github.com/makyo/juju@v0.0.0-20160425123129-2608902037e9/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  	"github.com/juju/errors"
     8  	"github.com/juju/names"
     9  
    10  	"github.com/juju/juju/apiserver/params"
    11  	"github.com/juju/juju/state"
    12  	"github.com/juju/juju/state/watcher"
    13  )
    14  
    15  // UnitsWatcher implements a common WatchUnits method for use by
    16  // various facades.
    17  type UnitsWatcher struct {
    18  	st          state.EntityFinder
    19  	resources   *Resources
    20  	getCanWatch GetAuthFunc
    21  }
    22  
    23  // NewUnitsWatcher returns a new UnitsWatcher. The GetAuthFunc will be
    24  // used on each invocation of WatchUnits to determine current
    25  // permissions.
    26  func NewUnitsWatcher(st state.EntityFinder, resources *Resources, getCanWatch GetAuthFunc) *UnitsWatcher {
    27  	return &UnitsWatcher{
    28  		st:          st,
    29  		resources:   resources,
    30  		getCanWatch: getCanWatch,
    31  	}
    32  }
    33  
    34  func (u *UnitsWatcher) watchOneEntityUnits(canWatch AuthFunc, tag names.Tag) (params.StringsWatchResult, error) {
    35  	nothing := params.StringsWatchResult{}
    36  	if !canWatch(tag) {
    37  		return nothing, ErrPerm
    38  	}
    39  	entity0, err := u.st.FindEntity(tag)
    40  	if err != nil {
    41  		return nothing, err
    42  	}
    43  	entity, ok := entity0.(state.UnitsWatcher)
    44  	if !ok {
    45  		return nothing, NotSupportedError(tag, "watching units")
    46  	}
    47  	watch := entity.WatchUnits()
    48  	// Consume the initial event and forward it to the result.
    49  	if changes, ok := <-watch.Changes(); ok {
    50  		return params.StringsWatchResult{
    51  			StringsWatcherId: u.resources.Register(watch),
    52  			Changes:          changes,
    53  		}, nil
    54  	}
    55  	return nothing, watcher.EnsureErr(watch)
    56  }
    57  
    58  // WatchUnits starts a StringsWatcher to watch all units belonging to
    59  // to any entity (machine or service) passed in args.
    60  func (u *UnitsWatcher) WatchUnits(args params.Entities) (params.StringsWatchResults, error) {
    61  	result := params.StringsWatchResults{
    62  		Results: make([]params.StringsWatchResult, len(args.Entities)),
    63  	}
    64  	if len(args.Entities) == 0 {
    65  		return result, nil
    66  	}
    67  	canWatch, err := u.getCanWatch()
    68  	if err != nil {
    69  		return params.StringsWatchResults{}, errors.Trace(err)
    70  	}
    71  	for i, entity := range args.Entities {
    72  		tag, err := names.ParseTag(entity.Tag)
    73  		if err != nil {
    74  			result.Results[i].Error = ServerError(ErrPerm)
    75  			continue
    76  		}
    77  		entityResult, err := u.watchOneEntityUnits(canWatch, tag)
    78  		result.Results[i] = entityResult
    79  		result.Results[i].Error = ServerError(err)
    80  	}
    81  	return result, nil
    82  }