Allow empty layer configs in manifests

Before the V2 registry changes, images with no config could be pushed.
This change fixes a regression that made those images not able to be
pushed to a registry.

Signed-off-by: Euan Kemp <euank@euank.com>

graph/manifest.go

@@ -3,7 +3,6 @@ package graph
 import (
 	"bytes"
 	"encoding/json"
-	"errors"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -71,14 +70,13 @@ func (s *TagStore) newManifest(localName, remoteName, tag string) ([]byte, error
 	if err != nil {
 		return nil, err
 	}
-	if layer.Config == nil {
-		return nil, errors.New("Missing layer configuration")
-	}
 	manifest.Architecture = layer.Architecture
 	manifest.FSLayers = make([]*registry.FSLayer, 0, 4)
 	manifest.History = make([]*registry.ManifestHistory, 0, 4)
 	var metadata runconfig.Config
-	metadata = *layer.Config
+	if layer.Config != nil {
+		metadata = *layer.Config
+	}
 
 	for ; layer != nil; layer, err = layer.GetParent() {
 		if err != nil {

integration-cli/docker_cli_push_test.go

@@ -2,10 +2,14 @@ package main
 
 import (
 	"fmt"
+	"io/ioutil"
+	"os"
 	"os/exec"
 	"strings"
 	"testing"
 	"time"
+
+	"github.com/docker/docker/vendor/src/code.google.com/p/go/src/pkg/archive/tar"
 )
 
 // pulling an image from the central registry should work
@@ -80,3 +84,35 @@ func TestPushInterrupt(t *testing.T) {
 
 	logDone("push - interrupted")
 }
+
+func TestPushEmptyLayer(t *testing.T) {
+	defer setupRegistry(t)()
+	repoName := fmt.Sprintf("%v/dockercli/emptylayer", privateRegistryURL)
+	emptyTarball, err := ioutil.TempFile("", "empty_tarball")
+	if err != nil {
+		t.Fatalf("Unable to create test file: %v", err)
+	}
+	tw := tar.NewWriter(emptyTarball)
+	err = tw.Close()
+	if err != nil {
+		t.Fatalf("Error creating empty tarball: %v", err)
+	}
+	freader, err := os.Open(emptyTarball.Name())
+	if err != nil {
+		t.Fatalf("Could not open test tarball: %v", err)
+	}
+
+	importCmd := exec.Command(dockerBinary, "import", "-", repoName)
+	importCmd.Stdin = freader
+	out, _, err := runCommandWithOutput(importCmd)
+	if err != nil {
+		t.Errorf("import failed with errors: %v, output: %q", err, out)
+	}
+
+	// Now verify we can push it
+	pushCmd := exec.Command(dockerBinary, "push", repoName)
+	if out, _, err := runCommandWithOutput(pushCmd); err != nil {
+		t.Fatalf("pushing the image to the private registry has failed: %s, %v", out, err)
+	}
+	logDone("push - empty layer config to private registry")
+}