State should not depend on the API server

[William Reade]

On Mon, Sep 1, 2014 at 8:03 AM, John Meinel <john at arbash-meinel.com> wrote:
> FWIW I'd favor 3 layers, though it does mean you have to do copying between
> structs that would likely otherwise be almost identical. A State layer for
> saving in the DB, an API layer for communication, and a Model layer for use
> in the Agents/Clients.

Yes please, in general: one set of types per layer boundary.
Independent of what Dave's doing, which is necessary regardless, I
agree with what you're saying: *except* that I think we really have to
consider the API layer to be *two* layers.

That is to say: if you can change some type in api/params and
everything still works, you are Doing It Wrong. We cannot depend on
servers and clients always running the same version -- so, every time
you thus change server/client in a single motion, you're almost
certainly introducing more or less subtle incompatibilities.

So, I would be very pleased if we would stop using the same
definitions (ie api/params) on both sides of the wire -- it's one of
those things that's nice and easy when everyone's running the same
version, but an active trap as soon as multiple versions exist (as
they do).

All the struct-copying is kinda boring, but the layering violations
are straight-up evil.

Dave, thanks very much for doing this.

Cheers
William