    # 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 fetching #{cache_filename}, as the cache is up to date.")
              Chef::Log.debug("current checksum: #{current_checksum}; manifest checksum: #{found_manifest_record['checksum']})")
            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