relay: allow dropping messages from user-less clients

This adds two new options, both defaulting to True:
- relay:accept_weird_senders (global)
- servers:<name>:relay_weird_senders (per-server)

Closes #404.

example-conf.yml

@@ -337,6 +337,12 @@ servers:
         # entire PyLink service than what's desired, even when PyLink is only connected as a bot.
         track_oper_statuses: false
 
+        # Determines whether messages from unknown clients (servers, clients not sharing in a -n
+        # channel, etc.) should be forwarded via the PyLink server. If this is disabled, these
+        # messages will be silently dropped. This overrides the "accept_weird_senders" option in the
+        # "relay:" configuration block, and defaults to True for consistency with older releases.
+        #relay_weird_senders: false
+
 # Plugins to load (omit the .py extension)
 plugins:
     # Commands plugin: Provides simple commands for things like checking login
@@ -573,6 +579,11 @@ relay:
     #
     #clientbot_modesync: none
 
+    # Determines whether messages from unknown clients (servers, clients not sharing in a -n channel,
+    # etc.) should be forwarded via the PyLink server. If this is disabled, these messages will be
+    # silently dropped. This defaults to True for consistency with older releases.
+    #accept_weird_senders: false
+
 #servprotect:
     # This block configures the servprotect plugin; you don't need this if you aren't using it.
 

plugins/relay.py

@@ -1079,6 +1079,11 @@ def handle_messages(irc, numeric, command, args):
             user = get_remote_user(irc, remoteirc, numeric, spawn_if_missing=False)
 
             if not user:
+                if not (irc.serverdata.get('relay_weird_senders',
+                        conf.conf.get('relay', {}).get('accept_weird_senders', True))):
+                    log.debug("(%s) Dropping message for %s from user-less sender %s", irc.name,
+                              real_target, numeric)
+                    continue
                 # No relay clone exists for the sender; route the message through our
                 # main client (or SID for notices).