How to set ToS field in IP header for a TCP connection using Golang - sockets

Question

I am trying to create a TCP server and client using Golang where I am able to set the Type of Service field in the IP header in order to prioritise different traffic flows.
The client and servers are able to communicate but I can not figure out how to set the ToS field.
I have tried using the ipv4 Golang package with the method described here: https://godoc.org/golang.org/x/net/ipv4#NewConn
A simplified server example:
func main () {
ln, err := net.Listen("tcp4", "192.168.0.20:1024")
if err != nil {
// error handling
}
defer ln.Close()
for {
c, err := ln.Accept()
if err != nil {
// error handling
}
go func(c net.Conn) {
defer c.Close()
if err := ipv4.NewConn(c).SetTOS(0x28); err != nil {
fmt.Println("Error: ", err.Error())
}
}(c)
}
And the corresponding client (also simplified)
func main () {
conn, err := net.Dial("tcp4", "192.168.0.20:1024")
if err != nil {
fmt.Println(err)
}
for {
writer := bufio.NewWriter(conn)
// Create "packet"
Data := make([]byte, 1200)
endLine := "\r\n"
//Set packetLength
length := strconv.FormatInt(int64(1200), 10)
copy(Data[0:], length)
//Set ID
idString := strconv.FormatInt(int64(1), 10)
if strings.Contains(idString, "\r") || strings.Contains(idString, "\n") || strings.Contains(idString, "\r\n") {
fmt.Println("This is gonna result in an error in the id string.")
}
idbuf := []byte(idString)
copy(Data[15:], idbuf)
//Set timestamp
timestamp0 := time.Now().UnixNano()
timestampString := strconv.FormatInt(timestamp0, 10)
if strings.Contains(timestampString, "\r") || strings.Contains(timestampString, "\n") || strings.Contains(timestampString, "\r\n") {
fmt.Println("This is gonna result in an error in the timestamp string.")
}
buf := []byte(timestampString)
copy(Data[50:], buf)
copy(Data[int(1200)-2:], endLine)
if len(Data) != int(1200) {
fmt.Println("This is also gonna be an error. Length is: ", len(Data))
}
//Send the data and flush the writer
writer.Write(Data)
writer.Flush()
}
//time.Sleep(1*time.Nanosecond)
}
I have also tried creating my own dialer with a control function that passes a syscall in order to set the socket like this:
dialer := &net.Dialer{
Timeout: 5 * time.Second,
Deadline: time.Time{},
LocalAddr: tcpAddr,
DualStack: false,
FallbackDelay: 0,
KeepAlive: 0,
Resolver: nil,
Control: highPrio,
}
func highPrio(network, address string, c syscall.RawConn) error {
return c.Control(func(fd uintptr) {
// set the socket options
err := syscall.SetsockoptInt(syscall.Handle(fd), syscall.IPPROTO_IP, syscall.IP_TOS, 128)
if err != nil {
log.Println("setsocketopt: ", err)
}
})
I am verifying that it does not work by inspecting the traffic with Wireshark and am using Windows 10 Pro as my OS.

Answer 1

I am try you ToS set method at Dial() with golang 1.15.5 and its worked:
dialer := net.Dialer{
Timeout: this.TcpWaitConnectTimeout,
}
dialer.Control = func(network, address string, c syscall.RawConn) error {
var err error
c.Control(func(fd uintptr) {
err = syscall.SetsockoptInt(int(fd), syscall.IPPROTO_IP, syscall.IP_TOS, 0x80)
})
return err
}
c, err := dialer.Dial("tcp", this.serverAddr)
tcpdump show me right ToS