iOS DefaultHttpEngine StreamingDataDelegate has a thread safety issue

[paxbun]

Version

4.0.0-rc.1

Summary

With HttpInterceptor, when invoking Apollo from multiple threads (e.g. using MultithreadedDispatchers), HashMap.put throws ArrayIndexOutOfBoundsException or IllegalStateException, which is called by StreamingDataDelegate.registerHandlerForTask. In our app on iOS 18, about 10% of the users experience this problem.

Steps to reproduce the behavior

1. Add an HttpInterceptor when building a ApolloClient.

addHttpInterceptor(object : HttpInterceptor {
    override suspend fun intercept(
        request: HttpRequest, chain: HttpInterceptorChain
    ): HttpResponse {
        val token = try {
            authenticationService.acquireToken()
        } catch (ex: CancellationException) {
            throw ex
        } catch (e: Exception) {
            null
        }
        return chain.proceed(
            when {
                token == null -> request
                else -> request
                    .newBuilder()
                    .addHeader("Authorization", "Bearer $token")
                    .build()
            },
        )
    }
})

2. Invoke multiple Apollo queries or mutations in a multithreaded coroutine context.
3. You'll experience an exception thrown from HashMap randomly.

Logs

ArrayIndexOutOfBoundsException stacktrace

IllegalStateException stacktrace

[martinbonnin]

Hi 👋 Thanks for sending this. Any chance you can try with version 4.1.0? I can't remember anything that would have fixed this but it's worth a try.

[paxbun]

I'm also unable to reproduce this problem with the machines I have; I'll let you know if there's any change after upgrading Apollo 4.0.0 to 4.1.0.

[martinbonnin]

Took a look at the code and I believe the issue is still there. Made a fix there: #6348

[paxbun]

This is the fix I wanted to apply. Thanks! By the way, can I close this as completed? Would this fix be released in the near future by any chance? If not, I'm going to do some workarounds for this issue in our app.

[martinbonnin]

By the way, can I close this as completed?

Sure thing!

Would this fix be released in the near future by any chance?

We're planning a 4.1.1 release soon-ish. Hopefully next week!

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[paxbun]

Thanks! Have a nice weekend :)

[jvanderwee]

Hey @martinbonnin 👋 do you have an update on the 4.1.1. release please?

[martinbonnin]

@jvanderwee We're working on it!

In the meantime, you can always use the previews:

repositories {
  maven {
    url = uri("https://storage.googleapis.com/apollo-previews/m2/")
  }
}

dependencies {
  implementation("com.apollographql.apollo:apollo-runtime:4.1.1-2025.01.21")
}

They have 1 year retention.