plugin/log: log remote port addr as well (#1573)

Log the remote's port, for IPv6 addr this means we should enclose the v6
address in brackets; make this the default for 'remote'.

plugin/pkg/replacer/replacer.go

@@ -43,7 +43,7 @@ func New(r *dns.Msg, rr *dnstest.Recorder, emptyValue string) Replacer {
 				return time.Now().Format(timeFormat)
 			}(),
 			"{size}":   strconv.Itoa(req.Len()),
-			"{remote}": req.IP(),
+			"{remote}": addrToRFC3986(req.IP()),
 			"{port}":   req.Port(),
 		},
 		emptyValue: emptyValue,
@@ -155,6 +155,14 @@ func flagsToString(h dns.MsgHdr) string {
 	return strings.Join(flags[:i], ",")
 }
 
+// addrToRFC3986 will add brackets to the address if it is an IPv6 address.
+func addrToRFC3986(addr string) string {
+	if strings.Contains(addr, ":") {
+		return "[" + addr + "]"
+	}
+	return addr
+}
+
 const (
 	timeFormat     = "02/Jan/2006:15:04:05 -0700"
 	headerReplacer = "{>"