Add decorators to specify when a REST endpoint was added

[graysonarts]

Needed to be able to show users meaningful errors if they are using a version of the REST api that does not support a certain feature. This is needed to fully address #54

[t8y8]

Currently there is only one serializer for each request type -- since the schemas aren't always compatible we'll need to deal with that somehow.

[graysonarts]

I don't follow what you mean here? As long as the major version number hasn't changed, the schemas should be compatible because we guarantee no breaking changes unless the major version is revved. I would imagine we'll branch and no longer add features to the 2.x version once 3.x comes in.

[t8y8]

We've added attributes over time, so a 2.3 type (connectionCredneitals for example) may have an attribute that 2.2 does not have. If the serializer doesn't know about those differences it'll get stripped out either on read or write.

The endpoint itself is backwards compatible because we ignore attributes we don't understand and treat them all as optional.

[graysonarts]

i still don't see where the problem is? If we ignore the extra attributes, then it doesn't matter as long as the serializer includes all of them, the rest endpoint should handle it properly. If we changed the meaning of attributes, then that's a breaking change and we should have revved the major version.

[t8y8]

Yeah, I guess I'm saying I don't know -- you're probably right.

I'm not aware of any places we changed the meaning of an attribute, just their existence.

[graysonarts]

yeah, I think there will be some exploration that happens when we implement this enhancement. If there are attributes we need to not serialize, we could have another decorator that says "remove this attribute if less than version x" or we could have separate serializers for each version where we need them. It's something to figure out, but I think it should all work.

[t8y8]

I hacked up a quick decorator and tested that this does in fact work:

def min_api(min_ver):
    def outter_api_decorator(func):
        @wraps(func)
        def wrapper(self, *args):
            server_version = self.parent_srv.version
            if float(server_version) < min_ver:
                error = "This endpoint is not support in version {}. Requires {}".format(server_version, min_ver)
                raise ValueError(error)
            return func(self, *args)
        return wrapper
    return outter_api_decorator

It should probably throw a specific exception EndpointNotSupported or something but this was copy/paste from an example to start.

1. Where to put it? What exception to use? Will this work? Etc.
2. I think it really needs the 'auto-detect' part of the version detection function to be the most useful

/cc @RussTheAerialist

[t8y8]

EDIT: Nope, I lied, but I had the funniest bug in our code ever. Nothing to see here, move along