ctr: add ctr snapshot info <key>

Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>

cmd/ctr/info.go

@@ -1,10 +1,6 @@
 package main
 
 import (
-	"encoding/json"
-
-	"fmt"
-
 	"github.com/pkg/errors"
 	"github.com/urfave/cli"
 )
@@ -31,11 +27,9 @@ var containerInfoCommand = cli.Command{
 		if err != nil {
 			return err
 		}
-		cjson, err := json.MarshalIndent(container.Info(), "", "    ")
-		if err != nil {
-			return err
-		}
-		fmt.Println(string(cjson))
+
+		printAsJSON(container.Info())
+
 		return nil
 	},
 }

cmd/ctr/shim.go

@@ -3,12 +3,9 @@
 package main
 
 import (
-	"bytes"
-	"encoding/json"
 	"fmt"
 	"io/ioutil"
 	"net"
-	"os"
 	"time"
 
 	gocontext "context"
@@ -185,15 +182,7 @@ var shimStateCommand = cli.Command{
 		if err != nil {
 			return err
 		}
-		data, err := json.Marshal(r)
-		if err != nil {
-			return err
-		}
-		buf := bytes.NewBuffer(nil)
-		if err := json.Indent(buf, data, " ", "    "); err != nil {
-			return err
-		}
-		buf.WriteTo(os.Stdout)
+		printAsJSON(r)
 		return nil
 	},
 }

cmd/ctr/snapshot.go

@@ -27,6 +27,7 @@ var snapshotCommand = cli.Command{
 		treeSnapshotCommand,
 		mountSnapshotCommand,
 		commitSnapshotCommand,
+		infoSnapshotCommand,
 	},
 }
 
@@ -312,6 +313,36 @@ var treeSnapshotCommand = cli.Command{
 	},
 }
 
+var infoSnapshotCommand = cli.Command{
+	Name:      "info",
+	Usage:     "get info about a snapshot",
+	ArgsUsage: "<key>",
+	Action: func(clicontext *cli.Context) error {
+		ctx, cancel := appContext(clicontext)
+		defer cancel()
+
+		if clicontext.NArg() != 1 {
+			return cli.ShowSubcommandHelp(clicontext)
+		}
+
+		key := clicontext.Args().Get(0)
+
+		snapshotter, err := getSnapshotter(clicontext)
+		if err != nil {
+			return err
+		}
+
+		info, err := snapshotter.Stat(ctx, key)
+		if err != nil {
+			return err
+		}
+
+		printAsJSON(info)
+
+		return nil
+	},
+}
+
 type snapshotTreeNode struct {
 	Name     string
 	Parent   string

cmd/ctr/utils.go

@@ -417,3 +417,11 @@ func labelArgs(labelStrings []string) map[string]string {
 
 	return labels
 }
+
+func printAsJSON(x interface{}) {
+	b, err := json.MarshalIndent(x, "", "    ")
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "can't marshal %+v as a JSON string: %v\n", x, err)
+	}
+	fmt.Println(string(b))
+}