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package main
import (
"encoding/binary"
"fmt"
"log"
"net"
"sync"
// "github.com/xitongsys/ethernet-go/header"
)
type TCP struct {
SrcPort uint16
DstPort uint16
Seq uint32
Ack uint32
Offset uint8
Flags uint8
Win uint16
Checksum uint16
UrgPointer uint16
Opt uint32
}
type IPv4Pseudo struct {
Src uint32
Dst uint32
Reserved uint8
Protocol uint8
Len uint16
}
func (h *IPv4Pseudo) Marshal() []byte {
headerLen := int(12)
res := make([]byte, headerLen)
binary.BigEndian.PutUint32(res[0:], h.Src)
binary.BigEndian.PutUint32(res[4:], h.Dst)
res[8] = byte(h.Reserved)
res[9] = byte(h.Protocol)
binary.BigEndian.PutUint16(res[10:], h.Len)
return res
}
func (h *TCP) Marshal() []byte {
res := make([]byte, 20)
binary.BigEndian.PutUint16(res, h.SrcPort)
binary.BigEndian.PutUint16(res[2:], h.DstPort)
binary.BigEndian.PutUint32(res[4:], h.Seq)
binary.BigEndian.PutUint32(res[8:], h.Ack)
res[12] = byte(h.Offset)
res[13] = byte(h.Flags)
binary.BigEndian.PutUint16(res[14:], h.Win)
binary.BigEndian.PutUint16(res[16:], h.Checksum)
binary.BigEndian.PutUint16(res[18:], h.UrgPointer)
return res
}
func ReCalTcpCheckSum(bs []byte, src, dst uint32) error {
if len(bs) < 20 {
return fmt.Errorf("too short")
}
ipps := IPv4Pseudo{}
ipps.Src = src
ipps.Dst = dst
ipps.Reserved = 0
ipps.Protocol = 6
ipps.Len = uint16(len(bs))
ippsbs := ipps.Marshal()
tcpbs := bs
tcpbs[16] = 0
tcpbs[17] = 0
if len(tcpbs)%2 == 1 {
tcpbs = append(tcpbs, byte(0))
}
s := uint32(0)
for i := 0; i < len(ippsbs); i += 2 {
s += uint32(binary.BigEndian.Uint16(ippsbs[i : i+2]))
}
for i := 0; i < len(tcpbs); i += 2 {
s += uint32(binary.BigEndian.Uint16(tcpbs[i : i+2]))
}
for (s >> 16) > 0 {
s = (s >> 16) + (s & 0xffff)
}
binary.BigEndian.PutUint16(tcpbs[16:], ^uint16(s))
return nil
}
// https://sourcegraph.com/github.com/xitongsys/ethernet-go@master/-/blob/header/tcp.go
func server(ch chan<- struct{}, wg *sync.WaitGroup) {
ipaddr, _ := net.ResolveIPAddr("ip4", "127.0.0.2")
con, err := net.ListenIP("ip4:6", ipaddr)
if err != nil {
log.Fatalf("tcp listening failed %+v\n", err)
}
buf := make([]byte, 1024)
fmt.Printf("开始接收%v\n", con.LocalAddr())
ch <- struct{}{}
for range 3 {
{
n, from, _ := con.ReadFromIP(buf)
if n > 20 {
fmt.Printf("[%s] for [%s]\n", string(buf[20:n]), from.String())
} else {
fmt.Printf("too short %d\n", n)
}
}
}
close(ch)
con.Close()
wg.Done()
}
const (
FIN = 0x01
SYN = 0x02
RST = 0x04
PSH = 0x08
ACK = 0x10
URG = 0x20
ECE = 0x40
CWR = 0x80
)
func BuildTcpHeader(src, dst uint32, sport, dport uint16, flag uint8, data []byte) []byte {
tcpheader := &TCP{
SrcPort: sport,
DstPort: dport,
Seq: 1,
Ack: 1,
Offset: 0x50,
Flags: flag,
Win: ^uint16(0),
Checksum: 0,
UrgPointer: 0,
}
result := make([]byte, len(data)+20)
copy(result, tcpheader.Marshal())
copy(result[20:], data)
ReCalTcpCheckSum(result, src, dst)
return result
}
func client(ch <-chan struct{}) {
laddr, _ := net.ResolveIPAddr("ip4", "127.0.0.3")
raddr, _ := net.ResolveIPAddr("ip4", "127.0.0.2")
con, err := net.DialIP("ip4:6", laddr, raddr)
if err != nil {
log.Fatalf("ip conn create failed %+v\n", err)
}
<-ch
for i := range 3 {
buf := BuildTcpHeader(binary.BigEndian.Uint32(laddr.IP.To4()), binary.BigEndian.Uint32(raddr.IP.To4()), 7742, 7743, SYN, []byte(fmt.Sprintf("test data packet%d", i)))
con.Write(buf)
}
<-ch
fmt.Println("has write")
con.Close()
}
func main() {
var wg sync.WaitGroup
ch := make(chan struct{})
wg.Add(1)
go server(ch, &wg)
fmt.Println("server start")
client(ch)
fmt.Println("client close")
wg.Wait()
}
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