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From Jeff Trawick <trawi...@bellsouth.net>
Subject concerns about the recent error checking added to APR
Date Thu, 06 Apr 2000 00:41:08 GMT
I just backed out (perhaps temporarily :) ) a change to
ap_open_stderr() which caused it to fail if it was passed NULL for
cont. 

The immediate reason is that apache can't log to stderr at startup
with that code.  Not even "httpd -h" will work.

There is storage allocated and it will be malloc()-ed if no context is
passed.  Do you really want to prevent the app from being able to do
that?  If so, then make sure apache can log to stderr at startup when
this is re-implemented.

Some of the other error checking (e.g., return APR_EBADARG if some
parameter is NULL) looks nice on the surface, but it is truly bad.

An app developer should hit the places where bad parms were passed to
APR in the course of their normal testing.

If you return a bad return code, it can be hidden because not all APR
calls are checked for errors by all apps.  The app may very well
continue with no apparent side-effects.  

If you blow up by dereferencing a NULL pointer, the developer
definitely finds out about it and they have the means to debug the
problem, even if they don't check return codes and/or don't have a way
to trace failures.

Even after the developer is done with the code, if they leave some
untested paths which pass bad parms to APR, it is still hard to
justify APR returning a bad return code instead of letting the
segfaults fall where they may.  If the developer didn't test that path
in the first place, there is no reason to think that there is an error
path to handle APR_EBADARG in an appropriate manner.  It is better to
go out with a boom than to silently fail.

Note that a check for NULL is a check for only one of quite a few
different invalid pointers :) , so its usefulness is quite limited to
start with.

Meanwhile all the code is slightly slower.

On the other hand...

. I'm not so sure that this is an appropriate strategy for APIs for
  which sources aren't available to help the debugger diagnose a core
  dump.  The supplier of object code only APIs can't spin its wheels
  looking at core dumps for app developers who pass bad parms to the
  API. 

. I'm not so sure this is an appropriate strategy for APIs which gain
  authority on entry to do their business.  (But these will have
  better mechanisms for accessing user storage carefully.)

. I remain quite interested in the handling of error codes that we can 
  actually expect at run-time due to the environment or due to user
  actions. 

-- 
Jeff Trawick | trawick@ibm.net | PGP public key at web site:
     http://www.geocities.com/SiliconValley/Park/9289/
          Born in Roswell... married an alien...

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