ctr: move push and pull to images command

Signed-off-by: Jess Valarezo <valarezo.jessica@gmail.com>

cmd/ctr/commands/images/pull.go

@@ -0,0 +1,49 @@
+package images
+
+import (
+	"fmt"
+
+	"github.com/containerd/containerd/cmd/ctr/commands"
+	"github.com/containerd/containerd/cmd/ctr/commands/content"
+	"github.com/containerd/containerd/log"
+	"github.com/urfave/cli"
+)
+
+var pullCommand = cli.Command{
+	Name:      "pull",
+	Usage:     "pull an image from a remote",
+	ArgsUsage: "[flags] <ref>",
+	Description: `Fetch and prepare an image for use in containerd.
+
+After pulling an image, it should be ready to use the same reference in a run
+command. As part of this process, we do the following:
+
+1. Fetch all resources into containerd.
+2. Prepare the snapshot filesystem with the pulled resources.
+3. Register metadata for the image.
+`,
+	Flags: append(commands.RegistryFlags, append(commands.SnapshotterFlags, commands.LabelFlag)...),
+	Action: func(context *cli.Context) error {
+		var (
+			ref = context.Args().First()
+		)
+
+		ctx, cancel := commands.AppContext(context)
+		defer cancel()
+
+		img, err := content.Fetch(ref, context)
+		if err != nil {
+			return err
+		}
+
+		log.G(ctx).WithField("image", ref).Debug("unpacking")
+
+		// TODO: Show unpack status
+		fmt.Printf("unpacking %s...\n", img.Target().Digest)
+		err = img.Unpack(ctx, context.String("snapshotter"))
+		if err == nil {
+			fmt.Println("done")
+		}
+		return err
+	},
+}