def _SOCKS5_request(self, conn, cmd, dst):
        """
        Send SOCKS5 request with given command (CMD field) and
        address (DST field). Returns resolved DST address that was used.
        """
        proxy_type, addr, port, rdns, username, password = self.proxy

        writer = conn.makefile("wb")
        reader = conn.makefile("rb", 0)  # buffering=0 renamed in Python 3
        try:
            # First we'll send the authentication packages we support.
            if username and password:
                # The username/password details were supplied to the
                # set_proxy method so we support the USERNAME/PASSWORD
                # authentication (in addition to the standard none).
                writer.write(b"\x05\x02\x00\x02")
            else:
                # No username/password were entered, therefore we
                # only support connections with no authentication.
                writer.write(b"\x05\x01\x00")

            # We'll receive the server's response to determine which
            # method was selected
            writer.flush()
            chosen_auth = self._readall(reader, 2)

            if chosen_auth[0:1] != b"\x05":
                # Note: string[i:i+1] is used because indexing of a bytestring
                # via bytestring[i] yields an integer in Python 3
                raise GeneralProxyError("SOCKS5 proxy server sent invalid data")

            # Check the chosen authentication method

            if chosen_auth[1:2] == b"\x02":
                # Okay, we need to perform a basic username/password
                # authentication.
                writer.write(b"\x01" + chr(len(username)).encode()
                             + username
                             + chr(len(password)).encode()
                             + password)
                writer.flush()
                auth_status = self._readall(reader, 2)
                if auth_status[0:1] != b"\x01":
                    # Bad response
                    raise GeneralProxyError("SOCKS5 proxy server sent invalid data")
                if auth_status[1:2] != b"\x00":
                    # Authentication failed
                    raise SOCKS5AuthError("SOCKS5 authentication failed")

                # Otherwise, authentication succeeded

            # No authentication is required if 0x00
            elif chosen_auth[1:2] != b"\x00":
                # Reaching here is always bad
                if chosen_auth[1:2] == b"\xFF":
                    raise SOCKS5AuthError("All offered SOCKS5 authentication methods were rejected")
                else:
                    raise GeneralProxyError("SOCKS5 proxy server sent invalid data")

            # Now we can request the actual connection
            writer.write(b"\x05" + cmd + b"\x00")
            resolved = self._write_SOCKS5_address(dst, writer)
            writer.flush()

            # Get the response
            resp = self._readall(reader, 3)
            if resp[0:1] != b"\x05":
                raise GeneralProxyError("SOCKS5 proxy server sent invalid data")

            status = ord(resp[1:2])
            if status != 0x00:
                # Connection failed: server returned an error
                error = SOCKS5_ERRORS.get(status, "Unknown error")
                raise SOCKS5Error("{0:#04x}: {1}".format(status, error))

            # Get the bound address/port
            bnd = self._read_SOCKS5_address(reader)

            super(socksocket, self).settimeout(self._timeout)
            return (resolved, bnd)
        finally:
            reader.close()
            writer.close()