build: support --format (pb and json)

commands/apply.go

@@ -1,7 +1,6 @@
 package commands
 
 import (
-	"io/ioutil"
 	"log"
 
 	"github.com/containerd/continuity"
@@ -14,14 +13,9 @@ var ApplyCmd = &cobra.Command{
 	Run: func(cmd *cobra.Command, args []string) {
 		root, path := args[0], args[1]
 
-		p, err := ioutil.ReadFile(path)
+		m, err := readManifest(path)
 		if err != nil {
-			log.Fatalf("error reading manifest: %v", err)
-		}
-
-		m, err := continuity.Unmarshal(p)
-		if err != nil {
-			log.Fatalf("error unmarshaling manifest: %v", err)
+			log.Fatal(err)
 		}
 
 		ctx, err := continuity.NewContext(root)

commands/build.go

@@ -1,6 +1,7 @@
 package commands
 
 import (
+	"fmt"
 	"log"
 	"os"
 
@@ -13,6 +14,13 @@ var (
 		format string
 	}
 
+	marshalers = map[string]func(*continuity.Manifest) ([]byte, error){
+		"pb": continuity.Marshal,
+		continuity.MediaTypeManifestV0Protobuf: continuity.Marshal,
+		"json": continuity.MarshalJSON,
+		continuity.MediaTypeManifestV0JSON: continuity.MarshalJSON,
+	}
+
 	BuildCmd = &cobra.Command{
 		Use:   "build <root>",
 		Short: "Build a manifest for the provided root",
@@ -31,9 +39,15 @@ var (
 				log.Fatalf("error generating manifest: %v", err)
 			}
 
-			p, err := continuity.Marshal(m)
+			marshaler, ok := marshalers[buildCmdConfig.format]
+			if !ok {
+				log.Fatalf("unknown format %s", buildCmdConfig.format)
+			}
+
+			p, err := marshaler(m)
 			if err != nil {
-				log.Fatalf("error marshaling manifest: %v", err)
+				log.Fatalf("error marshalling manifest as %s: %v",
+					buildCmdConfig.format, err)
 			}
 
 			if _, err := os.Stdout.Write(p); err != nil {
@@ -44,5 +58,7 @@ var (
 )
 
 func init() {
-	BuildCmd.Flags().StringVar(&buildCmdConfig.format, "format", "pb", "specify the output format of the manifest")
+	BuildCmd.Flags().StringVar(&buildCmdConfig.format, "format", "pb",
+		fmt.Sprintf("specify the output format of the manifest (\"pb\"|%q|\"json\"|%q)",
+			continuity.MediaTypeManifestV0Protobuf, continuity.MediaTypeManifestV0JSON))
 }

commands/commandsutil.go

@@ -0,0 +1,22 @@
+package commands
+
+import (
+	"fmt"
+	"io/ioutil"
+	"path/filepath"
+	"strings"
+
+	"github.com/containerd/continuity"
+)
+
+func readManifest(path string) (*continuity.Manifest, error) {
+	p, err := ioutil.ReadFile(path)
+	if err != nil {
+		return nil, fmt.Errorf("error reading manifest: %v", err)
+	}
+	ext := strings.ToLower(filepath.Ext(path))
+	if ext == ".json" {
+		return continuity.UnmarshalJSON(p)
+	}
+	return continuity.Unmarshal(p)
+}

commands/mount.go

@@ -1,7 +1,6 @@
 package commands
 
 import (
-	"io/ioutil"
 	"log"
 	"os"
 	"os/signal"
@@ -30,14 +29,9 @@ var MountCmd = &cobra.Command{
 
 		manifestName := filepath.Base(manifest)
 
-		p, err := ioutil.ReadFile(manifest)
+		m, err := readManifest(manifest)
 		if err != nil {
-			log.Fatalf("error reading manifest: %v", err)
-		}
-
-		m, err := continuity.Unmarshal(p)
-		if err != nil {
-			log.Fatalf("error unmarshaling manifest: %v", err)
+			log.Fatal(err)
 		}
 
 		driver, err := continuity.NewSystemDriver()

commands/verify.go

@@ -1,7 +1,6 @@
 package commands
 
 import (
-	"io/ioutil"
 	"log"
 
