kill a packStruct

Makefile

@@ -19,6 +19,7 @@ GOFILES=\
 	nsec3.go \
 	qnamestring.go\
 	server.go \
+	rawmsg.go \
 	tsig.go\
 	types.go\
 	xfr.go\

msg.go

@@ -829,11 +829,9 @@ func packRR(rr RR, msg []byte, off int) (off2 int, ok bool) {
 	if !ok {
 		return len(msg), false
 	}
-
-	// TODO make this quicker
-	// pack a third time; redo header with correct data length
-	rr.Header().Rdlength = uint16(off2 - off1)
-	packStruct(rr.Header(), msg, off)
+	if !RawSetRdlength(msg, uint16(off2-off1)) {
+                return len(msg), false
+        }
 	return off2, true
 }
 

rawmsg.go

@@ -0,0 +1,25 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package dns
+
+/* Function defined in this subpackage work on []byte and but still
+ * provide some higher level functions
+ */
+
+
+// SetRdlength sets the length of the length of the rdata
+// directly at the correct position in the buffer buf.
+// If buf does not look like a DNS message false is returned,
+// otherwise true.
+func RawSetRdlength(buf []byte, i uint16) bool {
+        var off int
+        var ok bool
+	if _, off, ok = unpackDomainName(buf, 0); !ok {
+		return false
+	}
+        // off + type(2) + class(2) + ttl(4) -> rdlength
+        buf[off+2+2+4], buf[off+2+2+4+1] = packUint16(i)
+        return true
+}