How to ping?

[Dar Scott]

Mac OS 9 or earlier, huh?

If no shell to ping, you might use appleScript to a utility.

Otherwise...

On Wednesday, March 19, 2003, at 12:55 PM, Ben Rubinstein wrote:

> Does this sound like a plan?

If you can put up with the delays in no-response failure, then you can 
try it without callbacks.

You will almost always get one of three responses:  Success.  Error 
because of rejection.  Open timeout.

If using a telnet port does not interfere with the serial link you are 
using then, you won't get the rejection.

Thus...  Off the top of my head (this probably needs fixing; I very 
rarely use blocking I/O):

function routerUp ipAddress
   local routerID
   put ipAddress & ":23" into routerID
   open socket routerID
   if result() is empty then
      close socket routerID
      return true
   else
      return false
   end if
end routerUp

If you will be using the telnet for maintenance or the serial control 
blocks it, then you might try an open to a non-existing port and test 
between a rejection and a timeout.  With a few tests you should see the 
difference in result() or sysError().  Or  you might discriminate on 
time.  (A rejection may be artificially delayed; it is delayed 9 
seconds on Windows.)  Note, if the router has filtering, it might be 
set up to run stealth even from the inside, in which case you won't get 
a rejection and this won't work.

> What I'm unclear about is whether there are
> conditions in which the open can fail without socketError?

If there are, I expect they will show up in result().

On OS X, some will show up as a socketClosed callback instead of 
socketError, so I'd watch out for Mac OS.

If the old Mac takes a long time to timeout, you might want to use 
callbacks and maybe send to work on timing.  Also, if you want to be 
doing other things at the same time, you don't want to use blocking 
calls.  (I very rarely use blocking calls.)  If you are checking dozens 
of routers, then you will want to use callbacks.

> And if so is
> there likely to be a problem if this is repeated thousands of times a 
> day?

There should not be, but there might be if your system has a memory 
leak or a port leak.  If you run into problems, you might automate a 
reboot every night.

> Also, the docs are unclear as to how I can access the ID that I can
> optionally specify when opening the socket.  Presumably this is 
> appended to
> the parameter to the callback message?

Yes.

> (Forgive me if your response is to
> "try it and you'll see", but I'm no longer at the office.)

To be comfortable with this you might want to look yourself at 
result(), sysError(), and time for several cases, anyway.  As a wimp, I 
would.

Dar Scott