build: support more variations on context and dockerfile + iidfile

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

vendor/github.com/moby/buildkit/session/upload/uploadprovider/provider.go

@@ -0,0 +1,66 @@
+package uploadprovider
+
+import (
+	"io"
+	"path"
+	"sync"
+
+	"github.com/moby/buildkit/identity"
+	"github.com/moby/buildkit/session/upload"
+	"github.com/pkg/errors"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/metadata"
+)
+
+func New() *Uploader {
+	return &Uploader{m: map[string]io.Reader{}}
+}
+
+type Uploader struct {
+	mu sync.Mutex
+	m  map[string]io.Reader
+}
+
+func (hp *Uploader) Add(r io.Reader) string {
+	id := identity.NewID()
+	hp.m[id] = r
+	return "http://buildkit-session/" + id
+}
+
+func (hp *Uploader) Register(server *grpc.Server) {
+	upload.RegisterUploadServer(server, hp)
+}
+
+func (hp *Uploader) Pull(stream upload.Upload_PullServer) error {
+	opts, _ := metadata.FromIncomingContext(stream.Context()) // if no metadata continue with empty object
+	var p string
+	urls, ok := opts["urlpath"]
+	if ok && len(urls) > 0 {
+		p = urls[0]
+	}
+
+	p = path.Base(p)
+
+	hp.mu.Lock()
+	r, ok := hp.m[p]
+	if !ok {
+		hp.mu.Unlock()
+		return errors.Errorf("no http response from session for %s", p)
+	}
+	delete(hp.m, p)
+	hp.mu.Unlock()
+
+	_, err := io.Copy(&writer{stream}, r)
+	return err
+}
+
+type writer struct {
+	grpc.ServerStream
+}
+
+func (w *writer) Write(dt []byte) (int, error) {
+	if err := w.SendMsg(&upload.BytesMessage{Data: dt}); err != nil {
+		return 0, err
+	}
+	return len(dt), nil
+}