You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: urls.go
    path of file: ./repos/docker-ce/components/engine/vendor/github.com/docker/distribution/registry/api/v2
    
    the code of the file until where you have to start completion: package v2

import (
	"fmt"
	"net/http"
	"net/url"
	"strings"

	"github.com/docker/distribution/reference"
	"github.com/gorilla/mux"
)

// URLBuilder creates registry API urls from a single base endpoint. It can be
// used to create urls for use in a registry client or server.
//
// All urls will be created from the given base, including the api version.
// For example, if a root of "/foo/" is provided, urls generated will be f
    
func (ub *URLBuilder) BuildManifestURL(ref reference.Named) (string, error) {
	route := ub.cloneRoute(RouteNameManifest)

	tagOrDigest := ""
	switch v := ref.(type) {
	case reference.Tagged:
		tagOrDigest = v.Tag()
	case reference.Digested:
		tagOrDigest = v.Digest().String()
	default:
		return "", fmt.Errorf("reference must have a tag or digest")
	}

	manifestURL, err := route.URL("name", ref.Name(), "reference", tagOrDigest)
	if err != nil {
		return "", err
	}

	return manifestURL.String(), nil
}