Asynchronous Network Security Manager

[Lars Ingebrigtsen <larsi@gnus.org>]

We've made the changes Eli suggested, so now we have the very final
problem associated with the async stuff: The network security manager.

We have not had asynchronous TLS connections until now, so we haven't
really had this problem before.

`open-network-stream', if given :type 'tls, would call
`network-stream-open-tls'.  It used to start like this:

(defun network-stream-open-tls (name buffer host service parameters)

[...]

	   (stream
	    (funcall (if (gnutls-available-p)
			 'open-gnutls-stream
		       'open-tls-stream)

[...]

      ;; Check certificate validity etc.
      (when (and (gnutls-available-p) stream)
	(setq stream (nsm-verify-connection stream host service)))

With async TLS, the negotiation takes place later, of course, and
calling `nsm-verify-connection' here makes no sense.

network-stream-open-tls could put a sentinel on the process, but the
common application use case is

(progn
  (setq proc (open-network-stream ...))
  (set-process-sentinel proc ...))

so that obviously doesn't work.

I see two solutions:

1) We require callers to call `nsm-verify-connection' themselves in
their own sentinels.  (Yuck.)

2) We call `nsm-verify-connection' after the asynchronous TLS
negotiation has finished, and before notifying the user sentinel that
the socket has connected.

Hm...  I've never called complex Lisp code from the C layer before.  Is
that an A-OK thing to do?

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no