relay: add workarounds for u-lined servers

- Allow ulines to join with modes (this status gets forwarded as part of relay_joins()), but *ignore* this status when checking for claim
    - For U-lined clients to set modes properly and kick, they be on the claim list
- Allow ulines to set modes on ulined clients including itself. These changes are ignored: not forwarded, not bounced, but just left there.
- Ignore uline attempts to set non-list modes - this is mostly for compatibility with Anope's DEFCON, as it would otherwise lead to a mode flood.

This requires commit 9113b34b46, i.e. the get_server() update.

example-conf.yml

@@ -228,6 +228,11 @@ servers:
         # This defaults to 4096 if not set.
         #maxsendq: 4096
 
+        # Defines a list of "U-lined" servers that should be given special treatment when overriding
+        # modes. Relay uses this as a list of servers to IGNORE some mode changes from on a claimed
+        # channel (versus bouncing the mode back, which may be floody).
+        #ulines: ["services.example.conf"]
+
         # InspIRCd specific option: determines whether we should display WHOIS extensions by overriding
         # InspIRCd's default WHOIS formatting. This defaults to true for consistency with PyLink 1.x.
         #force_whois_extensions: true

plugins/relay.py

@@ -533,7 +533,8 @@ def check_claim(irc, channel, sender, chanobj=None):
     2) The originating network is the one that created the relay.
     3) The CLAIM list for the relay in question is empty.
     4) The originating network is in the CLAIM list for the relay in question.
-    5) The sender is halfop or above in the channel.
+    5) The sender is halfop or above in the channel but NOT a U-line
+       (this is because we allow u-lines to override with ops to prevent mode floods).
     6) The sender is a PyLink client/server (checks are suppressed in this case).
     """
     relay = get_relay((irc.name, channel))
@@ -548,7 +549,8 @@ def check_claim(irc, channel, sender, chanobj=None):
     # XXX: stop hardcoding modes to check for and support mlist in isHalfopPlus and friends
     return (not relay) or irc.name == relay[0] or not db[relay]['claim'] or \
         irc.name in db[relay]['claim'] or \
-        any([mode in sender_modes for mode in ('y', 'q', 'a', 'o', 'h')]) \
+        (any([mode in sender_modes for mode in ('y', 'q', 'a', 'o', 'h')])
+         and not _is_uline(irc, sender)) \
         or irc.is_internal_client(sender) or \
         irc.is_internal_server(sender)
 
@@ -980,7 +982,9 @@ def handle_join(irc, numeric, command, args):
                       irc.name, user, channel, modediff, oldmodes, newmodes)
             for modename in modediff:
                 modechar = irc.cmodes.get(modename)
-                if modechar:
+                # Special case for U-lined servers: allow them to join with ops,
+                # but don't forward this mode change on.
+                if modechar and not _is_uline(irc, numeric):
                     modes.append(('-%s' % modechar, user))
 
         if modes:
@@ -1364,6 +1368,9 @@ def handle_chgclient(irc, source, command, args):
 for c in ('CHGHOST', 'CHGNAME', 'CHGIDENT'):
     utils.add_hook(handle_chgclient, c)
 
+def _is_uline(irc, client):
+    return irc.get_friendly_name(irc.get_server(client)) in irc.serverdata.get('ulines', [])
+
 def handle_mode(irc, numeric, command, args):
     def _handle_mode_loop(irc, remoteirc, numeric, command, args):
         target = args['target']
@@ -1387,9 +1394,24 @@ def handle_mode(irc, numeric, command, args):
                         remoteirc.mode(rsid, remotechan, supported_modes)
             else:  # Mode change blocked by CLAIM.
                 reversed_modes = irc.reverse_modes(target, modes, oldobj=oldchan)
+
+                if _is_uline(irc, numeric):
+                    # Special hack for "U-lined" servers - ignore changes to SIMPLE modes and
+                    # attempts to op u-lined clients (trying to change status for others
+                    # SHOULD be reverted).
+                    # This is for compatibility with Anope's DEFCON for the most part, as well as
+                    # silly people who try to register a channel multiple times via relay.
+                    reversed_modes = [modepair for modepair in reversed_modes if
+                                      # Mode is a prefix mode but target isn't ulined, revert
+                                      ((modepair[0][-1] in irc.prefixmodes and not
+                                        _is_uline(irc, modepair[1]))
+                                      # Tried to set a list mode, revert
+                                       or modepair[0][-1] in irc.cmodes['*A'])
+                                     ]
+
+                if reversed_modes:
                     log.debug('(%s) relay.handle_mode: Reversing mode changes of %r with %r (CLAIM).',
                               irc.name, modes, reversed_modes)
-                if reversed_modes:
                     irc.mode(irc.sid, target, reversed_modes)
                 return