Use the roundtripper during build

The roundtripper is responsible for giving back the build context when
it comes from a tar directly. So we add it to the source manager of the
containerd worker.

Signed-off-by: Djordje Lukic <djordje.lukic@docker.com>

builder/builder-next/controller.go

@@ -148,7 +148,7 @@ func newSnapshotterController(ctx context.Context, rt http.RoundTripper, opt Opt
 	}
 	wo.Executor = exec
 
-	w, err := mobyworker.NewContainerdWorker(ctx, wo, opt.Callbacks)
+	w, err := mobyworker.NewContainerdWorker(ctx, wo, opt.Callbacks, rt)
 	if err != nil {
 		return nil, err
 	}

builder/builder-next/worker/containerdworker.go

@@ -2,11 +2,14 @@ package worker
 
 import (
 	"context"
+	nethttp "net/http"
 
+	"github.com/containerd/log"
 	"github.com/docker/docker/builder/builder-next/exporter"
 	"github.com/moby/buildkit/client"
 	bkexporter "github.com/moby/buildkit/exporter"
 	"github.com/moby/buildkit/session"
+	"github.com/moby/buildkit/source/http"
 	"github.com/moby/buildkit/worker/base"
 )
 
@@ -17,11 +20,21 @@ type ContainerdWorker struct {
 }
 
 // NewContainerdWorker instantiates a local worker.
-func NewContainerdWorker(ctx context.Context, wo base.WorkerOpt, callbacks exporter.BuildkitCallbacks) (*ContainerdWorker, error) {
+func NewContainerdWorker(ctx context.Context, wo base.WorkerOpt, callbacks exporter.BuildkitCallbacks, rt nethttp.RoundTripper) (*ContainerdWorker, error) {
 	bw, err := base.NewWorker(ctx, wo)
 	if err != nil {
 		return nil, err
 	}
+	hs, err := http.NewSource(http.Opt{
+		CacheAccessor: bw.CacheManager(),
+		Transport:     rt,
+	})
+	if err == nil {
+		bw.SourceManager.Register(hs)
+	} else {
+		log.G(ctx).Warnf("Could not register builder http source: %s", err)
+	}
+
 	return &ContainerdWorker{Worker: bw, callbacks: callbacks}, nil
 }