work
  # Defaults to 'false'
  email: "[email protected]",

  # Each status code in the new "exceptions" block allows us to define whether email notifications are sent
  exceptions: {
    :all => { notification: true },
    :50x => { notification: false },
    500 =>  { notification: false }

<!-- Views --> ๐Ÿ‘“ Views

What most people want out of the view is to change the way it looks. This can be done without changing the "view" itself.

To better explain, if ExceptionsController is invoked (by exceptions_app), it has ONE method (show).

This method calls the show view, which is entirely dependent on the locales for content & the layout for the look.

This means that if you wish to change how the view "looks" - you're either going to want to change your layout or the locales. There is NO reason to change the show view itself - it's succinct and entirely modular. Whilst you're definitely at liberty to change it, you'll just be making the issue more complicated than it needs to be.


We've also included a number of routes which shows in [dev](dev) mode (allowing you to test):

<!-- Locales --> ๐Ÿ’ฌ Locales

Locales are used to create interchangeable text (translations/internationalization).


In ExceptionHandler, it provides the wording for each type of error code.

By default, the English name of the error is used ("404" will appear as "Not Found") - if you want to create custom messages, you're able to do so by referencing the error's "status_code" within your locales file:

# config/locales/en.yml
    not_found:              "Your message here" # -> 404 page
    unauthorized:           "You need to login to continue"
    internal_server_error:  "This is a test to show the %{status} of the error"

You get access to %{message} and %{status}, both inferring from an @exception object we invoke in the controller...

  • %{message} is the error's actual message ("XYZ file could not be shown")
  • %{status} is the error's status code ("Internal Server Error")


By default, only internal_server_error is customized by the gem:

# config/locales/en.yml
    internal_server_error: "<strong>%{status} Error</strong> %{message}"

<!-- Layouts --> ๐Ÿ“‹ Layouts

The most attractive feature of ExceptionHandler (for most) is its ability to manage layouts for HTTP status.


The reason for this is due to the way in which Rails works โ†’ the "layout" is a "wrapper" for the returned HTML (the "styling" of a page). If you have no layout, it will render the "view" HTML and nothing else.

This means if you want to change the "look" of a Rails action, you simply have to be able to change the layout. You should not change the view at all.

To this end, ExceptionHandler has been designed around providing a [SINGLE VIEW](app/controllers/exception_handler/exceptions_controller.rb#L44) for exceptions. This view does not need to change (although you're welcome to use a generator to do so) - the key is the layout that's assigned...

  • 4xx errors are given a nil layout (by default) (inherits from ApplicationController in your main app)
  • 5xx errors are assigned our own [exception](app/views/layouts/exception.html.erb) layout:
# config/application.rb
config.exception_handler = {

  # The new syntax allows us to assign different values to each HTTP status code
  # At the moment, only 'layout' & 'notification' are supported
  # We plan to include several more in the future...

  exceptions: {
    all: { layout: nil } # -> this will inherit from ApplicationController's layout

The layout system has changed between [](releases/tag/v0.7.7.0) and [](releases/tag/v0.8.0.0).

Building on the former's adoption of HTTP status-centric layouts, it is now the case that we have the all, 5xx and 4xx options - allowing us to manage the layouts for blocks of HTTP errors respectively:

# config/application.rb
config.exception_handler = {

  # Old (still works)
  # No "all" / "4xx"/"5xx" options
  layouts: {
    500 => 'exception',
    501 => 'exception'

  # New
  exceptions: {
    :all => { layout: 'exception' },
    :4xx => { layout: 'exception' },
    :5xx => { layout: 'exception' }, # -> this overrides the :all declaration
    500  => { layout: nil } # -> this overrides the 5xx declaration

We've bundled the [exception](app/views/layouts/exception.html.erb) layout for 5xx errors because since these denote internal server errors, it's best to isolate the view system as much as possible. Whilst you're at liberty to change it, we've found it sufficient for most use-cases.

<!-- Custom Exceptions --> โ›”๏ธ Custom Exceptions

As mentioned, Rails' primary role is to convert Ruby exceptions into HTTP errors.

Part of this process involves mapping Ruby/Rails exceptions to the equivalent HTTP status code.

This is done with config.action_dispatch.rescue_responses.

Whilst this works well, it may be the case that you want to map your own classes to an HTTP status code (default is Internal Server Error).

If you wanted to keep this functionality inside ExceptionHandler, you're able to do it as follows:

# config/application.rb
config.exception_handler = {
  custom_exceptions: {
    'CustomClass::Exception' => :not_found

Alternatively, you're able to still do it with the default Rails behaviour:

# config/application.rb
config.action_dispatch.rescue_responses = { 'CustomClass::Exception' => :not_found }

<!-- Generators --> ๐Ÿ’ผ Generators

If you want to edit the controller, views, model or assets, you're able to invoke them in your own application.

This is done - as with other gems - with a single generator which takes a series of arguments:

rails g exception_handler:views
rails g exception_handler:views -v views
rails g exception_handler:views -v controllers
rails g exception_handler:views -v models
rails g exception_handler:views -v assets
rails g exception_handler:views -v views controllers models assets

If you don't include any switches, this will copy all ExceptionHandler's folders put into your app.

Each switch defines which folders you want (EG -v views will only copy views dir).

<!-- Migrations --> โœ”๏ธ Migrations

You DON'T need to generate a migration anymore.

From 0.7.5, the migration generator has been removed in favour of our own [migration system](lib/exception_handler/engine.rb#L58).

The reason we did this was so not to pollute your migrations folder with a worthless file. Our migration doesn't need to be changed - we only have to get it into the database and the gem takes care of the rest...

If you set the db option in config, run rails db:migrate and the migration will be run.

To rollback, use the following:

rails db:migrate:down VERSION=000000

The drawback to this is that if you remove ExceptionHandler before you rollback the migration, it won't exist anymore.

You can only fire the rollback when you have ExceptionHandler installed.

<!-- Sep -->

<!-- Support--> โ˜Ž๏ธ Support

You're welcome to contact me directly at [email protected]. Alternatively, you may wish to post on our GitHub Issues, or StackOverflow. --

<!-- Sep -->

<!-- Changelog --> โญ Changelog

  • [ ] TBA

  • [x] README (focus on utility)
  • [x] Introduction of 4xx,5xx,:all for layouts config
  • [x] Changed layouts to exceptions in config
  • [x] Email improvement
  • [x] Streamlined migration
  • [x] Updated model

  • [x] Wildcard mime types
  • [x] Custom exceptions
  • [x] Test suite integration
  • [x] Model backend
  • [x] Sprockets 4+
  • [x] New layout
  • [x] Readme / wiki overhaul

  • [x] Streamlined interface
  • [x] ActiveRecord / Middleware overhaul
  • [x] Supports Sprockets 4+ (manifest.js)
  • [x] Email integration
  • [x] Asset overhaul & improvement
  • [x] Removed dependencies

  • [x] Locales
  • [x] Email notifications
  • [x] Full test suite
  • [x] Rails 4.2 & Rails 5.0 native (request.env fix)
  • [x] Controller fixed
  • [x] DB fixed
  • [x] Legacy initializer support (more)
  • [x] Rails asset management improvement
  • [x] Reduced gem file size

  • [x] New config system
  • [x] Fixed controller layout issues
  • [x] Streamlined middleware
  • [x] New layout & interface

<!-- Sep -->

[404 + 500 Errors][banner]

ExceptionHandler provides custom error pages gem for Rails 5+ No other gem is as simple or effective at providing branded exception pages in production

โžก๏ธ Download & Info โฌ…๏ธ

<!-- Sep -->


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