github.com/juju/juju@v0.0.0-20240430160146-1752b71fcf00/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  	"github.com/juju/worker/v3"
     9  	"github.com/juju/worker/v3/dependency"
    10  
    11  	"github.com/juju/juju/api/base"
    12  	"github.com/juju/juju/cmd/jujud/agent/engine"
    13  )
    14  
    15  // logger is here to stop the desire of creating a package level logger.
    16  // Don't do this, instead pass one passed as manifold config.
    17  type logger interface{}
    18  
    19  var _ logger = struct{}{}
    20  
    21  // ManifoldConfig holds the dependencies and configuration for a
    22  // Worker manifold.
    23  type ManifoldConfig struct {
    24  	APICallerName string
    25  	Check         Predicate
    26  
    27  	NewFacade func(base.APICaller) (Facade, error)
    28  	NewWorker func(Config) (worker.Worker, error)
    29  }
    30  
    31  // validate is called by start to check for bad configuration.
    32  func (config ManifoldConfig) validate() error {
    33  	if config.APICallerName == "" {
    34  		return errors.NotValidf("empty APICallerName")
    35  	}
    36  	if config.Check == nil {
    37  		return errors.NotValidf("nil Check")
    38  	}
    39  	if config.NewFacade == nil {
    40  		return errors.NotValidf("nil NewFacade")
    41  	}
    42  	if config.NewWorker == nil {
    43  		return errors.NotValidf("nil NewWorker")
    44  	}
    45  	return nil
    46  }
    47  
    48  // start is a StartFunc for a Worker manifold.
    49  func (config ManifoldConfig) start(context dependency.Context) (worker.Worker, error) {
    50  	if err := config.validate(); err != nil {
    51  		return nil, errors.Trace(err)
    52  	}
    53  	var apiCaller base.APICaller
    54  	if err := context.Get(config.APICallerName, &apiCaller); err != nil {
    55  		return nil, errors.Trace(err)
    56  	}
    57  	facade, err := config.NewFacade(apiCaller)
    58  	if err != nil {
    59  		return nil, errors.Trace(err)
    60  	}
    61  	modelTag, ok := apiCaller.ModelTag()
    62  	if !ok {
    63  		return nil, errors.New("API connection is controller-only (should never happen)")
    64  	}
    65  	worker, err := config.NewWorker(Config{
    66  		Facade: facade,
    67  		Model:  modelTag.Id(),
    68  		Check:  config.Check,
    69  	})
    70  	if err != nil {
    71  		return nil, errors.Trace(err)
    72  	}
    73  	return worker, nil
    74  }
    75  
    76  // Manifold packages a Worker for use in a dependency.Engine.
    77  func Manifold(config ManifoldConfig) dependency.Manifold {
    78  	return dependency.Manifold{
    79  		Inputs: []string{config.APICallerName},
    80  		Start:  config.start,
    81  		Output: engine.FlagOutput,
    82  		Filter: bounceErrChanged,
    83  	}
    84  }
    85  
    86  // bounceErrChanged converts ErrChanged to dependency.ErrBounce.
    87  func bounceErrChanged(err error) error {
    88  	if errors.Cause(err) == ErrChanged {
    89  		return dependency.ErrBounce
    90  	}
    91  	return err
    92  }