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// Copyright 2018 The gVisor Authors.
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
package header
const (
typeHLen = 0
encapProto = 1
// GUEFields contains the fields of a GUE packet. It is used to describe the
// fields of a packet that needs to be encoded.
type GUEFields struct {
// Type is the "type" field of the GUE header.
Type uint8
// Control is the "control" field of the GUE header.
Control bool
// HeaderLength is the "header length" field of the GUE header. It must
// be at least 4 octets, and a multiple of 4 as well.
HeaderLength uint8
// Protocol is the "protocol" field of the GUE header. This is one of
// the IPPROTO_* values.
Protocol uint8
// GUE represents a Generic UDP Encapsulation header stored in a byte array, the
// fields are described in
type GUE []byte
const (
// GUEMinimumSize is the minimum size of a valid GUE packet.
GUEMinimumSize = 4
// TypeAndControl returns the GUE packet type (top 3 bits of the first byte,
// which includes the control bit).
func (b GUE) TypeAndControl() uint8 {
return b[typeHLen] >> 5
// HeaderLength returns the total length of the GUE header.
func (b GUE) HeaderLength() uint8 {
return 4 + 4*(b[typeHLen]&0x1f)
// Protocol returns the protocol field of the GUE header.
func (b GUE) Protocol() uint8 {
return b[encapProto]
// Encode encodes all the fields of the GUE header.
func (b GUE) Encode(i *GUEFields) {
ctl := uint8(0)
if i.Control {
ctl = 1 << 5
b[typeHLen] = ctl | i.Type<<6 | (i.HeaderLength-4)/4
b[encapProto] = i.Protocol