Improve URL Builders

Handles an issue where mux.Route does not set the desired scheme
when building a url and always uses `http`.

Now uses X-Forwarded-Proto when creating a URLBuilder from a request.

Docker-DCO-1.1-Signed-off-by: Josh Hawn <josh.hawn@docker.com> (github: jlhawn)

api/v2/urls.go

@@ -43,9 +43,30 @@ func NewURLBuilderFromString(root string) (*URLBuilder, error) {
 // NewURLBuilderFromRequest uses information from an *http.Request to
 // construct the root url.
 func NewURLBuilderFromRequest(r *http.Request) *URLBuilder {
+	var scheme string
+
+	forwardedProto := r.Header.Get("X-Forwarded-Proto")
+
+	switch {
+	case len(forwardedProto) > 0:
+		scheme = forwardedProto
+	case r.TLS != nil:
+		scheme = "https"
+	case len(r.URL.Scheme) > 0:
+		scheme = r.URL.Scheme
+	default:
+		scheme = "http"
+	}
+
+	host := r.Host
+	forwardedHost := r.Header.Get("X-Forwarded-Host")
+	if len(forwardedHost) > 0 {
+		host = forwardedHost
+	}
+
 	u := &url.URL{
-		Scheme: r.URL.Scheme,
-		Host:   r.Host,
+		Scheme: scheme,
+		Host:   host,
 	}
 
 	return NewURLBuilder(u)
@@ -129,13 +150,28 @@ func (ub *URLBuilder) BuildBlobUploadChunkURL(name, uuid string, values ...url.V
 
 // clondedRoute returns a clone of the named route from the router. Routes
 // must be cloned to avoid modifying them during url generation.
-func (ub *URLBuilder) cloneRoute(name string) *mux.Route {
+func (ub *URLBuilder) cloneRoute(name string) clonedRoute {
 	route := new(mux.Route)
-	*route = *ub.router.GetRoute(name) // clone the route
+	root := new(url.URL)
 
-	return route.
-		Schemes(ub.root.Scheme).
-		Host(ub.root.Host)
+	*route = *ub.router.GetRoute(name) // clone the route
+	*root = *ub.root
+
+	return clonedRoute{Route: route, root: root}
+}
+
+type clonedRoute struct {
+	*mux.Route
+	root *url.URL
+}
+
+func (cr clonedRoute) URL(pairs ...string) (*url.URL, error) {
+	routeURL, err := cr.Route.URL(pairs...)
+	if err != nil {
+		return nil, err
+	}
+
+	return cr.root.ResolveReference(routeURL), nil
 }
 
 // appendValuesURL appends the parameters to the url.