[HTTPCLIENT-2284] BasicHttpCacheStorage leaking variant keys in root response's variantMap

• Type: Bug
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 4.5.13
• Fix Version/s: 5.4-alpha1
• Component/s: HttpCache
• Assignee: Unassigned
• Reporter: Pascal Lacombe
• Created: 20/Jul/23 18:33
• Updated: 31/Aug/23 15:00
• Resolved: 28/Aug/23 07:51

Description

BasicHttpCacheStorage has a memory leak in the root response's variantMap. When a variant cached entry is evicted due to CacheMap being too large, the root cache entry does not remove the variant key in its variantMap. This is a memory leak that can grow the variantMap indefinitely, or until the root entry get's evicted itself.

Simplified testcase:

1. A request is being sent from a client that contains a header "x-my-variant" with a hash of the current timestamp.
2. The server responds 200, with a cacheable response. The response Vary's on "x-my-variant"
3. These requests repeat, causing:
   1. The "root" CacheEntry to be kept in CacheMap
   2. The oldest variant CacheEntry to be evicted due to the CacheMap size limit
   3. However the "root" CacheEntry never removes the evicted variant keys from the variantMap