Re: [xml-dev] Perl XML::Parser and nested external entity references

["Ernest G. Allen" <ernestgallen@earthlink.net>]

At 2:54 PM -0700 2001-10-19, D.J. Miller II wrote:

(snipped)

(Ernest G. Allen wrote...)
>> but how about pushing the old base immediately upon entry to
>> ExternEnt and popping it just before exit?  That would do
>> the popping at the same point that the ExternEntFin hook in
>> the newer version would be used.

(D.J. Miller II wrote...)
>
>This wouldn't quite work.  These callbacks are called serially in time
>but are not recursive (on a stack); the ExternEntFin hook gets called
>after the ExternEnt hook has returned.
>

I guess I wasn't being precise when I wrote "That would do the
popping at the same point that the ExternEntFin hook in the
newer version would be used."  I wasn't precise about inside the
ExternEnt (at its very end, just before it returns) and just
after the return from ExternEnt.  Sorry for any confusion.

(D.J. Miller II wrote...
>
>Actually I had it wrong, too.  To keep track of this you'd have to push
>the base location each time you enter an external entity reference,
>apply this base to each sysid found in external entity *declarations*
>found in this reference (and then stash the result for each declaration
>for subsequent use), and then pop the base upon exit from the reference.
>

That's what I meant, except that the popping is inside your
ExternEnt, at its very end.

(D.J. Miller II wrote...
>
>The mechanisms for this roll-you-own scheme aren't all quite there in
>2.27 (no ExternEntFin hook, so you don't know when to pop the base) or,
>apparently, in 2.28 either (which does have the ExternEntFin hook, and
>which reports general entity declarations but, unlike 2.27, not
>parameter entity declarations to the Entity handler -- maybe there's a
>grungier way to catch the parameter entity declarations that I couldn't
>find).
>

Doing the popping inside ExternEnt, just before return, avoids
the need for ExternEntFin.  Roughly something like this, using a
global "stack" array.

    sub ExternEnt {
      1. push old base 
      2. set new base
      3. process
      4. pop old base
      5. return
    }

If ExternEnt is called during "3. process" the base set in 
"2. set new base" will be pushed by "1. push old base" in 
the recursive invocation of ExternEnt.


(snipped)

/s/ Ernest G. Allen
    Sunnyvale, CA, USA