Irc, clientbot: disallow unsetting bans that don't exist

This fixes an infinite loop when:
- Clientbot modesync is enabled
- 2 or more clientbot linked networks show unsetting modes that weren't enabled (e.g. charybdis)
- A user removes a ban

The workaround in clientbot prevents this process from triggering an infinite loop when a mode change acknowledgement is received for unsetting a non-existant ban,
though multiple -b mode changes may still be seen due to race conditions in updating the various networks' states.

classes.py

@@ -601,7 +601,13 @@ class Irc():
                         # Must have parameter.
                         log.debug('Mode %s: This mode must have parameter.', mode)
                         arg = args.pop(0)
-                        if prefix == '-' and mode in supported_modes['*B'] and arg == '*':
+                        if prefix == '-':
+                            log.debug('(%s) parseModes: checking if +%s %s is in old modes list: %s', self.name, mode, arg, oldmodes)
+                            if (mode, arg) not in oldmodes:
+                                # Ignore attempts to unset bans that don't exist.
+                                log.debug("(%s) parseModes(): ignoring removal of non-existent list mode +%s %s", self.name, mode, arg)
+                                continue
+                        elif prefix == '-' and mode in supported_modes['*B'] and arg == '*':
                             # Charybdis allows unsetting +k without actually
                             # knowing the key by faking the argument when unsetting
                             # as a single "*".

protocols/clientbot.py

@@ -184,7 +184,13 @@ class ClientbotWrapperProtocol(Protocol):
         """Sends channel MODE changes."""
         if utils.isChannel(channel):
             extmodes = []
-            for modepair in modes:
+            # Re-parse all channel modes locally to eliminate anything invalid, such as unbanning
+            # things that were never banned. This prevents the bot from getting caught in a loop
+            # with IRCd MODE acknowledgements.
+            # FIXME: More related safety checks should be added for this.
+            log.debug('(%s) mode: re-parsing modes %s', self.irc.name, modes)
+            joined_modes = self.irc.joinModes(modes)
+            for modepair in self.irc.parseModes(channel, joined_modes):
                 log.debug('(%s) mode: checking if %s a prefix mode: %s', self.irc.name, modepair, self.irc.prefixmodes)
                 if modepair[0][-1] in self.irc.prefixmodes:
                     if self.irc.isInternalClient(modepair[1]):
@@ -599,7 +605,8 @@ class ClientbotWrapperProtocol(Protocol):
         if self.irc.isInternalClient(target):
             log.debug('(%s) Suppressing MODE change hook for internal client %s', self.irc.name, target)
             return
-        return {'target': target, 'modes': changedmodes, 'channeldata': oldobj}
+        if changedmodes:
+            return {'target': target, 'modes': changedmodes, 'channeldata': oldobj}
 
     def handle_nick(self, source, command, args):
         """Handles NICK changes."""