Negotiates a connection through a SOCKS4 server.

def _negotiate_SOCKS4(self, dest_addr, dest_port):
        """
        Negotiates a connection through a SOCKS4 server.
        """
        proxy_type, addr, port, rdns, username, password = self.proxy

        writer = self.makefile("wb")
        reader = self.makefile("rb", 0)  # buffering=0 renamed in Python 3
        try:
            # Check if the destination address provided is an IP address
            remote_resolve = False
            try:
                addr_bytes = socket.inet_aton(dest_addr)
            except socket.error:
                # It's a DNS name. Check where it should be resolved.
                if rdns:
                    addr_bytes = b"\x00\x00\x00\x01"
                    remote_resolve = True
                else:
                    addr_bytes = socket.inet_aton(socket.gethostbyname(dest_addr))

            # Construct the request packet
            writer.write(struct.pack(">BBH", 0x04, 0x01, dest_port))
            writer.write(addr_bytes)

            # The username parameter is considered userid for SOCKS4
            if username:
                writer.write(username)
            writer.write(b"\x00")

            # DNS name if remote resolving is required
            # NOTE: This is actually an extension to the SOCKS4 protocol
            # called SOCKS4A and may not be supported in all cases.
            if remote_resolve:
                writer.write(dest_addr.encode('idna') + b"\x00")
            writer.flush()

            # Get the response from the server
            resp = self._readall(reader, 8)
            if resp[0:1] != b"\x00":
                # Bad data
                raise GeneralProxyError("SOCKS4 proxy server sent invalid data")

            status = ord(resp[1:2])
            if status != 0x5A:
                # Connection failed: server returned an error
                error = SOCKS4_ERRORS.get(status, "Unknown error")
                raise SOCKS4Error("{0:#04x}: {1}".format(status, error))

            # Get the bound address/port
            self.proxy_sockname = (socket.inet_ntoa(resp[4:]), struct.unpack(">H", resp[2:4])[0])
            if remote_resolve:
                self.proxy_peername = socket.inet_ntoa(addr_bytes), dest_port
            else:
                self.proxy_peername = dest_addr, dest_port
        finally:
            reader.close()
            writer.close()