@@ -3,7 +3,6 @@ package build // import "github.com/docker/docker/api/server/backend/build"

 import (

 	"context"

 	"fmt"

-	"strings"

 	"github.com/docker/distribution/reference"

 	"github.com/docker/docker/api/types"

@@ -44,11 +43,7 @@ func NewBackend(components ImageComponent, builder Builder, fsCache *fscache.FSC

 // Build builds an image from a Source

 func (b *Backend) Build(ctx context.Context, config backend.BuildConfig) (string, error) {

 	options := config.Options

-	useBuildKit := false

-	if strings.HasPrefix(options.SessionID, "buildkit:") {

-		useBuildKit = true

-		options.SessionID = strings.TrimPrefix(options.SessionID, "buildkit:")

-	}

+	useBuildKit := options.Version == types.BuilderBuildKit

 	tagger, err := NewTagger(b.imageComponent, config.ProgressWriter.StdoutFormatter, options.Tags)

 	if err != nil {

@@ -146,10 +146,25 @@ func newImageBuildOptions(ctx context.Context, r *http.Request) (*types.ImageBui

 	}

 	options.SessionID = r.FormValue("session")

 	options.BuildID = r.FormValue("buildid")

+	builderVersion, err := parseVersion(r.FormValue("version"))

+	if err != nil {

+		return nil, err

+	}

+	options.Version = builderVersion

 	return options, nil

 }

+func parseVersion(s string) (types.BuilderVersion, error) {

+	if s == "" || s == string(types.BuilderV1) {

+		return types.BuilderV1, nil

+	}

+	if s == string(types.BuilderBuildKit) {

+		return types.BuilderBuildKit, nil

+	}

+	return "", errors.Errorf("invalid version %s", s)

+}

+

 func (br *buildRouter) postPrune(ctx context.Context, w http.ResponseWriter, r *http.Request, vars map[string]string) error {

 	report, err := br.backend.PruneCache(ctx)

 	if err != nil {

@@ -181,9 +181,18 @@ type ImageBuildOptions struct {

 	Target      string

 	SessionID   string

 	Platform    string

+	Version     BuilderVersion

 	BuildID     string

 }

+// BuilderVersion sets the version of underlying builder to use

+type BuilderVersion string

+

+const (

+	BuilderV1       BuilderVersion = "1"

+	BuilderBuildKit                = "2"

+)

+

 // ImageBuildResponse holds information

 // returned by a server after building

 // an image.

@@ -17,6 +17,7 @@ import (

 	"github.com/moby/buildkit/control"

 	"github.com/moby/buildkit/identity"

 	"github.com/moby/buildkit/session"

+	"github.com/moby/buildkit/util/tracing"

 	"github.com/pkg/errors"

 	"golang.org/x/sync/errgroup"

 	grpcmetadata "google.golang.org/grpc/metadata"

@@ -29,20 +30,24 @@ type Opt struct {

 }

 type Builder struct {

-	controller *control.Controller

+	controller     *control.Controller

+	reqBodyHandler *reqBodyHandler

 	mu   sync.Mutex

 	jobs map[string]func()

 }

 func New(opt Opt) (*Builder, error) {

-	c, err := newController(opt)

+	reqHandler := newReqBodyHandler(tracing.DefaultTransport)

+

+	c, err := newController(reqHandler, opt)

 	if err != nil {

 		return nil, err

 	}

 	b := &Builder{

-		controller: c,

-		jobs:       map[string]func(){},

+		controller:     c,

+		reqBodyHandler: reqHandler,

+		jobs:           map[string]func(){},

 	}

 	return b, nil

 }

@@ -133,7 +138,13 @@ func (b *Builder) Build(ctx context.Context, opt backend.BuildConfig) (*builder.

 	}

 	if opt.Options.RemoteContext != "" {

-		frontendAttrs["context"] = opt.Options.RemoteContext

+		if opt.Options.RemoteContext != "client-session" {

+			frontendAttrs["context"] = opt.Options.RemoteContext

+		}

+	} else {

+		url, cancel := b.reqBodyHandler.newRequest(opt.Source)

+		defer cancel()

+		frontendAttrs["context"] = url

 	}

 	var cacheFrom []string

@@ -1,6 +1,7 @@

 package buildkit

 import (

+	"net/http"

 	"os"

 	"path/filepath"

@@ -24,7 +25,7 @@ import (

 	"github.com/pkg/errors"

 )

