dns

commit 1c3a28b4e3d5fcd9374467eac2287607a1a8e669
parent 2f4ad6437420a56d016b5d1ac5eb61c2a7234254
Author: Oliver Lowe <o@olowe.co>
Date:   Sat, 20 Nov 2021 11:32:21 +1100

Use fancy bit operations to encode message length

Instead of encoding/binary package. Removes that package dependency

Diffstat:
M
dns.go
 | 
9
+++++----

1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/dns.go b/dns.go
@@ -2,7 +2,6 @@ package dns
 
 import (
 	"crypto/tls"
-	"encoding/binary"
 	"errors"
 	"fmt"
 	"io"
@@ -81,8 +80,10 @@ func dnsPacketExchange(b []byte, conn net.Conn) ([]byte, error) {
 func dnsStreamExchange(b []byte, conn net.Conn) ([]byte, error) {
 	// DNS over TCP requires you to prepend the message with a
 	// 2-octet length field.
-	m := make([]byte, 2+len(b))
-	binary.BigEndian.PutUint16(m, uint16(len(b)))
+	l := len(b)
+	m := make([]byte, 2+l)
+	m[0] = byte(l >> 8)
+	m[1] = byte(l)
 	copy(m[2:], b)
 	if _, err := conn.Write(m); err != nil {
 		return nil, err
@@ -92,7 +93,7 @@ func dnsStreamExchange(b []byte, conn net.Conn) ([]byte, error) {
 	if _, err := io.ReadFull(conn, b[:2]); err != nil {
 		return nil, fmt.Errorf("read length: %w", err)
 	}
-	l := int(b[0])<<8 | int(b[1])
+	l = int(b[0])<<8 | int(b[1])
 	if l > len(b) {
 		b = make([]byte, l)
 	}