Fix item wrongly removed from http cache when error in subscriptions

[BoD]

Issue encountered here.

For the http cache, we add 2 interceptors:

1. an HttpInterceptor that deals with caching
2. an ApolloInterceptor which cleans up the cache if there was an error

The cache key is computed in 1. and used in 2. But 1. is executed for queries and mutations only, whereas 2. is also executed for subscriptions. When a subscription resulted in an error, an arbitrary (the most recent one) cache key would be incorrectly cleared from the cache. The proposed fix is to do this cleanup only for queries and mutations.

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[martinbonnin]

The root problem seems to be that cacheKey is global to an ApolloClient and not a request. There is still a bug if two request run concurrently. They might revert the wrong cache key.

[BoD]

Good point! Hmm, we could store the cacheKey as a header on the http response, which can be retrieved inside the .onEach { part, but not sure how to deal with the catch { part 🤔

[martinbonnin]

not sure how to deal with the catch { part 🤔

Mmmmm right. The issue is that the cache key is computed at the HTTP layer but we're reading it at the GraphQL layer.

You could maintain a map GraphQL request uuid : HTTP cache key in the HTTP interceptor, just after computing it. Then you can read this map in the catch {} block.

[martinbonnin]

This is still racy. This code can be accessed from multiple threads. requestUuid needs to be passed down to the interceptor and apolloRequestToCacheKey protected by a lock

[BoD]

You're right of course! 👍 A fix in 152e746.

[sam43]

Hi @BoD,
Hope you are doing well, and great work guys. I have tested the v3.7.2-SNAPSHOT version, by creating the .jar version. It works perfectly fine, I will be waiting for the next release for the library to integrate into my project which's release is kinda blocked right now! But no worries at all. Thanks for your support, regards.

[BoD]

Hi @sam43, thanks a lot for the feedback, glad that the fix works for you! We've just released v3.7.2 which includes the fix. Thanks again for reporting the issue 🙏