Re proton: I tried to use it in point-to-point mode, but haven't been able to figure out how; Javadoc reference is useless for that. There exist only Python examples but Python APIs don't map 1:1 to Java APIs.
For Java, have a look at vertx-proton which builds on top of proton-j and is a bit more intuitive (still not great) than proton-j for creating servers and clients. :)