From 35694256108aae7dbf72677359edd17ef94ba666 Mon Sep 17 00:00:00 2001
From: Jonni Liljamo <jonni@liljamo.com>
Date: Thu, 24 Oct 2024 12:14:06 +0300
Subject: [PATCH] feat: modified msgAcceptFunc to facilitate dynamic updates

---
 internal/dns/server.go | 50 ++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 48 insertions(+), 2 deletions(-)

diff --git a/internal/dns/server.go b/internal/dns/server.go
index c92b499..ea554f9 100644
--- a/internal/dns/server.go
+++ b/internal/dns/server.go
@@ -18,9 +18,55 @@ func Run(addr string, net string) error {
 	dns.HandleFunc(config.FeluConfig.DNSPattern, handleDNSRequest)
 
 	server := &dns.Server{
-		Addr: addr,
-		Net:  net,
+		Addr:          addr,
+		Net:           net,
+		MsgAcceptFunc: msgAcceptFunc,
 	}
 
 	return server.ListenAndServe()
 }
+
+// https://github.com/miekg/dns/blob/b77d1ed8e9282cadf21c4124f53a660fed55c8ca/types.go#L192
+const _QR = 1 << 15 // query/response (response=1)
+
+// Otherwise the same as the original, but:
+//
+//	1: Commented out dynamic update rejection.
+//	2: Commented out dh.Nscount > 1, for dynamic updates.
+//
+// TODO: Consider looking this over properly, and maybe ditching the default.
+//
+// https://github.com/miekg/dns/blob/b77d1ed8e9282cadf21c4124f53a660fed55c8ca/acceptfunc.go
+func msgAcceptFunc(dh dns.Header) dns.MsgAcceptAction {
+	if isResponse := dh.Bits&_QR != 0; isResponse {
+		return dns.MsgIgnore
+	}
+
+	/*
+		// Don't allow dynamic updates, because then the sections can contain a whole bunch of RRs.
+		opcode := int(dh.Bits>>11) & 0xF
+		if opcode != dns.OpcodeQuery && opcode != dns.OpcodeNotify {
+			return dns.MsgRejectNotImplemented
+		}
+	*/
+
+	if dh.Qdcount != 1 {
+		return dns.MsgReject
+	}
+	// NOTIFY requests can have a SOA in the ANSWER section. See RFC 1996 Section 3.7 and 3.11.
+	if dh.Ancount > 1 {
+		return dns.MsgReject
+	}
+	/*
+		// IXFR request could have one SOA RR in the NS section. See RFC 1995, section 3.
+		if dh.Nscount > 1 {
+			return dns.MsgReject
+		}
+	*/
+
+	if dh.Arcount > 2 {
+		return dns.MsgReject
+	}
+
+	return dns.MsgAccept
+}
-- 
2.44.1