plugins.go

/*
Copyright 2014 Google Inc. All rights reserved.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package cloudprovider

import (
	"io"
	"os"
	"sync"

	"github.com/golang/glog"
)

// Factory is a function that returns a cloudprovider.Interface.
// The config parameter provides an io.Reader handler to the factory in
// order to load specific configurations. If no configuration is provided
// the parameter is nil.
type Factory func(config io.Reader) (Interface, error)

// All registered cloud providers.
var providersMutex sync.Mutex
var providers = make(map[string]Factory)

// RegisterCloudProvider registers a cloudprovider.Factory by name.  This
// is expected to happen during app startup.
func RegisterCloudProvider(name string, cloud Factory) {
	providersMutex.Lock()
	defer providersMutex.Unlock()
	if _, found := providers[name]; found {
		glog.Fatalf("Cloud provider %q was registered twice", name)
	}
	glog.V(1).Infof("Registered cloud provider %q", name)
	providers[name] = cloud
}

// GetCloudProvider creates an instance of the named cloud provider, or nil if
// the name is not known.  The error return is only used if the named provider
// was known but failed to initialize. The config parameter specifies the
// io.Reader handler of the configuration file for the cloud provider, or nil
// for no configuation.
func GetCloudProvider(name string, config io.Reader) (Interface, error) {
	providersMutex.Lock()
	defer providersMutex.Unlock()
	f, found := providers[name]
	if !found {
		return nil, nil
	}
	return f(config)
}

// InitCloudProvider creates an instance of the named cloud provider.
func InitCloudProvider(name string, configFilePath string) Interface {
	var cloud Interface

	if name == "" {
		glog.Info("No cloud provider specified.")
		return nil
	}

	var err error
	if configFilePath != "" {
		config, err := os.Open(configFilePath)
		if err != nil {
			glog.Fatalf("Couldn't open cloud provider configuration %s: %#v",
				configFilePath, err)
		}

		defer config.Close()
		cloud, err = GetCloudProvider(name, config)
	} else {
		// Pass explicit nil so plugins can actually check for nil. See
		// "Why is my nil error value not equal to nil?" in golang.org/doc/faq.
		cloud, err = GetCloudProvider(name, nil)
	}

	if err != nil {
		glog.Fatalf("Couldn't init cloud provider %q: %v", name, err)
	}
	if cloud == nil {
		glog.Fatalf("Unknown cloud provider: %s", name)
	}

	return cloud
}