github.com/axw/juju@v0.0.0-20161005053422-4bd6544d08d4/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  	"gopkg.in/juju/names.v2"
     9  
    10  	"github.com/juju/juju/apiserver/facade"
    11  	"github.com/juju/juju/apiserver/params"
    12  	"github.com/juju/juju/state"
    13  	"github.com/juju/juju/state/watcher"
    14  )
    15  
    16  // UnitsWatcher implements a common WatchUnits method for use by
    17  // various facades.
    18  type UnitsWatcher struct {
    19  	st          state.EntityFinder
    20  	resources   facade.Resources
    21  	getCanWatch GetAuthFunc
    22  }
    23  
    24  // NewUnitsWatcher returns a new UnitsWatcher. The GetAuthFunc will be
    25  // used on each invocation of WatchUnits to determine current
    26  // permissions.
    27  func NewUnitsWatcher(st state.EntityFinder, resources facade.Resources, getCanWatch GetAuthFunc) *UnitsWatcher {
    28  	return &UnitsWatcher{
    29  		st:          st,
    30  		resources:   resources,
    31  		getCanWatch: getCanWatch,
    32  	}
    33  }
    34  
    35  func (u *UnitsWatcher) watchOneEntityUnits(canWatch AuthFunc, tag names.Tag) (params.StringsWatchResult, error) {
    36  	nothing := params.StringsWatchResult{}
    37  	if !canWatch(tag) {
    38  		return nothing, ErrPerm
    39  	}
    40  	entity0, err := u.st.FindEntity(tag)
    41  	if err != nil {
    42  		return nothing, err
    43  	}
    44  	entity, ok := entity0.(state.UnitsWatcher)
    45  	if !ok {
    46  		return nothing, NotSupportedError(tag, "watching units")
    47  	}
    48  	watch := entity.WatchUnits()
    49  	// Consume the initial event and forward it to the result.
    50  	if changes, ok := <-watch.Changes(); ok {
    51  		return params.StringsWatchResult{
    52  			StringsWatcherId: u.resources.Register(watch),
    53  			Changes:          changes,
    54  		}, nil
    55  	}
    56  	return nothing, watcher.EnsureErr(watch)
    57  }
    58  
    59  // WatchUnits starts a StringsWatcher to watch all units belonging to
    60  // to any entity (machine or service) passed in args.
    61  func (u *UnitsWatcher) WatchUnits(args params.Entities) (params.StringsWatchResults, error) {
    62  	result := params.StringsWatchResults{
    63  		Results: make([]params.StringsWatchResult, len(args.Entities)),
    64  	}
    65  	if len(args.Entities) == 0 {
    66  		return result, nil
    67  	}
    68  	canWatch, err := u.getCanWatch()
    69  	if err != nil {
    70  		return params.StringsWatchResults{}, errors.Trace(err)
    71  	}
    72  	for i, entity := range args.Entities {
    73  		tag, err := names.ParseTag(entity.Tag)
    74  		if err != nil {
    75  			result.Results[i].Error = ServerError(ErrPerm)
    76  			continue
    77  		}
    78  		entityResult, err := u.watchOneEntityUnits(canWatch, tag)
    79  		result.Results[i] = entityResult
    80  		result.Results[i].Error = ServerError(err)
    81  	}
    82  	return result, nil
    83  }