perform extra validation for private message rpc

lib/commands/channel.js

@@ -258,6 +258,11 @@ Channel.writePrivateMessage = function (Env, args, _cb, Server, netfluxId) {
                 return void cb('METADATA_ERR');
             }
 
+            // treat the broadcast channel as write-protected
+            if (channelId.length === HK.ADMIN_CHANNEL_LENGTH) {
+                metadata.restricted = true;
+            }
+
             if (!metadata || !metadata.restricted) {
                 return;
             }
@@ -265,10 +270,6 @@ Channel.writePrivateMessage = function (Env, args, _cb, Server, netfluxId) {
             var session = HK.getNetfluxSession(Env, netfluxId);
             var allowed = HK.listAllowedUsers(metadata);
 
-            // Special broadcast channel
-            if (channelId.length === HK.ADMIN_CHANNEL_LENGTH) {
-                allowed = Env.admins;
-            }
 
             if (HK.isUserSessionAllowed(allowed, session)) { return; }