fix #511

gencapdefs.py

         url="https://wiki.znc.in/Playback",
         standard="ZNC vendor",
     ),
+    CapDef(
+        identifier="Nope",
+        name="oragono.io/nope",
+        url="https://oragono.io/nope",
+        standard="Oragono vendor",
+    ),
 ]
 
 def validate_defs():

irc/caps/defs.go

 
 const (
 	// number of recognized capabilities:
-	numCapabs = 26
+	numCapabs = 27
 	// length of the uint64 array that represents the bitset:
 	bitsetLen = 1
 )
 	// ZNCPlayback is the ZNC vendor capability named "znc.in/playback":
 	// https://wiki.znc.in/Playback
 	ZNCPlayback Capability = iota
+
+	// Nope is the Oragono vendor capability named "oragono.io/nope":
+	// https://oragono.io/nope
+	Nope Capability = iota
 )
 
 // `capabilityNames[capab]` is the string name of the capability `capab`
 		"znc.in/self-message",
 		"draft/event-playback",
 		"znc.in/playback",
+		"oragono.io/nope",
 	}
 )

irc/handlers.go

 			}
 		}
 
+		// #511: oragono.io/nope is a fake cap to trap bad clients who blindly request
+		// every offered capability:
+		if toAdd.Has(caps.Nope) {
+			client.Quit(client.t("Requesting the oragono.io/nope CAP is forbidden"), rb.session)
+			return true
+		}
+
 		// update maxlenrest, just in case they altered the maxline cap
 		rb.session.SetMaxlenRest()