Obtain a socket-like object from `gateway`.

        :returns:
            A ``direct-tcpip`` `paramiko.channel.Channel`, if `gateway` was a
            `.Connection`; or a `~paramiko.proxy.ProxyCommand`, if `gateway`
            was a string.

        .. versionadded:: 2.0

def open_gateway(self):
        """
        Obtain a socket-like object from `gateway`.

        :returns:
            A ``direct-tcpip`` `paramiko.channel.Channel`, if `gateway` was a
            `.Connection`; or a `~paramiko.proxy.ProxyCommand`, if `gateway`
            was a string.

        .. versionadded:: 2.0
        """
        # ProxyCommand is faster to set up, so do it first.
        if isinstance(self.gateway, string_types):
            # Leverage a dummy SSHConfig to ensure %h/%p/etc are parsed.
            # TODO: use real SSH config once loading one properly is
            # implemented.
            ssh_conf = SSHConfig()
            dummy = "Host {}\n    ProxyCommand {}"
            ssh_conf.parse(StringIO(dummy.format(self.host, self.gateway)))
            return ProxyCommand(ssh_conf.lookup(self.host)["proxycommand"])
        # Handle inner-Connection gateway type here.
        # TODO: logging
        self.gateway.open()
        # TODO: expose the opened channel itself as an attribute? (another
        # possible argument for separating the two gateway types...) e.g. if
        # someone wanted to piggyback on it for other same-interpreter socket
        # needs...
        # TODO: and the inverse? allow users to supply their own socket/like
        # object they got via $WHEREEVER?
        # TODO: how best to expose timeout param? reuse general connection
        # timeout from config?
        return self.gateway.transport.open_channel(
            kind="direct-tcpip",
            dest_addr=(self.host, int(self.port)),
            # NOTE: src_addr needs to be 'empty but not None' values to
            # correctly encode into a network message. Theoretically Paramiko
            # could auto-interpret None sometime & save us the trouble.
            src_addr=("", 0),
        )