[outofmyshed]

If REST APIs are the worst, how does that account for their immense utility and popularity?

I wrangled XML-RPC and SOAP back in the day. It was bad enough when you had exactly the same stacks talking to each other. When you had to interop between systems, ie .NET talking to Java, which was half the point of it all, it was a whole new circle of hell.

[tannhaeuser]

Yes SOAP interoperability sucked, no arguing about that. The fact alone that you needed interoperability guidelines (WS-I) on top speaks volumes about W3C's derailed standardization effort - a similar problem is hunting today's OAuth standard btw.

But just that SOAP sucks doesn't mean "REST" is ideal. Fallacy of the excluded middle and all.

[Pamar]

I have to disagree.

I used XML-RPC exactly twice, but it proved to be a quick solution to nasty integration problems and we were very happy with it.

Case #1 - we had to implement an interface to book flights on Amadeus (https://amadeus.com/en). In order to guarantee the caller identity they provided a C library (binaries that you had to link with your stuff) that would generate tokens that you would then add to your own calls to them to guarantee your identity. We were trying to use it from a Solaris machine, and the library would bomb at each call. But their Windows binary module worked fine, so we basically put up an XML-RPC connection between our Solaris hosted main app and a little Windows service which would simply provide the token for us to embed in the subsequent call. (This was the only way we could find to hit our release date in time, and it worked fine for 5 years serving hundred of thousands of calls every year).

Case #2 - less "business critical", but still fine: I was on sick leave from the office recovering from minor trauma to my knee and here is what I suggested to a guy trying to use a PERL library as part of non-PERL stack: https://stackoverflow.com/a/2635719/54504

(it was part of his final exam for a degree in CS, I provided more assistance outside of StackOverflow and he was very happy with the results).

[akx]

Trying to get Python SOAP stacks to talk to Java/.NET banking services was another thing too.

I still get mild PTSD from thinking about XMLsec and XML c14n.