mirror of
https://github.com/tailscale/tailscale.git
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104 lines
2.6 KiB
Go
104 lines
2.6 KiB
Go
// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package packet
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import (
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"encoding/binary"
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"fmt"
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"inet.af/netaddr"
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)
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// IP4 is an IPv4 address.
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type IP4 uint32
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// IPFromNetaddr converts a netaddr.IP to an IP. Panics if !ip.Is4.
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func IP4FromNetaddr(ip netaddr.IP) IP4 {
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ipbytes := ip.As4()
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return IP4(binary.BigEndian.Uint32(ipbytes[:]))
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}
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// Netaddr converts an IP to a netaddr.IP.
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func (ip IP4) Netaddr() netaddr.IP {
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return netaddr.IPv4(byte(ip>>24), byte(ip>>16), byte(ip>>8), byte(ip))
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}
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func (ip IP4) String() string {
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return fmt.Sprintf("%d.%d.%d.%d", byte(ip>>24), byte(ip>>16), byte(ip>>8), byte(ip))
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}
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func (ip IP4) IsMulticast() bool {
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return byte(ip>>24)&0xf0 == 0xe0
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}
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func (ip IP4) IsLinkLocalUnicast() bool {
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return byte(ip>>24) == 169 && byte(ip>>16) == 254
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}
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// IPHeader represents an IP packet header.
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type IP4Header struct {
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IPProto IPProto
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IPID uint16
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SrcIP IP4
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DstIP IP4
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}
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const ip4HeaderLength = 20
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func (IP4Header) Len() int {
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return ip4HeaderLength
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}
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func (h IP4Header) Marshal(buf []byte) error {
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if len(buf) < ip4HeaderLength {
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return errSmallBuffer
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}
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if len(buf) > maxPacketLength {
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return errLargePacket
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}
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buf[0] = 0x40 | (ip4HeaderLength >> 2) // IPv4
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buf[1] = 0x00 // DHCP, ECN
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binary.BigEndian.PutUint16(buf[2:4], uint16(len(buf)))
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binary.BigEndian.PutUint16(buf[4:6], h.IPID)
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binary.BigEndian.PutUint16(buf[6:8], 0) // flags, offset
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buf[8] = 64 // TTL
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buf[9] = uint8(h.IPProto)
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binary.BigEndian.PutUint16(buf[10:12], 0) // blank IP header checksum
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binary.BigEndian.PutUint32(buf[12:16], uint32(h.SrcIP))
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binary.BigEndian.PutUint32(buf[16:20], uint32(h.DstIP))
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binary.BigEndian.PutUint16(buf[10:12], ipChecksum(buf[0:20]))
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return nil
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}
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// MarshalPseudo serializes the header into buf in the "pseudo-header"
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// form required when calculating UDP checksums. Overwrites the first
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// h.Length() bytes of buf.
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func (h IP4Header) MarshalPseudo(buf []byte) error {
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if len(buf) < ip4HeaderLength {
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return errSmallBuffer
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}
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if len(buf) > maxPacketLength {
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return errLargePacket
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}
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length := len(buf) - ip4HeaderLength
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binary.BigEndian.PutUint32(buf[8:12], uint32(h.SrcIP))
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binary.BigEndian.PutUint32(buf[12:16], uint32(h.DstIP))
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buf[16] = 0x0
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buf[17] = uint8(h.IPProto)
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binary.BigEndian.PutUint16(buf[18:20], uint16(length))
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return nil
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}
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// ToResponse implements Header.
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func (h *IP4Header) ToResponse() {
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h.SrcIP, h.DstIP = h.DstIP, h.SrcIP
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// Flip the bits in the IPID. If incoming IPIDs are distinct, so are these.
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h.IPID = ^h.IPID
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}
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