github.com/cloudbase/juju-core@v0.0.0-20140504232958-a7271ac7912f/state/apiserver/common/unitswatcher.go (about)

     1  // Copyright 2013 Canonical Ltd.
     2  // Licensed under the AGPLv3, see LICENCE file for details.
     3  
     4  package common
     5  
     6  import (
     7  	"launchpad.net/juju-core/state"
     8  	"launchpad.net/juju-core/state/api/params"
     9  	"launchpad.net/juju-core/state/watcher"
    10  )
    11  
    12  // UnitsWatcher implements a common WatchUnits method for use by
    13  // various facades.
    14  type UnitsWatcher struct {
    15  	st          state.EntityFinder
    16  	resources   *Resources
    17  	getCanWatch GetAuthFunc
    18  }
    19  
    20  // NewUnitsWatcher returns a new UnitsWatcher. The GetAuthFunc will be
    21  // used on each invocation of WatchUnits to determine current
    22  // permissions.
    23  func NewUnitsWatcher(st state.EntityFinder, resources *Resources, getCanWatch GetAuthFunc) *UnitsWatcher {
    24  	return &UnitsWatcher{
    25  		st:          st,
    26  		resources:   resources,
    27  		getCanWatch: getCanWatch,
    28  	}
    29  }
    30  
    31  func (u *UnitsWatcher) watchOneEntityUnits(canWatch AuthFunc, tag string) (params.StringsWatchResult, error) {
    32  	nothing := params.StringsWatchResult{}
    33  	if !canWatch(tag) {
    34  		return nothing, ErrPerm
    35  	}
    36  	entity0, err := u.st.FindEntity(tag)
    37  	if err != nil {
    38  		return nothing, err
    39  	}
    40  	entity, ok := entity0.(state.UnitsWatcher)
    41  	if !ok {
    42  		return nothing, NotSupportedError(tag, "watching units")
    43  	}
    44  	watch := entity.WatchUnits()
    45  	// Consume the initial event and forward it to the result.
    46  	if changes, ok := <-watch.Changes(); ok {
    47  		return params.StringsWatchResult{
    48  			StringsWatcherId: u.resources.Register(watch),
    49  			Changes:          changes,
    50  		}, nil
    51  	}
    52  	return nothing, watcher.MustErr(watch)
    53  }
    54  
    55  // WatchUnits starts a StringsWatcher to watch all units belonging to
    56  // to any entity (machine or service) passed in args.
    57  func (u *UnitsWatcher) WatchUnits(args params.Entities) (params.StringsWatchResults, error) {
    58  	result := params.StringsWatchResults{
    59  		Results: make([]params.StringsWatchResult, len(args.Entities)),
    60  	}
    61  	if len(args.Entities) == 0 {
    62  		return result, nil
    63  	}
    64  	canWatch, err := u.getCanWatch()
    65  	if err != nil {
    66  		return params.StringsWatchResults{}, err
    67  	}
    68  	for i, entity := range args.Entities {
    69  		entityResult, err := u.watchOneEntityUnits(canWatch, entity.Tag)
    70  		result.Results[i] = entityResult
    71  		result.Results[i].Error = ServerError(err)
    72  	}
    73  	return result, nil
    74  }