nydusify: add new option output-json

During convert, we can collect the metric: image size and convert time, etc.
Nydusify can dump the metric to local file if user needs.

Signed-off-by: Yadong Ding <[email protected]>

contrib/nydusify/cmd/nydusify.go

@@ -409,6 +409,12 @@ func main() {
 					Usage:   "Path to the nydus-image binary, default to search in PATH",
 					EnvVars: []string{"NYDUS_IMAGE"},
 				},
+				&cli.BoolFlag{
+					Name:    "output-json",
+					Value:   false,
+					Usage:   "Enable saving the metrics collected during conversion in JSON file output.json",
+					EnvVars: []string{"OUTPUT_JSON"},
+				},
 			},
 			Action: func(c *cli.Context) error {
 				setupLogLevel(c)
@@ -503,6 +509,8 @@ func main() {
 					OCIRef:       c.Bool("oci-ref"),
 					AllPlatforms: c.Bool("all-platforms"),
 					Platforms:    c.String("platform"),
+
+					OutputJSON: c.Bool("output-json"),
 				}
 
 				return converter.Convert(context.Background(), opt)

contrib/nydusify/pkg/converter/converter.go

@@ -48,6 +48,8 @@ type Opt struct {
 
 	AllPlatforms bool
 	Platforms    string
+
+	OutputJSON bool
 }
 
 func Convert(ctx context.Context, opt Opt) error {
@@ -87,6 +89,9 @@ func Convert(ctx context.Context, opt Opt) error {
 		return err
 	}
 
-	_, err = cvt.Convert(ctx, opt.Source, opt.Target)
+	metric, err := cvt.Convert(ctx, opt.Source, opt.Target)
+	if opt.OutputJSON {
+		dumpMetric(metric, opt.WorkDir)
+	}
 	return err
 }

contrib/nydusify/pkg/converter/metric.go

@@ -0,0 +1,28 @@
+// Copyright 2023 Nydus Developers. All rights reserved.
+//
+// SPDX-License-Identifier: Apache-2.0
+
+package converter
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+
+	"github.com/goharbor/acceleration-service/pkg/converter"
+	"github.com/pkg/errors"
+)
+
+func dumpMetric(metric *converter.Metric, workDir string) error {
+	file, err := os.Create(filepath.Join(workDir, "output.json"))
+	if err != nil {
+		return errors.Wrap(err, "Create file for metric")
+	}
+	defer file.Close()
+
+	encoder := json.NewEncoder(file)
+	if err := encoder.Encode(metric); err != nil {
+		return errors.Wrap(err, "Encode JSON from metric")
+	}
+	return nil
+}