Carrierwave validate remote url - Tested with v0.5.8

gistfile1.rb

#############################################
###uri_validator file:
#############################################
require 'net/http'

# Thanks Ilya! http://www.igvita.com/2006/09/07/validating-url-in-ruby-on-rails/
# Original credits: http://blog.inquirylabs.com/2006/04/13/simple-uri-validation/
# HTTP Codes: http://www.ruby-doc.org/stdlib/libdoc/net/http/rdoc/classes/Net/HTTPResponse.html

class UriValidator < ActiveModel::EachValidator
  def validate_each(object, attribute, value)
    raise(ArgumentError, "A regular expression must be supplied as the :format option of the options hash") unless options[:format].nil? or options[:format].is_a?(Regexp)
    configuration = { :message => "is invalid or not responding", :format => URI::regexp(%w(http https)) }
    configuration.update(options)
    
    if value =~ configuration[:format]
      begin # check header response
        case Net::HTTP.get_response(URI.parse(value))
          when Net::HTTPSuccess then true
          else object.errors.add(attribute, configuration[:message]) and false
        end
      rescue # Recover on DNS failures..
        object.errors.add(attribute, configuration[:message]) and false
      end
    else
      object.errors.add(attribute, configuration[:message]) and false
    end
  end
end

#################################################################
###image model
#################################################################
require "uri_validator"
class Image < ActiveRecord::Base
  attr_accessible :remote_url
  attr_accessor :remote_url
  attr_writer :remote_url
  
  mount_uploader :image, ImageUploader
  validates :remote_url, 
  :uri => { 
    :format => /(^$)|(^(http|https):\/\/[a-z0-9]+([\-\.]{1}[a-z0-9]+)*\.[a-z]{2,5}(([0-9]{1,5})?\/.*)?$)/ix, :unless => :blank_url?
  }
  
  after_validation do
    self.remote_image_url = self.remote_url if self.errors[:remote_url].blank?
  end
  
  private
  def blank_url?
    self.remote_url.blank?
  end
end