v2ray-core/transport/internet/sockopt_linux.go

package internet

import (
	"strings"
	"syscall"
)

const (
	// For incoming connections.
	TCP_FASTOPEN = 23
	// For out-going connections.
	TCP_FASTOPEN_CONNECT = 30
)

func applyOutboundSocketOptions(network string, address string, fd uintptr, config *SocketConfig) error {
	if config.Mark != 0 {
		if err := syscall.SetsockoptInt(int(fd), syscall.SOL_SOCKET, syscall.SO_MARK, int(config.Mark)); err != nil {
			return err
		}
	}

	if strings.HasPrefix(network, "tcp") {
		switch config.Tfo {
		case SocketConfig_Enable:
			if err := syscall.SetsockoptInt(int(fd), syscall.SOL_TCP, TCP_FASTOPEN_CONNECT, 1); err != nil {
				return err
			}
		case SocketConfig_Disable:
			if err := syscall.SetsockoptInt(int(fd), syscall.SOL_TCP, TCP_FASTOPEN_CONNECT, 0); err != nil {
				return err
			}
		}
	}

	return nil
}

func applyInboundSocketOptions(network string, fd uintptr, config *SocketConfig) error {
	if strings.HasPrefix(network, "tcp") {
		switch config.Tfo {
		case SocketConfig_Enable:
			if err := syscall.SetsockoptInt(int(fd), syscall.SOL_TCP, TCP_FASTOPEN, 1); err != nil {
				return err
			}
		case SocketConfig_Disable:
			if err := syscall.SetsockoptInt(int(fd), syscall.SOL_TCP, TCP_FASTOPEN, 0); err != nil {
				return err
			}
		}
	}

	return nil
}