monkey_patch_images_inline.rb

require 'net/http'

# Extend img tag to optionally embed images in-line into HTML instead of referencing as a URI
#
# This is a useful technique when sending HTML emails as it circumvents the prompt many mail clients 
# present seeking permission to 'display images from this sender?' when an email of mime-type 'html'
# contains <img> tags.
#
# ie. <%= image_tag('red_dot.gif', :embed_inline => "true") %>
#
# will produce:
#
# <img src="data:image/png;base64,
# iVBORw0KGgoAAAANSUhEUgAAAAoAAAAKCAYAAACNMs+9AAAABGdBTUEAALGP
# C/xhBQAAAAlwSFlzAAALEwAACxMBAJqcGAAAAAd0SU1FB9YGARc5KB0XV+IA
# AAAddEVYdENvbW1lbnQAQ3JlYXRlZCB3aXRoIFRoZSBHSU1Q72QlbgAAAF1J
# REFUGNO9zL0NglAAxPEfdLTs4BZM4DIO4C7OwQg2JoQ9LE1exdlYvBBeZ7jq
# ch9//q1uH4TLzw4d6+ErXMMcXuHWxId3KOETnnXXV6MJpcq2MLaI97CER3N0
# vr4MkhoXe0rZigAAAABJRU5ErkJggg==" />
#
# instead of:
#
# <img src="red_dot.gif" />
#
module ActionView::Helpers::AssetTagHelper
  alias_method :orig_image_tag, :image_tag
  
  def image_tag(source, options = {})
    # If an 'embed_inline' argument has been specified and is 'true', write the image data into
    # the tag as a data URI
    #
    # Example Usage:
    # <%= image_tag('red_dot.gif', :embed_inline => "true") %>
    options.symbolize_keys!
    if options[:embed_inline] and options[:embed_inline].to_s.downcase == 'true'
      include_host = true
      full_image_path = compute_public_path(source, 'images', nil, include_host)
      
      #TODO: improve!
      image_contents = if full_image_path.starts_with?("http")
        Net::HTTP.get(URI.parse(full_image_path))      
      else
        File.open(File.join(ASSETS_DIR, full_image_path).split("?").first).read
      end
      image_mime_type = "image/" + full_image_path.downcase.split(".").last.gsub('jpg', 'jpeg')
      
      encoded_image_contents = ActiveSupport::Base64.encode64(image_contents)
      
      # Make the magic happen - refer: http://en.wikipedia.org/wiki/Data_URI_scheme
      options[:src] = "data:#{image_mime_type};base64,#{encoded_image_contents}"

      # Begin duplication of rails image_tag - passing :src through to the orig_image_tag would get overridden
      options[:alt] ||= File.basename(options[:src], '.*').split('.').first.to_s.capitalize

      if size = options.delete(:size)
        options[:width], options[:height] = size.split("x") if size =~ %r{^\d+x\d+$}
      end

      if mouseover = options.delete(:mouseover)
        options[:onmouseover] = "this.src='#{image_path(mouseover)}'"
        options[:onmouseout]  = "this.src='#{image_path(options[:src])}'"
      end

      return tag("img", options)
    end
    return orig_image_tag(source, options)
  end
end