Update gomod and vendor

vendor/github.com/moby/buildkit/source/http/transport.go

@@ -0,0 +1,60 @@
+package http
+
+import (
+	"context"
+	"io"
+	"net/http"
+	"time"
+
+	"github.com/moby/buildkit/session"
+	"github.com/moby/buildkit/session/upload"
+	"github.com/pkg/errors"
+)
+
+func newTransport(rt http.RoundTripper, sm *session.Manager, id string) http.RoundTripper {
+	return &sessionHandler{rt: rt, sm: sm, id: id}
+}
+
+type sessionHandler struct {
+	sm *session.Manager
+	rt http.RoundTripper
+	id string
+}
+
+func (h *sessionHandler) RoundTrip(req *http.Request) (*http.Response, error) {
+	if req.URL.Host != "buildkit-session" {
+		return h.rt.RoundTrip(req)
+	}
+
+	if req.Method != "GET" {
+		return nil, errors.Errorf("invalid request")
+	}
+
+	timeoutCtx, cancel := context.WithTimeout(context.TODO(), 5*time.Second)
+	defer cancel()
+
+	caller, err := h.sm.Get(timeoutCtx, h.id)
+	if err != nil {
+		return nil, err
+	}
+
+	up, err := upload.New(context.TODO(), caller, req.URL)
+	if err != nil {
+		return nil, err
+	}
+
+	pr, pw := io.Pipe()
+	go func() {
+		_, err := up.WriteTo(pw)
+		pw.CloseWithError(err)
+	}()
+
+	resp := &http.Response{
+		Status:        "200 OK",
+		StatusCode:    200,
+		Body:          pr,
+		ContentLength: -1,
+	}
+
+	return resp, nil
+}