url_resolver.rb

require 'uri'
require 'net/http'
require 'openssl'

class UrlResolver
  def self.resolve(uri_str, agent = 'curl/7.43.0', max_attempts = 10, timeout = 10)
    attempts = 0
    cookie = nil

    until attempts >= max_attempts
      attempts += 1

      url = URI.parse(uri_str)
      http = Net::HTTP.new(url.host, url.port)
      http.open_timeout = timeout
      http.read_timeout = timeout
      path = url.path
      path = '/' if path == ''
      path += '?' + url.query unless url.query.nil?

      params = { 'User-Agent' => agent, 'Accept' => '*/*' }
      params['Cookie'] = cookie unless cookie.nil?
      request = Net::HTTP::Get.new(path, params)

      if url.instance_of?(URI::HTTPS)
        http.use_ssl = true
        http.verify_mode = OpenSSL::SSL::VERIFY_NONE
      end
      response = http.request(request)

      case response
        when Net::HTTPSuccess then
          break
        when Net::HTTPRedirection then
          location = response['Location']
          cookie = response['Set-Cookie']
          new_uri = URI.parse(location)
          uri_str = if new_uri.relative?
                      url + location
                    else
                      new_uri.to_s
                    end
        else
          raise 'Unexpected response: ' + response.inspect
      end

    end
    raise 'Too many http redirects' if attempts == max_attempts

    uri_str
    # response.body
  end
end

puts UrlResolver.resolve('http://www.ruby-lang.org')