Move RR header packing out of generated code (#885)

dns.go

@@ -41,8 +41,9 @@ type RR interface {
 	// size will be returned and domain names will be added to the map for future compression.
 	len(off int, compression map[string]struct{}) int
 
-	// pack packs an RR into wire format.
-	pack(msg []byte, off int, compression compressionMap, compress bool) (headerEnd int, off1 int, err error)
+	// pack packs the records RDATA into wire format. The header will
+	// already have been packed into msg.
+	pack(msg []byte, off int, compression compressionMap, compress bool) (off1 int, err error)
 
 	// unpack unpacks an RR from wire format.
 	//
@@ -87,6 +88,11 @@ func (h *RR_Header) len(off int, compression map[string]struct{}) int {
 	return l
 }
 
+func (h *RR_Header) pack(msg []byte, off int, compression compressionMap, compress bool) (off1 int, err error) {
+	// RR_Header has no RDATA to pack.
+	return off, nil
+}
+
 func (h *RR_Header) unpack(msg []byte, off int) (int, error) {
 	panic("dns: internal error: unpack should never be called on RR_Header")
 }

msg.go

@@ -621,7 +621,12 @@ func packRR(rr RR, msg []byte, off int, compression compressionMap, compress boo
 		return len(msg), len(msg), &Error{err: "nil rr"}
 	}
 
-	headerEnd, off1, err = rr.pack(msg, off, compression, compress)
+	headerEnd, err = rr.Header().packHeader(msg, off, compression, compress)
+	if err != nil {
+		return headerEnd, len(msg), err
+	}
+
+	off1, err = rr.pack(msg, headerEnd, compression, compress)
 	if err != nil {
 		return headerEnd, len(msg), err
 	}

msg_generate.go

@@ -80,17 +80,12 @@ func main() {
 		o := scope.Lookup(name)
 		st, _ := getTypeStruct(o.Type(), scope)
 
-		fmt.Fprintf(b, "func (rr *%s) pack(msg []byte, off int, compression compressionMap, compress bool) (int, int, error) {\n", name)
-		fmt.Fprint(b, `headerEnd, off, err := rr.Hdr.pack(msg, off, compression, compress)
-if err != nil {
-	return headerEnd, off, err
-}
-`)
+		fmt.Fprintf(b, "func (rr *%s) pack(msg []byte, off int, compression compressionMap, compress bool) (off1 int, err error) {\n", name)
 		for i := 1; i < st.NumFields(); i++ {
 			o := func(s string) {
 				fmt.Fprintf(b, s, st.Field(i).Name())
 				fmt.Fprint(b, `if err != nil {
-return headerEnd, off, err
+return off, err
 }
 `)
 			}
@@ -144,7 +139,7 @@ return headerEnd, off, err
 if rr.%s != "-" {
   off, err = packStringHex(rr.%s, msg, off)
   if err != nil {
-    return headerEnd, off, err
+    return off, err
   }
 }
 `, field, field)
@@ -176,7 +171,7 @@ if rr.%s != "-" {
 				log.Fatalln(name, st.Field(i).Name(), st.Tag(i))
 			}
 		}
-		fmt.Fprintln(b, "return headerEnd, off, nil }\n")
+		fmt.Fprintln(b, "return off, nil }\n")
 	}
 
 	fmt.Fprint(b, "// unpack*() functions\n\n")

msg_helpers.go

@@ -99,34 +99,34 @@ func unpackHeader(msg []byte, off int) (rr RR_Header, off1 int, truncmsg []byte,
 	return hdr, off, msg, err
 }
 
-// pack packs an RR header, returning the offset to the end of the header.
+// packHeader packs an RR header, returning the offset to the end of the header.
 // See PackDomainName for documentation about the compression.
-func (hdr RR_Header) pack(msg []byte, off int, compression compressionMap, compress bool) (int, int, error) {
+func (hdr RR_Header) packHeader(msg []byte, off int, compression compressionMap, compress bool) (int, error) {
 	if off == len(msg) {
-		return off, off, nil
+		return off, nil
 	}
 
 	off, err := packDomainName(hdr.Name, msg, off, compression, compress)
 	if err != nil {
-		return off, len(msg), err
+		return len(msg), err
 	}
 	off, err = packUint16(hdr.Rrtype, msg, off)
 	if err != nil {
-		return off, len(msg), err
+		return len(msg), err
 	}
 	off, err = packUint16(hdr.Class, msg, off)
 	if err != nil {
-		return off, len(msg), err
+		return len(msg), err
 	}
 	off, err = packUint32(hdr.Ttl, msg, off)
 	if err != nil {
-		return off, len(msg), err
+		return len(msg), err
 	}
 	off, err = packUint16(0, msg, off) // The RDLENGTH field will be set later in packRR.
 	if err != nil {
-		return off, len(msg), err
+		return len(msg), err
 	}
-	return off, off, nil
+	return off, nil
 }
 
 // helper helper functions.

privaterr.go

@@ -70,17 +70,13 @@ func (r *PrivateRR) copy() RR {
 	return rr
 }
 
-func (r *PrivateRR) pack(msg []byte, off int, compression compressionMap, compress bool) (int, int, error) {
-	headerEnd, off, err := r.Hdr.pack(msg, off, compression, compress)
-	if err != nil {
-		return off, off, err
-	}
+func (r *PrivateRR) pack(msg []byte, off int, compression compressionMap, compress bool) (int, error) {
 	n, err := r.Data.Pack(msg[off:])
 	if err != nil {
-		return headerEnd, len(msg), err
+		return len(msg), err
 	}
 	off += n
-	return headerEnd, off, nil
+	return off, nil
 }
 
 func (r *PrivateRR) unpack(msg []byte, off int) (int, error) {