    # File lib/fog/google/requests/storage/head_object.rb, line 27
            def head_object(bucket_name, object_name, options={})
              unless bucket_name
                raise ArgumentError.new('bucket_name is required')
              end
              unless object_name
                raise ArgumentError.new('object_name is required')
              end
              if version_id = options.delete('versionId')
                query = {'versionId' => version_id}
              end
              headers = {}
              headers['If-Modified-Since'] = Fog::Time.at(options['If-Modified-Since'].to_i).to_date_header if options['If-Modified-Since']
              headers['If-Unmodified-Since'] = Fog::Time.at(options['If-Unmodified-Since'].to_i).to_date_header if options['If-Modified-Since']
              headers.merge!(options)
              request({
                :expects  => 200,
                :headers  => headers,
                :host     => "#{bucket_name}.#{@host}",
                :method   => 'HEAD',
                :path     => CGI.escape(object_name),
                :query    => query
              })
            end