image exporter: return image descriptor in response

Signed-off-by: CrazyMax <crazy-max@users.noreply.github.com>

client/client_test.go

@@ -7,6 +7,7 @@ import (
 	"crypto/rand"
 	"crypto/rsa"
 	"crypto/x509"
+	"encoding/base64"
 	"encoding/json"
 	"encoding/pem"
 	"fmt"
@@ -143,6 +144,7 @@ func TestIntegration(t *testing.T) {
 		testMergeOpCacheMax,
 		testRmSymlink,
 		testMoveParentDir,
+		testExporterImageDescriptor,
 	)
 	tests = append(tests, diffOpTestCases()...)
 	integration.Run(t, tests, mirrors)
@@ -4860,6 +4862,44 @@ func testRelativeMountpoint(t *testing.T, sb integration.Sandbox) {
 	require.Equal(t, dt, []byte(id))
 }
 
+func testExporterImageDescriptor(t *testing.T, sb integration.Sandbox) {
+	skipDockerd(t, sb)
+	requiresLinux(t)
+	c, err := New(sb.Context(), sb.Address())
+	require.NoError(t, err)
+	defer c.Close()
+
+	st := llb.Image("busybox:latest")
+	def, err := st.Marshal(sb.Context())
+	require.NoError(t, err)
+
+	res, err := c.Solve(sb.Context(), def, SolveOpt{
+		Exports: []ExportEntry{
+			{
+				Type:  ExporterOCI,
+				Attrs: map[string]string{},
+				Output: func(m map[string]string) (io.WriteCloser, error) {
+					return nil, nil
+				},
+			},
+		},
+	}, nil)
+	require.NoError(t, err)
+
+	require.Contains(t, res.ExporterResponse, exptypes.ExporterImageDescriptorKey)
+	dt, err := base64.StdEncoding.DecodeString(res.ExporterResponse[exptypes.ExporterImageDescriptorKey])
+	require.NoError(t, err)
+
+	var desc *ocispecs.Descriptor
+	err = json.Unmarshal(dt, &desc)
+	require.NoError(t, err)
+
+	require.NotEmpty(t, desc.MediaType)
+	require.NotEmpty(t, desc.Digest.String())
+	require.True(t, strings.HasPrefix(desc.Digest.String(), "sha256:"))
+	require.Equal(t, res.ExporterResponse[exptypes.ExporterImageDigestKey], desc.Digest.String())
+}
+
 func tmpdir(appliers ...fstest.Applier) (string, error) {
 	tmpdir, err := ioutil.TempDir("", "buildkit-client")
 	if err != nil {

cmd/buildctl/build.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"context"
+	"encoding/base64"
 	"encoding/json"
 	"io"
 	"os"
@@ -315,7 +316,21 @@ func buildAction(clicontext *cli.Context) error {
 }
 
 func writeMetadataFile(filename string, exporterResponse map[string]string) error {
-	b, err := json.Marshal(exporterResponse)
+	out := make(map[string]interface{})
+	for k, v := range exporterResponse {
+		dt, err := base64.StdEncoding.DecodeString(v)
+		if err != nil {
+			out[k] = v
+			continue
+		}
+		var raw json.RawMessage
+		if json.Unmarshal(dt, &raw) != nil {
+			out[k] = v
+			continue
+		}
+		out[k] = raw
+	}
+	b, err := json.Marshal(out)
 	if err != nil {
 		return err
 	}

cmd/buildctl/build_test.go

@@ -19,6 +19,7 @@ import (
 	"github.com/moby/buildkit/client/llb"
 	"github.com/moby/buildkit/exporter/containerimage/exptypes"
 	"github.com/moby/buildkit/util/testutil/integration"
+	ocispecs "github.com/opencontainers/image-spec/specs-go/v1"
 	"github.com/stretchr/testify/require"
 )
 
@@ -142,15 +143,26 @@ func testBuildMetadataFile(t *testing.T, sb integration.Sandbox) {
 	metadataBytes, err := ioutil.ReadFile(metadataFile)
 	require.NoError(t, err)
 
-	var metadata map[string]string
+	var metadata map[string]interface{}
 	err = json.Unmarshal(metadataBytes, &metadata)
 	require.NoError(t, err)
 
+	require.Contains(t, metadata, "image.name")
 	require.Equal(t, imageName, metadata["image.name"])
 
+	require.Contains(t, metadata, exptypes.ExporterImageDigestKey)
 	digest := metadata[exptypes.ExporterImageDigestKey]
 	require.NotEmpty(t, digest)
 
+	require.Contains(t, metadata, exptypes.ExporterImageDescriptorKey)
+	var desc *ocispecs.Descriptor
+	dtdesc, err := json.Marshal(metadata[exptypes.ExporterImageDescriptorKey])
+	require.NoError(t, err)
+	err = json.Unmarshal(dtdesc, &desc)
+	require.NoError(t, err)
+	require.NotEmpty(t, desc.MediaType)
+	require.NotEmpty(t, desc.Digest.String())
+
 	cdAddress := sb.ContainerdAddress()
 	if cdAddress == "" {
 		t.Log("no containerd worker, skipping digest verification")

exporter/containerimage/export.go

@@ -2,6 +2,8 @@ package containerimage
 
 import (
 	"context"
+	"encoding/base64"
+	"encoding/json"
 	"fmt"
 	"strconv"
 	"strings"
@@ -347,6 +349,13 @@ func (e *imageExporterInstance) Export(ctx context.Context, src exporter.Source,
 	if v, ok := desc.Annotations[exptypes.ExporterConfigDigestKey]; ok {
 		resp[exptypes.ExporterImageConfigDigestKey] = v
 	}
+
+	dtdesc, err := json.Marshal(desc)
+	if err != nil {
+		return nil, err
+	}
+	resp[exptypes.ExporterImageDescriptorKey] = base64.StdEncoding.EncodeToString(dtdesc)
+
 	return resp, nil
 }
 

exporter/containerimage/exptypes/types.go

@@ -11,6 +11,7 @@ const (
 	ExporterImageDigestKey       = "containerimage.digest"
 	ExporterImageConfigKey       = "containerimage.config"
 	ExporterImageConfigDigestKey = "containerimage.config.digest"
+	ExporterImageDescriptorKey   = "containerimage.descriptor"
 	ExporterInlineCache          = "containerimage.inlinecache"
 	ExporterBuildInfo            = "containerimage.buildinfo"
 	ExporterPlatformsKey         = "refs.platforms"

exporter/oci/export.go

@@ -2,6 +2,8 @@ package oci
 
 import (
 	"context"
+	"encoding/base64"
+	"encoding/json"
 	"strconv"
 	"strings"
 	"time"
@@ -208,6 +210,13 @@ func (e *imageExporterInstance) Export(ctx context.Context, src exporter.Source,
 	desc.Annotations[ocispecs.AnnotationCreated] = time.Now().UTC().Format(time.RFC3339)
 
 	resp := make(map[string]string)
+
+	dtdesc, err := json.Marshal(desc)
+	if err != nil {
+		return nil, err
+	}
+	resp[exptypes.ExporterImageDescriptorKey] = base64.StdEncoding.EncodeToString(dtdesc)
+
 	resp[exptypes.ExporterImageDigestKey] = desc.Digest.String()
 	if v, ok := desc.Annotations[exptypes.ExporterConfigDigestKey]; ok {
 		resp[exptypes.ExporterImageConfigDigestKey] = v