Add support for running as a Rack app

This makes it so that users of the gem can optionally run the app as a
Rack app, making it easy to mount within a Rails or Sinatra app. Reasons
why would be to add authentication or have a nicer developer experience
instead of regenerating the docs over and over again.

Fixes #102

Author: brettchalupa

README.md

@@ -24,6 +24,13 @@ gem install graphql-docs
 
 ## Usage
 
+GraphQLDocs provides two ways to serve your documentation:
+
+1. **Static Site Generator (SSG)** - Pre-generate all HTML files (default)
+2. **Rack Application** - Serve documentation dynamically on-demand
+
+### Static Site Generation (SSG)
+
 GraphQLDocs can be used as a Ruby library to build the documentation website. Using it as a Ruby library allows for more control and using every supported option. Here's an example:
 
 ```ruby
@@ -54,6 +61,110 @@ See all of the supported CLI options with:
 graphql-docs -h
 ```
 
+### Rack Application (Dynamic)
+
+For more flexibility and control, you can serve documentation dynamically using the Rack application. This is useful for:
+
+- Internal tools with frequently changing schemas
+- Integration with existing Rails/Sinatra applications
+- Adding authentication/authorization middleware
+- Dynamic schema loading from databases or APIs
+
+**Requirements**: The Rack application feature requires the `rack` gem (version 2.x or 3.x). Add it to your Gemfile:
+
+```ruby
+gem 'rack', '~> 3.0'  # or '~> 2.0' for Rack 2.x
+```
+
+The gem is compatible with both Rack 2.x and 3.x, so you can use whichever version your application requires.
+
+#### Standalone Rack App
+
+Create a `config.ru` file:
+
+```ruby
+require 'graphql-docs'
+
+schema = File.read('schema.graphql')
+
+app = GraphQLDocs::App.new(
+  schema: schema,
+  options: {
+    base_url: '',
+    use_default_styles: true,
+    cache: true  # Enable page caching
+  }
+)
+
+run app
+```
+
+Then run with:
+
+```console
+rackup config.ru
+```
+
+Visit `http://localhost:9292` to view your docs.
+
+#### Mounting in Rails
+
+```ruby
+# config/routes.rb
+require 'graphql-docs'
+
+Rails.application.routes.draw do
+  mount GraphQLDocs::App.new(schema: MyGraphQLSchema) => '/docs'
+end
+```
+
+#### Mounting in Sinatra
+
+```ruby
+require 'sinatra'
+require 'graphql-docs'
+
+schema = File.read('schema.graphql')
+docs_app = GraphQLDocs::App.new(schema: schema)
+
+map '/docs' do
+  run docs_app
+end
+
+map '/' do
+  run Sinatra::Application
+end
+```
+
+#### Rack App Features
+
+- **On-demand generation** - Pages are generated when requested
+- **Built-in caching** - Generated pages are cached in memory (disable with `cache: false`)
+- **Schema reloading** - Update schema without restarting server:
+
+```ruby
+app = GraphQLDocs::App.new(schema: schema)
+
+# Later, reload with new schema
+new_schema = File.read('updated_schema.graphql')
+app.reload_schema!(new_schema)
+```
+
+- **Asset serving** - CSS, fonts, and images served automatically
+- **Error handling** - Friendly error pages for missing types
+
+#### SSG vs Rack Comparison
+
+| Feature | SSG | Rack App |
+|---------|-----|----------|
+| Setup complexity | Low | Medium |
+| First page load | Instant | Fast (with caching) |
+| Schema updates | Manual rebuild | Automatic/reload |
+| Hosting | Any static host | Requires Ruby server |
+| Memory usage | Minimal | Higher (cached pages) |
+| Authentication | Separate layer | Built-in middleware |
+| Best for | Public docs, open source | Internal tools, dynamic schemas |
+
 ## Breakdown
 
 There are several phases going on the single `GraphQLDocs.build` call:
@@ -395,20 +506,42 @@ an interactive prompt that will allow you to experiment.
 
 ## Sample Site
 
-Clone this repository and run:
+Clone this repository and try out both modes:
 
