Rework kms folder structure

Signed-off-by: Daniel Weiße <dw@edgeless.systems>

kms/storage/gcloudstorage.go

@@ -0,0 +1,83 @@
+package storage
+
+import (
+	"context"
+	"errors"
+	"io"
+
+	"cloud.google.com/go/storage"
+	"google.golang.org/api/option"
+)
+
+// GoogleCloudStorage is an implementation of the Storage interface, storing keys in Google Cloud Storage buckets.
+type GoogleCloudStorage struct {
+	projectID  string
+	bucketName string
+	opts       []option.ClientOption
+}
+
+// NewGoogleCloudStorage creates a Storage client for Google Cloud Storage: https://cloud.google.com/storage/docs/
+//
+// The parameter bucketOptions is optional, if not present default options will be created.
+func NewGoogleCloudStorage(ctx context.Context, projectID, bucketName string, bucketOptions *storage.BucketAttrs, opts ...option.ClientOption) (*GoogleCloudStorage, error) {
+	gcStorage := &GoogleCloudStorage{
+		projectID:  projectID,
+		bucketName: bucketName,
+		opts:       opts,
+	}
+
+	// Make sure the storage bucket exists, if not create it
+	client, err := storage.NewClient(ctx, gcStorage.opts...)
+	if err != nil {
+		return nil, err
+	}
+	defer client.Close()
+
+	_, err = client.Bucket(gcStorage.bucketName).Attrs(ctx)
+	if err == nil {
+		return gcStorage, nil
+	}
+
+	if errors.Is(err, storage.ErrBucketNotExist) {
+		err = client.Bucket(gcStorage.bucketName).Create(ctx, gcStorage.projectID, bucketOptions)
+	}
+
+	return gcStorage, err
+}
+
+// Get returns a DEK from Google Cloud Storage by key ID.
+func (s *GoogleCloudStorage) Get(ctx context.Context, keyID string) ([]byte, error) {
+	client, err := storage.NewClient(ctx, s.opts...)
+	if err != nil {
+		return nil, err
+	}
+	defer client.Close()
+
+	reader, err := client.Bucket(s.bucketName).Object(keyID).NewReader(ctx)
+	if err != nil {
+		if errors.Is(err, storage.ErrObjectNotExist) {
+			return nil, ErrDEKUnset
+		}
+		return nil, err
+	}
+	defer reader.Close()
+
+	return io.ReadAll(reader)
+}
+
+// Put saves a DEK to Google Cloud Storage by key ID.
+func (s *GoogleCloudStorage) Put(ctx context.Context, keyID string, data []byte) error {
+	client, err := storage.NewClient(ctx, s.opts...)
+	if err != nil {
+		return err
+	}
+	defer client.Close()
+
+	writer := client.Bucket(s.bucketName).Object(keyID).NewWriter(ctx)
+
+	if _, err := writer.Write(data); err != nil {
+		return err
+	}
+
+	return writer.Close()
+}