Steel Bank Common Lisp

A recent post on Usenet described a problem with socket-send and  
broadcast messages.  I've been playing around with it, but can't seem  
to crack it.  Here's what I've got:

(defparameter *broadcast-ip-address* #(192 168 0 255))
(defparameter *broadcast-port* 1234)

(defmacro with-udp-broadcast-socket (socket ip-address port &body body)
   "Create and close a UDP socket configured for broadcast around the  
body."
   `(let ((,socket (make-instance 'inet-socket
                                  :type :datagram
                                  :protocol :udp)))
      (setf (sockopt-broadcast ,socket) t)
      (socket-bind ,socket ,ip-address ,port)
      (unwind-protect (progn ,@body)
        (socket-close ,socket))))

Using socket-send without any address like this:

(with-udp-broadcast-socket socket *broadcast-ip-address* *broadcast- 
port*
   (socket-send socket "test" nil))

fails with the message:  Socket error in "sendto": 39 (Destination  
address required)

Specifying the destination address and port like this:

with-udp-broadcast-socket socket *broadcast-ip-address* *broadcast-port*
   (socket-send socket "test" nil
                :address '(*broadcast-ip-address* *broadcast-port*)))

fails with the message:  *BROADCAST-IP-ADDRESS* can't be converted to  
type (SIMPLE-ARRAY (UNSIGNED-BYTE 8) (4)).

Oddly, calling socket-send with just the address and no port succeeds:

with-udp-broadcast-socket socket *broadcast-ip-address* *broadcast-port*
   (socket-send socket "test" nil
                :address '(*broadcast-ip-address*)))

Clearly I'm missing something basic.  Any thoughts?

Thanks,

Patrick

Patrick May <pjm@...> writes:

> A recent post on Usenet described a problem with socket-send and  
> broadcast messages.  I've been playing around with it, but can't seem  
> to crack it.  Here's what I've got:
>
> (defparameter *broadcast-ip-address* #(192 168 0 255))
> (defparameter *broadcast-port* 1234)
>
> (defmacro with-udp-broadcast-socket (socket ip-address port &body body)
>    "Create and close a UDP socket configured for broadcast around the  
> body."
>    `(let ((,socket (make-instance 'inet-socket
>                                   :type :datagram
>                                   :protocol :udp)))
>       (setf (sockopt-broadcast ,socket) t)
>       (socket-bind ,socket ,ip-address ,port)
>       (unwind-protect (progn ,@body)
>         (socket-close ,socket))))
[...]
> with-udp-broadcast-socket socket *broadcast-ip-address* *broadcast-port*
                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                      These should be local address and port, not destination.
>    (socket-send socket "test" nil
>                 :address '(*broadcast-ip-address* *broadcast-port*)))
>
> fails with the message:  *BROADCAST-IP-ADDRESS* can't be converted to  
> type (SIMPLE-ARRAY (UNSIGNED-BYTE 8) (4)).

A symbol is not an array :-)

(with-udp-broadcast-socket socket *broadcast-ip-address* *broadcast-port*
    (socket-send socket "test" nil
                 :address (list *broadcast-ip-address* *broadcast-port*)))


-- 
Regards,
Alexey Dejneka

"Alas, the spheres of truth are less transparent than those of
illusion." -- L.E.J. Brouwer

On 23 Jun 2006, at 18:56, Alexey Dejneka wrote:
> Patrick May <pjm@...> writes:
>> A recent post on Usenet described a problem with socket-send and
>> broadcast messages.  I've been playing around with it, but can't seem
>> to crack it.  Here's what I've got:
>>
>> (defparameter *broadcast-ip-address* #(192 168 0 255))
>> (defparameter *broadcast-port* 1234)
>>
>> (defmacro with-udp-broadcast-socket (socket ip-address port &body  
>> body)
>>    "Create and close a UDP socket configured for broadcast around the
>> body."
>>    `(let ((,socket (make-instance 'inet-socket
>>                                   :type :datagram
>>                                   :protocol :udp)))
>>       (setf (sockopt-broadcast ,socket) t)
>>       (socket-bind ,socket ,ip-address ,port)
>>       (unwind-protect (progn ,@body)
>>         (socket-close ,socket))))
> [...]
>> with-udp-broadcast-socket socket *broadcast-ip-address* *broadcast- 
>> port*
>                                     
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>                       These should be local address and port, not  
> destination.

Ah!  Thank you very much.  I haven't used UDP broadcast before, so I  
expected to be able to bind to the broadcast address and then call  
socket-send with no address and port information.

>>    (socket-send socket "test" nil
>>                 :address '(*broadcast-ip-address* *broadcast-port*)))
>>
>> fails with the message:  *BROADCAST-IP-ADDRESS* can't be converted to
>> type (SIMPLE-ARRAY (UNSIGNED-BYTE 8) (4)).
>
> A symbol is not an array :-)

Yeah, I caught that after sending my email.  Debugging by public  
embarrassment is a very effective technique.  ;-)

Regards,

Patrick