NAME
	open_port - associate an object with an tcp/udp port

SYNOPSIS
	int open_port(string protocol, varargs int port)

DESCRIPTION
	Open a port on the host machine and connect it to this object, which
        is then known as a "port object".  The protocol may be any of "tcp",
        "udp", or "telnet".  Port objects behave differently, depending on
        the protocol. If the port number is omitted (meaning that the kfun
        is called with only _one_ argument) a random unused port will be
        selected.

	When a port is first opened, open(int port) is called in its port
        object.  When it is closed for any reason, close(int force) is 
	called in its port object, force indicaton whether we closed the
	connection with close_user (set to 1) or if something else
	closed the connection (set to 0).

	Destructing a port object will close its port first.                 

	In a telnet or tcp port,
             connection(string ipnumber, int port)
        will be called whenever a client connects to it.  This function
        should return an object that will then be known as a "user object"

	In an udp port,        
            receive_datagram(string data, string ipnumber, int port)
        will be called whenever a datagram arrives on its port.  The
        ipnumber and port will be those of the sender.  UDP port objects
        may also send datagrams.

ERRORS                         
        An error will result if the object was already has a connection,
        port, or editor associated with it.
        If the number of existing port and connection objects is equal
        to the value of status()[ST_UTABSIZE], calling open_port() results
        in an error.                                                           
        If it is immediately apparent that the port cannot be opened,
        an error will be reported.  In such a case, neither open() nor
        close() will be called in the port object.

NOTES
        This kfun is only active when the network extensions are enabled.

SEE ALSO
        kfun/ports, kfun/send_datagram, kfun/send_message, kfun/connect
	kfun/close_user