containerd integration: Passing a build context via tarball to the /build endpoint is broken

[vvoland]

Description

Building via the /build endpoint with Version=BuilderBuildkit fails with:

failed to read downloaded context: failed to load cache key: invalid response status 403

When passing a build context via a tar without a build session.

It works with graphdrivers, because the mobyworker makes use of the passed http.RoundTripper:

moby/builder/builder-next/controller.go

Line 355 in 8d5d655

Transport: rt,

moby/builder/builder-next/controller.go

Line 193 in 8d5d655

func newGraphDriverController(ctx context.Context, rt http.RoundTripper, opt Opt) (*control.Controller, error) {

which is used to respond to a fake url echoing the passed build context:

moby/builder/builder-next/builder.go

Line 294 in 8d5d655

url, cancel := b.reqBodyHandler.newRequest(rc)

With the containerd integration, the ContainerdWorker doesn't use this RoundTripper so it isn't able to access the build context.

Reproduce

package main

import (
	"context"
	"io"
	"os"

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

func main() {
	cli, err := client.NewClientWithOpts(client.FromEnv)
	if err != nil {
		panic(err)
	}

	rd, err := os.Open("context.tar")
	if err != nil {
		panic(err)
	}
	defer rd.Close()

	imageBuildResponse, err := cli.ImageBuild(context.Background(), rd, types.ImageBuildOptions{
		Version: types.BuilderBuildKit, // without this, classic builder is used
		Tags:    []string{"myimage:latest"},
	})
	if err != nil {
		panic(err)
	}
	defer imageBuildResponse.Body.Close()

	_, err = io.Copy(os.Stdout, imageBuildResponse.Body)
	if err != nil {
		panic(err)
	}
}

context.tar.zip
(zipping a tar, because github doesn't allow uploading tars 🙈)

Expected behavior

No response

docker version

Client:
 Cloud integration: v1.0.35+desktop.13
 Version:           26.0.0
 API version:       1.45
 Go version:        go1.21.8
 Git commit:        2ae903e
 Built:             Wed Mar 20 15:14:46 2024
 OS/Arch:           darwin/arm64
 Context:           desktop-linux

Server: Docker Desktop 4.30.0 (145546)
 Engine:
  Version:          26.0.0
  API version:      1.45 (minimum version 1.24)
  Go version:       go1.21.8
  Git commit:       8b79278
  Built:            Wed Mar 20 15:18:02 2024
  OS/Arch:          linux/arm64
  Experimental:     false
 containerd:
  Version:          1.6.28
  GitCommit:        ae07eda36dd25f8a1b98dfbf587313b99c0190bb
 runc:
  Version:          1.1.12
  GitCommit:        v1.1.12-0-g51d5e94
 docker-init:
  Version:          0.19.0
  GitCommit:        de40ad0

docker info

N/A

Additional Info

No response