-```
+### Static Site Generation
+
+Generate the sample documentation to the `output` directory:
+
+```console
 bin/rake sample:generate
 ```
 
-to see some sample output in the `output` dir.
+Then boot up a server to view the pre-generated files:
+
+```console
+bin/rake sample:serve
+```
+
+Visit `http://localhost:5050` to view the static documentation.
 
-Boot up a server to view it:
+### Rack Application (Dynamic)
 
+Run the sample docs as a dynamic Rack application:
+
+```console
+bin/rake sample:rack
 ```
-bin/rake sample:serve
+
+Or use the config.ru directly:
+
+```console
+rackup config.ru
 ```
 
+Visit `http://localhost:9292` to view the documentation served dynamically.
+
+**Key Difference**: The SSG version pre-generates all pages (faster initial load, no runtime cost), while the Rack version generates pages on-demand (better for dynamic schemas, easier integration).
+
 ## Credits
 
 Originally built by [gjtorikian](https://github.com/gjtorikian). Actively maintained by [brettchalupa](https://github.com/brettchalupa).

Rakefile

@@ -83,4 +83,34 @@ namespace :sample do
     server.start
   end
   task server: :serve
+
+  desc 'Run the sample docs as a Rack application (dynamic, on-demand generation)'
+  task :rack do
+    require 'rack'
+    require 'graphql-docs'
+
+    schema_path = File.join(File.dirname(__FILE__), 'test', 'graphql-docs', 'fixtures', 'gh-schema.graphql')
+    schema = File.read(schema_path)
+
+    app = GraphQLDocs::App.new(
+      schema: schema,
+      options: {
+        base_url: '',
+        use_default_styles: true,
+        cache: true
+      }
+    )
+
+    PORT = ENV.fetch('PORT', '9292')
+    puts "Starting Rack server in dynamic mode (on-demand generation)"
+    puts "Navigate to http://localhost:#{PORT} to view the sample docs"
+    puts "Press Ctrl+C to stop"
+    puts ""
+    puts "NOTE: This serves documentation dynamically - pages are generated on request"
+    puts "      Compare with 'rake sample:serve' which serves pre-generated static files"
+    puts ""
+
+    # Use rackup for Rack 3.x compatibility
+    sh "rackup config.ru -p #{PORT}"
+  end
 end

config.ru

@@ -0,0 +1,44 @@
+# frozen_string_literal: true
+
+# Rack configuration file for running GraphQL Docs as a web server
+#
+# This demonstrates using GraphQLDocs as a Rack application that serves
+# documentation dynamically on-demand instead of pre-generating static files.
+#
+# Run with: rackup config.ru
+# Or with specific port: rackup config.ru -p 9292
+
+require_relative 'lib/graphql-docs'
+
+# Load the sample GraphQL schema
+schema_path = File.join(__dir__, 'test', 'graphql-docs', 'fixtures', 'gh-schema.graphql')
+
+unless File.exist?(schema_path)
+  puts "Error: Sample schema not found at #{schema_path}"
+  puts "Please ensure the schema file exists before starting the server."
+  exit 1
+end
+
+schema = File.read(schema_path)
+
+# Create the Rack app
+app = GraphQLDocs::App.new(
+  schema: schema,
+  options: {
+    base_url: '',
+    use_default_styles: true,
+    cache: true
+  }
+)
+
+# Log requests in development
+use Rack::CommonLogger
+
+# Add reloader for development (optional, requires 'rack' gem)
+if ENV['RACK_ENV'] != 'production'
+  puts "Running in development mode"
+  puts "Visit http://localhost:9292 to view the documentation"
+  puts "Press Ctrl+C to stop the server"
+end
+
+run app

graphql-docs.gemspec

@@ -49,9 +49,17 @@ Gem::Specification.new do |spec|
   spec.add_dependency 'ostruct', '~> 0.6'
   spec.add_dependency 'logger', '~> 1.6'
 
+  # rack application support (optional, only needed for GraphQLDocs::App)
+  # Users can install rack separately if they want to use the Rack app feature:
+  #   gem 'rack', '~> 2.0' or gem 'rack', '~> 3.0'
+  # The gem works with both Rack 2.x and 3.x
+
   spec.add_development_dependency 'html-proofer', '~> 3.4'
   spec.add_development_dependency 'minitest', '~> 5.24'
   spec.add_development_dependency 'minitest-focus', '~> 1.1'
+  spec.add_development_dependency 'rack', '>= 2.0', '< 4'
+  spec.add_development_dependency 'rack-test', '~> 2.0'
+  spec.add_development_dependency 'rackup', '~> 2.0'
   spec.add_development_dependency 'rake', '~> 13.0'
   spec.add_development_dependency 'rubocop', '~> 1.37'
   spec.add_development_dependency 'rubocop-performance', '~> 1.15'

lib/graphql-docs.rb

@@ -7,6 +7,13 @@
 require 'graphql-docs/parser'
 require 'graphql-docs/version'
 
+# Lazy-load the Rack app - only loads if Rack is available
+begin
+  require 'graphql-docs/app' if defined?(Rack)
+rescue LoadError
+  # Rack not available, App class won't be loaded
+end
+
 # GraphQLDocs is a library for generating beautiful HTML documentation from GraphQL schemas.
 # It parses GraphQL schema files or schema objects and generates a complete documentation website
 # with customizable templates and styling.