mirror of
https://github.com/tailscale/tailscale.git
synced 2024-11-26 19:45:35 +00:00
128 lines
3.0 KiB
Go
128 lines
3.0 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 (
|
|
"fmt"
|
|
"net"
|
|
)
|
|
|
|
// 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))
|
|
}
|
|
|
|
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
|
|
}
|