dns

commit fcbc0eaeb5ac159cd2b10e70e5deaae703cf5189
parent 692accac0fc8763da7b9063b1948fa08415b4b7f
Author: Oliver Lowe <o@olowe.co>
Date:   Fri, 19 Nov 2021 12:58:15 +1100

error on receiving a message with the wrong message ID

Diffstat:
M
dns.go
 | 
10
++++++++--

1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/dns.go b/dns.go
@@ -3,6 +3,7 @@ package dns
 import (
 	"crypto/tls"
 	"encoding/binary"
+	"errors"
 	"fmt"
 	"net"
 
@@ -13,6 +14,8 @@ import (
 const MediaType string = "application/dns-message"
 const MaxMsgSize int = 65535 // max size of a message in bytes
 
+var errMismatchedID = errors.New("mismatched message id")
+
 // Exchange performs a synchronous, unencrypted UDP DNS exchange with addr and returns its
 // reply to msg.
 func Exchange(msg dnsmessage.Message, addr string) (dnsmessage.Message, error) {
@@ -44,18 +47,21 @@ func send(msg dnsmessage.Message, conn net.Conn) (dnsmessage.Message, error) {
 	if _, ok := conn.(net.PacketConn); ok {
 		b, err = dnsPacketExchange(packed, conn)
 		if err != nil {
-			return dnsmessage.Message{}, fmt.Errorf("exchange DNS packet: %v", err)
+			return dnsmessage.Message{}, fmt.Errorf("exchange DNS packet: %w", err)
 		}
 	} else {
 		b, err = dnsStreamExchange(packed, conn)
 		if err != nil {
-			return dnsmessage.Message{}, fmt.Errorf("exchange DNS TCP stream: %v", err)
+			return dnsmessage.Message{}, fmt.Errorf("exchange DNS TCP stream: %w", err)
 		}
 	}
 	var rmsg dnsmessage.Message
 	if err := rmsg.Unpack(b); err != nil {
 		return dnsmessage.Message{}, fmt.Errorf("parse response: %v", err)
 	}
+	if rmsg.Header.ID != msg.Header.ID {
+		return rmsg, errMismatchedID
+	}
 	return rmsg, nil
 }