django/django — pull request #1391 by webjunkie (2013-07-23 14:28:33+00:00)
Title: #20793 Add Last-Modified header to sitemap using lastmod from items

From each items lastmod attribute, we can infer the lastmod of the whole sitemap and set this as Last-Modified header for the sitemap. ConditionalGetMiddleware is then able to send 304 NOT MODIFIED and e.g. Google will request with an If-Modified-Since header and bytes are saved.