Replace caps.Type struct with an interface

[zyga]

The capability type is now an interface. This allows each type to freely
define appropriate logic in a non-declarative way. Some small changes
related to that are the change of the Validate() method to Sanitize()
which can also explicitly mutate a capability (currently this is not
used yet).

Along with this change, caps.Capability.Type is replaced with .TypeName
which is simply a string so that capabilities can be serialized easily.

Signed-off-by: Zygmunt Krynicki zygmunt.krynicki@canonical.com

[niemeyer]

For the record, I generally try to avoid such whitebox tests. There's really not much benefit in simply knowing something is inside a given attribute. The best kind of test is those that verify that the value interface behaves as it should. In other words, what is the observable result of this repository knowing about the bool-file type? This outcome cannot change because it's a promise we're making to clients of this API, so it's a better thing to ensure in a test too. The internals can be modified as long as this promise isn't broken.

[zyga]

Would this be better?

c.Assert(repo.Type("bool-file"), Not(IsNil))

[zyga]

Thanks, I agree about the internal-vs-contract point. I've tweaked the test to check what is really relevant -- that bool-file type is registered.

[niemeyer]

Can we avoid having this here? It just maps to Name.

[zyga]

Yeah, I think I just copied that over from older Type. I'll remove it.

[zyga]

Done

[niemeyer]

s/Mock/Test/? Mock tends to imply a certain kind of behavior from the value.

[zyga]

Done

[niemeyer]

A few comments above, but LGTM!

[mvo5]

I'm curious, why was the name changed to Sanitize? That is something you usually do on a toilet to clean it (and in the hospital of course). I'm not a native speaker so I could be wrong and this is bike-shed territory for sure. What exactly will this function do? What does "altering if necessary" means? What kind of alteration?

[zyga]

The name changed because the method can now modify the capability and we wanted to make it explicit. I'm open to a better name, we picked sanitize in a quick discussion.

Edit: modify == modify attributes.

[pedronis]

@zyga @mvo5 I have seen "sanitize" used but usually it has a connotation of also making something potentially unsafe safe, (like taking html text and removing dangerous tags), is that the case here? otherwise is a strange term here

[zyga]

@pedronis yes, we explicitly reserve the right to modify capability data or reject it entirely.
Sanitize() == Validate() + Alter()

[pedronis]

@zyga that's the weird bit, "sanitize" implies that you almost never reject but make innocuous

[mvo5]

I don't know what "Alter()" will do so I don't really know what to suggest. Its just a name, if there is no better idea lets use, we can always change it later :)

[mvo5]

Code looks good, just one question about the terminology. I'm not hung up on it so no blocker. I just wonder if there is something more fitting. Part of the problem is that I don't know enough about the future, i.e. what "altering the capability" means.