github.com/niedbalski/juju@v0.0.0-20190215020005-8ff100488e47/worker/migrationflag/manifold.go (about)

     1  // Copyright 2016 Canonical Ltd.
     2  // Licensed under the AGPLv3, see LICENCE file for details.
     3  
     4  package migrationflag
     5  
     6  import (
     7  	"github.com/juju/errors"
     8  	"gopkg.in/juju/worker.v1"
     9  	"gopkg.in/juju/worker.v1/dependency"
    10  
    11  	"github.com/juju/juju/api/base"
    12  	"github.com/juju/juju/cmd/jujud/agent/engine"
    13  )
    14  
    15  // ManifoldConfig holds the dependencies and configuration for a
    16  // Worker manifold.
    17  type ManifoldConfig struct {
    18  	APICallerName string
    19  	Check         Predicate
    20  
    21  	NewFacade func(base.APICaller) (Facade, error)
    22  	NewWorker func(Config) (worker.Worker, error)
    23  }
    24  
    25  // validate is called by start to check for bad configuration.
    26  func (config ManifoldConfig) validate() error {
    27  	if config.APICallerName == "" {
    28  		return errors.NotValidf("empty APICallerName")
    29  	}
    30  	if config.Check == nil {
    31  		return errors.NotValidf("nil Check")
    32  	}
    33  	if config.NewFacade == nil {
    34  		return errors.NotValidf("nil NewFacade")
    35  	}
    36  	if config.NewWorker == nil {
    37  		return errors.NotValidf("nil NewWorker")
    38  	}
    39  	return nil
    40  }
    41  
    42  // start is a StartFunc for a Worker manifold.
    43  func (config ManifoldConfig) start(context dependency.Context) (worker.Worker, error) {
    44  	if err := config.validate(); err != nil {
    45  		return nil, errors.Trace(err)
    46  	}
    47  	var apiCaller base.APICaller
    48  	if err := context.Get(config.APICallerName, &apiCaller); err != nil {
    49  		return nil, errors.Trace(err)
    50  	}
    51  	facade, err := config.NewFacade(apiCaller)
    52  	if err != nil {
    53  		return nil, errors.Trace(err)
    54  	}
    55  	modelTag, ok := apiCaller.ModelTag()
    56  	if !ok {
    57  		return nil, errors.New("API connection is controller-only (should never happen)")
    58  	}
    59  	worker, err := config.NewWorker(Config{
    60  		Facade: facade,
    61  		Model:  modelTag.Id(),
    62  		Check:  config.Check,
    63  	})
    64  	if err != nil {
    65  		return nil, errors.Trace(err)
    66  	}
    67  	return worker, nil
    68  }
    69  
    70  // Manifold packages a Worker for use in a dependency.Engine.
    71  func Manifold(config ManifoldConfig) dependency.Manifold {
    72  	return dependency.Manifold{
    73  		Inputs: []string{config.APICallerName},
    74  		Start:  config.start,
    75  		Output: engine.FlagOutput,
    76  		Filter: bounceErrChanged,
    77  	}
    78  }
    79  
    80  // bounceErrChanged converts ErrChanged to dependency.ErrBounce.
    81  func bounceErrChanged(err error) error {
    82  	if errors.Cause(err) == ErrChanged {
    83  		return dependency.ErrBounce
    84  	}
    85  	return err
    86  }