listener_linux.go

// Copyright (c) 2024 homuler
//
// Use of this source code is governed by an MIT-style
// license that can be found in the LICENSE file or at
// https://opensource.org/licenses/MIT.

//go:build linux

package mitm

import (
	"fmt"
	"net"
	"syscall"
)

func ListenTCPTProxy(network string, laddr *net.TCPAddr) (*net.TCPListener, error) {
	l, err := net.ListenTCP(network, laddr)
	if err != nil {
		return nil, err
	}

	fileDescriptorSource, err := l.File()
	if err != nil {
		return nil, &net.OpError{Op: "listen", Net: network, Source: nil, Addr: laddr, Err: fmt.Errorf("get file descriptor: %w", err)}
	}
	defer fileDescriptorSource.Close()

	fd := int(fileDescriptorSource.Fd())
	if err = syscall.SetsockoptInt(fd, syscall.SOL_IP, syscall.IP_TRANSPARENT, 1); err != nil {
		return nil, &net.OpError{Op: "listen", Net: network, Source: nil, Addr: laddr, Err: fmt.Errorf("set IP_TRANSPARENT: %w", err)}
	}

	if err = syscall.SetNonblock(fd, true); err != nil {
		return nil, &net.OpError{Op: "listen", Err: fmt.Errorf("set O_NONBLOCK: %w", err)}
	}

	return l, nil
}

func ListenUDPTProxy(network string, laddr *net.UDPAddr) (*net.UDPConn, error) {
	l, err := net.ListenUDP(network, laddr)
	if err != nil {
		return nil, err
	}

	fileDescriptorSource, err := l.File()
	if err != nil {
		return nil, &net.OpError{Op: "listen", Net: network, Source: nil, Addr: laddr, Err: fmt.Errorf("get file descriptor: %w", err)}
	}
	defer fileDescriptorSource.Close()

	fd := int(fileDescriptorSource.Fd())
	if err = syscall.SetsockoptInt(fd, syscall.SOL_SOCKET, syscall.SO_REUSEADDR, 1); err != nil {
		return nil, &net.OpError{Op: "listen", Err: fmt.Errorf("set SO_REUSEADDR: %w", err)}
	}

	if err = syscall.SetsockoptInt(fd, syscall.SOL_IP, syscall.IP_TRANSPARENT, 1); err != nil {
		return nil, &net.OpError{Op: "listen", Net: network, Source: nil, Addr: laddr, Err: fmt.Errorf("set IP_TRANSPARENT: %w", err)}
	}

	if err = syscall.SetsockoptInt(fd, syscall.SOL_IP, syscall.IP_RECVORIGDSTADDR, 1); err != nil {
		return nil, &net.OpError{Op: "listen", Net: network, Source: nil, Addr: laddr, Err: fmt.Errorf("set IP_RECVORIGDSTADDR: %w", err)}
	}

	if err = syscall.SetNonblock(fd, true); err != nil {
		return nil, &net.OpError{Op: "listen", Err: fmt.Errorf("set O_NONBLOCK: %w", err)}
	}

	return l, nil
}