97 lines
2 KiB
Go
97 lines
2 KiB
Go
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// +build linux
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package redir
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import (
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"fmt"
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"net"
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"os"
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"strconv"
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"syscall"
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)
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// dialUDP acts like net.DialUDP for transparent proxy.
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// It binds to a non-local address(`lAddr`).
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func dialUDP(network string, lAddr *net.UDPAddr, rAddr *net.UDPAddr) (*net.UDPConn, error) {
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rSockAddr, err := udpAddrToSockAddr(rAddr)
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if err != nil {
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return nil, err
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}
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lSockAddr, err := udpAddrToSockAddr(lAddr)
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if err != nil {
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return nil, err
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}
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fd, err := syscall.Socket(udpAddrFamily(network, lAddr, rAddr), syscall.SOCK_DGRAM, 0)
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if err != nil {
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return nil, err
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}
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if err = syscall.SetsockoptInt(fd, syscall.SOL_SOCKET, syscall.SO_REUSEADDR, 1); err != nil {
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syscall.Close(fd)
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return nil, err
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}
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if err = syscall.SetsockoptInt(fd, syscall.SOL_IP, syscall.IP_TRANSPARENT, 1); err != nil {
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syscall.Close(fd)
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return nil, err
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}
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if err = syscall.Bind(fd, lSockAddr); err != nil {
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syscall.Close(fd)
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return nil, err
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}
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if err = syscall.Connect(fd, rSockAddr); err != nil {
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syscall.Close(fd)
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return nil, err
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}
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fdFile := os.NewFile(uintptr(fd), fmt.Sprintf("net-udp-dial-%s", rAddr.String()))
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defer fdFile.Close()
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c, err := net.FileConn(fdFile)
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if err != nil {
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syscall.Close(fd)
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return nil, err
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}
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return c.(*net.UDPConn), nil
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}
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func udpAddrToSockAddr(addr *net.UDPAddr) (syscall.Sockaddr, error) {
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switch {
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case addr.IP.To4() != nil:
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ip := [4]byte{}
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copy(ip[:], addr.IP.To4())
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return &syscall.SockaddrInet4{Addr: ip, Port: addr.Port}, nil
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default:
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ip := [16]byte{}
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copy(ip[:], addr.IP.To16())
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zoneID, err := strconv.ParseUint(addr.Zone, 10, 32)
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if err != nil {
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zoneID = 0
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}
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return &syscall.SockaddrInet6{Addr: ip, Port: addr.Port, ZoneId: uint32(zoneID)}, nil
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}
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}
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func udpAddrFamily(net string, lAddr, rAddr *net.UDPAddr) int {
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switch net[len(net)-1] {
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case '4':
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return syscall.AF_INET
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case '6':
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return syscall.AF_INET6
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}
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if (lAddr == nil || lAddr.IP.To4() != nil) && (rAddr == nil || lAddr.IP.To4() != nil) {
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return syscall.AF_INET
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}
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return syscall.AF_INET6
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}
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