Understood, and apologies for a very terse comment (I was on my mobile on a train..) I commented as I did not know that there was a formal registry of sub-protocols so I wanted to bring this list to people's attention in case, like myself, they were unaware of them.
Looking at the published list I see things like WAMP (wamp-proto.org/) or even (god forbid) SOAP (docs.microsoft.com/en-us/openspecs...), which may well provide both a protocol specification and a client-side API / implementation that meets your needs.
I need to take some time to read the WAMP specs, but TBH it's kind of intimidating. If the spec doc is that long it probably complicated to implement, but if most of the majority fo that complexity is to implement security then it's worth it...
I'm not going to touch SOAP because I already know it's complicated for the sake of complicatedness.
Another option is to use Protocol Buffers' services to define the API and build a simple protocol (maybe use JSON-RPC? But with ProtoBuf?) that uses these?
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