NAME
  upload_cache.rb

DESCRIPTION
  a small utility library to facility caching http file uploads between
  form validation failures.  designed for rails, but usable anywhere.

USAGE
  in the controller

    def upload
      @upload_cache = UploadCache.for(params, :upload)

      @record = Model.new(params)

      if request.get?
        render and return
      end

      if request.post?
        @record.save!
        @upload_cache.clear!
      end
    end


  in the view

    <input type='file' name='upload />

    <%= @upload_cache.hidden %>

    <!-- optionally, you can show any uploaded upload -->

    <% if url = @upload_cache.url %>
      you already uploaded: <img src='<%= raw url %>' />
    <% end %>


  in a rake task

    UploadCache.clear!  ### nuke old files once per day