[iolib-devel] with-open-socket oddness

[Peter Keller]

Hello,

I discovered in my boundary testing of with-open-socket that it sort of has
a funny behavior I didn't expect.

Basically, I had a top level code like this in a blocking i/o tcp ipv4
client talking to a server:

(with-open-socket
    (socket :stuff :things)

  ;; set up i/o handlers, each wrap their reads and writes around
  ;; handler-case. A disconnector on the sockets removes the io handlers, but
  ;; doesn't close the socket since with-open-socket should do it.

  (handler-case
    ;; run forever until empty (meaning we disconnected from the server),
    ;; then return.
    (event-dispatch *base*)
  
  (hangup ()
    (format t "Hangup while writing to server~%"))

  (end-of-file ()
    (format t "End of file from server~%"))))

Now, what happened was, under certain conditions where there is inflight
data on the sockets, a registered handler could get a signaled condition,
specifically hangup, that tells me the server went away on a write. This
is expected. I disconnect the socket which removes the i/o handlers, which
causes event-dispatch to return since there are no registered handlers....
and then bam! The with-open-stream performs a (finish-output) and (close) on
the socket and I get _another_ hangup condition!

So I had to rewrite the code like this moving the handler-case up one scope:

(handler-case
 (with-open-socket
     (socket :things :stuff)
   ;; set up i/o handlers, each wrap their reads and writes around
   ;; handler-case. A disconnector on the sockets removes the io handlers, but
   ;; doesn't close the socket since with-open-socket should do it.
   (event-dispatch *base*))
 
 (hangup ()
   (format t "Hangup while writing to server~%"))

 (end-of-file ()
   (format t "End of file from server~%"))))

Is this a to be expected scenario in condition handling with respect to
with-open-socket? Is this idiomatic code?

Should the disconnector function close the socket even though with-open-socket
also closes it? I'm not sure of the right thing to do here.

Thank you.

-pete