Add kpod diff command

kpod diff reports on differences between two layers, specified as
layer IDs, containers, or images.  In the case of containers or
images, kpod diff produces a diff for the top layer

Signed-off-by: Ryan Cole <rcyoalne@gmail.com>

cmd/kpod/diff.go

@@ -0,0 +1,89 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+
+	"github.com/containers/storage/pkg/archive"
+	"github.com/kubernetes-incubator/cri-o/libkpod"
+	"github.com/pkg/errors"
+	"github.com/urfave/cli"
+)
+
+type diffJSONOutput struct {
+	Changed []string `json:"changed,omitempty"`
+	Added   []string `json:"added,omitempty"`
+	Deleted []string `json:"deleted,omitempty"`
+}
+
+var (
+	diffFlags = []cli.Flag{
+		cli.BoolFlag{
+			Name:   "archive",
+			Usage:  "Save the diff as a tar archive",
+			Hidden: true,
+		},
+		cli.BoolFlag{
+			Name:  "json",
+			Usage: "Format output as JSON",
+		},
+	}
+	diffDescription = fmt.Sprint(`Displays changes on a container or image's filesystem.  The
+	container or image will be compared to its parent layer`)
+
+	diffCommand = cli.Command{
+		Name:        "diff",
+		Usage:       "Inspect changes on container's file systems",
+		Description: diffDescription,
+		Flags:       diffFlags,
+		Action:      diffCmd,
+		ArgsUsage:   "ID-NAME",
+	}
+)
+
+func diffCmd(c *cli.Context) error {
+	if len(c.Args()) != 1 {
+		return errors.Errorf("container, layer, or image name must be specified: kpod diff [options [...]] ID-NAME")
+	}
+	config, err := getConfig(c)
+	if err != nil {
+		return errors.Wrapf(err, "could not get config")
+	}
+
+	server, err := libkpod.New(config)
+	if err != nil {
+		return errors.Wrapf(err, "could not get container server")
+	}
+
+	to := c.Args().Get(0)
+	changes, err := server.GetDiff("", to)
+	if err != nil {
+		return errors.Wrapf(err, "could not get changes for %q", to)
+	}
+
+	if c.Bool("json") {
+		jsonStruct := diffJSONOutput{}
+		for _, change := range changes {
+			if change.Kind == archive.ChangeModify {
+				jsonStruct.Changed = append(jsonStruct.Changed, change.Path)
+			} else if change.Kind == archive.ChangeAdd {
+				jsonStruct.Added = append(jsonStruct.Added, change.Path)
+			} else if change.Kind == archive.ChangeDelete {
+				jsonStruct.Deleted = append(jsonStruct.Deleted, change.Path)
+			} else {
+				return errors.Errorf("change kind %q not recognized", change.Kind.String())
+			}
+		}
+		b, err := json.MarshalIndent(jsonStruct, "", "  ")
+		if err != nil {
+			return errors.Wrapf(err, "could not marshal json for %+v", jsonStruct)
+		}
+		fmt.Println(string(b))
+	} else {
+		for _, change := range changes {
+			fmt.Println(change.String())
+		}
+	}
+
+	return nil
+}

cmd/kpod/main.go

@@ -22,6 +22,7 @@ func main() {
 	app.Version = Version
 
 	app.Commands = []cli.Command{
+		diffCommand,
 		exportCommand,
 		historyCommand,
 		imagesCommand,