Allow for capabilities to be marked as "required".

If capability negotiation fails on these capabilities, then the server link is dropped.

include/s_serv.h

@@ -51,6 +51,7 @@ struct Capability
 {
 	const char *name;	/* name of capability */
 	unsigned int cap;	/* mask value */
+	unsigned int required;  /* 1 if required, 0 if not */
 };
 
 #define CAP_CAP         0x00001	/* received a CAP to begin with */

modules/m_capab.c

@@ -1,6 +1,6 @@
 /*
  *  ircd-ratbox: A slightly useful ircd.
- *  m_away.c: Negotiates capabilities with a remote server.
+ *  m_capab.c: Negotiates capabilities with a remote server.
  *
  *  Copyright (C) 1990 Jarkko Oikarinen and University of Oulu, Co Center
  *  Copyright (C) 1996-2002 Hybrid Development Team
@@ -96,6 +96,23 @@ mr_capab(struct Client *client_p, struct Client *source_p, int parc, const char
 		}
 	}
 
+	/* check to ensure any "required" caps are set. --nenolod */
+	for (cap = captab; cap->name; cap++)
+	{
+		if (!cap->required)
+			continue;
+
+		if (!(client_p->localClient->caps & cap->cap))
+		{
+			char exitbuf[BUFSIZE];
+
+			rb_snprintf(exitbuf, BUFSIZE, "Missing required CAPAB [%s]", cap->cap);
+			exit_client(client_p, client_p, client_p, exitbuf);
+
+			return 0;
+		}
+	}
+
 	return 0;
 }