client: Change ImageSave to use functional options

Signed-off-by: Paweł Gronowski <pawel.gronowski@docker.com>

client/image_save.go

@@ -2,24 +2,58 @@ package client // import "github.com/docker/docker/client"
 
 import (
 	"context"
+	"fmt"
 	"io"
 	"net/url"
 
 	"github.com/docker/docker/api/types/image"
+	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
 )
 
+type ImageSaveOption interface {
+	Apply(*imageSaveOpts) error
+}
+type imageSaveOptionFunc func(opt *imageSaveOpts) error
+
+func (f imageSaveOptionFunc) Apply(o *imageSaveOpts) error {
+	return f(o)
+}
+
+func ImageSaveWithPlatforms(platforms ...ocispec.Platform) ImageSaveOption {
+	return imageSaveOptionFunc(func(opt *imageSaveOpts) error {
+		if opt.apiOptions.Platforms != nil {
+			return fmt.Errorf("platforms already set to %v", opt.apiOptions.Platforms)
+		}
+		opt.apiOptions.Platforms = platforms
+		return nil
+	})
+}
+
+type imageSaveOpts struct {
+	apiOptions image.SaveOptions
+}
+
 // ImageSave retrieves one or more images from the docker host as an io.ReadCloser.
-// It's up to the caller to store the images and close the stream.
-func (cli *Client) ImageSave(ctx context.Context, imageIDs []string, opts image.SaveOptions) (io.ReadCloser, error) {
+//
+// Platforms is an optional parameter that specifies the platforms to save from the image.
+// This is only has effect if the input image is a multi-platform image.
+func (cli *Client) ImageSave(ctx context.Context, imageIDs []string, saveOpts ...ImageSaveOption) (io.ReadCloser, error) {
+	var opts imageSaveOpts
+	for _, opt := range saveOpts {
+		if err := opt.Apply(&opts); err != nil {
+			return nil, err
+		}
+	}
+
 	query := url.Values{
 		"names": imageIDs,
 	}
 
-	if len(opts.Platforms) > 0 {
+	if len(opts.apiOptions.Platforms) > 0 {
 		if err := cli.NewVersionError(ctx, "1.48", "platform"); err != nil {
 			return nil, err
 		}
-		p, err := encodePlatforms(opts.Platforms...)
+		p, err := encodePlatforms(opts.apiOptions.Platforms...)
 		if err != nil {
 			return nil, err
 		}