Last-Modified headers for individual comment feeds are incorrect
|Reported by:||solarissmoke||Owned by:||jgci|
|Severity:||normal||Keywords:||dev-feedback gci has-patch 3.2-early|
The WP::send_headers function currently uses get_lastcommentmodified() to set the Last-Modified header for all comment feeds. This is a problem when used for individual post comment feeds. The function gets the last modified comment across all blog posts. That means that every time a comment is posted anywhere, the Last-Modified header for ALL comment feeds is refreshed. Issues:
- This is technically incorrect, since only the global comment feed and one specific post's comment feed have changed with the last comment (not all possible comment feeds); and
- It means that If-Modified-Since requests for other post comment feeds will not receive a 304 response when they should do (since their content hasn't changed). On blogs with many posts and many comment feeds, this will have a large impact on bandwidth because lots of requests will receive 200 responses where 304's would have done, just because a comment was posted on some other post.
If I've understood the flow correctly, $wp_query hasn't been fully set up at the time this function is called, so changing this behaviour would require some change in the flow of things (e.g., the handling of last modified headers for feeds moves into the do_feed() function). But doing so would mean that Last-Modified headers are correct/meaningful and that many more 304 responses can be served.