I'm wrapping up a REST layer to the service backend I've been developing for my still-unnamed-employer (find out when we launch, real soon now!). I had never developed a service under the "REST" acronym before, so my boss gave me a crash course, I read some things, I thought I got it. REST, a buzzword in its own right, is like stapling smoke to water when you try to define it. That isn't because its vague, its because most of the people who talk about it don't know what they're talking about.
Maybe I'm one of them and I shouldn't be posting this.
REST is Not:
- A protocol, format, or even much of a specification
- An idea(l)
- Agnostic on just about every specification associated with it
- Atomic. No request relies on any other made before or after it.
- Self Authenticating. Every request must include any credentials. See point 1.
- Self Describing. This is most commonly XML, and sometimes people think it must be, but it can be anything. We use JSON.
In particular, you are not always transfering a state. There is a distinct difference between state transfer and a request to perform some operation upon a state. Unfortunately, any ways around some of the problems posed are directly rejected by the rules of REST.
For example, say you want to provide as a service a simple counter. You expose PUT on /counter/foobar to register a new counter, and then GET on /counter/foobar will provide the current level of the counter. Following the rules of REST, how do you provide an interface to safely increment such a counter? We can not perform a GET and a PUT, because it violates that each request be self contained, and it will break when any other client of the service is incrementing at the same time. We need a single operation to alter the state, without performing a state transfer.
The best thing you can do is use POST on a resource, and transfer a request to increment. It seems to violate the tenents of REST that the resource you POST will not actually reside at some permenant location, as they are throw-away requests. You either have to live with a not-exactly-REST interface (but, isn't that it works the important thing?) or actually keep requests around for some time. Maybe put them at some location, where they can be checked for review of their status.
I don't know if this is helpful to anyone else writing REST services, but the information around isn't always accurate, so why should I worry if I am?