support rfc7828 (#402)

edns.go

@@ -4,6 +4,7 @@ import (
 	"encoding/binary"
 	"encoding/hex"
 	"errors"
+	"fmt"
 	"net"
 	"strconv"
 )
@@ -19,6 +20,7 @@ const (
 	EDNS0SUBNET       = 0x8     // client-subnet (RFC6891)
 	EDNS0EXPIRE       = 0x9     // EDNS0 expire
 	EDNS0COOKIE       = 0xa     // EDNS0 Cookie
+	EDNS0TCPKEEPALIVE = 0xb     // EDNS0 tcp keep alive (RFC7828)
 	EDNS0SUBNETDRAFT  = 0x50fa  // Don't use! Use EDNS0SUBNET
 	EDNS0LOCALSTART   = 0xFDE9  // Beginning of range reserved for local/experimental use (RFC6891)
 	EDNS0LOCALEND     = 0xFFFE  // End of range reserved for local/experimental use (RFC6891)
@@ -540,3 +542,56 @@ func (e *EDNS0_LOCAL) unpack(b []byte) error {
 	}
 	return nil
 }
+
+type EDNS0_TCP_KEEPALIVE struct {
+	Code    uint16 // Always EDNSTCPKEEPALIVE
+	Length  uint16 // the value 0 if the TIMEOUT is omitted, the value 2 if it is present;
+	Timeout uint16 // an idle timeout value for the TCP connection, specified in units of 100 milliseconds, encoded in network byte order.
+}
+
+func (e *EDNS0_TCP_KEEPALIVE) Option() uint16 {
+	return EDNS0TCPKEEPALIVE
+}
+
+func (e *EDNS0_TCP_KEEPALIVE) pack() ([]byte, error) {
+	if e.Timeout != 0 && e.Length != 2 {
+		return nil, errors.New("dns: timeout specified but length is not 2")
+	}
+	if e.Timeout == 0 && e.Length != 0 {
+		return nil, errors.New("dns: timeout not specified but length is not 0")
+	}
+	b := make([]byte, 4+e.Length)
+	binary.BigEndian.PutUint16(b[0:], e.Code)
+	binary.BigEndian.PutUint16(b[2:], e.Length)
+	if e.Length == 2 {
+		binary.BigEndian.PutUint16(b[4:], e.Timeout)
+	}
+	return b, nil
+}
+
+func (e *EDNS0_TCP_KEEPALIVE) unpack(b []byte) error {
+	if len(b) < 4 {
+		return ErrBuf
+	}
+	e.Length = binary.BigEndian.Uint16(b[2:4])
+	if e.Length != 0 && e.Length != 2 {
+		return errors.New("dns: length mismatch, want 0/2 but got " + strconv.FormatUint(uint64(e.Length), 10))
+	}
+	if e.Length == 2 {
+		if len(b) < 6 {
+			return ErrBuf
+		}
+		e.Timeout = binary.BigEndian.Uint16(b[4:6])
+	}
+	return nil
+}
+
+func (e *EDNS0_TCP_KEEPALIVE) String() (s string) {
+	s = "use tcp keep-alive"
+	if e.Length == 0 {
+		s += ", timeout omitted"
+	} else {
+		s += fmt.Sprintf(", timeout %dms", e.Timeout*100)
+	}
+	return
+}