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tailscale/net/packet/udp4.go

56 lines
1.4 KiB
Go

// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package packet
import "encoding/binary"
// udpHeaderLength is the size of the UDP packet header, not including
// the outer IP header.
const udpHeaderLength = 8
// UDP4Header is an IPv4+UDP header.
type UDP4Header struct {
IP4Header
SrcPort uint16
DstPort uint16
}
// Len implements Header.
func (h UDP4Header) Len() int {
return h.IP4Header.Len() + udpHeaderLength
}
// Marshal implements Header.
func (h UDP4Header) Marshal(buf []byte) error {
if len(buf) < h.Len() {
return errSmallBuffer
}
if len(buf) > maxPacketLength {
return errLargePacket
}
// The caller does not need to set this.
h.IPProto = UDP
length := len(buf) - h.IP4Header.Len()
binary.BigEndian.PutUint16(buf[20:22], h.SrcPort)
binary.BigEndian.PutUint16(buf[22:24], h.DstPort)
binary.BigEndian.PutUint16(buf[24:26], uint16(length))
binary.BigEndian.PutUint16(buf[26:28], 0) // blank checksum
// UDP checksum with IP pseudo header.
h.IP4Header.marshalPseudo(buf)
binary.BigEndian.PutUint16(buf[26:28], ip4Checksum(buf[ip4PseudoHeaderOffset:]))
h.IP4Header.Marshal(buf)
return nil
}
// ToResponse implements Header.
func (h *UDP4Header) ToResponse() {
h.SrcPort, h.DstPort = h.DstPort, h.SrcPort
h.IP4Header.ToResponse()
}