func (s *StorageAPI) watchOneStorageAttachment(id params.StorageAttachmentId, canAccess func(names.Tag) bool) (params.NotifyWatchResult, error) {
// Watching a storage attachment is implemented as watching the
// underlying volume or filesystem attachment. The only thing
// we don't necessarily see in doing this is the lifecycle state
// changes, but these may be observed by using the
// WatchUnitStorageAttachments watcher.
nothing := params.NotifyWatchResult{}
unitTag, err := names.ParseUnitTag(id.UnitTag)
if err != nil || !canAccess(unitTag) {
return nothing, common.ErrPerm
}
storageTag, err := names.ParseStorageTag(id.StorageTag)
if err != nil {
return nothing, err
}
machineTag, err := s.st.UnitAssignedMachine(unitTag)
if err != nil {
return nothing, err
}
watch, err := storagecommon.WatchStorageAttachment(s.st, storageTag, machineTag, unitTag)
if err != nil {
return nothing, errors.Trace(err)
}
if _, ok := <-watch.Changes(); ok {
return params.NotifyWatchResult{
NotifyWatcherId: s.resources.Register(watch),
}, nil
}
return nothing, watcher.EnsureErr(watch)
}
func (s *watchStorageAttachmentSuite) testWatchStorageAttachment(c *gc.C, change func()) {
w, err := storagecommon.WatchStorageAttachment(
s.st,
s.storageTag,
s.machineTag,
s.unitTag,
)
c.Assert(err, jc.ErrorIsNil)
wc := statetesting.NewNotifyWatcherC(c, nopSyncStarter{}, w)
wc.AssertOneChange()
change()
wc.AssertOneChange()
}