apiserver: Extract common.UnitsWatcher mixin

apiserver: Extract common.UnitsWatcher mixin

Both the deployer and the upcoming firewaller
server-side APIs have a WatchUnits() method,
which is now extracted to a common.UnitsWatcher
mixin in apiserver, as a prerequiste to the firewaller
API implementation. The deployer is also changed
to use the new mixin.

https://code.launchpad.net/~dimitern/juju-core/234-apiserver-common-unitswatcher/+merge/202348

Requires: https://code.launchpad.net/~dimitern/juju-core/233-state-SortedPorts-to-instance/+merge/202347

(do not edit description out of merge proposal)

[dimitern, 2014-01-20 17:32:24]

Please take a look.

[rog, 2014-01-21 14:21:49]

LGTM with one suggestion below.

https://codereview.appspot.com/54630043/diff/1/state/apiserver/deployer/deplo...
File state/apiserver/deployer/deployer.go (right):

https://codereview.appspot.com/54630043/diff/1/state/apiserver/deployer/deplo...
state/apiserver/deployer/deployer.go:57: _, _, err := names.ParseTag(tag,
names.MachineTagKind)
Is this necessary? Surely the AuthOwner test will fail unless the tag matches
exactly, and we know that the tag we're checking against is valid, so if the
test succeeds, we know that ParseTag must have succeeded.

I'd just do:
getCanWatch := func() (common.AuthFunc, error) {
    return authorizer.AuthOwner, nil
}

[dimitern, 2014-01-21 16:03:25]

Please take a look.

https://codereview.appspot.com/54630043/diff/1/state/apiserver/deployer/deplo...
File state/apiserver/deployer/deployer.go (right):

https://codereview.appspot.com/54630043/diff/1/state/apiserver/deployer/deplo...
state/apiserver/deployer/deployer.go:57: _, _, err := names.ParseTag(tag,
names.MachineTagKind)
On 2014/01/21 14:21:49, rog wrote:
> Is this necessary? Surely the AuthOwner test will fail unless the tag matches
> exactly, and we know that the tag we're checking against is valid, so if the
> test succeeds, we know that ParseTag must have succeeded.
> 
> I'd just do:
> getCanWatch := func() (common.AuthFunc, error) {
>     return authorizer.AuthOwner, nil
> }

Done.