Getting Started with Lennarb

Overview

Lennarb is a minimalist, thread-safe Rack-based web framework for Ruby that focuses on simplicity and performance. It provides a clean routing DSL and straightforward request/response handling.

Installation

Add Lennarb to your project's Gemfile:

gem 'lennarb'

Or install it directly via RubyGems:

gem install lennarb

Quick Start

Basic Application

Create a new file named config.ru:

require 'lennarb'

app = Lennarb.new do |app|
  app.get '/' do |req, res|
    res.status = 200
    res.html('<h1>Welcome to Lennarb!</h1>')
  end
end

app.initializer!
run app

Start the server:

rackup

Your application will be available at http://localhost:9292.

Core Concepts

Request Handling

Each route handler receives two arguments:

• req: A Request object wrapping the Rack environment
• res: A Response object for building the HTTP response

Response Types

Lennarb provides three main response helpers:

app.get '/text' do |req, res|
  res.text('Plain text response')
end

app.get '/html' do |req, res|
  res.html('<h1>HTML response</h1>')
end

app.get '/json' do |req, res|
  res.json('{"message": "JSON response"}')
end

Redirects

app.get '/redirect' do |req, res|
  res.redirect('/new-location', 302) # 302
end

Routes are defined using HTTP method helpers:

app = Lennarb.new do |l|
  # Basic route
  l.get '/' do |req, res|
    res.html('Home page')
  end

  # Route with parameters
  l.get '/users/:id' do |req, res|
    user_id = req.params[:id]
    res.json("{\"id\": #{user_id}}")
  end
end

Route Parameters

Parameters from dynamic route segments are available in req.params:

app.get '/hello/:name' do |req, res|
  name = req.params[:name]
  res.text("Hello, #{name}!")
end

Thread Safety

Lennarb is thread-safe by design:

• All request processing is synchronized using a mutex
• The router tree is frozen after initialization
• Response objects are created per-request

Application Lifecycle

Initialization

app = Lennarb.new do |l|
  # Define routes and configuration
end

# Initialize and freeze the application
app.initializer!

The initializer! method:

• Loads environment-specific dependencies
• Freezes the route tree
• Freezes the Rack application

Environment

Lennarb uses the LENNA_ENV environment variable (defaults to "development"):

LENNA_ENV=production rackup

Error Handling

Lennarb provides basic error handling:

app.get '/api' do |req, res|
  # Errors are caught and return 500 with error message
  raise "Something went wrong"
end

Default error responses:

• 404 for unmatched routes
• 500 for application errors

Best Practices

1. Always call initializer!

   app = Lennarb.new { |l| ... }
   app.initializer!
   run app
   

2. Set response status

   app.get '/api' do |req, res|
     res.status = 200
     res.json('{"status": "ok"}')
   end
   

3. Use appropriate response types

   # HTML for web pages
   res.html('<h1>Web Page</h1>')
   
   # JSON for APIs
   res.json('{"data": "value"}')
   
   # Text for simple responses
   res.text('Hello')
   

Support

For help and bug reports, please visit:

• GitHub Issues: lennarb/issues

Now you can run your app!