allow multiple images pull (#975)

* allow multiple images pull

* run hack/update-codegen.sh

* implement MultiWriteXXX

* add doc for MultiWrite api and rework MultiSaveOCI

cmd/crane/cmd/pull.go

@@ -19,6 +19,7 @@ import (
 	"log"
 
 	"github.com/google/go-containerregistry/pkg/crane"
+	v1 "github.com/google/go-containerregistry/pkg/v1"
 	"github.com/google/go-containerregistry/pkg/v1/cache"
 	"github.com/spf13/cobra"
 )
@@ -29,29 +30,34 @@ func NewCmdPull(options *[]crane.Option) *cobra.Command {
 
 	cmd := &cobra.Command{
 		Use:   "pull IMAGE TARBALL",
-		Short: "Pull a remote image by reference and store its contents in a tarball",
-		Args:  cobra.ExactArgs(2),
+		Short: "Pull remote images by reference and store their contents in a tarball",
+		Args:  cobra.MinimumNArgs(2),
 		Run: func(_ *cobra.Command, args []string) {
-			src, path := args[0], args[1]
-			img, err := crane.Pull(src, *options...)
-			if err != nil {
-				log.Fatal(err)
-			}
-			if cachePath != "" {
-				img = cache.Image(img, cache.NewFilesystemCache(cachePath))
+			imageMap := map[string]v1.Image{}
+			srcList, path := args[:len(args)-1], args[len(args)-1]
+			for _, src := range srcList {
+				img, err := crane.Pull(src, *options...)
+				if err != nil {
+					log.Fatal(err)
+				}
+				if cachePath != "" {
+					img = cache.Image(img, cache.NewFilesystemCache(cachePath))
+				}
+
+				imageMap[src] = img
 			}
 
 			switch format {
 			case "tarball":
-				if err := crane.Save(img, src, path); err != nil {
+				if err := crane.MultiSave(imageMap, path); err != nil {
 					log.Fatalf("saving tarball %s: %v", path, err)
 				}
 			case "legacy":
-				if err := crane.SaveLegacy(img, src, path); err != nil {
+				if err := crane.MultiSaveLegacy(imageMap, path); err != nil {
 					log.Fatalf("saving legacy tarball %s: %v", path, err)
 				}
 			case "oci":
-				if err := crane.SaveOCI(img, path); err != nil {
+				if err := crane.MultiSaveOCI(imageMap, path); err != nil {
 					log.Fatalf("saving oci image layout %s: %v", path, err)
 				}
 			default:

pkg/crane/pull.go

@@ -45,26 +45,36 @@ func Pull(src string, opt ...Option) (v1.Image, error) {
 
 // Save writes the v1.Image img as a tarball at path with tag src.
 func Save(img v1.Image, src, path string) error {
-	ref, err := name.ParseReference(src)
-	if err != nil {
-		return fmt.Errorf("parsing ref %q: %v", src, err)
-	}
+	imgMap := map[string]v1.Image{src: img}
+	return MultiSave(imgMap, path)
+}
+
+// MultiSave writes collection of v1.Image img with tag as a tarball.
+func MultiSave(imgMap map[string]v1.Image, path string) error {
+	tagToImage := map[name.Tag]v1.Image{}
+
+	for src, img := range imgMap {
+		ref, err := name.ParseReference(src)
+		if err != nil {
+			return fmt.Errorf("parsing ref %q: %v", src, err)
+		}
 
-	// WriteToFile wants a tag to write to the tarball, but we might have
-	// been given a digest.
-	// If the original ref was a tag, use that. Otherwise, if it was a
-	// digest, tag the image with :i-was-a-digest instead.
-	tag, ok := ref.(name.Tag)
-	if !ok {
-		d, ok := ref.(name.Digest)
+		// WriteToFile wants a tag to write to the tarball, but we might have
+		// been given a digest.
+		// If the original ref was a tag, use that. Otherwise, if it was a
+		// digest, tag the image with :i-was-a-digest instead.
+		tag, ok := ref.(name.Tag)
 		if !ok {
-			return fmt.Errorf("ref wasn't a tag or digest")
+			d, ok := ref.(name.Digest)
+			if !ok {
+				return fmt.Errorf("ref wasn't a tag or digest")
+			}
+			tag = d.Repository.Tag(iWasADigestTag)
 		}
-		tag = d.Repository.Tag(iWasADigestTag)
+		tagToImage[tag] = img
 	}
-
 	// no progress channel (for now)
-	return tarball.WriteToFile(path, tag, img)
+	return tarball.MultiWriteToFile(path, tagToImage)
 }
 
 // PullLayer returns the given layer from a registry.
@@ -80,9 +90,20 @@ func PullLayer(ref string, opt ...Option) (v1.Layer, error) {
 
 // SaveLegacy writes the v1.Image img as a legacy tarball at path with tag src.
 func SaveLegacy(img v1.Image, src, path string) error {
-	ref, err := name.ParseReference(src)
-	if err != nil {
-		return fmt.Errorf("parsing ref %q: %v", src, err)
+	imgMap := map[string]v1.Image{src: img}
+	return MultiSave(imgMap, path)
+}
+
+// MultiSaveLegacy writes collection of v1.Image img with tag as a legacy tarball.
+func MultiSaveLegacy(imgMap map[string]v1.Image, path string) error {
+	refToImage := map[name.Reference]v1.Image{}
+
+	for src, img := range imgMap {
+		ref, err := name.ParseReference(src)
+		if err != nil {
+			return fmt.Errorf("parsing ref %q: %v", src, err)
+		}
+		refToImage[ref] = img
 	}
 
 	w, err := os.Create(path)
@@ -91,18 +112,30 @@ func SaveLegacy(img v1.Image, src, path string) error {
 	}
 	defer w.Close()
 
-	return legacy.Write(ref, img, w)
+	return legacy.MultiWrite(refToImage, w)
 }
 
 // SaveOCI writes the v1.Image img as an OCI Image Layout at path. If a layout
 // already exists at that path, it will add the image to the index.
 func SaveOCI(img v1.Image, path string) error {
+	imgMap := map[string]v1.Image{"": img}
+	return MultiSaveOCI(imgMap, path)
+}
+
+// MultiSaveOCI writes collection of v1.Image img as an OCI Image Layout at path. If a layout
+// already exists at that path, it will add the image to the index.
+func MultiSaveOCI(imgMap map[string]v1.Image, path string) error {
 	p, err := layout.FromPath(path)
 	if err != nil {
 		p, err = layout.Write(path, empty.Index)
 		if err != nil {
 			return err
 		}
 	}
-	return p.AppendImage(img)
+	for _, img := range imgMap {
+		if err = p.AppendImage(img); err != nil {
+			return err
+		}
+	}
+	return nil
 }