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// 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 (
"fmt"
"net"
"inet.af/netaddr"
)
// IP is an IPv4 address.
type IP uint32
// NewIP converts a standard library IP address into an IP.
// It panics if b is not an IPv4 address.
func NewIP(b net.IP) IP {
b4 := b.To4()
if b4 == nil {
panic(fmt.Sprintf("To4(%v) failed", b))
}
return IP(get32(b4))
}
// IPFromNetaddr converts a netaddr.IP to an IP.
func IPFromNetaddr(ip netaddr.IP) IP {
ipbytes := ip.As4()
return IP(get32(ipbytes[:]))
}
// Netaddr converts an IP to a netaddr.IP.
func (ip IP) Netaddr() netaddr.IP {
return netaddr.IPv4(byte(ip>>24), byte(ip>>16), byte(ip>>8), byte(ip))
}
func (ip IP) String() string {
return fmt.Sprintf("%d.%d.%d.%d", byte(ip>>24), byte(ip>>16), byte(ip>>8), byte(ip))
}
// IPProto is either a real IP protocol (ITCP, UDP, ...) or an special value like Unknown.
// If it is a real IP protocol, its value corresponds to its IP protocol number.
type IPProto uint8
const (
// Unknown represents an unknown or unsupported protocol; it's deliberately the zero value.
Unknown IPProto = 0x00
ICMP IPProto = 0x01
TCP IPProto = 0x06
UDP IPProto = 0x11
// IPv6 and Fragment are special values. They're not really IPProto values
// so we're using the unassigned 0xFE and 0xFF values for them.
// TODO(dmytro): special values should be taken out of here.
IPv6 IPProto = 0xFE
Fragment IPProto = 0xFF
)
func (p IPProto) String() string {
switch p {
case Fragment:
return "Frag"
case ICMP:
return "ICMP"
case UDP:
return "UDP"
case TCP:
return "TCP"
case IPv6:
return "IPv6"
default:
return "Unknown"
}
}
// IPHeader represents an IP packet header.
type IPHeader struct {
IPProto IPProto
IPID uint16
SrcIP IP
DstIP IP
}
const ipHeaderLength = 20
func (IPHeader) Len() int {
return ipHeaderLength
}
func (h IPHeader) Marshal(buf []byte) error {
if len(buf) < ipHeaderLength {
return errSmallBuffer
}
if len(buf) > maxPacketLength {
return errLargePacket
}
buf[0] = 0x40 | (ipHeaderLength >> 2) // IPv4
buf[1] = 0x00 // DHCP, ECN
put16(buf[2:4], uint16(len(buf)))
put16(buf[4:6], h.IPID)
put16(buf[6:8], 0) // flags, offset
buf[8] = 64 // TTL
buf[9] = uint8(h.IPProto)
put16(buf[10:12], 0) // blank IP header checksum
put32(buf[12:16], uint32(h.SrcIP))
put32(buf[16:20], uint32(h.DstIP))
put16(buf[10:12], ipChecksum(buf[0:20]))
return nil
}
// MarshalPseudo serializes the header into buf in pseudo format.
// It clobbers the header region, which is the first h.Length() bytes of buf.
// It explicitly initializes every byte of the header region,
// so pre-zeroing it on reuse is not required. It does not allocate memory.
func (h IPHeader) MarshalPseudo(buf []byte) error {
if len(buf) < ipHeaderLength {
return errSmallBuffer
}
if len(buf) > maxPacketLength {
return errLargePacket
}
length := len(buf) - ipHeaderLength
put32(buf[8:12], uint32(h.SrcIP))
put32(buf[12:16], uint32(h.DstIP))
buf[16] = 0x0
buf[17] = uint8(h.IPProto)
put16(buf[18:20], uint16(length))
return nil
}
func (h *IPHeader) ToResponse() {
h.SrcIP, h.DstIP = h.DstIP, h.SrcIP
// Flip the bits in the IPID. If incoming IPIDs are distinct, so are these.
h.IPID = ^h.IPID
}
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