Use Go code to extract rootfs from system containers

- this removes the use of riddler to extract the rootfs, use code
  we were using for rootfs. riddler now just geenrates the config,
  next stage is to generate this ourselves
- change the naming of the daemons so no longer include number as we
  do not guarantee ordering as they start up simultaneously

Signed-off-by: Justin Cormack <justin.cormack@docker.com>

src/cmd/moby/image.go

@@ -164,23 +164,69 @@ nameserver 2001:4860:4860::8844
 	"etc/hostname": "moby",
 }
 
-func imageExtract(image string) ([]byte, error) {
+// ImageExtract extracts the filesystem from an image and returns a tarball with the files prefixed by the given path
+func ImageExtract(image, prefix string) ([]byte, error) {
+	out := new(bytes.Buffer)
+	tw := tar.NewWriter(out)
+	err := tarPrefix(prefix, tw)
+	if err != nil {
+		return []byte{}, err
+	}
+	err = imageTar(image, prefix, tw)
+	if err != nil {
+		return []byte{}, err
+	}
+	err = tw.Close()
+	if err != nil {
+		return []byte{}, err
+	}
+	return out.Bytes(), nil
+}
+
+// tarPrefix creates the leading directories for a path
+func tarPrefix(path string, tw *tar.Writer) error {
+	if path == "" {
+		return nil
+	}
+	if path[len(path)-1] != byte('/') {
+		return fmt.Errorf("path does not end with /: %s", path)
+	}
+	path = path[:len(path)-1]
+	if path[0] == byte('/') {
+		return fmt.Errorf("path should be relative: %s", path)
+	}
+	mkdir := ""
+	for _, dir := range strings.Split(path, "/") {
+		mkdir = mkdir + dir
+		hdr := &tar.Header{
+			Name:     mkdir,
+			Mode:     0755,
+			Typeflag: tar.TypeDir,
+		}
+		tw.WriteHeader(hdr)
+		mkdir = mkdir + "/"
+	}
+	return nil
+}
+
+func imageTar(image, prefix string, tw *tar.Writer) error {
+	if prefix != "" && prefix[len(prefix)-1] != byte('/') {
+		return fmt.Errorf("prefix does not end with /: %s", prefix)
+	}
 	container, err := dockerCreate(image)
 	if err != nil {
-		return []byte{}, fmt.Errorf("Failed to docker create image %s: %v", image, err)
+		return fmt.Errorf("Failed to docker create image %s: %v", image, err)
 	}
 	contents, err := dockerExport(container)
 	if err != nil {
-		return []byte{}, fmt.Errorf("Failed to docker export container from container %s: %v", container, err)
+		return fmt.Errorf("Failed to docker export container from container %s: %v", container, err)
 	}
 	err = dockerRm(container)
 	if err != nil {
-		return []byte{}, fmt.Errorf("Failed to docker rm container %s: %v", container, err)
+		return fmt.Errorf("Failed to docker rm container %s: %v", container, err)
 	}
 
 	// now we need to filter out some files from the resulting tar archive
-	out := new(bytes.Buffer)
-	tw := tar.NewWriter(out)
 
 	r := bytes.NewReader(contents)
 	tr := tar.NewReader(r)
@@ -191,21 +237,58 @@ func imageExtract(image string) ([]byte, error) {
 			break
 		}
 		if err != nil {
-			return []byte{}, err
+			return err
 		}
 		if exclude[hdr.Name] {
 			io.Copy(ioutil.Discard, tr)
 		} else if replace[hdr.Name] != "" {
-			hdr.Size = int64(len(replace[hdr.Name]))
+			contents := replace[hdr.Name]
+			hdr.Size = int64(len(contents))
+			hdr.Name = prefix + hdr.Name
 			tw.WriteHeader(hdr)
-			buf := bytes.NewBufferString(replace[hdr.Name])
+			buf := bytes.NewBufferString(contents)
 			io.Copy(tw, buf)
+			io.Copy(ioutil.Discard, tr)
 		} else {
+			hdr.Name = prefix + hdr.Name
 			tw.WriteHeader(hdr)
 			io.Copy(tw, tr)
 		}
 	}
 	err = tw.Close()
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+// ImageBundle produces an OCI bundle at the given path in a tarball, given an image and a config.json
+func ImageBundle(path, image, config string) ([]byte, error) {
+	out := new(bytes.Buffer)
+	tw := tar.NewWriter(out)
+	err := tarPrefix(path+"/rootfs/", tw)
+	if err != nil {
+		return []byte{}, err
+	}
+	hdr := &tar.Header{
+		Name: path + "/" + "config.json",
+		Mode: 0644,
+		Size: int64(len(config)),
+	}
+	err = tw.WriteHeader(hdr)
+	if err != nil {
+		return []byte{}, err
+	}
+	buf := bytes.NewBufferString(config)
+	_, err = io.Copy(tw, buf)
+	if err != nil {
+		return []byte{}, err
+	}
+	err = imageTar(image, path+"/rootfs/", tw)
+	if err != nil {
+		return []byte{}, err
+	}
+	err = tw.Close()
 	if err != nil {
 		return []byte{}, err
 	}