dlna: fix root XML service descriptor

The SCPD URL was being set after marshalling the XML, and thus coming
out blank.  Now works on my Samsung TV, and likely fixes some issues
reported by others in #2648.

cmd/serve/dlna/dlna.go

@@ -86,6 +86,13 @@ var services = []*service{
 	},
 }
 
+func init() {
+	for _, s := range services {
+		p := path.Join("/scpd", s.ServiceId)
+		s.SCPDURL = p
+	}
+}
+
 func devices() []string {
 	return []string{
 		"urn:schemas-upnp-org:device:MediaServer:1",
@@ -250,9 +257,6 @@ func (s *server) initMux(mux *http.ServeMux) {
 
 	// Install handlers to serve SCPD for each UPnP service.
 	for _, s := range services {
-		p := path.Join("/scpd", s.ServiceId)
-		s.SCPDURL = p
-
 		mux.HandleFunc(s.SCPDURL, func(serviceDesc string) http.HandlerFunc {
 			return func(w http.ResponseWriter, r *http.Request) {
 				w.Header().Set("content-type", `text/xml; charset="utf-8"`)

cmd/serve/dlna/dlna_test.go

@@ -59,6 +59,8 @@ func TestRootSCPD(t *testing.T) {
 	// Make sure that the SCPD contains a CDS service.
 	require.Contains(t, string(body),
 		"<serviceType>urn:schemas-upnp-org:service:ContentDirectory:1</serviceType>")
+	// Ensure that the SCPD url is configured.
+	require.Regexp(t, "<SCPDURL>/.*</SCPDURL>", string(body))
 }
 
 // Make sure that it serves content from the remote.