From 3996b17d1944cd34bc6ac78ccdd21bb338fdf9ca Mon Sep 17 00:00:00 2001
From: Tom Thorogood <me+github@tomthorogood.net>
Date: Mon, 6 Nov 2023 16:56:49 +1030
Subject: [PATCH] Avoid using a goto loop in unpackDataOpt (#1505)

We definitely shouldn't be using goto for a simple loop.

This is technically a behaviour change when off == len(msg), but we're
always called with off < len(msg) so this is unobservable.
---
 msg_helpers.go | 39 +++++++++++++++++----------------------
 1 file changed, 17 insertions(+), 22 deletions(-)

diff --git a/msg_helpers.go b/msg_helpers.go
index 210313022..acec21f7d 100644
--- a/msg_helpers.go
+++ b/msg_helpers.go
@@ -406,29 +406,24 @@ func packStringTxt(s []string, msg []byte, off int) (int, error) {
 
 func unpackDataOpt(msg []byte, off int) ([]EDNS0, int, error) {
 	var edns []EDNS0
-Option:
-	var code uint16
-	if off+4 > len(msg) {
-		return nil, len(msg), &Error{err: "overflow unpacking opt"}
-	}
-	code = binary.BigEndian.Uint16(msg[off:])
-	off += 2
-	optlen := binary.BigEndian.Uint16(msg[off:])
-	off += 2
-	if off+int(optlen) > len(msg) {
-		return nil, len(msg), &Error{err: "overflow unpacking opt"}
-	}
-	e := makeDataOpt(code)
-	if err := e.unpack(msg[off : off+int(optlen)]); err != nil {
-		return nil, len(msg), err
-	}
-	edns = append(edns, e)
-	off += int(optlen)
-
-	if off < len(msg) {
-		goto Option
+	for off < len(msg) {
+		if off+4 > len(msg) {
+			return nil, len(msg), &Error{err: "overflow unpacking opt"}
+		}
+		code := binary.BigEndian.Uint16(msg[off:])
+		off += 2
+		optlen := binary.BigEndian.Uint16(msg[off:])
+		off += 2
+		if off+int(optlen) > len(msg) {
+			return nil, len(msg), &Error{err: "overflow unpacking opt"}
+		}
+		opt := makeDataOpt(code)
+		if err := opt.unpack(msg[off : off+int(optlen)]); err != nil {
+			return nil, len(msg), err
+		}
+		edns = append(edns, opt)
+		off += int(optlen)
 	}
-
 	return edns, off, nil
 }