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Posted to dev@hc.apache.org by "Oleg Kalnichevski (Jira)" <ji...@apache.org> on 2024/05/16 13:34:00 UTC
[jira] [Resolved] (HTTPCLIENT-2327) MemcachedHttpAsyncCacheStorage propagates CancellationException from cancelled cache requests to caller
[ https://issues.apache.org/jira/browse/HTTPCLIENT-2327?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Oleg Kalnichevski resolved HTTPCLIENT-2327.
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Fix Version/s: 5.4-alpha3
Resolution: Fixed
> MemcachedHttpAsyncCacheStorage propagates CancellationException from cancelled cache requests to caller
> -------------------------------------------------------------------------------------------------------
>
> Key: HTTPCLIENT-2327
> URL: https://issues.apache.org/jira/browse/HTTPCLIENT-2327
> Project: HttpComponents HttpClient
> Issue Type: Bug
> Components: HttpCache
> Reporter: Jovan Attisha
> Priority: Major
> Fix For: 5.4-alpha3
>
> Time Spent: 40m
> Remaining Estimate: 0h
>
> Spymemcached provides options to handle failure modes when an in-flight request to a Memcached instance fails (for example, when deploying to a Memcached server that is currently serving requests). One of the modes, and the most logical for our scenario in particular, is [Cancel|https://github.com/couchbase/spymemcached/blob/master/src/main/java/net/spy/memcached/FailureMode.java#L51-L54]. This, as you would expect, cancels any futures that are in-flight when a Memcached node becomes unreachable.
>
> The issue that we're having is that the {{[MemcachedHttpAsyncCacheStorage|https://github.com/apache/httpcomponents-client/blob/master/httpclient5-cache/src/main/java/org/apache/hc/client5/http/impl/cache/memcached/MemcachedHttpAsyncCacheStorage.java#L184]}} (for restore linked here, as this is our issue, but also for other methods), doesn't handle the {{CancellationException}} gracefully, and instead propagates this Exception up to the caller. Since this is a cache for an HTTP client, I would expect the client to handle the cancellation as a "cache miss" (I would almost expect this behavior for {_}all exceptions{_}, though I'm likely not thinking of some edge cases here) and proceed to make the request to the resource originally requested, since the cache is a mere optimization, and a failure in the cache should not impact the actual request to the resource we're targeting.
>
> We did POC this by extending the {{[MemcachedHttpAsyncCacheStorage|https://github.com/apache/httpcomponents-client/blob/master/httpclient5-cache/src/main/java/org/apache/hc/client5/http/impl/cache/memcached/MemcachedHttpAsyncCacheStorage.java#L184]}} and overriding the {{restore}} method to explicitly handle {{{}CancellationException{}}}s and complete the future to treat it as a cache miss, but before we proceed with this, we want to understand if:
> 1. The Apache HTTPClient agrees that this is the desired behavior
> 2. If so, would the Apache HTTP Client accept this behavior in the client itself, rather than us extending to override this behavior
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