0f09bcd16a
This commit adds context-specific documentation on StorageDriver, StorageDriverFactory, and the factory’s Register func, explaining how the internal registration mechanism should be used. This documentation follows from the thread starting at https://github.com/deis/builder/pull/262/files#r56720200. cc/ @stevvooe Signed-off-by: Aaron Schlesinger <aschlesinger@deis.com>
64 lines
2.7 KiB
Go
64 lines
2.7 KiB
Go
package factory
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import (
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"fmt"
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storagedriver "github.com/docker/distribution/registry/storage/driver"
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)
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// driverFactories stores an internal mapping between storage driver names and their respective
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// factories
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var driverFactories = make(map[string]StorageDriverFactory)
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// StorageDriverFactory is a factory interface for creating storagedriver.StorageDriver interfaces
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// Storage drivers should call Register() with a factory to make the driver available by name.
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// Individual StorageDriver implementations generally register with the factory via the Register
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// func (below) in their init() funcs, and as such they should be imported anonymously before use.
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// See below for an example of how to register and get a StorageDriver for S3
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//
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// import _ "github.com/docker/distribution/registry/storage/driver/s3-aws"
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// s3Driver, err = factory.Create("s3", storageParams)
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// // assuming no error, s3Driver is the StorageDriver that communicates with S3 according to storageParams
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type StorageDriverFactory interface {
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// Create returns a new storagedriver.StorageDriver with the given parameters
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// Parameters will vary by driver and may be ignored
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// Each parameter key must only consist of lowercase letters and numbers
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Create(parameters map[string]interface{}) (storagedriver.StorageDriver, error)
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}
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// Register makes a storage driver available by the provided name.
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// If Register is called twice with the same name or if driver factory is nil, it panics.
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// Additionally, it is not concurrency safe. Most Storage Drivers call this function
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// in their init() functions. See the documentation for StorageDriverFactory for more.
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func Register(name string, factory StorageDriverFactory) {
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if factory == nil {
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panic("Must not provide nil StorageDriverFactory")
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}
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_, registered := driverFactories[name]
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if registered {
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panic(fmt.Sprintf("StorageDriverFactory named %s already registered", name))
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}
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driverFactories[name] = factory
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}
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// Create a new storagedriver.StorageDriver with the given name and
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// parameters. To use a driver, the StorageDriverFactory must first be
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// registered with the given name. If no drivers are found, an
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// InvalidStorageDriverError is returned
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func Create(name string, parameters map[string]interface{}) (storagedriver.StorageDriver, error) {
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driverFactory, ok := driverFactories[name]
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if !ok {
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return nil, InvalidStorageDriverError{name}
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}
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return driverFactory.Create(parameters)
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}
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// InvalidStorageDriverError records an attempt to construct an unregistered storage driver
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type InvalidStorageDriverError struct {
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Name string
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}
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func (err InvalidStorageDriverError) Error() string {
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return fmt.Sprintf("StorageDriver not registered: %s", err.Name)
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}
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