Output correct image ID when using Docker with the containerd-snapshotter.

Prior to this change, the following command emits the wrong image ID when buildx
uses the "docker-container" driver and Docker is configured with the
containerd-snapshotter.

$ docker buildx build --load --iidfile=img.txt

$ docker run --rm "$(cat img.txt)" echo hello
docker: Error response from daemon: No such image: sha256:4ac37e81e00f242010e42f3251094e47de6100e01d25e9bd0feac6b8906976df.
See 'docker run --help'.

The problem is that buildx is outputing the incorrect image ID in this scenario
(it's outputing the container image config digest, instead of the container
image digest used by the containerd-snapshotter).

This commit fixes this. See moby/moby#45458.

Signed-off-by: Cesar Talledo <cesar.talledo@docker.com>

Author: ctalledo

build/build.go

@@ -525,7 +525,6 @@ func BuildWithResultHandler(ctx context.Context, nodes []builder.Node, opts map[
 							}
 						}
 					}
-
 					node := dp.Node().Driver
 					if node.IsMobyDriver() {
 						for _, e := range so.Exports {
@@ -561,6 +560,14 @@ func BuildWithResultHandler(ctx context.Context, nodes []builder.Node, opts map[
 							}
 						}
 					}
+					// if prefer-image-digest is set in the solver options, remove the image
+					// config digest from the exporter's response
+					for _, e := range so.Exports {
+						if e.Attrs["prefer-image-digest"] == "true" {
+							delete(rr.ExporterResponse, exptypes.ExporterImageConfigDigestKey)
+							break
+						}
+					}
 					return nil
 				})
 			}

build/opt.go

@@ -237,6 +237,11 @@ func toSolveOpt(ctx context.Context, node builder.Node, multiDriver bool, opt *O
 					opt.Exports[i].Output = func(_ map[string]string) (io.WriteCloser, error) {
 						return w, nil
 					}
+					// if docker is using the containerd snapshotter, prefer to export the image digest
+					// (rather than the image config digest). See https://github.com/moby/moby/issues/45458.
+					if features[dockerutil.OCIImporter] {
+						opt.Exports[i].Attrs["prefer-image-digest"] = "true"
+					}
 				}
 			} else if !nodeDriver.Features(ctx)[driver.DockerExporter] {
 				return nil, nil, notSupported(driver.DockerExporter, nodeDriver, "https://docs.docker.com/go/build-exporters/")

tests/build.go

@@ -399,18 +399,25 @@ func testImageIDOutput(t *testing.T, sb integration.Sandbox) {
 
 	require.Equal(t, dgst.String(), strings.TrimSpace(stdout.String()))
 
+	// read the md.json file
 	dt, err = os.ReadFile(filepath.Join(targetDir, "md.json"))
 	require.NoError(t, err)
 
 	type mdT struct {
+		Digest       string `json:"containerimage.digest"`
 		ConfigDigest string `json:"containerimage.config.digest"`
 	}
+
 	var md mdT
 	err = json.Unmarshal(dt, &md)
 	require.NoError(t, err)
 
 	require.NotEmpty(t, md.ConfigDigest)
-	require.Equal(t, dgst, digest.Digest(md.ConfigDigest))
+	require.NotEmpty(t, md.Digest)
+
+	// verify the image ID output is correct
+	// XXX: improve this by checking that it's one of the two expected digests depending on the scenario.
+	require.Contains(t, []digest.Digest{digest.Digest(md.ConfigDigest), digest.Digest(md.Digest)}, dgst)
 }
 
 func testBuildMobyFromLocalImage(t *testing.T, sb integration.Sandbox) {