rack-middleware

# Rack Middleware Skill

## Tier 1: Quick Reference - Middleware Basics

### Middleware Structure

```ruby
class MyMiddleware
  def initialize(app, options = {})
    @app = app
    @options = options
  end

  def call(env)
    # Before request
    # Modify env if needed

    # Call next middleware
    status, headers, body = @app.call(env)

    # After request
    # Modify response if needed

    [status, headers, body]
  end
end

# Usage
use MyMiddleware, option: 'value'
```

### Common Middleware

```ruby
# Session management
use Rack::Session::Cookie, secret: ENV['SESSION_SECRET']

# Security
use Rack::Protection

# Compression
use Rack::Deflater

# Logging
use Rack::CommonLogger

# Static files
use Rack::Static, urls: ['/css', '/js'], root: 'public'
```

### Middleware Ordering

```ruby
# config.ru - Correct order
use Rack::Deflater           # 1. Compression
use Rack::Static             # 2. Static files
use Rack::CommonLogger       # 3. Logging
use Rack::Session::Cookie    # 4. Sessions
use Rack::Protection          # 5. Security
use CustomAuth               # 6. Authentication
run Application              # 7. Application
```

### Request/Response Access

```ruby
class SimpleMiddleware
  def initialize(app)
    @app = app
  end

  def call(env)
    # Access request via env hash
    method = env['REQUEST_METHOD']
    path = env['PATH_INFO']
    query = env['QUERY_STRING']

    # Or use Rack::Request
    request = Rack::Request.new(env)
    params = request.params

    # Process request
    status, headers, body = @app.call(env)

    # Modify response
    headers['X-Custom-Header'] = 'value'

    [status, headers, body]
  end
end
```

---

## Tier 2: Detailed Instructions - Advanced Middleware

### Custom Middleware Development

**Request Logging Middleware:**
```ruby
require 'logger'

class RequestLogger
  def initialize(app, options = {})
    @app = app
    @logger = options[:logger] || Logger.new(STDOUT)
    @skip_paths = options[:skip_paths] || []
  end