On the other hand, plain URLs with JSON are much easier to work with without writing any code. You can do everything want with curl from the shell, and often an API allows doing almost anything from a browser (Elasticsearch comes to mind). The simplicity of it all comes in handy when you want to do something trivial — load a small piece of data into the server, do some diagnostics, run some ad-hoc queries, etc. — without really wanting to write a program.
Debugging with lower-level tools like strace and tcpdump is also something that's trivial with JSON-over-HTTP/1.1, but virtually impossible with gRPC. (I mean, you could grab the payload and run it through gRPC deserialization, but would you?)
I'm a big fan of gRPC, but it is pretty top-heavy — lots of code to accomplish relatively little. If you have a language that can build client bindings dynamically from .proto files without recompilation, that would ease things a lot, but if you're using Go, for example, the bar is pretty high going from zero to productive.
I think the only RPC mechanism I've been happy with, that required little work and didn't constantly get in the way was Stubby - the precursor to gRPC used inside Google.
For a few years inside Google I experienced zero discussions about almost every aspect of RPC. It took a trivial amount of time to implement stuff interfaces, clients and servers in multiple languages and it was trivial to understand the interface of, and implement a client for, other people's code.
I didn't necessarily like everything in Stubby, but I absolutely loved not needing to have pointless discussions about RPC mechanisms or protocol design.
Since I left Google, anything even remotely resembling RPC (including REST) has been an utter waste of time mostly spent bickering over this crap solution or that crap solution – mostly with people who don't care about the same things you care about.
REST is a crap solution in my eyes because it invites absolutely endless discussions on an endless list of subtopics. From the dogmatic/fundamentalist HATEOAS end of the spectrum to the RPC-using-HTTP-and-JSON-and-let's-call-it-REST camp. Not to mention that in addition you need to have an IDL and toolchain discussion. (Of course, none of the toolchains or ways to describe interfaces are very good. In fact, they all suck in part because the attention is being spread across so many efforts that don't get the job done).
I have yet to see an IDL that works better than a commented .proto file from a "get stuff done" point of view.
I completely understand where you are coming from when it comes to having human readable wire format. For 20 years I was a strong believer in the same, and for some systems I still believe in human readable formats.
But RPC and RPC-like mechanisms is no longer among them. RPC is for computers to talk to each other and not for humans trying to manually repair stuff.
(I'm a pragmatist, so I'm allowed to both change my mind and have seemingly inconsistent opinions :-))
For RPC you should encourage the creation of tools. If you need to look at the traffic manually: fine, make a Wireshark plugin or a proxy that can view calls in real time. That's annoying, but cheaper than going off and inventing yet another mechanism. And once it is done, it is done and there's one more thing that is sane.
We should really encourage people to build tools so we can automate things and have more precise and predictable control over what we are doing without having to reimplement parsing (which is what happens if people think they understand your protocol - which they often don't)
Also, make sure it works for a large enough set of implementation languages and understand how to work in mechanical sympathy with build systems. I don't care if Cap'n Proto is marginally better than Protobuf if it lacks decent support for languages I have to care about.
I have no idea how much time we wasted on trying to get Thrift to work in a Java project that needed to build on Windows, Linux and OSX back in the day, but I was ready to strangle the makers of Thrift for not paying attention to this.
At this point I'm beyond caring about the design of RPC systems. I just want something that works for software development and doesn't have to be a discussion. Hence, I get annoyed every time I see a new RPC mechanism instead of attempts to make some of the existing mechanisms work by just making just one aspect of them a bit more sane and exhibit a bit more empathy with programmers rather than the egos of protagonists of various libraries, frameworks and formats.
I imagine part of the lack of friction around Stubby was that Google was the only consumer, and could maintain client and server bindings/tools for the strict subset of the languages that Google standardized on.
It was pretty similar, but gRPC is a bit simpler since Stubby had a lot of other stuff to deal with authorization etc.
I wouldn't say the lack of friction was mostly due to Google being the only consumer. It was mostly because there was a clear path from A to B when you wanted to give something an RPC interface and that this path was made efficient.
Or at least more efficient than trying to use REST-like stuff in a large organization with lots of different teams using different technologies.
It also helped that it wasn't a democracy. You had to use it. If you didn't like that you were free to leave. As a result people will focus more effort on making the tools better and make friction points go away.
In practical terms: we can spend weeks on getting a REST-like interface to work with other projects because everyone has an opinion on every bit of the design, and everyone uses different, and quirky libraries and tools. For Stubby in Google back then, it was mostly about defining the data structures, the RPC calls, discuss semantics and then the mechanics were taken care of. This is far, far, far from the actual case for many other technologies.
(And while I appreciate HATEOAS as a design philosophy, and I've tried to make use of it several times, it just is not worth the effort. It is just takes too much time to do right and to get everyone on the same page. Most proponents are more keen on telling everyone how they are using it wrong, than on writing good tools that actually help people use it right. There's very little empathy with the developer).
We ran into problems where we had embedded Ruby and Python interpreters (Chef/SaltStack) that made it a big pain to ship new libraries. It was much easier to use the grpc-gateway (HTTP/JSON) for those clients and the generated grpc bindings (HTTP2/proto) for services.
Debugging with lower-level tools like strace and tcpdump is also something that's trivial with JSON-over-HTTP/1.1, but virtually impossible with gRPC. (I mean, you could grab the payload and run it through gRPC deserialization, but would you?)
I'm a big fan of gRPC, but it is pretty top-heavy — lots of code to accomplish relatively little. If you have a language that can build client bindings dynamically from .proto files without recompilation, that would ease things a lot, but if you're using Go, for example, the bar is pretty high going from zero to productive.