Re: DSK format specification

[mjmahon@aol.com (Michael J. Mahon)]

Bill Garber noted:

>"Andy McFadden" <fadden@fadden.com> wrote in message
>news:jfrQa.1595$dk4.78076@typhoon.sonic.net...
>> In comp.sys.apple2 Michael Pender <mpender@hotmail.com> wrote:
>
>> I should probably point out that you get most of that with ShrinkIt.
>> Empty blocks can be "zapped" with ProDOS 8 ShrinkIt, and then compress
>> down to nothing.  Date and volume name info are stored.  It's always
>> ProDOS-ordered, so there's no confusion.  There's a widely-tested utility
>> for creating and unpacking images on the Apple II, and (if I may say so
>> myself) solid support under pretty much every other platform via NuLib2.
>
>But even SHK files give us trouble as Andy and I found out earlier
>today, or was that yesterday as of now, anyway, apparently people
>have uploaded files thru a browser or were not posted to the folder
>properly on GROUND and the files ended up with an HTML header.
>128 bytes of it. Once removed the file is fine, but does not work without
>taking off the header. We must be careful of how we treat all archive
>files, or there will be even more problems than we now have.

I have also noticed a tendency of some sites to prepend a header
unless a binary mode FTP transfer is done.  Then there is the
occasional MacBinary header or the Binary II header--both of
which are completely redundant for archives and disk images.
(Yes, I remember the "gotta put a Binary II header on ShrinkIt
archives" dicta, but the truth is that ShrinkIt is smart enough
to not need one.  All the needed info is internal to the archive,
and ShrinkIt doesn't care _what_ its "type" is, as long as the
data is a valid archive.)

While it would be nice to eliminate this behavior, it seems unlikely
to me that universal compliance with the desired conventions can
be obtained.

What is more likely to work is to adopt the convention that most
utilities or emulators that work with disk images or file archives
skip over up to, say, 512 bytes of meaningless header searching
for the signature of a good archive or image.  This is admittedly
another heuristic, and is not foolproof--but it is pretty good.

Of course, a stand-alone utility to header-strip archives/images
is a great contribution to this cross-platform, 5%-never-get-the-
word world that we live in.  This could also be useful in adapting
newer image formats with headers to older software expecting
a raw image.

-michael

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