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manifold.go
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manifold.go
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// Copyright 2016 Canonical Ltd.
// Licensed under the AGPLv3, see LICENCE file for details.
package migrationflag
import (
"github.com/juju/errors"
"github.com/juju/worker/v3"
"github.com/juju/worker/v3/dependency"
"github.com/juju/juju/api/base"
"github.com/juju/juju/cmd/jujud/agent/engine"
)
// logger is here to stop the desire of creating a package level logger.
// Don't do this, instead pass one passed as manifold config.
type logger interface{}
var _ logger = struct{}{}
// ManifoldConfig holds the dependencies and configuration for a
// Worker manifold.
type ManifoldConfig struct {
APICallerName string
Check Predicate
NewFacade func(base.APICaller) (Facade, error)
NewWorker func(Config) (worker.Worker, error)
}
// validate is called by start to check for bad configuration.
func (config ManifoldConfig) validate() error {
if config.APICallerName == "" {
return errors.NotValidf("empty APICallerName")
}
if config.Check == nil {
return errors.NotValidf("nil Check")
}
if config.NewFacade == nil {
return errors.NotValidf("nil NewFacade")
}
if config.NewWorker == nil {
return errors.NotValidf("nil NewWorker")
}
return nil
}
// start is a StartFunc for a Worker manifold.
func (config ManifoldConfig) start(context dependency.Context) (worker.Worker, error) {
if err := config.validate(); err != nil {
return nil, errors.Trace(err)
}
var apiCaller base.APICaller
if err := context.Get(config.APICallerName, &apiCaller); err != nil {
return nil, errors.Trace(err)
}
facade, err := config.NewFacade(apiCaller)
if err != nil {
return nil, errors.Trace(err)
}
modelTag, ok := apiCaller.ModelTag()
if !ok {
return nil, errors.New("API connection is controller-only (should never happen)")
}
worker, err := config.NewWorker(Config{
Facade: facade,
Model: modelTag.Id(),
Check: config.Check,
})
if err != nil {
return nil, errors.Trace(err)
}
return worker, nil
}
// Manifold packages a Worker for use in a dependency.Engine.
func Manifold(config ManifoldConfig) dependency.Manifold {
return dependency.Manifold{
Inputs: []string{config.APICallerName},
Start: config.start,
Output: engine.FlagOutput,
Filter: bounceErrChanged,
}
}
// bounceErrChanged converts ErrChanged to dependency.ErrBounce.
func bounceErrChanged(err error) error {
if errors.Cause(err) == ErrChanged {
return dependency.ErrBounce
}
return err
}