SYNOPSIS
	int socket_udp(int port, closure callback, int|void opts)

	void callback(int fd, int action, mixed a, mixed b, mixed c)

DESCRIPTION
	Opens a udp datagram port.  Returns the file descriptor for
	the socket.

CALLBACK
	SOCKET_READY
	  The socket is open and awaiting connections.

	SOCKET_READ
	  An incoming datagram has been received.
	  A contains the message.
	  B contains the remote host.
	  C contains the remote port.

	SOCKET_CLOSE
	  The socket has closed.

	SOCKET_ERROR
	  An error has been detected on the socket.
	  A contains the error code obtained from the erq daemon.
	  B contains the value of errno in most cases.

SEE ALSO
	sockets, socket_sendto(), socket_close()