 	"github.com/containerd/continuity"
@@ -18,14 +17,9 @@ var VerifyCmd = &cobra.Command{
 
 		root, path := args[0], args[1]
 
-		p, err := ioutil.ReadFile(path)
+		m, err := readManifest(path)
 		if err != nil {
-			log.Fatalf("error reading manifest: %v", err)
-		}
-
-		m, err := continuity.Unmarshal(p)
-		if err != nil {
-			log.Fatalf("error unmarshaling manifest: %v", err)
+			log.Fatal(err)
 		}
 
 		ctx, err := continuity.NewContext(root)

manifest.go

@@ -1,30 +1,37 @@
 package continuity
 
 import (
+	"bytes"
 	"fmt"
 	"io"
 	"log"
 	"os"
 	"sort"
 
 	pb "github.com/containerd/continuity/proto"
+	"github.com/golang/protobuf/jsonpb"
 	"github.com/golang/protobuf/proto"
 )
 
+const (
+	// MediaTypeManifestV0Protobuf is the media type for manifest formatted as protobuf.
+	// The format is unstable during v0.
+	MediaTypeManifestV0Protobuf = "application/vnd.continuity.manifest.v0+pb"
+	// MediaTypeManifestV0JSON is the media type for manifest formatted as JSON.
+	// JSON is marshalled from protobuf using jsonpb.Marshaler
+	// ({EnumAsInts = false, EmitDefaults = false, OrigName = false})
+	// The format is unstable during v0.
+	MediaTypeManifestV0JSON = "application/vnd.continuity.manifest.v0+json"
+)
+
 // Manifest provides the contents of a manifest. Users of this struct should
 // not typically modify any fields directly.
 type Manifest struct {
 	// Resources specifies all the resources for a manifest in order by path.
 	Resources []Resource
 }
 
-func Unmarshal(p []byte) (*Manifest, error) {
-	var bm pb.Manifest
-
-	if err := proto.Unmarshal(p, &bm); err != nil {
-		return nil, err
-	}
-
+func manifestFromProto(bm *pb.Manifest) (*Manifest, error) {
 	var m Manifest
 	for _, b := range bm.Resource {
 		r, err := fromProto(b)
@@ -34,26 +41,48 @@ func Unmarshal(p []byte) (*Manifest, error) {
 
 		m.Resources = append(m.Resources, r)
 	}
-
 	return &m, nil
 }
 
-func Marshal(m *Manifest) ([]byte, error) {
+func Unmarshal(p []byte) (*Manifest, error) {
 	var bm pb.Manifest
-	for _, resource := range m.Resources {
-		bm.Resource = append(bm.Resource, toProto(resource))
+	if err := proto.Unmarshal(p, &bm); err != nil {
+		return nil, err
 	}
+	return manifestFromProto(&bm)
+}
 
-	return proto.Marshal(&bm)
+func UnmarshalJSON(p []byte) (*Manifest, error) {
+	var bm pb.Manifest
+	if err := jsonpb.Unmarshal(bytes.NewReader(p), &bm); err != nil {
+		return nil, err
+	}
+	return manifestFromProto(&bm)
 }
 
-func MarshalText(w io.Writer, m *Manifest) error {
+func manifestToProto(m *Manifest) *pb.Manifest {
 	var bm pb.Manifest
 	for _, resource := range m.Resources {
 		bm.Resource = append(bm.Resource, toProto(resource))
 	}
+	return &bm
+}
 
-	return proto.MarshalText(w, &bm)
+func Marshal(m *Manifest) ([]byte, error) {
+	return proto.Marshal(manifestToProto(m))
+}
+
+func MarshalText(w io.Writer, m *Manifest) error {
+	return proto.MarshalText(w, manifestToProto(m))
+}
+
+func MarshalJSON(m *Manifest) ([]byte, error) {
+	var b bytes.Buffer
+	marshaler := &jsonpb.Marshaler{}
+	if err := marshaler.Marshal(&b, manifestToProto(m)); err != nil {
+		return nil, err
+	}
+	return b.Bytes(), nil
 }
 
 // BuildManifest creates the manifest for the given context