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ip6.go
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ip6.go
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// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause
package packet
import (
"encoding/binary"
"net/netip"
"tailscale.com/types/ipproto"
)
// ip6HeaderLength is the length of an IPv6 header with no IP options.
const ip6HeaderLength = 40
// IP6Header represents an IPv6 packet header.
type IP6Header struct {
IPProto ipproto.Proto
IPID uint32 // only lower 20 bits used
Src netip.Addr
Dst netip.Addr
}
// Len implements Header.
func (h IP6Header) Len() int {
return ip6HeaderLength
}
// Marshal implements Header.
func (h IP6Header) Marshal(buf []byte) error {
if len(buf) < h.Len() {
return errSmallBuffer
}
if len(buf) > maxPacketLength {
return errLargePacket
}
binary.BigEndian.PutUint32(buf[:4], h.IPID&0x000FFFFF)
buf[0] = 0x60
binary.BigEndian.PutUint16(buf[4:6], uint16(len(buf)-ip6HeaderLength)) // Total length
buf[6] = uint8(h.IPProto) // Inner protocol
buf[7] = 64 // TTL
src, dst := h.Src.As16(), h.Dst.As16()
copy(buf[8:24], src[:])
copy(buf[24:40], dst[:])
return nil
}
// ToResponse implements Header.
func (h *IP6Header) ToResponse() {
h.Src, h.Dst = h.Dst, h.Src
// Flip the bits in the IPID. If incoming IPIDs are distinct, so are these.
h.IPID = (^h.IPID) & 0x000FFFFF
}
// marshalPseudo serializes h into buf in the "pseudo-header" form
// required when calculating UDP checksums.
func (h IP6Header) marshalPseudo(buf []byte, proto ipproto.Proto) error {
if len(buf) < h.Len() {
return errSmallBuffer
}
if len(buf) > maxPacketLength {
return errLargePacket
}
src, dst := h.Src.As16(), h.Dst.As16()
copy(buf[:16], src[:])
copy(buf[16:32], dst[:])
binary.BigEndian.PutUint32(buf[32:36], uint32(len(buf)-h.Len()))
buf[36] = 0
buf[37] = 0
buf[38] = 0
buf[39] = byte(proto) // NextProto
return nil
}