Support saving more than one image at a time

README.md

@@ -463,7 +463,7 @@ Successfully tagged jess/thing as jess/otherthing
 
 ```console
 $ img save -h
-save -  Save an image to a tar archive (streamed to STDOUT by default).
+save -  Save one or more images to a tar archive (streamed to STDOUT by default).
 
 Usage: img save [OPTIONS] IMAGE [IMAGE...]
 

client/save.go

@@ -10,16 +10,10 @@ import (
 	"github.com/docker/distribution/reference"
 )
 
-// SaveImage exports an image as a tarball which can then be imported by docker.
-func (c *Client) SaveImage(ctx context.Context, image, format string, writer io.WriteCloser) error {
-	// Parse the image name and tag.
-	named, err := reference.ParseNormalizedNamed(image)
-	if err != nil {
-		return fmt.Errorf("parsing image name %q failed: %v", image, err)
-	}
-	// Add the latest lag if they did not provide one.
-	named = reference.TagNameOnly(named)
-	image = named.String()
+// SaveImages exports a list of images as a tarball which can then be imported by docker.
+func (c *Client) SaveImages(ctx context.Context, images []string, format string, writer io.WriteCloser) error {
+
+	exportOpts := []archive.ExportOpt{}
 
 	// Create the worker opts.
 	opt, err := c.createWorkerOpt(false)
@@ -31,8 +25,18 @@ func (c *Client) SaveImage(ctx context.Context, image, format string, writer io.
 		return errors.New("image store is nil")
 	}
 
-	exportOpts := []archive.ExportOpt{
-		archive.WithImage(opt.ImageStore, image),
+	for _, image := range images {
+		// Parse the image name and tag.
+		named, err := reference.ParseNormalizedNamed(image)
+		if err != nil {
+			return fmt.Errorf("parsing image name %q failed: %v", image, err)
+		}
+
+		// Add the latest lag if they did not provide one.
+		named = reference.TagNameOnly(named)
+		image = named.String()
+
+		exportOpts = append(exportOpts, archive.WithImage(opt.ImageStore, image))
 	}
 
 	switch format {
@@ -46,7 +50,7 @@ func (c *Client) SaveImage(ctx context.Context, image, format string, writer io.
 	}
 
 	if err := archive.Export(ctx, opt.ContentStore, writer, exportOpts...); err != nil {
-		return fmt.Errorf("exporting image %s failed: %v", image, err)
+		return fmt.Errorf("exporting images %v failed: %v", images, err)
 	}
 
 	return writer.Close()

save.go

@@ -3,10 +3,11 @@ package main
 import (
 	"context"
 	"fmt"
-	"github.com/spf13/cobra"
 	"io"
 	"os"
 
+	"github.com/spf13/cobra"
+
 	"github.com/containerd/containerd/namespaces"
 	"github.com/docker/docker/pkg/term"
 	"github.com/genuinetools/img/client"
@@ -15,8 +16,8 @@ import (
 )
 
 // TODO(AkihiroSuda): support OCI archive
-const saveUsageShortHelp = `Save an image to a tar archive (streamed to STDOUT by default).`
-const saveUsageLongHelp = `Save an image to a tar archive (streamed to STDOUT by default).`
+const saveUsageShortHelp = `Save one or more images to a tar archive (streamed to STDOUT by default).`
+const saveUsageLongHelp = `Save one or more images to a tar archive (streamed to STDOUT by default).`
 
 func newSaveCommand() *cobra.Command {
 
@@ -76,11 +77,9 @@ func (cmd *saveCommand) Run(args []string) (err error) {
 		return err
 	}
 
-	// Loop over the arguments as images and run save.
-	for _, image := range args {
-		if err := c.SaveImage(ctx, image, cmd.format, writer); err != nil {
-			return err
-		}
+	// Assume that the arguments are all image references
+	if err := c.SaveImages(ctx, args, cmd.format, writer); err != nil {
+		return err
 	}
 
 	return nil

save_test.go

@@ -1,6 +1,12 @@
 package main
 
 import (
+	"archive/tar"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"io/ioutil"
 	"os"
 	"path/filepath"
 	"testing"
@@ -54,3 +60,95 @@ func TestSaveImageInvalid(t *testing.T) {
 		t.Fatalf("expected invalid format to fail but did not: %s", string(out))
 	}
 }
+
+func TestSaveMultipleImages(t *testing.T) {
+	var cases = []struct {
+		format string
+	}{
+		{
+			"",
+		},
+		{
+			"docker",
+		},
+		{
+			"oci",
+		},
+	}
+
+	for _, tt := range cases {
+		testname := tt.format
+		t.Run(testname, func(t *testing.T) {
+
+			runBuild(t, "multiimage1", withDockerfile(`
+			FROM busybox
+			RUN echo multiimage1
+			`))
+
+			runBuild(t, "multiimage2", withDockerfile(`
+			FROM busybox
+			RUN echo multiimage2
+			`))
+
+			tmpf := filepath.Join(os.TempDir(), fmt.Sprintf("save-multiple-%s.tar", tt.format))
+			defer os.RemoveAll(tmpf)
+
+			if tt.format != "" {
+				run(t, "save", "--format", tt.format, "-o", tmpf, "multiimage1", "multiimage2")
+			} else {
+				run(t, "save", "-o", tmpf, "multiimage1", "multiimage2")
+			}
+
+			// Make sure the file exists
+			if _, err := os.Stat(tmpf); os.IsNotExist(err) {
+				t.Fatalf("%s should exist after saving the image but it didn't", tmpf)
+			}
+
+			count, err := getImageCountInTarball(tmpf)
+
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			if count != 2 {
+				t.Fatalf("should have 2 images in archive but have %d", count)
+			}
+		})
+	}
+}
+
+func getImageCountInTarball(tarpath string) (int, error) {
+	file, err := os.Open(tarpath)
+
+	if err != nil {
+		return -1, err
+	}
+
+	defer file.Close()
+
+	tr := tar.NewReader(file)
+
+	for {
+		header, err := tr.Next()
+
+		if err == io.EOF {
+			return -1, errors.New("did not find manifest in tarball")
+		}
+		if err != nil {
+			return -1, err
+		}
+
+		if header.Name == "manifest.json" {
+			jsonFile, err := ioutil.ReadAll(tr)
+
+			if err != nil {
+				return -1, err
+			}
+
+			var result []map[string]string
+			json.Unmarshal([]byte(jsonFile), &result)
+
+			return len(result), nil
+		}
+	}
+}