builder: return image ID in API when using buildkit

Signed-off-by: Tibor Vass <tibor@docker.com>

api/server/backend/build/backend.go

@@ -73,7 +73,7 @@ func (b *Backend) Build(ctx context.Context, config backend.BuildConfig) (string
 			return "", err
 		}
 		if config.ProgressWriter.AuxFormatter != nil {
-			if err = config.ProgressWriter.AuxFormatter.Emit(types.BuildResult{ID: imageID}); err != nil {
+			if err = config.ProgressWriter.AuxFormatter.Emit("moby.image.id", types.BuildResult{ID: imageID}); err != nil {
 				return "", err
 			}
 		}

api/server/router/build/build_routes.go

@@ -243,6 +243,10 @@ func (br *buildRouter) postBuild(ctx context.Context, w http.ResponseWriter, r *
 		return errdefs.InvalidParameter(errors.New("squash is only supported with experimental mode"))
 	}
 
+	if buildOptions.Version == types.BuilderBuildKit && !br.daemon.HasExperimental() {
+		return errdefs.InvalidParameter(errors.New("buildkit is only supported with experimental mode"))
+	}
+
 	out := io.Writer(output)
 	if buildOptions.SuppressOutput {
 		out = notVerboseBuffer
@@ -255,10 +259,6 @@ func (br *buildRouter) postBuild(ctx context.Context, w http.ResponseWriter, r *
 		return progress.NewProgressReader(in, progressOutput, r.ContentLength, "Downloading context", buildOptions.RemoteContext)
 	}
 
-	if buildOptions.Version == types.BuilderBuildKit && !br.daemon.HasExperimental() {
-		return errdefs.InvalidParameter(errors.New("buildkit is only supported with experimental mode"))
-	}
-
 	wantAux := versions.GreaterThanOrEqualTo(version, "1.30")
 
 	imgID, err := br.backend.Build(ctx, backend.BuildConfig{

builder/builder-next/builder.go

@@ -2,7 +2,6 @@ package buildkit
 
 import (
 	"context"
-	"encoding/json"
 	"io"
 	"strings"
 	"sync"
@@ -14,7 +13,7 @@ import (
 	"github.com/docker/docker/api/types/backend"
 	"github.com/docker/docker/builder"
 	"github.com/docker/docker/daemon/images"
-	"github.com/docker/docker/pkg/jsonmessage"
+	"github.com/docker/docker/pkg/streamformatter"
 	controlapi "github.com/moby/buildkit/api/services/control"
 	"github.com/moby/buildkit/control"
 	"github.com/moby/buildkit/identity"
@@ -228,6 +227,8 @@ func (b *Builder) Build(ctx context.Context, opt backend.BuildConfig) (*builder.
 		Session:       opt.Options.SessionID,
 	}
 
+	aux := streamformatter.AuxFormatter{opt.ProgressWriter.Output}
+
 	eg, ctx := errgroup.WithContext(ctx)
 
 	eg.Go(func() error {
@@ -240,7 +241,7 @@ func (b *Builder) Build(ctx context.Context, opt backend.BuildConfig) (*builder.
 			return errors.Errorf("missing image id")
 		}
 		out.ImageID = id
-		return nil
+		return aux.Emit("moby.image.id", types.BuildResult{ID: id})
 	})
 
 	ch := make(chan *controlapi.StatusResponse)
@@ -258,25 +259,9 @@ func (b *Builder) Build(ctx context.Context, opt backend.BuildConfig) (*builder.
 			if err != nil {
 				return err
 			}
-
-			auxJSONBytes, err := json.Marshal(dt)
-			if err != nil {
+			if err := aux.Emit("moby.buildkit.trace", dt); err != nil {
 				return err
 			}
-			auxJSON := new(json.RawMessage)
-			*auxJSON = auxJSONBytes
-			msgJSON, err := json.Marshal(&jsonmessage.JSONMessage{ID: "moby.buildkit.trace", Aux: auxJSON})
-			if err != nil {
-				return err
-			}
-			msgJSON = append(msgJSON, []byte("\r\n")...)
-			n, err := opt.ProgressWriter.Output.Write(msgJSON)
-			if err != nil {
-				return err
-			}
-			if n != len(msgJSON) {
-				return io.ErrShortWrite
-			}
 		}
 		return nil
 	})

builder/dockerfile/builder.go

@@ -257,7 +257,7 @@ func emitImageID(aux *streamformatter.AuxFormatter, state *dispatchState) error
 	if aux == nil || state.imageID == "" {
 		return nil
 	}
-	return aux.Emit(types.BuildResult{ID: state.imageID})
+	return aux.Emit("", types.BuildResult{ID: state.imageID})
 }
 
 func processMetaArg(meta instructions.ArgCommand, shlex *shell.Lex, args *BuildArgs) error {

pkg/streamformatter/streamformatter.go

@@ -139,14 +139,14 @@ type AuxFormatter struct {
 }
 
 // Emit emits the given interface as an aux progress message
-func (sf *AuxFormatter) Emit(aux interface{}) error {
+func (sf *AuxFormatter) Emit(id string, aux interface{}) error {
 	auxJSONBytes, err := json.Marshal(aux)
 	if err != nil {
 		return err
 	}
 	auxJSON := new(json.RawMessage)
 	*auxJSON = auxJSONBytes
-	msgJSON, err := json.Marshal(&jsonmessage.JSONMessage{Aux: auxJSON})
+	msgJSON, err := json.Marshal(&jsonmessage.JSONMessage{ID: id, Aux: auxJSON})
 	if err != nil {
 		return err
 	}

pkg/streamformatter/streamformatter_test.go

@@ -106,7 +106,7 @@ func TestAuxFormatterEmit(t *testing.T) {
 	sampleAux := &struct {
 		Data string
 	}{"Additional data"}
-	err := aux.Emit(sampleAux)
+	err := aux.Emit("", sampleAux)
 	assert.NilError(t, err)
 	assert.Check(t, is.Equal(`{"aux":{"Data":"Additional data"}}`+streamNewline, b.String()))
 }