github.com/niedbalski/juju@v0.0.0-20190215020005-8ff100488e47/api/lifeflag/facade.go (about)

     1  // Copyright 2016 Canonical Ltd.
     2  // Licensed under the AGPLv3, see LICENCE file for details.
     3  
     4  package lifeflag
     5  
     6  import (
     7  	"github.com/juju/errors"
     8  	"gopkg.in/juju/names.v2"
     9  
    10  	"github.com/juju/juju/api/base"
    11  	"github.com/juju/juju/apiserver/params"
    12  	"github.com/juju/juju/core/life"
    13  	"github.com/juju/juju/core/watcher"
    14  )
    15  
    16  // NewWatcherFunc exists to let us test Watch properly.
    17  type NewWatcherFunc func(base.APICaller, params.NotifyWatchResult) watcher.NotifyWatcher
    18  
    19  // Facade makes calls to the LifeFlag facade.
    20  type Facade struct {
    21  	caller     base.FacadeCaller
    22  	newWatcher NewWatcherFunc
    23  }
    24  
    25  // NewFacade returns a new Facade using the supplied caller.
    26  func NewFacade(caller base.APICaller, newWatcher NewWatcherFunc) *Facade {
    27  	return &Facade{
    28  		caller:     base.NewFacadeCaller(caller, "LifeFlag"),
    29  		newWatcher: newWatcher,
    30  	}
    31  }
    32  
    33  // ErrNotFound indicates that the requested entity no longer exists.
    34  //
    35  // We avoid errors.NotFound, because errors.NotFound is non-specific, and
    36  // it's our job to communicate *this specific condition*. There are many
    37  // possible sources of errors.NotFound in the world, and it's not safe or
    38  // sane for a client to treat a generic NotFound as specific to the entity
    39  // in question.
    40  //
    41  // We're still vulnerable to apiservers returning unjustified CodeNotFound
    42  // but at least we're safe from accidental errors.NotFound injection in
    43  // the api client mechanism.
    44  var ErrNotFound = errors.New("entity not found")
    45  
    46  // Watch returns a NotifyWatcher that sends a value whenever the
    47  // entity's life value may have changed; or ErrNotFound; or some
    48  // other error.
    49  func (facade *Facade) Watch(entity names.Tag) (watcher.NotifyWatcher, error) {
    50  	args := params.Entities{
    51  		Entities: []params.Entity{{Tag: entity.String()}},
    52  	}
    53  	var results params.NotifyWatchResults
    54  	err := facade.caller.FacadeCall("Watch", args, &results)
    55  	if err != nil {
    56  		return nil, errors.Trace(err)
    57  	}
    58  	if count := len(results.Results); count != 1 {
    59  		return nil, errors.Errorf("expected 1 Watch result, got %d", count)
    60  	}
    61  	result := results.Results[0]
    62  	if err := result.Error; err != nil {
    63  		if params.IsCodeNotFound(err) {
    64  			return nil, ErrNotFound
    65  		}
    66  		return nil, errors.Trace(result.Error)
    67  	}
    68  	w := facade.newWatcher(facade.caller.RawAPICaller(), result)
    69  	return w, nil
    70  }
    71  
    72  // Life returns the entity's life value; or ErrNotFound; or some
    73  // other error.
    74  func (facade *Facade) Life(entity names.Tag) (life.Value, error) {
    75  	args := params.Entities{
    76  		Entities: []params.Entity{{Tag: entity.String()}},
    77  	}
    78  	var results params.LifeResults
    79  	err := facade.caller.FacadeCall("Life", args, &results)
    80  	if err != nil {
    81  		return "", errors.Trace(err)
    82  	}
    83  	if count := len(results.Results); count != 1 {
    84  		return "", errors.Errorf("expected 1 Life result, got %d", count)
    85  	}
    86  	result := results.Results[0]
    87  	if err := result.Error; err != nil {
    88  		if params.IsCodeNotFound(err) {
    89  			return "", ErrNotFound
    90  		}
    91  		return "", errors.Trace(result.Error)
    92  	}
    93  	life := life.Value(result.Life)
    94  	if err := life.Validate(); err != nil {
    95  		return "", errors.Trace(err)
    96  	}
    97  	return life, nil
    98  }