Adds StorageDriverFactory, unifying creation of StorageDrivers

Custom storage drivers can register a factory to create the driver by
name, similar to the database/sql package's Register and Open
factory.Create returns an in-process driver if registered or an IPC
driver if one can be found, erroring otherwise
This standardizes parameter passing for creation of storage drivers

Also adds documentation for storagedriver package and children

storagedriver/s3/s3.go

@@ -2,6 +2,7 @@ package s3
 
 import (
 	"bytes"
+	"fmt"
 	"io"
 	"net/http"
 	"strconv"
@@ -9,21 +10,82 @@ import (
 	"github.com/crowdmob/goamz/aws"
 	"github.com/crowdmob/goamz/s3"
 	"github.com/docker/docker-registry/storagedriver"
+	"github.com/docker/docker-registry/storagedriver/factory"
 )
 
-/* Chunks need to be at least 5MB to store with a multipart upload on S3 */
+const DriverName = "s3"
+
+// Chunks need to be at least 5MB to store with a multipart upload on S3
 const minChunkSize = uint64(5 * 1024 * 1024)
 
-/* The largest amount of parts you can request from S3 */
+// The largest amount of parts you can request from S3
 const listPartsMax = 1000
 
+func init() {
+	factory.Register(DriverName, &s3DriverFactory{})
+}
+
+// Implements the factory.StorageDriverFactory interface
+type s3DriverFactory struct{}
+
+func (factory *s3DriverFactory) Create(parameters map[string]string) (storagedriver.StorageDriver, error) {
+	return FromParameters(parameters)
+}
+
+// Storage Driver backed by Amazon S3
+// Objects are stored at absolute keys in the provided bucket
 type S3Driver struct {
 	S3      *s3.S3
 	Bucket  *s3.Bucket
 	Encrypt bool
 }
 
-func NewDriver(accessKey string, secretKey string, region aws.Region, encrypt bool, bucketName string) (*S3Driver, error) {
+// Constructs a new S3Driver with a given parameters map
+// Required parameters:
+// - accesskey
+// - secretkey
+// - region
+// - bucket
+// - encrypt
+func FromParameters(parameters map[string]string) (*S3Driver, error) {
+	accessKey, ok := parameters["accesskey"]
+	if !ok || accessKey == "" {
+		return nil, fmt.Errorf("No accesskey parameter provided")
+	}
+
+	secretKey, ok := parameters["secretkey"]
+	if !ok || secretKey == "" {
+		return nil, fmt.Errorf("No secretkey parameter provided")
+	}
+
+	regionName, ok := parameters["region"]
+	if !ok || regionName == "" {
+		return nil, fmt.Errorf("No region parameter provided")
+	}
+	region := aws.GetRegion(regionName)
+	if region.Name == "" {
+		return nil, fmt.Errorf("Invalid region provided: %s", region)
+	}
+
+	bucket, ok := parameters["bucket"]
+	if !ok || bucket == "" {
+		return nil, fmt.Errorf("No bucket parameter provided")
+	}
+
+	encrypt, ok := parameters["encrypt"]
+	if !ok {
+		return nil, fmt.Errorf("No encrypt parameter provided")
+	}
+
+	encryptBool, err := strconv.ParseBool(encrypt)
+	if err != nil {
+		return nil, fmt.Errorf("Unable to parse the encrypt parameter: %v", err)
+	}
+	return New(accessKey, secretKey, region, encryptBool, bucket)
+}
+
+// Constructs a new S3Driver with the given AWS credentials, region, encryption flag, and bucketName
+func New(accessKey string, secretKey string, region aws.Region, encrypt bool, bucketName string) (*S3Driver, error) {
 	auth := aws.Auth{AccessKey: accessKey, SecretKey: secretKey}
 	s3obj := s3.New(auth, region)
 	bucket := s3obj.Bucket(bucketName)

storagedriver/s3/s3_test.go

@@ -2,6 +2,7 @@ package s3
 
 import (
 	"os"
+	"strconv"
 	"testing"
 
 	"github.com/crowdmob/goamz/aws"
@@ -14,23 +15,34 @@ import (
 func Test(t *testing.T) { TestingT(t) }
 
 func init() {
-	accessKey := os.Getenv("ACCESS_KEY")
-	secretKey := os.Getenv("SECRET_KEY")
+	accessKey := os.Getenv("AWS_ACCESS_KEY")
+	secretKey := os.Getenv("AWS_SECRET_KEY")
 	region := os.Getenv("AWS_REGION")
 	bucket := os.Getenv("S3_BUCKET")
 	encrypt := os.Getenv("S3_ENCRYPT")
 
 	s3DriverConstructor := func() (storagedriver.StorageDriver, error) {
-		return NewDriver(accessKey, secretKey, aws.GetRegion(region), true, bucket)
+		shouldEncrypt, err := strconv.ParseBool(encrypt)
+		if err != nil {
+			return nil, err
+		}
+		return New(accessKey, secretKey, aws.GetRegion(region), shouldEncrypt, bucket)
 	}
 
+	// Skip S3 storage driver tests if environment variable parameters are not provided
 	skipCheck := func() string {
 		if accessKey == "" || secretKey == "" || region == "" || bucket == "" || encrypt == "" {
-			return "Must set ACCESS_KEY, SECRET_KEY, AWS_REGION, S3_BUCKET, and S3_ENCRYPT to run S3 tests"
+			return "Must set AWS_ACCESS_KEY, AWS_SECRET_KEY, AWS_REGION, S3_BUCKET, and S3_ENCRYPT to run S3 tests"
 		}
 		return ""
 	}
 
 	testsuites.RegisterInProcessSuite(s3DriverConstructor, skipCheck)
-	testsuites.RegisterIPCSuite("s3", map[string]string{"accessKey": accessKey, "secretKey": secretKey, "region": region, "bucket": bucket, "encrypt": encrypt}, skipCheck)
+	testsuites.RegisterIPCSuite(DriverName, map[string]string{
+		"accesskey": accessKey,
+		"secretkey": secretKey,
+		"region":    region,
+		"bucket":    bucket,
+		"encrypt":   encrypt,
+	}, skipCheck)
 }