Add diff service implementation

Add snapshot subcommand to ctr for creating diffs of RW layers.

Signed-off-by: Derek McGowan <derek@mcgstyle.net>

cmd/ctr/main.go

@@ -61,6 +61,7 @@ containerd client
 		execCommand,
 		pauseCommand,
 		resumeCommand,
+		snapshotCommand,
 		versionCommand,
 	}
 	app.Commands = append(app.Commands, extraCmds...)

cmd/ctr/run.go

@@ -54,6 +54,10 @@ var runCommand = cli.Command{
 			Name:  "net-host",
 			Usage: "enable host networking for the container",
 		},
+		cli.BoolFlag{
+			Name:  "keep",
+			Usage: "keep container after running",
+		},
 	},
 	Action: func(context *cli.Context) error {
 		var (
@@ -110,7 +114,11 @@ var runCommand = cli.Command{
 				return err
 			}
 
-			mounts, err = snapshotter.Prepare(ctx, id, identity.ChainID(diffIDs).String())
+			if context.Bool("readonly") {
+				mounts, err = snapshotter.View(ctx, id, identity.ChainID(diffIDs).String())
+			} else {
+				mounts, err = snapshotter.Prepare(ctx, id, identity.ChainID(diffIDs).String())
+			}
 			if err != nil {
 				if !snapshot.IsExist(err) {
 					return err
@@ -192,10 +200,12 @@ var runCommand = cli.Command{
 		if err != nil {
 			return err
 		}
-		if _, err := containers.Delete(ctx, &execution.DeleteRequest{
-			ID: response.ID,
-		}); err != nil {
-			return err
+		if !context.Bool("keep") {
+			if _, err := containers.Delete(ctx, &execution.DeleteRequest{
+				ID: response.ID,
+			}); err != nil {
+				return err
+			}
 		}
 		if status != 0 {
 			return cli.NewExitError("", int(status))

cmd/ctr/snapshot.go

@@ -0,0 +1,50 @@
+package main
+
+import (
+	"context"
+	"errors"
+	"fmt"
+
+	"github.com/containerd/containerd/rootfs"
+	"github.com/urfave/cli"
+)
+
+var snapshotCommand = cli.Command{
+	Name:      "snapshot",
+	Usage:     "snapshot a container into an archive",
+	ArgsUsage: "",
+	Flags: []cli.Flag{
+		cli.StringFlag{
+			Name:  "id",
+			Usage: "id of the container",
+		},
+	},
+	Action: func(clicontext *cli.Context) error {
+		id := clicontext.String("id")
+		if id == "" {
+			return errors.New("container id must be provided")
+		}
+
+		snapshotter, err := getSnapshotter(clicontext)
+		if err != nil {
+			return err
+		}
+
+		differ, err := getDiffService(clicontext)
+		if err != nil {
+			return err
+		}
+
+		contentRef := fmt.Sprintf("diff-%s", id)
+
+		d, err := rootfs.Diff(context.TODO(), id, contentRef, snapshotter, differ)
+		if err != nil {
+			return err
+		}
+
+		// TODO: Track progress
+		fmt.Printf("%s %s\n", d.MediaType, d.Digest)
+
+		return nil
+	},
+}

cmd/ctr/utils.go

@@ -13,6 +13,7 @@ import (
 
 	"github.com/Sirupsen/logrus"
 	contentapi "github.com/containerd/containerd/api/services/content"
+	diffapi "github.com/containerd/containerd/api/services/diff"
 	"github.com/containerd/containerd/api/services/execution"
 	imagesapi "github.com/containerd/containerd/api/services/images"
 	snapshotapi "github.com/containerd/containerd/api/services/snapshot"
@@ -21,6 +22,7 @@ import (
 	"github.com/containerd/containerd/content"
 	"github.com/containerd/containerd/images"
 	contentservice "github.com/containerd/containerd/services/content"
+	"github.com/containerd/containerd/services/diff"
 	imagesservice "github.com/containerd/containerd/services/images"
 	snapshotservice "github.com/containerd/containerd/services/snapshot"
 	"github.com/containerd/containerd/snapshot"
@@ -62,6 +64,14 @@ func getImageStore(clicontext *cli.Context) (images.Store, error) {
 	return imagesservice.NewStoreFromClient(imagesapi.NewImagesClient(conn)), nil
 }
 
+func getDiffService(context *cli.Context) (diff.DiffService, error) {
+	conn, err := getGRPCConnection(context)
+	if err != nil {
+		return nil, err
+	}
+	return diff.NewDiffServiceFromClient(diffapi.NewDiffClient(conn)), nil
+}
+
 func getVersionService(context *cli.Context) (versionservice.VersionClient, error) {
 	conn, err := getGRPCConnection(context)
 	if err != nil {