Path: utzoo!attcan!uunet!munnari.oz.au!uniwa!wacsvax!peter
From: peter@wacsvax.OZ (Peter Dodd)
Newsgroups: aus.mac,comp.sys.mac.programmer
Subject: Restricting printer access
Keywords: printing, INIT, trap, PrGlue
Message-ID: <1594@wacsvax.OZ>
Date: 28 May 90 11:48:20 GMT
Organization: Comp Sci, Uni. Western Australia.
Lines: 20

Hello - this may save someone some development time.

We have recently developed an INIT to restrict access to network printers.
The INIT installs a ToolBox trap in the system heap at startup time.
The installed code is a patch to the PrGlue trap - at print time, it determines
whether the user has correct privileges to use the selected printer. 

The problem we encountered lies in the use of the Print Manager
by some applications.  We can live with the fact that the older applications
don't use the PrGlue routine described in Inside Macintosh Vol V,
hence don't even "see" our patch.  Of the applications which DO use
the PrGlue routine, some implement their own dialog to replace the standard
PRJobDialog routine (which is reasonable), but some applications do not
check the retured value of routines such as PrOpenDoc, or test the value of 
PrError. This seems to make it impossible to write a general Print Manager 
trap which can perform the desired checking in a regular way with all 
applications.

Peter Dodd                         Andrew D. Nielsen
peter@wacsvax.cs.uwa.oz.au         Nielsen_AD@cc.curtin.edu.au