Jets Config: Shim

You can configure the Jets Shim settings with.

config/jets/shim.rb

Jets.shim.configure do
  config.boot_path = "app.rb"
  config.rack_app = App
end

How it works:

1. The boot_path is required and “boots” the framework. IE: require "config/environment". It should be at the top of the configure block.
2. The rack_app config is a rack-compatible app that must respond to .call(env), IE: Rails.application.call

Conventions

Jets can conventionally infer the shim settings. So most of the time, you do not have to configure the shim and do not need a config/jets/shim.rb at all.

Rails

For Rails, it automatically does something like this:

config/jets/shim.rb

Jets.shim.configure do |config|
  config.boot_path = "config/environment.rb"
  config.rack_app = Rails.application
end

Rack App

If you have a general Rack app, you can name it app.rb the shim settings can also be entirely inferred. We’ll explain with an example.

Create app.rb

The app.rb provides the interface for the jets shim.

It must respond to a call method.

app.rb

class App
  def self.call(env)
    [200, {}, ["Hello"]]
  end
end

The inferred shim:

config/jets/shim.rb

Jets.shim.configure do |config|
  config.boot_path = "app.rb"
  config.rack_app = App
end

Explicit Overrides

When the rack app settings cannot be inferred, you can configure config/jets/shim.rb with overrides.

Sinatra Example

Here’s a Sinatra example

sinatra_app.rb

class SinatraApp < Sinatra::Base
  get '/' do
    "SinatraApp homepage"
  end
end

Here’s a shim for Sinatra.

config/jets/shim.rb

Jets.shim.configure do |config|
  config.boot_path = "sinatra_app.rb"
  config.rack_app = SinatraApp
end

Another approach is creating an app.rb and “aliases” it. Here’s an app.rb for Sinatra. It aliases the SinatraApp to App. Example:

app.rb

require_relative "sinatra_app"
App = SinatraApp