package socks4 import ( "bytes" "encoding/binary" "errors" "io" "net" "strconv" "github.com/Dreamacro/clash/component/auth" ) const Version = 0x04 type Command = uint8 const ( CmdConnect Command = 0x01 CmdBind Command = 0x02 ) type Code = uint8 const ( RequestGranted Code = 90 RequestRejected Code = 91 RequestIdentdFailed Code = 92 RequestIdentdMismatched Code = 93 ) var ( errVersionMismatched = errors.New("version code mismatched") errCommandNotSupported = errors.New("command not supported") errIPv6NotSupported = errors.New("IPv6 not supported") ErrRequestRejected = errors.New("request rejected or failed") ErrRequestIdentdFailed = errors.New("request rejected because SOCKS server cannot connect to identd on the client") ErrRequestIdentdMismatched = errors.New("request rejected because the client program and identd report different user-ids") ErrRequestUnknownCode = errors.New("request failed with unknown code") ) func ServerHandshake(rw io.ReadWriter, authenticator auth.Authenticator) (addr string, command Command, err error) { var req [8]byte if _, err = io.ReadFull(rw, req[:]); err != nil { return } if req[0] != Version { err = errVersionMismatched return } if command = req[1]; command != CmdConnect { err = errCommandNotSupported return } var ( dstIP = req[4:8] // [4]byte dstPort = req[2:4] // [2]byte ) var ( host string port string code uint8 userID []byte ) if userID, err = readUntilNull(rw); err != nil { return } if isReservedIP(dstIP) { var target []byte if target, err = readUntilNull(rw); err != nil { return } host = string(target) } port = strconv.Itoa(int(binary.BigEndian.Uint16(dstPort))) if host != "" { addr = net.JoinHostPort(host, port) } else { addr = net.JoinHostPort(net.IP(dstIP).String(), port) } // SOCKS4 only support USERID auth. if authenticator == nil || authenticator.Verify(string(userID), "") { code = RequestGranted } else { code = RequestIdentdMismatched err = ErrRequestIdentdMismatched } var reply [8]byte reply[0] = 0x00 // reply code reply[1] = code // result code copy(reply[4:8], dstIP) copy(reply[2:4], dstPort) _, wErr := rw.Write(reply[:]) if err == nil { err = wErr } return } func ClientHandshake(rw io.ReadWriter, addr string, command Command, userID string) (err error) { host, portStr, err := net.SplitHostPort(addr) if err != nil { return err } port, err := strconv.ParseUint(portStr, 10, 16) if err != nil { return err } ip := net.ParseIP(host) if ip == nil /* HOST */ { ip = net.IPv4(0, 0, 0, 1).To4() } else if ip.To4() == nil /* IPv6 */ { return errIPv6NotSupported } dstIP := ip.To4() req := &bytes.Buffer{} req.WriteByte(Version) req.WriteByte(command) binary.Write(req, binary.BigEndian, uint16(port)) req.Write(dstIP) req.WriteString(userID) req.WriteByte(0) /* NULL */ if isReservedIP(dstIP) /* SOCKS4A */ { req.WriteString(host) req.WriteByte(0) /* NULL */ } if _, err = rw.Write(req.Bytes()); err != nil { return err } var resp [8]byte if _, err = io.ReadFull(rw, resp[:]); err != nil { return err } if resp[0] != 0x00 { return errVersionMismatched } switch resp[1] { case RequestGranted: return nil case RequestRejected: return ErrRequestRejected case RequestIdentdFailed: return ErrRequestIdentdFailed case RequestIdentdMismatched: return ErrRequestIdentdMismatched default: return ErrRequestUnknownCode } } // For version 4A, if the client cannot resolve the destination host's // domain name to find its IP address, it should set the first three bytes // of DSTIP to NULL and the last byte to a non-zero value. (This corresponds // to IP address 0.0.0.x, with x nonzero. As decreed by IANA -- The // Internet Assigned Numbers Authority -- such an address is inadmissible // as a destination IP address and thus should never occur if the client // can resolve the domain name.) func isReservedIP(ip net.IP) bool { subnet := net.IPNet{ IP: net.IPv4zero, Mask: net.IPv4Mask(0xff, 0xff, 0xff, 0x00), } return !ip.IsUnspecified() && subnet.Contains(ip) } func readUntilNull(r io.Reader) ([]byte, error) { buf := &bytes.Buffer{} var data [1]byte for { if _, err := r.Read(data[:]); err != nil { return nil, err } if data[0] == 0 { return buf.Bytes(), nil } buf.WriteByte(data[0]) } }