Make use of a request factory for filter/interceptor

[m11r9000]

This PR involves creating a request factory that will be used to convert incoming HTTP requests from ReactorLoadBalancerExchangeFilterFunction/LoadBalancerInterceptor to org.springframework.cloud.client.loadbalancer.reactive.Request.

RequestFactory has one method that allows developers to plug in their own implementation for doing the conversion ClientRequest -> Request<?> or HttpRequest -> Request<?> or any other request object for that matter. It also contains default implementations that represents the default strategy of checking the loadBalancerHint.

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[spencergibb]

Thanks, but we've already started work on this in #714

https://github.com/spring-cloud/spring-cloud-commons/pull/714/files#diff-400f286716d58d0e3a20e3b639b706b0R51

[andersenleo]

@spencergibb this PR was (is) related to the discussion in #672 -- it's not obvious to me how the referenced PR solved the issue of extracting a hint (or a concrete Request<T> from a http request (or I'm missing something)?

[spencergibb]

The line I linked to has a create request method that can be implemented. Anyway, I think it's too early to consider something like this until #672 is done. I can reopen and put it on hold.

[andersenleo]

The line I linked to has a create request method that can be implemented

Thanks for the quick response. Our purpose was to inject the strategy in the WebClient/RestTemplate filter/interceptor. The createRequest() in the linked issue seems to be scoped to the LoadBalancer (at which point the http-request context is gone)?

Either way - as mentioned in #672 - we can find a way to work around this in our own code, but it would be much better if our work-around was somewhat aligned to your future design :)

[spencergibb]

Sure. We can revisit after #672.

[spencergibb]

The build fails BTW

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.8.0:compile (default-compile) on project spring-cloud-commons: Compilation failure

[ERROR] /home/appuser/project/spring-cloud-commons/src/main/java/org/springframework/cloud/client/loadbalancer/reactive/ReactiveLoadBalancer.java:[49,9] Unexpected @FunctionalInterface annotation

[ERROR]   org.springframework.cloud.client.loadbalancer.reactive.ReactiveLoadBalancer.Factory is not a functional interface

[ERROR]     multiple non-overriding abstract methods found in interface org.springframework.cloud.client.loadbalancer.reactive.ReactiveLoadBalancer.Factory

[ERROR] -> [Help 1]

[m11r9000]

Hi and thank you for the quick replies @spencergibb . I'll fix the compile errors in this PR. Apologies for that. Sloppiness on my end.

And for clarifying regarding intent of this PR; it's a suggestion to showcase how one could extract the loadbalancer hint from the incoming request while also giving developers the power to do so as they see fit e.g. checking a header called loadBalancerHint or any other strategy that suits them.