debug_middleware.rb

class DebugMiddleware
  def initialize(app, message)
    @app = app
    @message = message
  end

  def call(*args)
    STDERR.puts "BEGIN #{request_id} -- #{@message}"
    status, headers, body = @app.call(*args)
    consumed_body = consume_body(body)
    [status, headers, consumed_body]
  ensure
    STDERR.puts "END   #{request_id} -- #{@message} | status = #{status}, body size = #{get_body_size(consumed_body)}"
  end

private
  def request_id
    Thread.current[:name] || Thread.current.object_id.to_s(36)
  end

  def consume_body(body)
    return nil if body.nil?
    return [body] if body.is_a?(String)
    begin
      result = []
      body.each do |part|
        result << part
      end
      result
    ensure
      body.close if body.respond_to?(:close)
    end
  end

  def get_body_size(consumed_body)
    return 'nil' if consumed_body.nil?
    result = 0
    consumed_body.each { |part| result += part.bytesize }
    result
  end
end