distribution/storagedriver/factory/factory.go

package factory

import (
	"fmt"

	"github.com/docker/docker-registry/storagedriver"
)

// driverFactories stores an internal mapping between storage driver names and their respective
// factories
var driverFactories = make(map[string]StorageDriverFactory)

// StorageDriverFactory is a factory interface for creating storagedriver.StorageDriver interfaces
// Storage drivers should call Register() with a factory to make the driver available by name
type StorageDriverFactory interface {
	// Create returns a new storagedriver.StorageDriver with the given parameters
	// Parameters will vary by driver and may be ignored
	// Each parameter key must only consist of lowercase letters and numbers
	Create(parameters map[string]interface{}) (storagedriver.StorageDriver, error)
}

// Register makes a storage driver available by the provided name.
// If Register is called twice with the same name or if driver factory is nil, it panics.
func Register(name string, factory StorageDriverFactory) {
	if factory == nil {
		panic("Must not provide nil StorageDriverFactory")
	}
	_, registered := driverFactories[name]
	if registered {
		panic(fmt.Sprintf("StorageDriverFactory named %s already registered", name))
	}

	driverFactories[name] = factory
}

// Create a new storagedriver.StorageDriver with the given name and parameters
// To run in-process, the StorageDriverFactory must first be registered with the given name
// If no in-process drivers are found with the given name, this attempts to create an IPC driver
// If no in-process or external drivers are found, an InvalidStorageDriverError is returned
func Create(name string, parameters map[string]interface{}) (storagedriver.StorageDriver, error) {
	driverFactory, ok := driverFactories[name]
	if !ok {
		return nil, InvalidStorageDriverError{name}

		// NOTE(stevvooe): We are disabling storagedriver ipc for now, as the
		// server and client need to be updated for the changed API calls and
		// there were some problems libchan hanging. We'll phase this
		// functionality back in over the next few weeks.

		// No registered StorageDriverFactory found, try ipc
		// driverClient, err := ipc.NewDriverClient(name, parameters)
		// if err != nil {
		// 	return nil, InvalidStorageDriverError{name}
		// }
		// err = driverClient.Start()
		// if err != nil {
		// 	return nil, err
		// }
		// return driverClient, nil
	}
	return driverFactory.Create(parameters)
}

// InvalidStorageDriverError records an attempt to construct an unregistered storage driver
type InvalidStorageDriverError struct {
	Name string
}

func (err InvalidStorageDriverError) Error() string {
	return fmt.Sprintf("StorageDriver not registered: %s", err.Name)
}