Consider switching to Project Reactor

At the time when we began Armeria, we ended up with StreamMessage which is a specialized variant of Reactive Stream Publisher mainly because there was no suitable Reactive Stream implementation that meets our requirements:

• Few third party dependencies
• Stable
• Rich set of Publisher implementations that’s suitable for publishing network traffic

Project Reactor was in a very early stage when I reviewed it and now it seems to meet our requirements. It even looks way richer than StreamMessage:

• Read from here to learn the basics: http://projectreactor.io/docs/core/release/reference/docs/index.html#intro-reactive
• Read about their Processor implementations which could replace DefaultStreamMessage and StreamMessageDuplicator: http://projectreactor.io/docs/core/release/reference/docs/index.html#processors

This change would guarantee huge undertaking and broken backward compatibility. We will get richer API and potentially better interoperability/migration opportunaty against other libraries that use Project Reactor such as Spring Webflux.

Thoughts? /cc @hyangtack @minwoox @anuraaga @imasahiro @kojilin @taicki @kshgizmo and everyone interested

[trustin]

We may also want to do some research on other reactive stream implementations such as RxJava 2.

[trustin]

I think we went too far already and our implementation has interesting features like SubscriptionOption which cannot be replaced easily with Reactor. I also tend to prefer shorter stack trace 😉