examples/dockerfile2llb: add --partial-image-config-file, --partial-metadata-file

examples/dockerfile2llb/main.go

@@ -2,30 +2,41 @@ package main
 
 import (
 	"context"
+	"encoding/json"
 	"flag"
 	"io"
-	"log"
 	"os"
 
 	"github.com/moby/buildkit/client/llb"
 	"github.com/moby/buildkit/client/llb/imagemetaresolver"
 	"github.com/moby/buildkit/frontend/dockerfile/dockerfile2llb"
 	"github.com/moby/buildkit/solver/pb"
 	"github.com/moby/buildkit/util/appcontext"
+	"github.com/sirupsen/logrus"
 )
 
 type buildOpt struct {
-	target string
+	target                 string
+	partialImageConfigFile string
+	partialMetadataFile    string
 }
 
 func main() {
+	if err := xmain(); err != nil {
+		logrus.Fatal(err)
+	}
+}
+
+func xmain() error {
 	var opt buildOpt
 	flag.StringVar(&opt.target, "target", "", "target stage")
+	flag.StringVar(&opt.partialImageConfigFile, "partial-image-config-file", "", "Output partial image config as a JSON file")
+	flag.StringVar(&opt.partialMetadataFile, "partial-metadata-file", "", "Output partial metadata sa a JSON file")
 	flag.Parse()
 
 	df, err := io.ReadAll(os.Stdin)
 	if err != nil {
-		panic(err)
+		return err
 	}
 
 	caps := pb.Caps.CapSet(pb.Caps.All())
@@ -36,16 +47,36 @@ func main() {
 		LLBCaps:      &caps,
 	})
 	if err != nil {
-		log.Printf("err: %+v", err)
-		panic(err)
+		return err
 	}
 
-	_ = img
-	_ = bi
-
 	dt, err := state.Marshal(context.TODO())
 	if err != nil {
-		panic(err)
+		return err
+	}
+	if err := llb.WriteTo(dt, os.Stdout); err != nil {
+		return err
+	}
+	if opt.partialImageConfigFile != "" {
+		if err := writeJSON(opt.partialImageConfigFile, img); err != nil {
+			return err
+		}
+	}
+	if opt.partialMetadataFile != "" {
+		if err := writeJSON(opt.partialMetadataFile, bi); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func writeJSON(f string, x interface{}) error {
+	b, err := json.Marshal(x)
+	if err != nil {
+		return err
+	}
+	if err := os.RemoveAll(f); err != nil {
+		return err
 	}
-	llb.WriteTo(dt, os.Stdout)
+	return os.WriteFile(f, b, 0o644)
 }