https://bugzilla.wikimedia.org/show_bug.cgi?id=21916
Summary: $wgFeedCacheTimeout client caching issue
Product: MediaWiki
Version: 1.14.1
Platform: All
OS/Version: All
Status: NEW
Severity: minor
Priority: Normal
Component: Syndication
AssignedTo: wikibugs-l@lists.wikimedia.org
ReportedBy: vita...@yourcmc.ru
Created an attachment (id=6898)
--> (https://bugzilla.wikimedia.org/attachment.cgi?id=6898)
Patch for Wikilog (code similar to MediaWiki's)
Special:RecentChanges MUST NOT output the Last-Modified header greater than the
effective outputted feed modification timestamp.
Suppose the following situation:
0. RSS reader ("client") updates some recentchanges feed.
1. Wiki caches OLD version of feed with OLD timestamp
2. So client caches OLD version of feed with OLD timestamp
3. Some new change is added to the feed - now it has NEW update timestamp
4. It happens that client updates feed BEFORE $wgFeedCacheTimeout seconds
passed after the first update
5. So Wiki outputs OLD version of feed with NEW (!!!) timestamp
6. Client caches OLD version of feed with NEW timestamp
7. In the future, client sends requests with If-Modified-Since = NEW timestamp
8. So Wiki outputs 304 Not Modified
9. So client does not get the new version of feed! (client thinks it already
has the newest version)
This buggy behaviour was copied into Wikilog extension by its author, and this
bug was found there at first :-) it isn't so important in RecentChanges feed
because it usually contains more items, and RecentChanges don't need such
freshness.
Wikilog author wants to hear your opinion about this bug before committing a
fix for this bug into his repository.
The fix is getting effective feed modification timestamp from cache and
outputting it as Last-Modified header instead of getting modification timestamp
of the actual data.
The patch for Wikilog is attached, it's code is very similar (copy-paste), but
in MediaWiki it's dispersed into includes/ChangesFeed.php and
includes/specials/SpecialRecentchanges.php, so it'll be slightly harder to
create an equal fix.
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