From fef7f3addc593d1315e1067c1932909cf2e7a5b6 Mon Sep 17 00:00:00 2001
From: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>
Date: Tue, 15 Aug 2017 06:24:43 +0000
Subject: [PATCH 1/2] ctr: add `ctr snapshot info <key>`

Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>
---
 cmd/ctr/info.go     | 12 +++---------
 cmd/ctr/shim.go     | 13 +------------
 cmd/ctr/snapshot.go | 31 +++++++++++++++++++++++++++++++
 cmd/ctr/utils.go    |  8 ++++++++
 4 files changed, 43 insertions(+), 21 deletions(-)

diff --git a/cmd/ctr/info.go b/cmd/ctr/info.go
index fcbc28e3a..c2a9f9395 100644
--- a/cmd/ctr/info.go
+++ b/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
 	},
 }
diff --git a/cmd/ctr/shim.go b/cmd/ctr/shim.go
index 3fbbed179..c5625f35a 100644
--- a/cmd/ctr/shim.go
+++ b/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
 	},
 }
diff --git a/cmd/ctr/snapshot.go b/cmd/ctr/snapshot.go
index ad07c4c1e..c48a35a94 100644
--- a/cmd/ctr/snapshot.go
+++ b/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
diff --git a/cmd/ctr/utils.go b/cmd/ctr/utils.go
index 2f9d99fe9..32e8f3327 100644
--- a/cmd/ctr/utils.go
+++ b/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))
+}

From 525bffd194fe8ec3595811dcde9b69c9f8e01782 Mon Sep 17 00:00:00 2001
From: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>
Date: Wed, 16 Aug 2017 03:10:24 +0000
Subject: [PATCH 2/2] snapshot: support JSON marshalling for Info

Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>
---
 snapshot/snapshotter.go | 51 ++++++++++++++++++++++++++++++-----------
 1 file changed, 37 insertions(+), 14 deletions(-)

diff --git a/snapshot/snapshotter.go b/snapshot/snapshotter.go
index 35d645000..a75a70c51 100644
--- a/snapshot/snapshotter.go
+++ b/snapshot/snapshotter.go
@@ -2,6 +2,8 @@ package snapshot
 
 import (
 	"context"
+	"encoding/json"
+	"strings"
 	"time"
 
 	"github.com/containerd/containerd/mount"
@@ -17,27 +19,48 @@ const (
 	KindCommitted
 )
 
-func (k Kind) String() string {
-	switch k {
-	case KindView:
-		return "View"
-	case KindActive:
-		return "Active"
-	case KindCommitted:
-		return "Committed"
-	default:
-		return "Unknown"
+var (
+	kindStrings = map[Kind]string{
+		KindView:      "view",
+		KindActive:    "active",
+		KindCommitted: "committed",
 	}
+)
+
+func (k Kind) String() string {
+	if s, ok := kindStrings[k]; ok {
+		return s
+	}
+	return "unknown"
+}
+
+func (k Kind) MarshalJSON() ([]byte, error) {
+	return json.Marshal(k.String())
+}
+
+func (k *Kind) UnmarshalJSON(b []byte) error {
+	var s string
+	if err := json.Unmarshal(b, &s); err != nil {
+		return err
+	}
+	for kk, ks := range kindStrings {
+		if strings.EqualFold(s, ks) {
+			*k = kk
+			return nil
+		}
+	}
+	return nil
 }
 
 // Info provides information about a particular snapshot.
+// JSON marshallability is supported for interactive with tools like ctr,
 type Info struct {
 	Kind    Kind              // active or committed snapshot
 	Name    string            // name or key of snapshot
-	Parent  string            // name of parent snapshot
-	Labels  map[string]string // Labels for snapshot
-	Created time.Time         // Created time
-	Updated time.Time         // Last update time
+	Parent  string            `json:",omitempty"` // name of parent snapshot
+	Labels  map[string]string `json:",omitempty"` // Labels for snapshot
+	Created time.Time         `json:",omitempty"` // Created time
+	Updated time.Time         `json:",omitempty"` // Last update time
 }
 
 // Usage defines statistics for disk resources consumed by the snapshot.