-func newController(opt Opt) (*control.Controller, error) {

+func newController(rt http.RoundTripper, opt Opt) (*control.Controller, error) {

 	if err := os.MkdirAll(opt.Root, 0700); err != nil {

 		return nil, err

 	}

@@ -133,6 +134,7 @@ func newController(opt Opt) (*control.Controller, error) {

 		Exporters: map[string]exporter.Exporter{

 			"moby": exp,

 		},

+		Transport: rt,

 	}

 	wc := &worker.Controller{}

new file mode 100644

@@ -0,0 +1,74 @@

+package buildkit

+

+import (

+	"bufio"

+	"io"

+	"net/http"

+	"strings"

+	"sync"

+

+	"github.com/moby/buildkit/identity"

+	"github.com/pkg/errors"

+)

+

+const urlPrefix = "build-context-"

+

+type reqBodyHandler struct {

+	mu sync.Mutex

+	rt http.RoundTripper

+

+	requests map[string]io.ReadCloser

+}

+

+func newReqBodyHandler(rt http.RoundTripper) *reqBodyHandler {

+	return &reqBodyHandler{

+		rt:       rt,

+		requests: map[string]io.ReadCloser{},

+	}

+}

+

+func (h *reqBodyHandler) newRequest(rc io.ReadCloser) (string, func()) {

+	// handle expect-continue vs chunked output

+	r := bufio.NewReader(rc)

+	r.Peek(1)

+	id := identity.NewID()

+	h.mu.Lock()

+	h.requests[id] = &readCloser{Reader: r, Closer: rc}

+	h.mu.Unlock()

+	return "http://" + urlPrefix + id, func() {

+		h.mu.Lock()

+		delete(h.requests, id)

+		h.mu.Unlock()

+	}

+}

+

+func (h *reqBodyHandler) RoundTrip(req *http.Request) (*http.Response, error) {

+	host := req.URL.Host

+	if strings.HasPrefix(host, urlPrefix) {

+		if req.Method != "GET" {

+			return nil, errors.Errorf("invalid request")

+		}

+		id := strings.TrimPrefix(host, urlPrefix)

+		h.mu.Lock()

+		rc, ok := h.requests[id]

+		delete(h.requests, id)

+		h.mu.Unlock()

+

+		if !ok {

+			return nil, errors.Errorf("context not found")

+		}

+

+		return &http.Response{

+			Status:        "200 OK",

+			StatusCode:    200,

+			Body:          rc,

+			ContentLength: -1,

+		}, nil

+	}

+	return h.rt.RoundTrip(req)

+}

+

+type readCloser struct {

+	io.Reader

+	io.Closer

+}

@@ -5,6 +5,7 @@ import (

 	"fmt"

 	"io"

 	"io/ioutil"

+	nethttp "net/http"

 	"runtime"

 	"time"

@@ -53,6 +54,7 @@ type WorkerOpt struct {

 	Exporters         map[string]exporter.Exporter

 	DownloadManager   distribution.RootFSDownloadManager

 	V2MetadataService distmetadata.V2MetadataService

+	Transport         nethttp.RoundTripper

 }

 // Worker is a local worker instance with dedicated snapshotter, cache, and so on.

@@ -85,6 +87,7 @@ func NewWorker(opt WorkerOpt) (*Worker, error) {

 	hs, err := http.NewSource(http.Opt{

 		CacheAccessor: cm,

 		MetadataStore: opt.MetadataStore,

+		Transport:     opt.Transport,

 	})

 	if err != nil {

 		return nil, err

@@ -125,7 +128,7 @@ func (w *Worker) ResolveOp(v solver.Vertex, s frontend.FrontendLLBBridge) (solve

 	case *pb.Op_Source:

 		return ops.NewSourceOp(v, op, w.SourceManager, w)

 	case *pb.Op_Exec:

-		return ops.NewExecOp(v, op, w.CacheManager, w.Executor, w)

+		return ops.NewExecOp(v, op, w.CacheManager, w.MetadataStore, w.Executor, w)

 	case *pb.Op_Build:

 		return ops.NewBuildOp(v, op, s, w)

 	default:

@@ -136,5 +136,6 @@ func (cli *Client) imageBuildOptionsToQuery(options types.ImageBuildOptions) (ur

 	if options.BuildID != "" {

 		query.Set("buildid", options.BuildID)

 	}

+	query.Set("version", string(options.Version))

 	return query, nil

 }