# File lib/chef/cookbook/remote_file_vendor.rb, line 37
      def get_filename(filename)
        if filename =~ /([^\/]+)\/(.+)$/
          segment = $1
        else
          raise "get_filename: Cannot determine segment/filename for incoming filename #{filename}"
        end
        
        raise "No such segment #{segment} in cookbook #{@cookbook_name}" unless @manifest[segment]
        found_manifest_record = @manifest[segment].find {|manifest_record| manifest_record[:path] == filename }
        raise "No such file #{filename} in #{@cookbook_name}" unless found_manifest_record
        
        cache_filename = File.join("cookbooks", @cookbook_name, found_manifest_record['path'])
        
        # update valid_cache_entries so the upstream cache cleaner knows what
        # we've used.
        validate_cached_copy(cache_filename)

        current_checksum = nil
        if Chef::FileCache.has_key?(cache_filename)
          current_checksum = Chef::CookbookVersion.checksum_cookbook_file(Chef::FileCache.load(cache_filename, false))
        end

        # If the checksums are different between on-disk (current) and on-server
        # (remote, per manifest), do the update. This will also execute if there
        # is no current checksum.
        if current_checksum != found_manifest_record['checksum']
          raw_file = @rest.get_rest(found_manifest_record[:url], true)

          Chef::Log.debug("Storing updated #{cache_filename} in the cache.")
          Chef::FileCache.move_to(raw_file.path, cache_filename)
        else
          Chef::Log.debug("Not storing #{cache_filename}, as the cache is up to date.")
        end

        full_path_cache_filename = Chef::FileCache.load(cache_filename, false)

        # return the filename, not the contents (second argument= false)
        full_path_cache_filename
      end